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      01-17-2017, 06:43 PM   #14
NiNeTyOne
Touring cars rock
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Drives: e91 330xi / 997 GT3 Cup
Join Date: Jan 2016
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Quote:
Originally Posted by ajsalida View Post
The front bar fixes the latter issue so that loss of lateral traction (and forward due to AWD!) in front if it happens, happens in the best fashion: only after getting ALL the stick you can out of the front tire, then ALL the tread is overcome by side loads, not just a small portion of it. So fix this first then add rear bar to suit.
Snap oversteer after understeer is without question a damping and spring rate issue that is possibly exacerbated by inadequate rear brakes. This is made all that much uglier by the fact most car's rear toe links are shot (and are sloppy rubber to start with). If you can this is one area where the highest durometer poly makes a big difference. I have seen this issue so many times on student cars I cannot tell you.

This is probably the most common setup problem I've seen over the years (like 30+ of them). Most people mod the front brakes, put inadequate springs for the job on the car and then pile into corners pitching all the weight on the front, then the toe link ends are moving all over the place as the rear suspension comes back into play... Plowwwwwww and then, wait for it... SNAP!

BTW, Dinan has a nice fix for this but it's not cheap.

If I had $10 for every time I've seen cars set up like this I could retire in Monaco.

One other pro tip here.. add a tiny bit of toe to the rear when you do all this. Not much, just a couple seconds of arc. It will radically improve the stability of the car under hard braking once you add more rear bar. As a bonus, the car will be significantly more planted off the corner on throttle and not have a tendency to step out as much, giving you much better drive out of corners. I think factory is 0/0 toe in the rear.

On the e91 I run 0/0 front and toe the rears in 0°0'02"

Depending on the age of the car, what's worn and what's being replaced it's almost impossible to guess what the car will really handle like out of the box, but corner balancing the car will be a good start once the new dampers and bushings are in. I'd calculate the rake as it comes from the factory, lower the car on all four corners about 1-1.3" till it balances and you have essentially OE corner weight distribution and then drop the front about 2-3mm more. Much more than that and the camber is going to be too extreme for good tire wear on street until you get adjustable upper arms.

Keep in mind the car will settle over a couple weeks when you put all the new bits in.

Drive it and report back, but keep in mind, if the car has even 20k on it your bushings are garbage by any performance measure, so start there and at least make sure the chassis connection is solid.
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Last edited by NiNeTyOne; 01-17-2017 at 07:09 PM..
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