Thursday, January 2, 2014

RE-Xtreme RC Drift Bible. Suspension Arcs

When you are setting up your car. there are so many holes for the upper suspension arms. Why? Which one do I need? The answer could be ... all of them.

I'm starting with a simple example the lower sus arm is parallel to the ground.

This image above is default equal length double wishbone suspension. As you look at this all seems well. the tyre remains in a very similar position as the suspension rises. about the only thing that happens is that the tyre moves slightly inward.

But, When you introduce chassis roll the old camber scenario comes into play. It's all a bit skewed.

thats why you need to play with your chassis and not just sit it on a setup station. look at what the suspension is doing under compression and roll, imagine what the chassis position might be under power or decelleration with and without steering lock. It's all connected.


There is a reason why suspension engineers are engineers. they understand these curves and movements with ease. 

Lets look at what happens when you put your ball joints in different holes...

Moving the upper arm of the same length higher moves the arc. It immediately creates negative camber but the upper arc no longer only travels in an inward motion. It moves out then in. Creating a positive camber situation under compression. this is useful on the rear to get more traction as the chassis squats. 

This next situation changes the length and position of the upper arm.  Starting with zero camber, the effect is very noticible. but shorten the upper arm further and you may be able to start with negative camber and maintain it. But there are other ways.

This is a typical cambered setup. The upper arm outer link is moved inward. Unequal length non parallel arms and the offset basically maintain negative camber with little change. As the chassis rolls the tyres remain flat for traction.

But wait there is more. This variation creates the effect where both arcs only move inward. It provides a constant negative camber through the compression arc.

When roll is introduced the tyre becomes flat. Or does it? What about the other side of the car?

how much tyre contact do you really need?  These are things I'll leave you to experiment with.  A tight slow track or a long fast track has different demands as larger forces act on the car. But at least now you can understand what these are for.

Why is the upper arm mounted way inside the wheel hub on my DIB Rear. Look back through the images and see if you can understand the theory in practice?

Maybe next time we shall look at damper hole position(s)


Got a question or a comment. It doesn't hurt to ask.