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Re: bmw-digest V5 #241 (Speedo and Larger Diameter Wheels)

I am curious abou this! I was told by a BBS distributer that my car 
('95 530i) had an electronic speedo and it didn't matter if I stayed 
within 3% of the rev's per mile (rolling radius) when considering tire 
sizes for plus sizing. When I checked with my BMW dealer I was told 
there is no such thing on ANY BMW! I was told (by numerous sources) I
had to stay within 3% of the rolling radius so as not to mess up the ABS.
Does anyone know what the real story is? Please post to the digest since 
I think this would be interesting to others.

Regards,

Kim Watters
E34/'95/530i/5-speed 
BMWCCA

> From: Jonathan Lukens <jlukens@domain.elided>
> Date: Mon, 16 Sep 1996 18:17:59 -0500
> Subject: Speedo and Larger Diameter Wheels
> 
> >The speedometer on later BMWs are electronically triggered from a sessor
> >mounted
> >on the diff.  This is counting the revs of the half shaft so a tire diameter
> >change will affect the sppdo but the gear changes are prior to this so
> >they will
> >not.
> 
> Just how much does going to a larger-than-stock wheel affect the
> electronics and accurracy of the speedo in late model Bimmers?  An
> interesting subject to explore...
> 
> Jonathan
> jlukens@domain.elided
> 
> 
>