Rear suspension design - squat and toe? - Page 2

Malek@MRF · 11-13-2012, 10:15 PM

The suspension is designed to reduce toe in during squat and will increase toe in when weight is transferred off the back end.

Meaning if you have 3/32nd inch static toe in, during squat the toe will decrease to lets say arbitrarily 1/32nd-1/16th. It will NOT increase toe while squatting.

Malek

CanAutM3 · 11-13-2012, 10:19 PM

Just to throw something more to think about:

Let's assume that the rear suspension yields toe in when compressed and toe out when relaxed, as with BigJae's original assumption.

When under a cornering load the outside tire would toe-in and the inside tire would to-out, this would yield a nice rear steering into the turn. Great for high speed stability but not the best to rotate the car.

Further, when you accelerate, the traction force pulls the rear wheels forward thus increasing toe-in. If the suspension dials in more toe-in as it compresses it would make the situation worse. The same applies to braking where traction pulls the wheels back increasing toe-out. If the suspension increases toe-out as it relaxes, it would also make the situation worse under braking.

This is what leads me to believe that the suspension is tuned the other way around. Just based on intuition though. It is not easy to come to a conclusion here

...

bigjae1976 · 11-13-2012, 10:39 PM

Sheesh...I have no idea which way it goes. I might throw it back on the alignment rack to check it again. My shop is super cool about it...they'd be in!

CanAutM3 · 11-13-2012, 10:44 PM

Quote:

Originally Posted by bigjae1976

Sheesh...I have no idea which way it goes. I might throw it back on the alignment rack to check it again. My shop is super cool about it...they'd be in!

Please let us know, you definitely spiked my interest

JamesClay · 11-14-2012, 08:57 PM

Lots more going on in the rear of that car than some toe change. In a stock rear suspension geometry, the anti-squat plays more of a part than almost anything. Set toe in slightly like normal - will put you in the right place.

The only time we have messed with exotic toe settings was combined with Motorsport geometry where we could get rid of a bit of the anti and move the toe link point to induce rear steer, which made the toe in under braking, out (or straight) under squat, and steered the car with roll.

Malek@MRF · 11-14-2012, 09:44 PM

Quote:

Originally Posted by bigjae1976

Sheesh...I have no idea which way it goes. I might throw it back on the alignment rack to check it again. My shop is super cool about it...they'd be in!

Read my post. It will clear any confusion.

Car will TOE OUT under squat, car will TOE IN when braking or diving and the rear end goes up.

11-13-2012, 10:15 PM	#23
Malek@MRF BimmerPost Supporting Vendor Drives: E92 ZCP Melbourne 6MT Join Date: Jan 2008 Location: Irvine, California Posts: 2,832 iTrader: (5)	The suspension is designed to reduce toe in during squat and will increase toe in when weight is transferred off the back end. Meaning if you have 3/32nd inch static toe in, during squat the toe will decrease to lets say arbitrarily 1/32nd-1/16th. It will NOT increase toe while squatting. Malek __________________ MRF on Facebook Southern California's largest & most reputable E9x M3 forced induction & suspension facility. *"Performance; Uncompromised."*

11-13-2012, 10:19 PM	#24
CanAutM3 Major Drives: 2008 E92 M3 SS2 DCT Join Date: Jan 2012 Location: Montreal Posts: 1,275 iTrader: (0) Garage List 2006 Audi S4 [0.00] 2008 BMW M3 [0.00]	Just to throw something more to think about: Let's assume that the rear suspension yields toe in when compressed and toe out when relaxed, as with BigJae's original assumption. When under a cornering load the outside tire would toe-in and the inside tire would to-out, this would yield a nice rear steering into the turn. Great for high speed stability but not the best to rotate the car. Further, when you accelerate, the traction force pulls the rear wheels forward thus increasing toe-in. If the suspension dials in more toe-in as it compresses it would make the situation worse. The same applies to braking where traction pulls the wheels back increasing toe-out. If the suspension increases toe-out as it relaxes, it would also make the situation worse under braking. This is what leads me to believe that the suspension is tuned the other way around. Just based on intuition though. It is not easy to come to a conclusion here ... Last edited by CanAutM3; 11-13-2012 at 10:41 PM.

11-13-2012, 10:39 PM	#25
bigjae1976 Brigadier General Drives: 04 330Ci, 11 E90 M3 Individual Join Date: Mar 2006 Location: Milwaukee, WI Posts: 4,066 iTrader: (8)	Sheesh...I have no idea which way it goes. I might throw it back on the alignment rack to check it again. My shop is super cool about it...they'd be in! __________________ Sponsored by Momentum BMW #593...We Bleed BMW BLUE!

11-14-2012, 08:57 PM	#27
JamesClay BimmerPost Supporting Vendor Drives: BMW 3 Join Date: May 2005 Location: Virginia Posts: 232 iTrader: (0) Garage List 1996 320iT [0.00] 2003 M3 [0.00] 2006 325i [0.00] 2008 M3 [0.00]	Lots more going on in the rear of that car than some toe change. In a stock rear suspension geometry, the anti-squat plays more of a part than almost anything. Set toe in slightly like normal - will put you in the right place. The only time we have messed with exotic toe settings was combined with Motorsport geometry where we could get rid of a bit of the anti and move the toe link point to induce rear steer, which made the toe in under braking, out (or straight) under squat, and steered the car with roll. __________________ James Clay http://www.bimmerworld.com http://www.bimmerworldracing.com

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