Comp Clinic Handling Presentation

[2BWise]

Where does rake come in here? In the past I might have altered rear ride height with (say) half a turn on the rear pushrods and this would quickly sort exit oversteer.

I guess my puzzle is both rear ARB and rake alter exit oversteer/understeer but when should I use one tool vs the other. Clearly I want to keep my nice turn in while having a balanced exit.

Dave's comment in regard to the roll center height is spot on. I just want to comment on using one versus the other. Generally speaking, in my experience, ARB changes have a greater magnitude to handling balance change relative to RCH (roll center height) changes. There is a caveat though, it depends on how much your RCH changes with ride height. Without measuring the RCH and knowing the roll stiffness contribution of the ARB it is impossible to be sure, but you can evaluate both of those and quantify their respective changes in magnitude. Personally, beyond simply a handling adjustment knob I also use this to data evaluate ride height changes vs spring rate changes. That way I can change both at the same time and end up with a car that has the same oversteer/understeer balance.

[DaveW]

Dave's comment in regard to the roll center height is spot on. I just want to comment on using one versus the other. Generally speaking, in my experience, ARB changes have a greater magnitude to handling balance change relative to RCH (roll center height) changes. There is a caveat though, it depends on how much your RCH changes with ride height. Without measuring the RCH and knowing the roll stiffness contribution of the ARB it is impossible to be sure, but you can evaluate both of those and quantify their respective changes in magnitude. Personally, beyond simply a handling adjustment knob I also use this to data evaluate ride height changes vs spring rate changes. That way I can change both at the same time and end up with a car that has the same oversteer/understeer balance.

I have had both scenarios. On my Z16, the rear swaybar was quite soft, and made little difference in balance. OTOH, rear ride height (roll center height) was my main tuning tool. 1/8" change in RH was a BIG change in balance.

On other cars, rear swaybar stiffness made more difference. So it depends on the exact setup of your particular car.

[mark elder]

Thanks guys. I had not thought this through properly. It now seems obvious to state that an ARB only affects a car dynamically when roll is changing (shocks would be in the same situation; they are not changing length in a steady state).

And in a smooth transition from turning in through to the exit, roll change is slow and gradual.

I am guessing that around the apex region, the amount of roll does not alter much (assuming a smooth driver etc). Therefore any change in power around this will be mainly affected by rake (assuming no loss of traction on exit). If this is true, my power induced oversteer is best modulated by altering rake.

Have I got this correct?

Thanks

[DaveW]

Thanks guys. I had not thought this through properly. It now seems obvious to state that an ARB only affects a car dynamically when roll is changing (shocks would be in the same situation; they are not changing length in a steady state).

And in a smooth transition from turning in through to the exit, roll change is slow and gradual.

I am guessing that around the apex region, the amount of roll does not alter much (assuming a smooth driver etc). Therefore any change in power around this will be mainly affected by rake (assuming no loss of traction on exit). If this is true, my power induced oversteer is best modulated by altering rake.

Have I got this correct?

Thanks

It would seem so. But, obviously, you need to try it to definitively assess its effect.

And, of course, you have to remember that power application should cause the rear to squat, reducing rake and power oversteer unless:

o the springs are too stiff
o the bump damping is too high
o the rear suspension has anti-squat built in - one of the main offenders in creating power oversteer.

So there are a lot of variables to consider when diagnosing power oversteer. Nothing is as simple as it first appears.