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      02-01-2019, 08:02 PM   #45
72dan's Avatar

Drives: 2009 M3 DCT coupe white/beige
Join Date: Nov 2010
Location: Los Angeles

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adjustable sway bars front and rear

The car came with a rear bar and still under steers. I cannot imagine running no rear sway bar. I run adjustable bars front and rear.

Spring rate is not the correct way to balance the car. It can be done within reason but if you put enough rear spring in the car to eliminate the need for a rear sway bar the car will skip over bumps coming out of corners and lose traction.

Someone here posted front engine race cars don't use a rear sway bar. That is incorrect. Some classes may not allow you to add a bar if the car didn't come with one, but in most instances better handling is achieved with a rear bar.

In fact, front engine front wheel drive cars generally have a larger rear bar than front bar. I tracked a 1988 Acura Integra for years, 3/4" front bar, 1" rear bar.
The reason being is that the front tires are overloaded with 60% of the weight already, then also used for traction, the front tires overheat. A stiffer rear bar transfers more load to the outside rear tire. I could lift throttle into the corner and the back would come out and rotate, then as soon as I got back on the power it went to neutral to slight understeer. That car was really fast at 2200 lbs I used to go out to Street of Willow with Porsche Owners Club and run faster than the 993 and 997 turbos on street tires and really piss them off with 185/60/14 Yoko A008RS2 tires on stamped steel $25 wrecking yard wheels off a Honda.

The E92 is still a little front heavy. You will end up with a front bar that is larger diameter than the rear for neutral balance. The first time I ran my E92 at the track with factory EDC and factory sway bars I had a brand new Michelin Pilot Super Sports. I chunked and ruined a brand new set of front tires in a day at Streets of Willow, back tires looked brand new. Needs more rear sway bar. When I put aftermarket bars with factory coilovers and sticky tires it balanced the car until I eventually cracked and broke the rear sway bar causing extreme under steer.
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