Reducing understeer

[Defpo]

I have been reading about stock setup understeer issues on the 15+ STI and have experienced it to some degree. I haven't honed my driving skills quite enough to push the car hard enough that it is a real issue for me, but it is something I would like to improve. It seems that there are generally 3 methods to employ to deal with the understeer on these cars.

1. increase size of rear sway bar (effectively increasing oversteer tendency to approach a more neutral steering balance)
2. adjust front camber, more negative (to potentially tire wearing levels)
3. deal with it and learn to trail brake and transfer weight to combat understeer

#1 will likely 'neutralise' the steering, but would achieve this by sacrificing grip in the rear.
#2 would likely solve the issues of understeer and grip, but I don't feel a sacrifice of tire wear is acceptable.
#3 is surely a great skill to master, but there must be a way to improve the understeer tendencies by way of suspension/alignment tuning without sacrificing grip or tire wear.

Not entirely sure where I was going with this, but it was something I wanted to put out there and get some opinions on. I am by no means an expert on any of this so my assumptions and research may be flawed.

Thanks in advance to anyone who cares to chime in!

 

[Alin]

I can't offer much help, but you should look into the tactic that drivers use to reduce understeer/induce oversteer. They turn the wheel slightly in the opposite direction of the upcoming turn to control chassis flex. Something like this or another. I don't know the technical terms.

Maybe these two gentlemen know: [MENTION=662]Batmobile_Engage[/MENTION] [MENTION=1868]Boogieman98[/MENTION]


Sent from my iPad using Tapatalk

 

[Grinder34]

Well, there are lots of options.

1) A stiffer rear swaybar does help. Unless you're going super stiff on very soft springs, you're probably not sacrificing too much overall grip. But EVEN IF you are...do you need that extra grip? I'd rather have a balanced car that can do .95 Gs vs an unbalanced car that can do .98 Gs. Even if I'm at the track, i'm having fun, not winning prize money.

2) You can also do a softer front swaybar. It'll help keep both front tires planted giving a bit more grip.

Ideally, you can combine #1 , #2 with adjustable swaybars and tune it to where you like it. However I'd guess about 90% of the people who get adjustable, end up setting it and leaving it without ever toying with the actual stiffness.

3) Changing springs can help control weight transfer for your advantage. There are a LOT of dynamics to talk about, but if you're turning in under braking, a SOFTER front spring will allow more weight to transfer to the front, giving the front extra grip.

4) Camber/Toe can help give you extra grip.

5) Depending on where in the corner (turn in, mid, or exit) you can play with dampers if you have adjustable coilovers.

6) Again, if this is on turn in, adding more front brake bias can help (not too much to make the rear unstable). Changing brake bias is probably the last thing i'd consider unless racecar.

7) I'm sure there are others i'm not including, such as radically altering suspension geometry.

 

[Defpo]

Well, there are lots of options.

1) A stiffer rear swaybar does help. Unless you're going super stiff on very soft springs, you're probably not sacrificing too much overall grip. But EVEN IF you are...do you need that extra grip? I'd rather have a balanced car that can do .95 Gs vs an unbalanced car that can do .98 Gs. Even if I'm at the track, i'm having fun, not winning prize money.

2) You can also do a softer front swaybar. It'll help keep both front tires planted giving a bit more grip.

Ideally, you can combine #1 , #2 with adjustable swaybars and tune it to where you like it. However I'd guess about 90% of the people who get adjustable, end up setting it and leaving it without ever toying with the actual stiffness.

3) Changing springs can help control weight transfer for your advantage. There are a LOT of dynamics to talk about, but if you're turning in under braking, a SOFTER front spring will allow more weight to transfer to the front, giving the front extra grip.

4) Camber/Toe can help give you extra grip.

5) Depending on where in the corner (turn in, mid, or exit) you can play with dampers if you have adjustable coilovers.

6) Again, if this is on turn in, adding more front brake bias can help (not too much to make the rear unstable). Changing brake bias is probably the last thing i'd consider unless racecar.

7) I'm sure there are others i'm not including, such as radically altering suspension geometry.

Thanks for the detailed reply. Definitely an alignment is in order regardless of what else I decide. I want to get it set up for a mild negative camber all around. probably -1.5 in front -1 rear.

As far as swaybars, I think i would prefer to go to a softer front sway bar but it seems that noone actually makes a softer bar for the 15+ STI. with that in mind, I think I am going to go with adjustable endlinks up front to try to dial the front a little softer, and a slightly larger adjustable bar in the rear with adjustable endlinks to tune that where I want it. Will probably buy everything from Whiteline as I have been very satisfied with their products in the past.

 

[Grinder34]

Thanks for the detailed reply. Definitely an alignment is in order regardless of what else I decide. I want to get it set up for a mild negative camber all around. probably -1.5 in front -1 rear.

As far as swaybars, I think i would prefer to go to a softer front sway bar but it seems that noone actually makes a softer bar for the 15+ STI. with that in mind, I think I am going to go with adjustable endlinks up front to try to dial the front a little softer, and a slightly larger adjustable bar in the rear with adjustable endlinks to tune that where I want it. Will probably buy everything from Whiteline as I have been very satisfied with their products in the past.

I dont know as much about the newer generations, but you might be able to get a WRX front swaybar to fit as a softer alternative.

I don't think adjustable endlinks do much. IIRC they're really only needed if you're going to corner-balance your car on coilovers.

 

[Defpo]

I dont know as much about the newer generations, but you might be able to get a WRX front swaybar to fit as a softer alternative.

I don't think adjustable endlinks do much. IIRC they're really only needed if you're going to corner-balance your car on coilovers.

It looks like the 15+ WRX has the same size sway bars so no luck there. Maybe I'll just go a little bigger in the rear and skip the adjustable links. Going to have to do some more reading about how the adjustable links affect the rate of the bar or if its more for correcting geometry...

 

[Batmobile_Engage]

I have been reading about stock setup understeer issues on the 15+ STI and have experienced it to some degree. I haven't honed my driving skills quite enough to push the car hard enough that it is a real issue for me, but it is something I would like to improve. It seems that there are generally 3 methods to employ to deal with the understeer on these cars.

1. increase size of rear sway bar (effectively increasing oversteer tendency to approach a more neutral steering balance)
2. adjust front camber, more negative (to potentially tire wearing levels)
3. deal with it and learn to trail brake and transfer weight to combat understeer

#1 will likely 'neutralise' the steering, but would achieve this by sacrificing grip in the rear.
#2 would likely solve the issues of understeer and grip, but I don't feel a sacrifice of tire wear is acceptable.
#3 is surely a great skill to master, but there must be a way to improve the understeer tendencies by way of suspension/alignment tuning without sacrificing grip or tire wear.

Not entirely sure where I was going with this, but it was something I wanted to put out there and get some opinions on. I am by no means an expert on any of this so my assumptions and research may be flawed.

Thanks in advance to anyone who cares to chime in!

Well, there are lots of options.

1) A stiffer rear swaybar does help. Unless you're going super stiff on very soft springs, you're probably not sacrificing too much overall grip. But EVEN IF you are...do you need that extra grip? I'd rather have a balanced car that can do .95 Gs vs an unbalanced car that can do .98 Gs. Even if I'm at the track, i'm having fun, not winning prize money.

2) You can also do a softer front swaybar. It'll help keep both front tires planted giving a bit more grip.

Ideally, you can combine #1 , #2 with adjustable swaybars and tune it to where you like it. However I'd guess about 90% of the people who get adjustable, end up setting it and leaving it without ever toying with the actual stiffness.

3) Changing springs can help control weight transfer for your advantage. There are a LOT of dynamics to talk about, but if you're turning in under braking, a SOFTER front spring will allow more weight to transfer to the front, giving the front extra grip.

4) Camber/Toe can help give you extra grip.

5) Depending on where in the corner (turn in, mid, or exit) you can play with dampers if you have adjustable coilovers.

6) Again, if this is on turn in, adding more front brake bias can help (not too much to make the rear unstable). Changing brake bias is probably the last thing i'd consider unless racecar.

7) I'm sure there are others i'm not including, such as radically altering suspension geometry.

Props to Grinder, as he hit all the important points. I especially agree with 1, 2 and 3. If you have adjustable coilovers or shocks, let me know and I can offer some advice on tuning them to get the handling characteristics that you desire.

One thing many people, and often myself, forget to consider is tire pressure. I know it sounds crazy to some people but consider this. If you normally roll around with 35 psi in the front and 30-32 psi in the rear, make a mental note of how it corners and then change your tire pressures to 30 psi in the front and 34 in the rear.

This may cause a slightly rougher ride in the rear end, so daily driving like this may not be for you. But if you are going out for some spirited driving or a track day of some sort, you might want to try this. It makes a bigger difference that you think.

 

[Grinder34]

One thing many people, and often myself, forget to consider is tire pressure. I know it sounds crazy to some people but consider this. If you normally roll around with 35 psi in the front and 30-32 psi in the rear, make a mental note of how it corners and then change your tire pressures to 30 psi in the front and 34 in the rear.

This may cause a slightly rougher ride in the rear end, so daily driving like this may not be for you. But if you are going out for some spirited driving or a track day of some sort, you might want to try this. It makes a bigger difference that you think.

I didn't include tire pressure for two important reasons. The first is that i totally forgot. :lol: The second is that it's somewhat of a bandaid.

Tire pressure affects the shape of the contact patch. Higher pressure causes the center to bulge outward, and lower causes it to sag inward. There IS an ideal tire pressure. You'll see race teams tweak pressures, but it's usually to make small adjustments after the suspension settings on the car have been "locked" due to regulations.

That being said, you can definitely use it the same way. If you're at the track, auto-x, mountain road, and its not handling how you want it...its much easier to adjust the tire pressure than a swaybar (but only marginally easier than adjusting bump/rebound on coilovers).

Anyways, if you find yourself fixing tire pressures, consider making another adjustment elsewhere when given the chance, and putting the pressures back where they should be.

 

[Defpo]

So I found a nice lightly used 22mm (2mm over stock) rear sway bar with kartboy links for a very good deal so I will be giving that a try. Will try playing with tire pressures as well and see if that helps.

Have been looking at adjustable coilovers, probably going to go with ohlins, but that will be a ways off. Other priorities in the budget right now :lol:

 

[Batmobile_Engage]

Ohlins are nice if you can find them for a decent price. Tokico D-specs are also very popular. I have a set on my STi and I really like the adjustable rebound damping.

 

[Defpo]

Ohlins are nice if you can find them for a decent price. Tokico D-specs are also very popular. I have a set on my STi and I really like the adjustable rebound damping.

I will take a look at the Tokicos. Thanks :tup: