Wheel and tire tech

Spamby

Meat Product Toy
After a short while of being a member on this site I have answered quite a few questions regarding wheels and tires. I realized that wheel and tire mods are one of the, if not biggest, most done and anticipated mods of our cars, or any car for that matter.

Wheel and tire changes are done for various reasons such as performance, looks and necessity. However, it seems that there is some mystery regarding those all too common donuts under or fenders. Within this thread, I will attempt to take some of the mystery out of those round things so as to help others make more intelligent and informed decisions when buying your next set of bling for your whip.
In part one, I will attempt to cover the highlights of such things as wheels, wheel materials, finishes, manufacturing processes and all of those crazy dimensions and numbers you see.
In part two, I will also attempt to touch base on tires, tire types, tread design and sizes.
In part three, I will attempt to give you some pros and cons about wheel and tire changes, specifically how they may impact your driving experience.

This is a works in progress and I suspect that it always will be. Therefore, I encourage others to comment, adding suggestions where necessary and most importantly, pointing out unclear or nonfactual information.

Wheel tech 101:


Class is in session.

Wheels, rims, bling, mags, discs, what have you, are the usually metal things that mount to the hub of your vehicle. These hard and round objects are what your tires are mounted to. They are typically made of steel or aluminum and come in a plethora of diameters and widths. To complicated things, they also come in different offsets, backspacing, hub bores, stud bores and stud spacing. Throwing more salt into the wound, they can come in one piece, two and three piece configurations, the former either being pressed in, screwed or riveted.
With that said, onto the metal of it. Do you have the metal?



Wheel types and manufacturing processes.

Steel wheels:

These are low tech and have been around for ages. These used to be some of the most common wheels on the market. Cheap and easy to make and actually quite easy to repair when damaged.
These wheels were typically stamped and formed from steel and the hub holes, stud holes and center pattern cut or punched out.
Steel wheels are typically thin but heavy compared to alloy wheels. They are still used on autos today but are slowly being phased out. Most vehicles that use them still are either economy cars or light and heavy duty trucks.
Steel wheels are usually made from a two piece process. The barrel is one and the face is the another. The barrel is the rim and is sculpted into a round shape with a continuous bead and lip, formed on the inner and outer edge, to hold the tire on. The face is the pretty part. The face is stamped, punched or carved for the pretty pattern and the mounting points. The two are joined together, usually by welding.
Steel wheels are usually heavy and thus regarded as not a good option for our cars. A good thing is that custom steel wheels are easily made and if one were so inclined, you could enlist a manufacturer to build you a set.

Magnesium wheels:

Or simply mags. These wheels became popular during the 60’s. Peace, love and grass… oops wait must not trip… innagadadavida!!! Sorry.
These wheels as stated are simply made of a magnesium alloy. The properties of magnesium are very light but that’s about where the good ends. Mag wheels deteriorate very quickly, like almost immediately begin to pit and decay. Mag wheels also tend to crack easily. One nasty thing about mag wheels is that they burn, burn very hot!! Magnesium is used in things like road flares. Magnesium can burn underwater and in the presence of high CO2. Magnesium in its state as a wheel is pretty docile. But if your car were to catch fire and those puppies heated up? Whoosh!! You’ve got one helluva fireball and the firemen trying to put out that fire are going to be pissed!
With all of that fancy fire crap said, mag wheels are just not used very much today. They deteriorate quickly and have a tendency to crack. No bueno. This is due to the properties of magnesium and the low ductility of the material. (low ductility is rigid or brittle). For that, they are usually reserved for specific racing applications where aluminum or steel is too heavy.


Aluminum wheels:


Ahhh, finally we come to the most familiar wheel material most of us look at, aluminum. This stuff is awesome. It comes in various grades and can be formed with many different methods. It is strong and lightweight and relatively resistant to age and abuse.
Aluminum wheels can be made in one of four ways, low pressure casting (LPDC), high pressure casting (HPDE), gravity casting and forging. After casting or forging is done, hole drilling and final prep is performed to make the desired product.

LPDC is the act of placing the die over a crucible, or bowl, of molten metal and forcing the molten mass up into the die using air/gas.
HPDE is the act of smashing/hammering/squeezing the molten metal into a sealed die. Once the alloy has solidified then the die is opened.
Gravity casting is the act of pouring the metal into a mold, sand mold or permanent mold, and basically letting it cool to the shape of the mold.
Flow form is the act of pouring molten metal into a mold. Letting it cool to a basic form and then heating and spinning it at high speed while using rollers to pull and form the wheel into its final shape. The act of spinning, heating and pressure can create a wheel barrel with like strength as a forged unit.

Forging is the act of hammering or cutting the wheel from a heated solid or solid billet or hunk of metal until the desired shape is completed. Without going into another threads worth of discussion, forging, by its process, can create the strongest and lightest wheels today. With that said, comes a larger price tag.

**Note** Some wheel manufacturers such as BBS, O.Z., Rays and Alcoa have propriety casting techniques to make wheels. Some of theses casting methods can produce wheels with comparable strength, weight and designs as forging. O.Z. and BBS supply F1 cars with CAST WHEELS!!! These secretive methods are just that. Only a little information is to be had about their methods. Basically from what I have learned is that those methods they implore are most likely flow forming casting method and then backed with a heat treat.

All of these methods can produce good results in wheel strengths and characteristics but forging is arguably the best end product but the most expensive. Cast wheels depend on a lot of care to make a good product. But because of flow characteristics in the casting process, especially with gravity casting, voids, pinholes, cracks, impurities etc. can find there way into the product.

Heat treating, annealing, quenching and aging can also be performed on wheels to add strength. There are different applications of these processes and the grade of aluminum and desired effect would determine the method used. In short, heat is applied, held and either slow cooled or rapidly cooled. This changes the grain pattern of the metal and thus its properties. I.E. soft to hard or vice versa.
Heat treating step is a process I believe is a must. This is where a crappy cast wheel can turn into a very strong and quality wheel.

One piece, two and three?

A one piece wheel is just that. A wheel cast or forged in one piece.
A two piece wheel has two separately made parts. These parts are then joined together. One part is the barrel, the other the face. These parts are usually welded, glued, or riveted/screwed together. Two piece wheels allow for unique offsets and widths.
A three piece wheel has three parts. The face, one half of the barrel and another half of the barrel. These types of wheels are uber expensive and allow for very customizable construction.









Wheel finishes:

I won’t spend too much time on this one. Basically there are 5 types of finishes available.

1. Powder coating. A baked on and very durable finish. If damaged you can’t just touch it up. You will have to redo the entire piece.
2. Paint. With or without clear coat; gloss, flat, semi gloss, satin. The most common color application. This method is cheap and fairly easy to correct if damaged.
3. Polished/natural. With or without a coating. This is basically just raw aluminum polished to a specific luster. Uncoated, this is a pain to upkeep and requires constant attention.
4. Chrome. A very hard and durable finish. A tried and true method that has relatively easy care and maintenance. If damaged, the entire part needs to be refinished. No touch ups here.
5. Anodizing. This is the act of dropping the part into a chemical bath and a adding electrical current to sort of dye the item. Anodizing finishes can be very durable but this is not very common in wheels.


Enough, you say!! I just wanna know about the wheels themselves!! OK so here we go. Sheesh!


Wheel measurements and fitment:


When selecting wheels, there are six measurements that you want to pay attention to:

1. Diameter. This is the height of the wheel. I.E. 18”, 19” rolling on twenny fo’s, fo realz.
2. Width. This is the barrel width from lip to lip. 8”, 8.5”, 9.5” etc. Skinny to fatty.
3. Offset. This is the measurement of the mounting surface, or hub, in relation to the centerline of the wheel. Flush, inset, concave goodness and deep lips. The further out from the centerline (towards the face), the more positive the offset. The hub at centerline would be a zero offset. The hub further in from centerline (towards the car or inner lip) would be a negative offset.
4. Backspacing. This is similar to offset but is the measurement of the hub to the inside lip of the wheel. Sorta like 3.
5. Bolt pattern. The measurement of the stud mounting hole spacing and number of studs. 5x5, 5x4.5, 5x100, 5x114.3, 5x130... Blah, blah. So if I were to have a 5x130mm bolt pattern that would mean that I have five mounting studs and they are spaced 130mm from center of the stud to center of the opposite stud.
6. Hub bore diameter. Measurement of the center hole of the wheel. The hole in the middle of the bolt holes that mounts to the round thingy, hub, on your hub. 56mm bore, 73mm bore, 40mm bore., etc.
***hub centric means that this will fit your hub without the addition of hub rings.


Hopefully the illustrations will help you in seeing how the measurements are taken and how they effect wheel fitment.

1268236269_Wheel_Dimensions_Diagram.jpg


wheel_dimensions1.jpg





So how does this apply to my Subaru and what wheels fit?
We have Brembo brakes. These brakes are large and have a huge impact on wheel fitment and choices. For the most part, wheel offsets will be fairly positive for our cars. This means that deep lips and deep concaved wheels are not seen too much.

OFFSET!!! A GR has a factory offset of positive 55mm. Or +55. Going more positive may not even be possible. The face would extend out beyond the outer lip and the barrel would sink in further towards the car running into suspension and chassis components. Going more negative would mean that for each millimeter less than 55 the wheel hub would extend inwards towards the car and thus the barrel of the wheel outwards. The face of the wheel usually would be more concave and/or a lip, with each negative mm, formed between the face and outer edge. This helps with fitment of wider wheels and thus wider tires. Basically, this is where you are going to get the flush look that so many desire. Paying close attention to offset is a must for fitment. Too negative and your looking at a lot of work to make that wheel fit.
A great example is diesel dully trucks. Look at the rear wheels. See how deep the rim is? This is an example of either a zero or negative offset. Now look at the front of the truck. See how the mounting hub or face protrudes out beyond the tire? This a great example of way positive offset.

Special considerations for the face have to be taken into account in order to clear the brakes. These design considerations, coupled with offset, can actually change the look of the wheel. One wheel at one offset and width may look a bit different than another wheel of the same type.

Hub centric means that the wheels hub bore will fit the hub ring/mounting flange of your car without the addition of hub rings. The use of larger hub bore wheels may need the use of hub rings to fit properly and/or to minimize vibrations and other undesirables. The use of hub rings is debatable. I myself have seen no difference when I do or don’t use them. When mounting wheels to the car, the practice of proper mounting may mitigate the need for hub rings. I.E. hand tighten the lugs in a crisscross pattern, each opposite lug and so on, then torquing incrementally, to the specified torque in that same crisscross pattern. This in effect should seat the wheel properly and centered.


GR specific general wheel fitments:


These are basic guidelines for wheel fitments on the GR chassis. Tire size will also contribute to fitment.
There are way too many variables to give a specific answer to what will fit on the STi. These are general rules with maximums and minimums as reference points only.
5x114.3 bolt pattern
56.1mm hub bore. Larger bores are ok and common. Use of hub centric rings may be needed.
Factory offset: positive or +55mm. Offsets as low as +38mm without work on the stock height suspension. Lower offsets than +38mm may need fender rolling, negative camber, fender pulling etc. especially on lowered suspensions. I would regard +38mm as the absolute max low offset on lowered STi’s before work is needed… more than just camber.
17”, 18” and 19” diameter wheels.
8”-10” wheel widths. Larger may require extensive work.


GD specific general wheel fitments
:

These are basic guidelines for wheel fitment on the GD chassis. Tire size will also contribute to fitment.
Same as before, way too many variables for specifics other than hub bore and bolt patterns. I will say that the GD chassis and fenders limit wheel choices. The narrow fenders and different suspension design inhibit lower offset and wider wheels without running into issues and putting much work into making them fit. Basically the choices are less, in regards to wheels and tires, than the GR platform.
04 STi 5x100 bolt pattern
05+ 5x114.3 bolt pattern
Factory offset +53mm. Offsets to +42ish without work and depending on wheel width. +45mm seems the safe bet.
Hub bore 56.1mm
8”-9 or 9.5”. Strut rubbing issues can be had with wide wheels and tires, even at stock height.
****Please comment about GD fitments. I have only little experience with the older STi’s.


Cliff notes anyone?
There are several different wheel materials but aluminum is the king for us.
There are several different manufacturing processes but flow forming and forging are supreme. Add some heat treating and you have a very strong and lightweight wheel.
Wheel finishes are a toss up. No one seems better than the other. They all seem to have their own advantages and disadvantages.
Offset, offset, offset coupled with wheel width. This is your biggest thing to pay attention to. These will determine where the wheel sits in your fender, or not in some cases. Different width wheels with the same offset will sit differently in relation to a static point such as the fender lip or the mounting hub of the car.
I.E.: Scenario one: Your wheel is ten inches wide and has an offset of positive one inch. Given the centerline separates the wheel into 5 inch halves, you would have 6 inches of wheel inwards, from the mounting flange to the inner lip. Four inches of depth from outer lip to flange
Scenario two: Your wheel is 8 inches wide and has a positive offset of one inch. Given the centerline separates the wheel into equal 4 inch halves, you would have 5 inches of wheel inwards from the mounting flange to the inner lip. Three inches of depth from outer lip to flange.


Is your head spinning yet? Mine is rotating like Linda Blair’s in the Exorcist. A priest, anyone???
 
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Spamby

Meat Product Toy
Part two: tires

And you thought making wheels was involved? Tire manufacturing is a very involved and complicated process. This one is hopefully going to change the way you look at those air filled rubbers wrapped around those wheels.

Tires. Yes, those round usually black and rubbery things your car rides on. Tires are the only thing that keeps your car in contact with the road. This point alone should make choosing tires as vital to your car as keeping quality oil in the engine.
Tires come in many different sizes, tread styles, compounds, load ratings, speed ratings and service descriptions.
Being a 4 season performance car, STi’s can benefit from many different types of tires. Live in SoCal? Summer tires may be worn throughout the year. Live in Minnesota? Summer and winter tires may be needed. So on and so forth. Basically, given the Subaru’s fantastic AWD system, year round performance can be had but tire changes may be needed for your particular seasonal patterns.
Now, I will attempt to give you some information that may help you the next time you are in the market for new shoes.



What tires are made of:


Since tire manufacturers seem to hold their tread compounds secretive, it is almost impossible to give information on just what each tire is made of and what makes one particular type so stellar or not.

Rubber! And a bunch of other stuff. Lol. Basically tires are made of rubber, silica, carbon black, nylon, chemicals and steel to name a few. Some tires have additions and others have subtractions.
The three main points of a tire are the carcass, tread area and the sidewall.
Tires are a layered item. This means that they are made of many different layers of different materials.
Carbon black is a major compnent of tires. This material is a product of refining and is used to color and reinforce the rubber of the tire. Rubber, in it’s virgin state, would shred quickly under your car. Carbon black is used to make that donut tougher and black. It is added to varying degrees depending on the desired outcome.
Silica is well, sand. They do magical things to it to add to tires. Scientists hope one day to replace carbon black with silica. But for now silica has some drawbacks. It doesn’t have the longevity of carbon and doesn’t seem to get that good of dry traction like carbon black. However, they do offer good wet and snow traction.
Fabric! Cotton, rayon, polyester, fiberglass and steel make up the integrity of the tire. Without these a tire would surely pop quickly. Just as making a dress, the fabric is woven and layered in such a way to give the carcass a strong shell. Steel wire is used in making steel belted tires. These would be the most common on road going cars today.
That’s basically it. Just a bunch of rubber, additives, fabric and metal. All thrown into a witches brew with eye of newt. Not really.


How tires are made:

http://www.maxxis.com/AutomobileLight-Truck/How-a-Tire-is-Made.aspx#Intro

We’re gonna keep this short as it is complicated. Above is a link explaining the process if you so desire to read it.
Basically the rubber is mixed with the additives and chemicals in vat. Heated and then formed into sheets. These sheets are then sent throughout the factory to add things like the belts, fabric, bead/sidewall forming and tread forming. Once all of those are made they come together in a lustful display of machinery and formed into the tire itself. After that they are cured and inspected.
Manufacturers then do testing to ensure the tire is of good quality. They can also do testing to make sure the tire meets speed, load and noise requirements. Some manufacturers go as far as to test the tires in various weather conditions, roads and other terrains.
So just when you think that dumb rubber thing is just that, think again. There is probably more tech in that tire than the wheels they are mounted to.

tirecrosssection.jpg









Tire types:

The tires we are going to look at for our cars are summer performance tires, all seasons, winter tires and track tires.

Summer performance tires


Just as it says, these tires are intended for warm weather/climate driving. These tires, due to their tread compounds are not meant to be driven in near freezing conditions. In my experience,, their effectiveness is drastically reduced below about 50*f when they become hard and lose their ability to maintain traction.
These tires are the ones your going to want if you want the best traction and cornering in warm weather. They come on varying degrees of aggressiveness that range from DOT approved racing tires to mildly aggressive touring tires.
Summer tires tend to have stiff sidewalls and squared shoulders. This helps in cornering stability but not allowing the shoulder to roll over during hard cornering. This is also what makes a summer tire a bit harsher in ride quality.
Summer tires usually have large tread blocks or patches of tread. The large tread areas are what helps it gain all of that wonderful traction. Those tread sections are often broken up by cuts along the circumference of the tire. Those cuts are there to allow a little more conformity and stability and to channel water. Some of those cuts, closer to the sidewall, allow for noise cancellation duty.
Summer tires also tend to wear out quickly. This is due to the stickier rubber compound. Stickier tire equals more rolling resistance which makes longevity an issue.
There is no clear cut winner in who makes the best summer tire. Each has their own set of pros and cons.
When selecting a summer tire, take into account your weather climate and what you intend to do with the tire. Some are good for rain, others not. Some are good on the track vs. street and vice versa.

In recap, summer tires are what is going to make your car shine on the paved stuff. Cornering and traction will be about the best sans track tires. However, a tradeoff exists. A lose of fuel mileage, tire longevity and quiet. Yep, quiet. Those suckers can be quite noisy ranging from slight hum and thump to a B-17 at full tilt dodging 88mm flak over the Rhineland.
These tires are not to be used in cold winter areas and definitely do not try and run them on snow or ice. I tried this once, once. I still have alcantra in my rear from that winter. Lol

summertire.jpg



All season tires:

The jack of all trades and master of none, the all season tire. Probably the most widely used tire on the road. This tire is supposed to fit the bill for everyone on everything. Since we drive performance cars, I will focus on performance all season tires. These tires are supposed to be able to corner and grip in the dry, wet and snow/ice. And they do, just not stellar, by any means.
Lets take a look at this most often used and underappreciated rubber. This tire’s compound is of course secretive and different from every make but it seems that this tire utilizes a higher percentage of silica in the batter. The silica would enable it to grip in the wet/snow/ice and remain flexible in freezing temps… to a certain point. The addition of this silica also may detract in its ability to make good grip in dry conditions.
Aside from the tread compound, the design of the tread itself is what makes this your go to tire. There is a ton of water channeling, usually, and little lateral cuts called sipes. These little cuts allow the tire to grip wet and slick surfaces and to squeeze that thin layer of water out so the tire can actually grip something more traction able. The many small tread blocks may also contribute to the lack of traction.
Shoulder design is that of usually softer than say the performance tire. This will take away the “on rails” cornering you may be used to with a summer tire. But this allows for a more comfortable ride absorbing impacts with a less jarring effect.
In recap, the all season does everything well but nothing great. This tire will get you there but without the gusto of a summer tire or the surefootedness of the winter tire. This is a good compromise for those that can only use one tire and their climate may dictate the need for two. These tires also tend to be better on fuel mileage and longevity.

allseasontire.jpg


Winter tires:

These tires are the track tires of the snow season. They grip ice like Velcro and offer stellar snow and slush duties. These tires also remain pliable in sub zero conditions, a must for traction.
These tires compounds are probably of a high, if not total, silica percentage. Again, the silica helps make the tire grippier in the wet and pliable in freezing temps.
If you look at the tire you will notice a few things different than any other. There are a lot of these little cuts running longitude and latitude all over the tire. These cuts are the almighty sipes. The siping along with the small tread blocks are what makes this thing awesome. The sipes are what squeezes the water out to allow for the tire to grip ice. The sipes pack with snow in order to allow for snow on snow traction. The larger voids, in between the tread blocks, shovel the powder away to get to a grippier surface. Couple this with a super pliable tread and sidewall and you have a tire that will blast through a blizzard with ease.
Some tires come with studs or the ability to be studded. These little metal spikes help grip the frozen stuff even more.
The trade off with snow tires is that mileage is horrible and they don’t last very long. They also don’t like warm pavement.
Winter tires should be bought in narrower than normal sizes with more sidewall profile. This narrow tread width help the tire in slickery stuff. This is due to flotation and physics. Basically, the less contact patch the tire has with ice, the better the traction. The taller sidewall will help the tire conform and grip. No rubber bands need apply when it’s 10 below and 15 inches of snow.
In recap: Snow tires are the bees knees if you live in snowmageddon country. They offer the best ability in snow and ice situations. They can be had in speed ratings and decent cornering abilities. Newer tires aren’t as picky in warmer winters but tread life still suffers when the pavement heats up. Studs are offered but remember many locations they are against the law because they tear up the pavement and throw sparks.

wintertire.jpg





Track tires:

These are either DOT approved or not. They come in special tread compounds for dry and/or wet. Some are grooved slightly and some are nearly a slick. These tires are what you want if you are more than the average track guy. The DOT versions are allowed on the street.
These tires offer the best in cornering and traction for the track days. They usually heat up quicker than street tires and remain consistently grippy throughout the day.
The DOT versions are legal on the road but offer only two dimensions in street driving, grip and cornering. Even the rain tires don’t allow for as good of traction as some summer street tires. These tires offer very low mileage and will wear out quickly.

bfg_gforce_r1_ci2_1.jpg



Reading a tire:

There are many different numbers and letters stamped on a tire. All of these you should know when purchasing a tire. Width, rim diameter, aspect ratio, traction rating, temperature rating, wear rating, load range, load index and speed rating. Other marks are the M&S and snowflake designation.

There are three ways, basically, that tire sizes are advertised, p metric, metric and flotation.

P metric tires: This sizing was developed some 40 years ago. There load capacity is based on the engineering formula that takes into account their size and psi rating. Since they are designed around tire load formula, auto makers can design autos around existing tires. P225/35R16.

Metric sizing: Basicall ythe same as P Metric but without the P. These tires tend to be manufactured based on the auto makers request for load and dimensions rather than making a car that fit’s an existing tire. 225/35R16.

Flotation sizing: This is basically the measurement of a tire in inches: 35x15.50R15. This means the tire is 35 inches tall by 15.50 inches wide for a 15 inch wheel. These tire sizes are usually found on truck tires and remain pretty constant in the offloading market.

Reading the sizes:


A tire stating 265/35 R18 is read as the following in metric. 265mm tread width by 35 percent aspect ratio by 18 inch wheel and is a radial tire.

Tread width is just that. How wide the tread section of the tire is. This is usually expressed in millimeters.

Aspect ratio is read in percentages and is the percentage of the tread width. So if I have a 265mm wide tire and the aspect ratio is 35 percent, it means that the sidewall is 35 percent of the tread width. The higher the percentage the more meaty the sidewall is. The lower the more of a rubber band you have.

Rim diameter is expressed in inches and I have never seen otherwise.

Further tire lingo:

Traction rating:
Traction rating is a grade and expressed in letters. AA, A, B, C. AA being the best and less as the list descends. Traction grades are based on the tires wet straight line coefficient traction and is based in g force on wet asphalt and concrete, separately.

Treadwear grades: UTQG Treadwear grades are based on real world road use. The tire is run in a group with Course monitoring tires and for 400 miles and until 7200 miles is achieved. The tires are assigned a grade at the end of the course. The course monitoring tire is givena grade and the test tire is givena grade indicating its relative treadwear. 100 would indicate it last as long as the tire. 200 would be twice and so on and so forth.
This measurement is not quite so accurate given that the tire is only driven for a short period and some guesstimation is applied. Basically a manufacturer can embellish a bit and make that particular tire seem better than it really is.

Temperature grades:
A tire is given a grade from A, B or C. A being 115+ mph and C being 85-100mph. If the tire can not resist heat buildup, its ability to run at high speeds is reduced. The grade is based on loading an inflated tire and then running it at high speed on a test wheel.

Load range:
Load range is the tires ability to carry a load at it’s specified or max pressure. These ratings range from passenger car tires to light truck and even trailer tires. The designation looks like these: LL, SL, RF, XL, B,C,D,E,F.

Load index: A tire is given a load index and it is expressed as a numerical value, typically 70-110. Each one of those numbers represents the tires ability to carry a specific weight. The higher the load index number the higher the weight the tire can carry.

Speed rating:
This is the tires ability to safely travel at a given speed for ten minutes. Yep, ten minutes is all the test runs. The tire is then given a letter designation. Those letters are: L,M,N,P,Q,R,S,T,U,H,V,W and Y. The L rating being 75mph and the Y rating being 186mph and above.

M+S branding: this means that the tire is approved for mud and snow use. This tire should perform better than a similar tire that is not branded.

Mountain with a snowflake symbol:
This means the tire is approved for severe winter driving. This tire will perform very well in the white stuff.

tire_diagram3_lg.gif



Approved rim widths:

A manufacturer designates a specific tire size will only safely fit a certain number of rim widths. A 265/35-18 tire is only approved to fit a wheel width from 9 to10.5 inches. This doesn’t mean you can’t put it on an 8.5 in wheel or an 11 inch wheel, it just means that the manufacturer does not endorse this nor would probably help with any claim you might have.
When mounting wide tires on narrow wheels, be forewarned that this will cause crowning of the tread. Essentially you will be riding on the middle portion of the tread and not utilizing it’s full contact patch. This will cause undesirable handling and center wear pattern.
A too wide of wheel and small tire will cause the center tread to dip and you will ride on the edges of the tread section this will cause undesirable handling and wear the outside edges excessively.
It’s best to keep that tire within the rim width specs. Yes, that means no herrafrush if you value handling and tire performance.


Tire pressure:

Be an air head! Check it, pay attention to it and adjust it. Not only does it help maintain longevity of the tire it also helps with handling of the vehicle. It also affects fuel mileage. A simple adjustment in pressure can yield a few mpg’s. I have seen it.
Every tire reacts differently to different pressures and every car as well. Each person may find their own unique settings that work best for their tire and vehicle.
Remember that tire pressures increase as the tire and ambient temps heat up and decrease as the tire cools down and the ambient temps plummet. In a summer morning the tire may be at 35 psi but when the temp heats up and on your way home that tire may be at 42 psi. The same goes for the winter. In the cold morning that tire may be at 27 psi and needs adjustment.
Tire pressure will decrease 1-2 psi per -10* temperature change. So if your tire was at 40psi when the ambient temp was 60*, and the temperature dropped 20*, your tires should have about 2-4psi less of air.
Low tire pressure is probably the worst thing you can do. A low tire rides on the sidewalls and cause excessive wear in that area. It also generates more than usual amounts of heat causing a situation for a potential blow out. It also adds rolling resistance which cause lose of mpg’s and poor performance since the cars engine has to work harder to overcome said resistance.


Air vs. Nitrogen:

Air is roughly 78% nitrogen and 21% oxygen. The other 1% is water vapor and other inert gases. The fact the oxygen molecule is smaller than the nitrogen molecule, the O2 molecule will bleed out of the tire faster than the N. Nitrogen molecules aren’t as easily excited as oxygen so the molecules don’t get as hot and bothered when the temperature increases thus keeping a more consistent PSI. The other issue is that water vapor, from O2 fill, reacts more drastically to temperature changes and can make that PSI go whacky. Nitrogen that is dry, when done right, should be filled into a dry tire.
I have used both and have only noticed a small advantage to nitrogen when daily driving. Nitrogen seems to not be as picky as air during temp swings. The tire pressure also remains more consistent when the tire heats up. However, these observations are only marginal and the convenience of my garage air compressor, with a dryer, dictates my decision for air usage. Plus most shops charge for nitrogen.


Cliffsnotes:

Tires are made from many different things. Each tire category has an intended purpose and also each tire within those categories have their own intended purposes. Summer for summer, winter for winter and 4 season tires for the year. Track tires should stay on the track.
Keep the proper tire for your car on your car. Nothing worse than an STi with touring tires blazing down the tarmac at 100+ mph. Put your granny’s tires on and watch the AWD burnout ensue.
Make sure your tire fits your rim within the specs. Stretching a tire may seem like the right thing but for safeties sake, don’t do it. Get tires that fit and gain some common sense.
There are vast number of well, numbers and letters that are stamped on the tires. All of these mean something and you should know what they mean.
Tire sizes should stay within the specified wheel range. A small change one way or another shouldn’t hurt things but lets not overdo this.
Tire pressure is a big deal and often neglected. Check those pressures at least once a month. Check them when the ambient temperatures start to swing.
Nitrogen may be the answer for track cars when half psi changes affect a lot. Otherwise, standard O2 is probably the cheapest and most convenient option.
 
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Spamby

Meat Product Toy
Part 3:

Knowledge, cause and effect and references


This is the last and final chapter in the tire and wheel tech. This will be more informal. Covering some cause and effect, background knowledge and of course, citing references.
Some of the cause and effect will have to include some suspension and chassis tech. I only plan on keeping this tech minimal and where required in order to give the audience complete information and to avoid a whole other topic. Otherwise, a wheel and tire guide would be a suspension guide and this is not my intended purpose and actually would require a separate technical guide.


Cause and effect:

What is this, you ask? This part is to discuss the desirable and undesirable effects that wheel and tire changes may have on your cars handling, performance, comfort and overall feel. Wheel and tire changes, especially when deviating from factory sizes, will in effect, cause your car to handle and drive differently. This is something that few people probably take in to account, at least the undesirable aspect. I can’t tell you how many times I read a post or talk to people who made a tire and wheel size change and now report that their beloved car is handling differently.
Remember that our Subarus are designed by some pretty smart individuals. Some things they don’t get right but most of them they do. Each component is made to work with another and thus produce an acceptable or desirable outcome. Any deviation from that original formula can produce a negative result. E.G. Lowering your car makes it look cool and corner better but the steering arm angle has increased and now bump steer is a problem.
People tend to not share their negative experiences when they make a major financial decision. They blabber about how great the decision was but hide the negative impacts it may have had. Basically, they tend to feel not so smart and don’t want someone to think the same.

The impact:


The factory determined the offset of our cars to be more positive. The suspension and chassis was set up to accommodate a higher positive wheel offset. Changing the wheel offset can and does change the scrub radius and ackerman angles.
I haven’t found any clear answers as to whether the STI has a postivie or negative scrub radius but I am going to venture a guess that the scrub radius is negative. I base this on the use of high postive offset wheels and the lackluster steering response, in part.
Each millimeter you decrease the offset, go more negative, you effectively change the scrub radius to a more positive. This can help make turn in more positive and feel sharper, quicker or just generally better. Adding too much offset can make the scrub radius too positive and add an element of twitchiness and unstableness and a heavy wheel. Combine this with other suspension goodies, ALK, coilovers, etc, and you can change this drastically and subsequently the feeling of the car. Basically, it can lead to unequal traction between the tires, on the front.

A more negative offset can also increase the load on the bearings, ball joints and knuckles of the vehicle. This is due to the load bearing portion of the tire no resting further outboard or closer to the outside of the car. This also produces more leverage on said bearings and knuckles. This can produce early bearing failures, knuckle fractures and ball joint issues. When will this occur? I can’t answer that and I don’t believe anyone truly can but be aware that from an engineering standpoint this can and does occur. Remember that disturbing trend in the late eighties and into the nineties when urban orientated individuals put ultra low offset wheels and tires on their ride? This made the entire wheel and tire combo come completely out from under the fenders. I have seen many axle, bearing and knuckle failures due to this. This is an extreme case but offers insight to the before.

ghetto.jpg



Another negative to decreasing offset is that your wheel is now doing different things to your suspension. The extra leverage is decreasing the spring rating of your coils. This means for every millimeter you decrease your offset you are applying more leverage and decreasing that spring rating. This makes the ride softer but can create traction issues, handling issues and more body roll. A Honda tech article stated for every 10mm of negative offset a 5% decrease in spring rate occurred.

Wider tires can increase traction, in the dry, but can decrease the traction in the wet. This has to do with contact patch. This is especially true when it comes to winter driving. This has to do with the traction coefficient that a wider tire has on slippery surfaces. Without going into all of the scientific reasoning it is better to keep your tires thin in the wet and slippery stuff.

stang.jpg



Narrower tires can decrease traction in the dry. Combine this with high powered cars and track duty, this can make for an unpleasant driving situation when pushing the cars limits.

Wider tires can increase a thing called tram lining. This is the undesirable condition defined as when the tire tends to grab ruts in the road and generally following the pavements imperfections. When driving you’ll notice that steering corrections are needed more frequently than when a narrower tire was used. There is no way to figure this out of the equation and a tradeoff that we must all deal with.

Wider tires don’t necessarily mean better traction. The compound of the tire has more to do with that. A 245 series track tire will out perform a 265 series summer tire and a narrower summer tire will outperform a wider all season. Get the point? This wide tire effect can inspire overconfidence and make you look like a dweeb amongst others.

Wider tires increase the rolling resistance. This is especially true with stickier compounds. This will make for a decrease in MPG’s and actually cause more power to be needed to overcome that resistance. This decreasing the efficiency of the engine, cause slower track and trap times.

Stickier tires can cause axle shafts, bearing, joints, gears, etc to become fatigued. This is due in part to the increased traction of the tire and its decreased ability to slip thus causing more shock to the driveline, chassis and suspension.

Wider wheels and tires also increase the unsprung weight of the vehicle. This is why so many preach the benefits of lighter weight wheels when increase diameters and widths of wheels. This is where good quality wheels come into play, practicing forging and flow forming techniques to reduce that weight.

When using wider wheels and tires, especially when on lowered suspension, the tire may come into contact with the fenders outer edge. Rolling and pulling of the fender may be needed to facilitate the fitment of aggressive wheel/tire combos. Upfront, the fender liner may need to be trimmed, reformed by heat or removed entirely. The afore is especially true on aggressively lowered cars. Camber will also need to be negatively increased. At some point, the camber is good for cornering but after a certain degree, the negative camber can increase instability when driving due to the fact that your are driving on a narrower contact patch. I.e. the inner sidewall. The more negative the offset and the more negative camber is dialed in, the more wackiness can be felt when traveling, especially at speed.

A taller aspect ratio tire can cause the sidewall to roll under hard cornering. The increased sidewall height can cause vagueness in steering feel and tire squirm under acceleration or on less than perfect roads. A taller aspect ratio may increase the ride comfort offering a more compliant ride.

Stretching a tire is the act of putting a smaller width tire on a wider width wheel, beyond manufacturer recommendations. People usually do this when they are trying to get a very aggressive width/offset combo and the tire sidewall keeps impacting things like fender lips. Most notably, the “hellaflush” crowd is the biggest offender. The negative of this is that you have just screwed up every performance aspect of the tire. Stretching the tire beyond it’s limits rolls the sidewalls in and cups or bowls the tread section. What happens now is your effective contact patch is now on the sidewalls and not on the tread, where it should be. This can cause the tire to excessively heat, blowout, unseat the bead, have funky handling, loss of traction, corner unpredictably and make you want to pose and park hard. The other pitfall is that the wheel lip is now unprotected and can be damaged from curbs, potholes, and other road debris or obstacles. My advice is to get a combo that fits and save the fair entry for your trailer queen. Under inflation can cause similar characteristics.

herrafrush.jpg



Smashing a tire is the act of putting a too wide of tire on a smaller than recommended wheel width. What this causes is the sidewall to bulge out over the wheel, excessively, bulge or crown the tread section and actually increase the overall height of the tire. This cause early wear of the tire in the center of the tread section. This also cause adverse handling since the tread contact patch has been effectively decreased to a small footprint in the center of the tread. Go over inflate your tires and you’ll feel what I’m sayin’.

bogger.jpg




Wider wheels demand a more negative offset. The width of the wheel and offset that brings the wheel further outboard can increase the stability of the vehicle when cornering. In effect the width and offset increases the track width. The increased track width is desirable when cornering at high speeds.

Wider wheels also demand the use of wider tires. Wider tires increase the contact patch to the road. This increased traction helps in straight line performance and cornering. This is especially true when added power finds it’s way to the wheels.

Aside from the increased track width and traction, a new set of bigger wheels and tires does nothing more for the performance of the vehicle.

Extra cool points for filling up the fenders. Lol


In recap:

The tires and wheels on your car require more thought than you have imagined. Heck, even I started to realize just how much thought goes into making these things and how much thought should be used in order to fit them. There are pros and cons to deviating from the factory engineering. Deviate too much, and you can possibly make the car handle unpredictably and dangerously. Too little, and you have not effectively changed anything and your intended goal may not be met.
Tire selection is key to your locale and the intended use for the car. Safety generally dictates this rule. Air pressure is a simple and easy way to alter the handling of your car and to increase the longevity of your investment. Too many people overlook air pressure until there actually is a problem.
Cheap deals abound, buyer beware. In this day and age of internet shopping, there are a bazillion times more options for us when buying wheels and tires. It is best to stick with the well known and reputable manufacturers when selecting a new set of blings. This may cost you more but could potentially save money, time and headache in the long run. Cheap wheel and tire manufacturers tend to cut expenses by leaving out key processes in manufacturing, such as quality control, substandard materials, and quantity over quality mentality. It is best to save your pennies and opt for a more reputable brand.
Our cars AWD and modest power ratings, stock, seem to benefit the best when the stock wheel and tire platform is retained; stock sized or within stock specs. Go bigger on the stock setup and I believe and have experienced more adverse effects than positive ones. With increased power outputs and suspension upgrades, a new and different sized wheel and tire may then become beneficial. Pros may start to outweigh the cons. This is more of an opinion but I believe to be a sound one. Aesthetics seem to be a major decision factor in the wheel and tire quest.
Remember, our cars are enthusiasts cars and not commuter cars. These cars require attention and thought and thus demand respect. They may not be a Porsche but they definitely are not a Camry. Our cars are worthy of quality, taste and thought.
Hellaflush to rally, whatever your tastes, bear in mind the positives and negatives and execute with an informed decision.

Citing references:
Part if this comes from my own practical knowledge. Knowledge I have gained over the last few decades of being an automotive enthusiast, ranging from off-roading to sport bikes. Another part of knowledge I have gained was from the experience of working with my father at his businesses. One division focused on heat treating services and another division was focused on supplying the foundry and die casting industries with goods and services. Those two have given me a unique perspective into how things are made and just what it takes to make them.
The other is just simply good old fashioned research. And for that, I must give credit where it is due. I am sure I miss a few so my deepest apologies to those parties.

tirerack.com
Discounttiredirect.com
O.Z. wheels
BBS wheels
Alcoa
Rays Engineering
Advan racing
Maxxis tire
youtube.com
Rennlist.com
Sixspeedonline.com
Renntech.com
Th3clap.com
Continental Tire
Bridgestone/Firestone tires
Michelin Tires
BFGoodrich tires
Interco Tire Corp.
H&R Suspension
Ehow
How things are made
 
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Spamby

Meat Product Toy
"I.E.: Scenario one: Your wheel is ten inches wide and has an offset of positive one inch. Given the centerline separates the wheel into 5 inch halves, you would have 6 inches of wheel inwards, from the mounting flange to the inner lip. Four inches of depth from outer lip to flange
Scenario two: Your wheel is 8 inches wide and has a positive offset of one inch. Given the centerline separates the wheel into equal 4 inch halves, you would have 5 inches of wheel inwards from the mounting flange to the inner lip. Three inches of depth from outer lip to flange."

Ok. Got the offset thingy changed. Added an example but I think I am going to make a drawing sometime to give people a better idea.
Please read it and see if it makes sense.

Working on the tire part still. I hope to maybe get that up tonight... at least a partial. If not, it will be in the next few days.
 

Alin

Diehard Car Enthusiast!
Ok here is what has been on my mind lately and i figured this was the thread for it. Ive read and been told by countless people that if your tires have a greater difference than 2/32 tread depth then the awd system gets damaged. Could you please verify or go in detail about this? In the past 3 years of ownership and research and learning i have never heard or read about a wrx or sti to have a damaged awd system because of the tire tread differences. This has been bugging me lately!
 

Batmobile_Engage

Squirrel Meat Aficionado.
Staff member
Ok here is what has been on my mind lately and i figured this was the thread for it. Ive read and been told by countless people that if your tires have a greater difference than 2/32 tread depth then the awd system gets damaged. Could you please verify or go in detail about this? In the past 3 years of ownership and research and learning i have never heard or read about a wrx or sti to have a damaged awd system because of the tire tread differences. This has been bugging me lately!

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=18

Matching Tires on Four-Wheel Drive and All-Wheel Drive Vehicles

The ability of four-wheel drive and all-wheel drive vehicles to divide the engine's horsepower between its four tires is especially useful on loose or slippery surfaces such as sand and dirt, as well as on wet, icy or snow-covered roads. However it's important to remember that in order to transfer this extra power, the four-wheel drive and all-wheel drive vehicle's driveline mechanically connects the tires so they work in unison.Four-wheel drive and all-wheel drive vehicles are equipped with additional differentials and/or viscous couplings that are designed to allow momentary differences in wheel speeds when the vehicle turns a corner or temporarily spins a tire. However, if the differentials or viscous couplings are forced to operate 100% of the time because of mismatched tires, they will experience excessive heat and unwarranted wear until they fail.
This necessitates that four-wheel drive and all-wheel drive vehicles use tires that are very closely matched. This is because different diameter tires roll a different number of times each mile as a result of the variations in their circumferences. Tire diameter variations can be caused by accidentally using different sized tires, tires with different tread designs, tires made by different manufacturers, different inflation pressures or even tires worn to different tread depths.

As an example of different tire diameters resulting from tires worn to different tread depths, we'll compare two 225/45R17-sized tires, a new tire with its original tread depth of 10/32-inch and a second tire worn to 8/32-inch of remaining tread depth. The new 225/45R17-sized tire has a calculated diameter of 24.97", a circumference of 78.44" and will roll 835 times each mile. The same tire worn to 8/32-inch of remaining tread depth is calculated to be 1/8" shorter with a diameter of 24.84", have a circumference of 78.04" and will roll 839 times per mile. While the difference of 1/8" in overall diameter doesn't seem excessive, the resulting 4 revolutions per mile difference can place a continuous strain on the tires and vehicle's driveline. Obviously, the greater the difference in the tires' circumferences, the greater the resulting strain.
This makes maintaining the vehicle manufacturer's recommended tire inflation pressures and using "matched" tires on all wheel positions necessary procedures to reduce strain on the vehicle's driveline. Using "matched" tires means all four tires are the same brand, design and tread depth. Mixing tire brands, tread designs and tread depths may cause components in the vehicle's driveline to fail.
Mismatched tires or using improper inflation pressures for all-wheel drive and four-wheel drive vehicles can also result in immediate drivability problems. Some Control Trac equipped vehicles in 4Auto mode may exhibit a shutter on acceleration and/or a noise from the front driveline and transfer case while driving. Some all-wheel drive and four-wheel drive vehicles may exhibit axle windup or binding while driving. Some four-wheel drive vehicles (manual or electronic shift) with a two-wheel drive mode may refuse to shift "on the fly" into 4x4 Auto or 4x4 High at highway speeds.

Rotating Tires


Because the front and rear tires of all-wheel drive and four-wheel drive vehicles perform different duties while accelerating, braking and cornering, tire rotation is important to even out, and maintain equivalent treadwear of all of the vehicle's tires to minimize potential driveline stresses.
If the vehicle is equipped with a matching road wheel and full-sized spare tire, they should be integrated into the vehicle's rotation pattern at the first tire rotation. This will allow all five of the vehicle's tires to share in the workload and wear at similar rates. In the event that a single tire is damaged and has to be removed from service, this will allow the tread depth equivalent spare tire to be used with the remaining three tires.
If the spare is not integrated into the vehicle's tire rotation pattern, it will not match the tread depth of the four worn tires on the ground when called into service. Additionally, if a single tire is replaced by the full size spare tire, hopefully the new replacement tire can remain as the spare tire until the other four tires have worn out and need to be replaced.

Replacing Pairs of Tires or Individual Tires


There are several suggestions that have been offered to drivers who are replacing pairs or individual tires on their four-wheel drive and all-wheel drive vehicles. Some vehicle manufacturers recommend that all tires maintain the same rolling radius and circumference, while others suggest that all tire circumferences remain within 1/4- to 1/2-inch of each other. Other vehicle manufacturers recommend that all four tires remain within 2/32-, 3/32- or 4/32-inch of each other, or within 30% of each other in relative remaining tread depth.
Regardless of the vehicle manufacturer's recommendations, the least stressful application is when all four tires are the same tire brand, tread design and equivalent tread depth.
Before buying pairs or individual tires for all-wheel drive and four-wheel drive vehicles, drivers should read their vehicle's owners manual or contact the dealer's service department for confirmation of their specific vehicle's requirements.

Matching Tires By Shaving Them to Maintain Equivalent Tire Tread Depths


What does a driver do if one tire has to be removed from service when it and the other three tires have already worn to two-thirds to one-half of their original tread depth? Simply installing one new tire runs the risk of drivability problems or expensive driveline damage. Replacing the other three partially worn tires along with the damaged tire significantly increases the cost.
Tire Rack can provide a solution by matching the tread depth of the replacement tire to the tread depth of the partially worn tires that will remain on the vehicle by removing tread rubber from a new tire on a specialized machine that operates as a tire lathe. While this may seem counterintuitive, the value of the mileage sacrificed by the one replacement tire is considerably less than the cost of rebuilding worn driveline components.
Tire Rack has offered a tire shaving service that has been primarily used for preparing competition tires for racetrack use. This same service can also be used to remove tread rubber from new pairs or individual street tires used on four-wheel drive and all-wheel drive vehicles to allow them to match the remaining tread depth of the other partially worn tires that will remain on the vehicle. In addition to providing equivalent tread depth to eliminate driveline stress, shaved tires will also better match the traction and handling qualities of the remaining worn tires.
While the cost of our street tire shaving service will range from $25 to $35 for each tire, it is significantly less than the cost of unnecessarily replacing the remaining two or three good tires with lots of mileage still available from them.
Here are recommendations from some of the manufactures that Tire Rack currently serves for matching the tires used on their four-wheel drive and all-wheel drive vehicles. Additional recommendations from other Original Equipment Vehicle Manufacturers is pending.

AudiAs published in their vehicle owner's manual, "rolling radius of all 4 tires must remain the same" or within 4/32-inch of each other in remaining tread depth.
PorscheCayenne within 30% of the other tire on the same axle's remaining treadwear.
SubaruWithin 1/4-inch of tire circumference or about 2/32-inch of each other in remaining tread depth.
 

Batmobile_Engage

Squirrel Meat Aficionado.
Staff member
"Recently we had a 2004 Chrysler Pacifica come into our shop for service. Two of the tires were worn beyond the safe point to drive, which is 2/32nds of an inch in tread depth (New is 10-12/32nds). The other two tires were measured at 7/32nds. The rule of thumb is to keep the difference in tread depth less than 3/32nds.

I know, this is confusing even for us sometimes. So, what did we do? We sold him two new tires that had a tread depth of 10-32nds affectively reducing the difference between the depths. It was a difference of 5/32nds, now it's 3/32nds. Well that turned out to be the wrong decision. When we replaced the tires, the model of tire that he had was no longer available, so we went with a similar but not exact match to the tread design.
The next day the customer was on a two hour trip, when his differential literally exploded. The differential is a component on all four-wheel drive vehicles that transfers the energy to each wheel from the engine/transmission. Once this happens, the vehicle will no longer move as was the case. Thank God no one was hurt.
So why did this happen?
Once the vehicle was towed in, the damage was obvious. We started assessing the vehicle..."

Read more...

http://www.weareaccurateautomotive.com/blog-0/bid/128677/Tires-for-All-Wheel-drive-vehicle-Beware
 

Alin

Diehard Car Enthusiast!
Thanks for first post and wow at second. Thats some serious shit. Have you ever heard of a wrx or sti getting messed up from cause of tires?
 

Spamby

Meat Product Toy
To sum it up, it has to do with different diameter tires wanting to cover distances in a shorter or greater amount of time. Add a mechanical link in between them and you have a recipe for disaster. It would be like you hopped up on meth and then popping a bunch of quaaludes at the same time. The mechanical link, your heart, can not figure out a speed to beat at and eventually explodes.

I had an eye opening experience about a decade ago. i walked into a very long lived and respectable specialty tire shop. I was talking to the guy about getting a setup on a project truck I had been doing. I needed the tires to be around the same diameter as the factory setup. I asked for what tire sizes, width, aspect ratio, etc I could run. He smiled and went to the shop only to return with four tires. The tires were stamped the same sizes but from different manufacturers. He lined them up side by side and low and behold, they were all different sizes! From left to right the tires grew about 2 inches and varied in width from one to the other.
So beware, tire manufacturers sizes actually vary from one to the next.

AWD and 4wd (when 4wd is engaged) vehicles, who see driving at speeds on a regular should always have their tires replaced in sets of fours.
4wd vehicles who's speeds, when in 4wd and speeds are very low like most off-road vehicles, can get away with smallerish tire diameter differences. The reason is because at low speeds, the tire RPM is miniscule enough to not want to tear the transfer case apart.

Another note: Many AWD vehicles still use a system based on the transfer case. Meaning, there is no differentiation front vs. rear. I am going to assume the Chrysler in Bat's example is T-case setup and why immediate failure happened.
 

Batmobile_Engage

Squirrel Meat Aficionado.
Staff member
Thanks for first post and wow at second. Thats some serious shit. Have you ever heard of a wrx or sti getting messed up from cause of tires?

I have personally only heard of one person to ever have serious DCCD damage. From what I understand, it was a $3,700 repair job from the stealership. The thing is though, his tires were way off and he always drove like a complete asshat. I drive like a maniac sometimes and even I was afraid to ride with him.

Other people I know who have driven on tires 2-3 32nd's out of tolerance said they had some noticeable drivetrain whine, but drove very carefully and remedied the problem soon after.

When I was on my 18's and I had a flat, my donut is a 17 so I was really worried about this. I didn't have a whole lot of choice so I put it on and had to drive about 8 miles with it. I was very careful, didn't go very fast, took turns oh so gingerly and I never ending up having any issues.
 

Alin

Diehard Car Enthusiast!
Ok so its not a common thing. Good to know though. Great insight definitely.
 

Batmobile_Engage

Squirrel Meat Aficionado.
Staff member

Alin

Diehard Car Enthusiast!
I still wouldn't push my luck...

No no no. :lol:

All my tires that ive ever had were exactly the same tread all around. This was just on my mind lately thats all.
 

Alin

Diehard Car Enthusiast!

Spamby

Meat Product Toy
I don't know but I'm trying to find out. My thoughts right now are that the pressures would have to be significantly different, maybe nearly flat vs. full.
Reasons I'll explain later but I can say that there will be many parts to this answer.
Report back later
 

Batmobile_Engage

Squirrel Meat Aficionado.
Staff member
That is completely dependent on the specific tire(s) in question so it is difficult to generalize. Some tires are down 10 psi or more until a "belly" in the tire is even visibly noticeable.

I remember a friend noticing some faint drivetrain whine on the highway, pulled over at a gas station and found his left front tire was at 22 psi. I believe he kept his tires at 35f/32r.
 

finallymysti

New member
so I guess my question is. depending on the course and day I may run a differential pressure of 7 psi. figure the tire is a 225/45/17 hankook rs3 or same size nitto nto1. is this acceptable.
 

Batmobile_Engage

Squirrel Meat Aficionado.
Staff member
I don't think 7 psi would be an issue considering the tires we're all running are generally low profile with stiff sidewalls. Also, I can't remember where I heard this from, but I believe that tire pressure differences between L-R sides of the car are more damaging than differences F-R.
 
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