Slotting inner trailing arm mount Options

[yeahmag]

Let me start out by saying I think too much... With that out of the way, I'm wondering what the viability is of slotting the inner trailing arm mount to lower it, giving me more static camber. Here's the idea:

* Small slot of inner ear
* 8mm "elevator" with welded tab to control the location of the inner mount prior to tightening the bolt.
* Switch from the RSR Teflon bushings to monoballs and custom pivot shafts to allow for the increased angle

Nuts or brilliant?

I'm at something like 2.4 and would like to see 3+ if I could. Car is already pretty much in the weeds...

-Aaron

[Superhawk996]

OK. . . . still thinking about this some more and after reviewing Race Car Vehicle Dynamics by William F. Milliken and Douglas L. Milliken I'm going to retract my previous statement that lowering the inner point will lower the roll center. It will not.

It will increase static camber as you desire.

However, the problem of a semi-trailing arm is that camber gain also leads to toe-in which is not what you want either.

I'd go back to the previous question of whether you know where your camber gain is vs. bump steer. Camber gain on a semi trailing arm is a linear constant where bump steer is a non-linear curve. Depending on where you are at in that curve you might be able to tolerate the increased camber or not. Lap times would tell you the answer quicker than seat of the pants engineering.


I'd argue what you want is less body roll which is what you're trying to offset via the increased static camber.

less body roll is changed by altering the relationship between the roll center and the CG height. Either move roll center up (affected by the plan view angle of the semi-trailing arm pivot to body center line) or move CG down. Moving roll center up increases jacking effect which you don't want much of either.

You might also like this video about vehicle dynamics and suspension design which references 914's specifically in the segment between 5:44 and about 20:00.

https://www.youtube.com/watch?v=4wnpAGqVIAg

Maybe make your change reversible just in case you don't get the effect you want.