corner entry push

[John Hannaford]

Scott,

Exactly, and it does include the roll rate from both springs and bars - and should include tire rate and chassis effects, but for practical use these are ignored. I would prefer to use "total roll resistance rate" rather than "wheel rate" for this discussion, to be clearer, as wheel rate in roll can be dfferent than the wheel rate in bump, depending on the suspension design (your bump and roll rates from the springs should be equal with independent A arms). They become very different if sway bars are in the mix.

So the expanded version would be (Front Total Roll Resistance Rate/(Front Total Roll Resistance + Rear Total Roll Resistance)) Roll resistance is usually expressed in different units than wheel rate in roll, being a torque rather than a linear force, but they are proportional and since we are looking for a ratio, the units drop out anyway.

For your setup, and this is a just a guess because of your unknown sway bar rate, but working backward from the result you got - that it's noticeably more neutral to loose, an effective bar rate of 150 would give an initial FRRD of .50 and your changed setup would be at .45 This would predict some shift in balance toward loose, but also better transients and improved camber control.

If you know the dimensions of your sway bar, (inside and outside diameters, effective bar length, effective arm length and motion ratio of the end mounting points - same as the spring value if the attach to the same point) there are formulas to calculate the rate, although the effective rate is usually less than that because of bar and mount deflections.

I should have pointed out that because a given car is neutral at an FRRD of .45, for example, that doesn't mean that the next one will be. I didn't mean to imply that because some Cobras have FRRD % of .6 to .7 that they will push because of that number. It's merely an observation that the ones I've seen in that range do seem tight. The number only tells you approximately how the setup will balance. You really have to test the setup to find what FRRD % will give the best handling compromise, but once you know it, it's real use is revealed as you can use it to calculate how to increase or decrease your total roll rate, or change the amount you get from bars versus springs to adjust to specific track conditions, while maintaining the balance you've found works best.

Sorry for the novel, but it's a favourite subject.