Handling issues? This site can help.

[rwh11385]

Great reference IMO

http://www.wtrscca.org/tech.htm

[Sean]

Sweet, nice little page!

[Axxe]

Bookmarked. From what I have experienced, this is VERY accurate.

BTW, you're going to love the IE Stg 3's Heeter :)

[mspiegle]

Increase front rate only: Front ride rate increases. Front roll resistance increases, increasing understeer or reducing oversteer.
Increase rear rate only: Rear ride rate increases. Rear roll resistance increases, increasing oversteer or reducing understeer.

I'm confused. I thought if you increase the front rate, your weight won't transfer as easilly and the car won't lean into that corner. If you're increasing the front rate, shouldn't your understeer be reduced due to reduced chassis roll?


EDIT: They say this at the end:
Steady state understeer All turns or low-speed turns only:
If front tire temps are optimum and rears are low, stiffen rear antiroll bar; if front temps are too hot, soften front (most likely).
If front tire pressures are optimum, decrease rear tire pressure. Increase if chunking occurs.
Improper front camber.
Too much body roll at front, causing excessive camber change.

So, if you're understeering, a cause could be too much body roll at front. Doesn't that directly contradict the statement above? (front spring rate increase will reduce roll but increase understeer)

[Axxe]

Increase front rate only: Front ride rate increases. Front roll resistance increases, increasing understeer or reducing oversteer.
Increase rear rate only: Rear ride rate increases. Rear roll resistance increases, increasing oversteer or reducing understeer.

I'm confused. I thought if you increase the front rate, your weight won't transfer as easilly and the car won't lean into that corner. If you're increasing the front rate, shouldn't your understeer be reduced due to reduced chassis roll?


EDIT: They say this at the end:
Steady state understeer All turns or low-speed turns only:
If front tire temps are optimum and rears are low, stiffen rear antiroll bar; if front temps are too hot, soften front (most likely).
If front tire pressures are optimum, decrease rear tire pressure. Increase if chunking occurs.
Improper front camber.
Too much body roll at front, causing excessive camber change.

So, if you're understeering, a cause could be too much body roll at front. Doesn't that directly contradict the statement above? (front spring rate increase will reduce roll but increase understeer)

And how do you counter body roll without changing spring rates? Anti-roll bars.

[mspiegle]

And how do you counter body roll without changing spring rates? Anti-roll bars.

I've heard it said a few times that you aren't supposed to control body roll with anti-roll bars, but with spring rates. If this is true, how would you tune the understeer out?

[Sean]

One thing I've noticed when playing with my shocks:

I set the fronts to COMPLETE FULL STIFF and the rears were at half. The car oversteered VERY easily in the autocross - I was drifting around EVERY turn. It was actually quite fun, but hurt my time pretty bad.

However, on the way to my friends house later, I took a long sweeper, at a pretty quick pace- and the car plowed like a mofo.

So, what that leads me to believe is at lower speeds, the fronts on stiff will cause massive oversteer - but when you're taking a long turn, it plows. The true way to increase oversteer is to stiffen up the rear and loosen the fronts.

[1991 318is]

Think about it!

I've heard it said a few times that you aren't supposed to control body roll with anti-roll bars, but with spring rates.

So what are those bars for? Why are they called anti-roll bars? Why do you see Indy car driver's changing their adjustable bars? If you use springs to take out body roll what do you do when the wheels hop over rough pavement? I feel it is a mistake to put so much emphasis on springs and think of bars last. Lower the car a little with slightly stiffer springs and then look at bars. An E30 with over 400# front springs will go to fecal matter on washboard pavement. It will go right off line but at least it will have no body roll! Small consolation. There is a formula for weight transfer and it does not include spring rates or bar stiffness.

[rwh11385]

I set the fronts to COMPLETE FULL STIFF and the rears were at half. The car oversteered VERY easily in the autocross - I was drifting around EVERY turn. It was actually quite fun, but hurt my time pretty bad.

That might explain my issues last weekend.... or not rly.

my rake and soft rear shocks might be it.

[Dave]

nice link, Roberto.

[Bavarian3]

Stop spreading misinformation!!!11123

[mspiegle]

Stop spreading misinformation!!!11123

Then spread the non-misinformation!

[redcarbon]

Here are some things you have to know:

1) Tires are nonlinear. That is, past a certain normal load, increasing the normal load on a tire does not increase the lateral grip by the same amount it used to (at a lower normal load).

2) Normal loads on tires are determined by the weight of the car plus/minus the weight transfer

3) Total weight transfer of a car in a turn is based solely on cg height, track width, mass and lateral acceleration.

4) Changing the proportion of roll stiffness front to rear does not change the TOTAL weigh transfer but it changes how much of that total transfers at the front versus how much transfers at the rear.

5) The relatively stiffer end of the of the car will get proportionally more of the total weight transfer

6) The stiffer end's outer tire has a higher load on it, thus less lateral force (see 1) than the other end's outer tire, thus the stiffer end has less total lateral grip

In review, if you stiffen the front end, there will be more weight transfer in the front, then front tires will have less grip and thus understeer. The same thing can happen if you soften the rear end.

If you stiffen the front and rear ends in a constant proportion, you will not change the front to rear weight transfer distribution and it won't change how the car handles, it just will react faster.

Dampers only have an effect in the transients, they should have no effect on steady state cornering. I can't explain why stiffening the front made you oversteer...that should not happen, I'll have to think about that one.

- Derek

[BimmerToad]

You can stiffen the front to some extent and gain grip with a McPherson (sp?) front end. This is caused by limiting the amount of suspension travel experienced in the front during cornering. This limited movement keeps the front suspension in the 'good area' of the McPherson camber curve.

Generally, once your lower wishbones are parallel with the ground, any more suspension compression will result in a decrease in camber. If the static camber at parallel isn't enough to compensate for the decrease in camber experienced by suspension compression, when the car rolls during cornering, the tire will not have a proper contact with the ground, and grip will be lost.

Eliminating some suspension movement = more dynamic neg. camber = more grip during cornering.

This is a small exception to what was stated above.