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Date: Fri, 9 Nov 2001 11:38:01 -0800
Subject: ABS system on 95 M3s

The ABS system on 95 M3s is a 4 detector (one at each wheel), 3 channel activated system. The rear brakes are on a common line. Each of the fronts are on their own line. This means that if the system detects lock-up on one of the rear wheels it will cut back on brake pressure until that single wheel begins to rotate again. Obviously this cuts down on the brake pressure being applied to the opposite non-locked rear wheel as well. Hence your braking efficiency might be slightly less. However, since the majority of your braking is done on the front wheels the rear brake might only be seen under severe duty or extreme circumstances with a significant difference between left and right traction (one wheel in sand or snow, the other on asphalt perhaps?)

The 1996+ M3s have ABS that is 4 channel sensor, 4 channel brake line actuation and so can vary the brake pressure independently on each wheel for presumably better braking under extreme conditions or significant differences between left and right traction surfaces to the rear wheel.

I personally don't see much of a problem with moderately different wear amounts on rear or front. It becomes a problem if it is extreme leading to different traction from side to side, or, if it is extreme you will be asking the LSD (limited slip differential) to be doing more work than it usually does. I have heard that if you are using a limited use spare on a LSD axle then you shouldn't use it for a significant amount of time because the LSD (and its oil) may significantly heat up potentially causing damage. I don't know if this is true or not. But it does make sense.

And, in cars with traction control systems or systems that detect a "differential" rotation between all 4 corners a significant difference in wear of the tires may show up as activation of the traction control system or dynamic stability system, or in the new E46M3, telling you that one tire is low on air (the system works on the basis that a tire that is low on air will have a smaller effective diameter and hence showing up as a different rotational speed than the pumped up tires).

95M3CSL (no traction control, no DSC, no flats either.....just bald tires happily worn evenly!).

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