Antisquat Effect On Handling

[BillyShope]

I'm starting this thread both as an aid and to correct some of my comments.
When considering the entire car as a "free body," it's easy to calculate front and rear wheel pair loads for a given acceleration. Normally, we can ignore internal forces and that would be that. Unfortunately, with a suspension, oscillatory internal forces can have a significant effect on wheel loads. With a rear wheel drive car, for instance, the front will always rise on forward acceleration. This not only changes the center of gravity height, but also starts an oscillatory motion in pitch which must be controlled by the shocks. And, of course, there is an oscillatory change in wheel loading.



At the rear, we can control rise and squat with antisquat geometry. Since the front is rising, this is difficult, but, with a static setting of 100% antisquat, we can come pretty close.

At launch time zero, it is generally recognized that a car which squats will start to "lose" wheel loading while one which rises wil "gain" wheel loading. From this has arisen the notion that any increase in antisquat geometry will change wheel loading and that would affect handling. This is NOT true.

In the first place, remember that any change in loading is oscillatory and will be quickly damped. But, more importantly, remember that we can control squat and rise with suspension geometry.

So, though we cannot avoid the load variations caused by the front end rising, we can certainly minimize such problems at the rear with 100% antisquat.

I mentioned...in the other thread...that this can be achieved with IRS. I would suggest that, rather than trying to "hit" that constant antisquat line with the intersection of your trailing links (or A-arm mounts), that you instead "go parallel" to that line and place the instant center at infinity. This normally minimizes the changes and the results are the same.

http://www.shopeshop.org

[Norm Peterson]

What happens when the car has rolled in a turn and the left and right side antisquat percentages have presumably changed and are no longer identical?

Wouldn't the be a brief period of time while the rear suspension's elastic elements are taking up however much squat the antisquats didn't prevent . . . that one rear tire would be providing slightly more traction than the other, and ultimately some small yaw effect?


Norm

[BillyShope]

What happens when the car has rolled in a turn and the left and right side antisquat percentages have presumably changed and are no longer identical?

Wouldn't the be a brief period of time while the rear suspension's elastic elements are taking up however much squat the antisquats didn't prevent . . . that one rear tire would be providing slightly more traction than the other, and ultimately some small yaw effect?


Norm

Yes, Norm, with transverse loading differences, you'll always have antisquat differences. Fortunately, the maximum difference occurs at the apex, when forward acceleration is zero, and gradually decreases as the acceleration increases (ideally). This is a condition with which we must live. (Doesn't proper grammar sound strange?) Incidentally, with a beam axle car, one might actually prefer more antisquat on the right than on the left in order to cancel driveshaft torque (C-type Jaguar).