I'll probably be sorry for this input, haha...

But that sounds like a bad thing. Maybe thats what you are saying, I dunno. To be clear, your saying a shorter arm will cause more negative camber under compression (at least thats what I'm picturing happening in my mind). Wouldn't you want more positive camber during the compression motion, say in a corner? If I'm already running a bit negative and the shorter arm brings in even further, I seem to be canceling out the benefit of the negative camber to bring the tire straight up in a corner?


Either I just made a complete ass of myself or... well, yea.

 

Thank you Epstein.

 

So I turned this thread around from a bash-fest into a tech thread. I hope you don't mind!

 

Camber gain is a good thing. Knowing the camber curve is even better. Yes I can see where it seems reasonable to not want more camber when you're already running 3* and burning up the inside of your tires. The idea is to match your camber gain to your body roll. Camber gain is added angle to the ground. Body roll is subtracted angle to the ground. For example, if your car handles pretty flat, you might compress 1" on the outside (in a hard turn) and lift 1" on the inside. Seems reasonable... and inch isn't a whole lot. Well 2" of difference total and a 66" width, throw some Sine in there and it's about 2* of body roll. That's 2* of camber angle you've lost. So if you had 2* static camber and no camber gain, the tire would be completely vertical. Camber gain is adding a few degrees to keep a good angle to the ground during a turn. Want less? Decrease the camber gain or run less static camber. You don't need any camber to go straight. You need it in turns. Wouldn't you want a model where camber increases as compression/effort increases? BTW, camber also decreases in lift on inside of the car. That's the other side of camber gain under compression... camber subtraction under lift.

Also BTW, slammed cars have very little to no camber gain in the front due to geometry. Tendancy to understeer, anyone?

 

^Awesome post Epstein! Thank you.

 

Awesome!! I knew they did something!!

Sean...

 

Thanks for the reply. I do understand what you are saying, but I think I just have a different opinion still. For instance, camber curves are only consistant to a certain point, and it seems the arm length directly effects the amount of time that they stay that consistant. So like I said, the shorter arm will bring the compressed wheel's camber in further than what seems desireable, and before you know it, you have two totally unrelated wheel/suspension angles in that hard corner. If I have a longer arm, I will be able to keep a more specific camber angle throughout the entire turn (it will take longer for the camber to change under compression/lift)...

p.s. - I know what i'm thinking, but i had a really hard time putting it into words, or at least typing them. sorry if I'm still unclear, haha.

 

I noticed a little bit of understeer a while back when I lowerd my car to where it would almost be considered slammed. But I found that it was understeering because I couldnt get the back end to rotate, which in turn would cause loose front end grip and I had to back off entering a corner or getting on throttle sooner. So I ran less dampening adjustment (softened up) in the rear so it would roll a bit more and the understeer went away for the most part and I havent had any trouble after that.

As for traction rods. I got the SPL units and ran Epsteins mentioned 8" length and it made a huge difference in cornering. It felt like the car would roll a bit more but it was much more stable and the rear didnt hop around over less than smooth surfaces like it did before and I could stay on the throttle all the way through a long sweeper or get on it so much more quickly in a turn.

 

hahaha, I dont.
I'm actually interested in that post you made.
But I REALLY didn't feel a difference in the stock vs any other traction rods..
Is it really that noticeable or does it just slightly clean up the slop of bump steer when cornering hard?

 

I think I know what you're saying, and the theory is basically true. I just don't think your perception is right. Yes, in unequal length a-arm suspensions (technically the Ruca and Trac arm together make the top A-arm), the shorter the upper arm relative to the lower arm, the quicker the camber angle increases.

Again, your problem is that you keep referencing the angle between the tire and car's vertical; camber. That's not what matters. It's the tire's angle with the ground that is the important part. The difference is body roll. And the effect that makes up for body roll is camber gain. Therefore it's feasible to build/tune a system to keep the tire at a fixed angle with the ground at all rolls/compressions. Now the rest of the misperception is the assumption that you don't need more camber gain. And you can't say that without measurements. And yes I have them. But then you can get into a debate about increasing loads and proper camber angles, so it really don't progress the topic much.

Basically, at a ride height of -2", the stock length traction arm and RUCA length set to -2.25* camber will gain 1* of camber per 1" of compression. If you shorten the traction arm by 1/4", the camber will gain 1.5" per 1" of compression. All measurements done in my garage.