Diameter of the tire is important on an 8 too.
Sensors at each wheel and in the differential send speed signals to the computers. Standard answer is within 3% of each other front to back and within 3% of stock diameter on the rear for the speedometer accuracy.
18 inch wheels need 35 series in the 265 to 285 width ranges
19s need 30s and 20s should run 25 series (IE 275/25 x 20)
That isn't much protection for the wheels from potholes!
Terry,
Thanks for the info and nice to hear from you. I've been away from the boards for a while as life just keeps me busy. But now I'm getting to relax with my 8 again.
I've done some inquiries to the few wheel companies that make 20" and some claim that you can run a 30 series tire on the rear and 35 series on the front. I know that increases the overall diameter, but other than the speed sensors, what else can be affected? I heard one enthusiast say the 20" are too much load on the axle. I beg to differ if you are staying with the same over all tire diameter.
I still haven't had a chance to install the chip you gave me. I had to fix other things and been caught up. I even sacraficed upgrading my 8 with a nice sound system and touching up parking lot bruises (those inevitable dings) to get my wife an 02 530i (Welcome to the family!) and now matching cars.
To make a long story make sense (or atleast stay on tehn topic of wheels) I'm giving my wife my Breyton Magics and now looking for wheels for my 8.
Signing off for now,
John P.
Zitat von TerryYAlles anzeigenDiameter of the tire is important on an 8 too.
Sensors at each wheel and in the differential send speed signals to the computers. Standard answer is within 3% of each other front to back and within 3% of stock diameter on the rear for the speedometer accuracy.
18 inch wheels need 35 series in the 265 to 285 width ranges
19s need 30s and 20s should run 25 series (IE 275/25 x 20)
That isn't much protection for the wheels from potholes!
ABS and ASC traction control depend on the wheels matching each other front to rear with less than 3% difference. Alarm lights will be forthcoming with a bigger difference.
The Speedometer will be the casuality with more than 3% change from stock.
Hi all,
I have a good chance to buy a set of used 'M' wheels at relatively low price. They are with tyres that are 255/45R18 and 235/50R18, seems to be big, supposedly came from e38.
As far I know they are not at the e31 size but...
Change tyres or live all set all? (tyres not to be thrown away based on their conditions)
direct question:
which is the highest diameter that can be fitted to e31? (original one is about 630-640 mm)
Thanks for any idea, or advice,
Lorenzo
The limitation is in the front. The Spring perch sticks out over the tire.
I have had 265/35 18s on the front-- mind you this is with an offset of only 6mm. Clearance was relatively small at that size.
So whatever the rolling diameter of that tire is puts it pretty close to the limit.
Also if you do E38 wheels don't forget the Hub Centric adapter rings or you will be shaking pretty badly at speed 
Terry,
Thanks for your reply. I felt, it won't be fitted.
It wold have ben too nice. 
I should look for another set.
Lorenzo
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