Goodbye Kansas

[strictlypersonl]

Lateral movement of the roll centers is an inherent characteristic of a short-long-arm design. The basic ERA intent is to keep the outer roll center fairly close to the ground so that there is minimal laterally-induced instability on the outer tire under cornering loads.

[ERA2076]

Bob - I read this as you want to control jacking.

Trivia -

If one believes the car rolls around the geometric roll centers; at 3 degrees of roll, the front has moved laterally 20 inches (still inside the ball joint) and the rear has moved 1.5. Our roll axis is now at a significant angle (in plan) to the mass centroid line which does not intuitively seem like a good thing to me.

If I did not want to run it so bad, I would seriously look at moving the front inner pivots inboard .5 inch and lengthening the arms accordingly.

.5 inches cause it looks like it could be done and it would cut the difference by half.



chr

[Bobcat]

Bob ... does this also mean that keeping the lower control arms as level/parallel to the ground is more important to handling than lowering the front and changing the roll centers ??

Bob

[ERA2076]

It is in my world. Lower it and the roll moment increases. Raise it and jacking is increased. Raise it or lower it and the camber curve is more aggressive which could or could not be beneficial. Putting them parallel is a good compromise. A rule of thumb is to run the longest virtual swing arm you can. One would have to test if raising or lowering the roll centers would be of benefit. i.e. the car is quicker with more roll as opposed to more jacking and the reverse. With mine set parallel the front is 1.2 off the ground and the rear is 1.9. It seems one would opt for lowering and controlling the roll with bars or springs provided it did not ruin the camber curve and or mechanical grip.

I can't see how adding jacking could ever be good which is why I never opt to raise them beyond parallel to the ground. That said, the 26.5 tires have not helped me

chr

[strictlypersonl]

Originally Posted by ERA2076

... A rule of thumb is to run the longest virtual swing arm you can...
chr

When we first started out, we did tire testing with BF Goodrich. (Back then the CompTA was the hot tire.) It was their recommendation that we shorten the virtual swing arm length in order to increase the camber gain. Street tires haven't changed that much since then. We're still using the same sizes and profiles in 15" sizes. The profile of 17" wheels is somewhat different, but the tires still require some camber correction on roll.

Formula cars are different. Roll is negligible and tires are very wide. For them, roll compensation is neither necessary nor desirable.

On our cars, you could run a lot of negative camber, but that has negative consequences on tire wear and loss of traction of the inside tire. We're still better off with the compromise of some partial camber gain on roll.

Or you could put in springs so stiff that roll would be near zero, and bounce down the road from hump to bump.

[ERA2076]

Or we could spring it for max grip and screw with the bars to manage the roll.

chr