Determining ride height.

[Scootsmcgreggor]

Rake is just one of the spices in a soup that can be made many different ways.

I've gotten that feeling, thanks for the confirmation. Now I suppose I'm interested in the general effect of rake changes (aside from weight shift) and the "why" behind it or when to suspect that a rake change may be a spice to try out in my horse soup.

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[TeeLew]

I've gotten that feeling, thanks for the confirmation. Now I suppose I'm interested in the general effect of rake changes (aside from weight shift) and the "why" behind it or when to suspect that a rake change may be a spice to try out in my horse soup.

1: If you raise either end of the car enough, it will put weight on the opposite, but rake adjustments are not enough to do this, so that's not really what we're doing.

What we are doing is making fine tuning adjustments on the roll-center heights with respect to each other, which slightly effects roll couple distribution, but, more importantly, we're changing the response of one end of the car with respect to the other. Rolling loads which are countered by suspension geometry happen quickly and have an effect greater than we might suspect.

2. Rake adjustments have their greatest effects during transitions. Raising the rear will often cause a quicker turn-in and lowering it will often produce better powerdown on exit. Both can be overdone. Too much rake, and the car will be nervous/unstable on entry. If it's too low, you may have to overslow the entry to get to the apex. This is just an example of some of the compromises to expect when testing rake changes.

 

[Norm Peterson]

Can someone explain why it is recommended on these chassis to run some rake? Why is it not as viable to run it "flat" and tune spring rates and bars accordingly to get the balance you desire?

Rake doesn't really do much in and of itself. It's the related raising and/or lowering of the front and rear geometric roll centers that does most of whatever changes. Roll center heights go to the early stages of lateral load transfer, like starting almost immediately. You have to be thinking about load transfer developing over a finite span of time, where roll center effects happen first while roll stiffness effects (springs and sta-bars) reach their steady-state last. Damper effects peak somewhere in between.

You could probably use the calculated suspension frequencies to estimate the lag between roll center effects happening and roll stiffness effects stabilizing . . . I'm guessing on the order of 200 milliseconds or so. It matters.


Don't use rake to assume that the end that was lowered more than the other is lower because you somehow made that end of the car heavier. Minor geometry effects aside, that didn't happen.


Norm

 

[Scootsmcgreggor]

Thank you guys. Hadn’t thought about roll center changes. Makes perfect sense. Now let’s see if I can learn the car well enough to make educated guesses on what to change when it’s behaving a certain way.

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