Suspension Tuning Guide

[Grinder34]

I feel like there could be a good reference for suspension tweaks. Here's the first swing at what I'm talking about:

To Fix Understeer:
General
More negative front camber
Decrease front/rear weight ratio
Decrease front/rear spring ratio
Decrease front/rear swaybar thickness ratio

Corner Entry
Soften front compression
Add front toe-out

Corner Exit
Stiffen rear compression

High Speed
Increase front/rear downforce ratio

To Fix Oversteer
Simply reverse what you see above!

I dont know the effect of some of the add-on bits like ALKs. My guess is that adding an ALK will help understeer a bit. I feel like there are lots of other bushings and suspension bits that affect handling, and nuances that I'm missing. Plus STI-specific (perhaps DCCD-related) bits that could be added in.

What do you think?

 

[IGOTASTi]

So far so good. We need stuff like this to give people a reason to support us.

 

[Grinder34]

I've heard that front toe-out on our cars can help with corner entry understeer.

I'd like to add more about ride height, toe, caster, etc...

 

[Spamby]

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=58


Ran into this when doing my tire/wheel research.

I personally add a few more pounds in the front tires to help alleviate understeer.

The springs on my coilovers are a bit softer than most, very streetable. I set them at max height and the crank it down a few more turns. Kinda preloads the springs and helps with the turn in feel.

 

[Cat in Hat]

I know this is stating the obvious but - Tuning suspension for a street car and an Auto-X or track car are two completely different things. What works on track is actually very dangerous on the street because it does not cater for surface changes and bumps etc.
To dial out understeer on a car with stock suspension I would suggest using slightly thicker sway bars (22mm) front and rear, slightly softer front tire pressures (0,2 bar) and a touch of toe out (about 6~8 minutes on each side = total of 12 ~16 minutes).

If you want to start spending money on suspension then a good set of coilovers will go a long way, this will offer you many more parameters and adjustments for tuning your suspension.

What some regular kits do for suspension:
Anti lift kit (ALK) - this increases caster and lowers the back end of the lower front control arm. This helps with keeping the car's nose down during mid-corner acceleration and corner exit.
Roll centre adjustment kit - eliminates bump-steer when a car has been significantly lowered.
Sway bars - Reduce body roll (obviously) but their effect is keeping the inside wheel on the ground during cornering thereby offering a bit more grip from the inside wheels.
Rake = difference in ride height (chassis height) between the front and rear of the car. The ideal is for the front of the car to be slightly (5~10mm) lower than the rear...too low in front will result in car being unstable during braking and too low at the back will make the front end very "light" and car may start wondering at higher speeds. This can only be adjusted when coil overs are fitted.
Toe : Toe in will make the car more stable in a straight line but slower on turn-in. Toe out is the opposite. This applies to front and rear.
Tire pressure - softer will offer more grip to a point, then it will start to roll-over the edges and lose grip fast in addition to trashing your tires.
Spring Pre-load: this is not an adjustment that one should use because it effectively reduces the coilover's travel. Any coil over or suspension for that matter must move up and down. Almost all Coilovers, with the exception of very expensive rally styles, have a very limited amount of travel between full droop and bottoming out (about 100mm or so) this travel is split between upward and downward travel. When you pre-load the spring it forces the shock absorber shaft further out thereby reducing the downward (droop) travel. This will result in the tire leaving the ground on relatively small bumps. Reducing spring pre-load will have the opposite effect. The ideal setting is the point where the spring is under just enough load to stop it from rattling around when the shock absorber is not under any load.
Rather use dampening settings to adjust the nature of the suspension. Soft dampening for street (uneven and bumpy), hard dampening for track (Flat) and settings in between for a particular type of event or road surface.

I am not claiming that all of the above is 100% accurate but this is what I have discovered works for me and what I have learned over the years.

 

[finallymysti]

an alk reduces the anti geometry meaning a softer front = more dive and lift.

swaybars actually lift the inside wheel on the same axle if you will. the way it works is that when you take a turn the body rolls to the outside the inside body lifts and brings the suspension with it. this also pulls up on the bar, causing it to do the same on the out side tire increasing spring rate.

roll center adjustment does reduce bump steer but it also changes other things such as the roll couple. there is a lot that i won't get into here.

toe out in the rear you need to be very carefull with. some people say toe out in the rear will just make you crash

 

[Grinder34]

Wouldn't it be fair to say that swaybars resist body roll, so your car leans less. But for the same angle of lean, the inside wheel is closer to lifting.