Re: M-Contours from Bekkers (8.5 x 17 et 13) (archive)

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I have those exact wheels on my E28 M5 and wish I had bought them at the reduced price! I emailed Mel when he had his M5 and those are also the wheels he installed. I don't remember which tires he had but I actually have clearance problems while he did not. He indicated to me that he had 235-45-17, as I do. I have Potenza RE-71's. After installing the 17x8.5, ET13 wheels, I had interference with the rear wheel well lips. The outer side wall of the tires rubbed against the top, inside edge of the wheel well lips. I had a lot of rubbing on the left side with very little on the right. I did some calculations before buying them and knew it would be close but thought that since Mel didn't have any problems that I wouldn't as well. I guess all cars have a little "manufacturing slop" built into them and so I think the rear suspension assembly sits slightly to the drivers side. Since I wanted to keep the wheels, I did two things to gain the needed clearance. By the way, I have a stock rear self-leveling suspension which kept things from rubbing most of the time. First of all, the fit was so tight that "rolling the fender" was not going to work. I got my grinder out and removed a fair amount off the top of the left inner lip and then recoated with undercoating. I did this several times to try to get just enough material removed. Well, after removing a lot of metal, I decided to take a different approach. I checked the clearnce up front, which there isn't much of between the tire and strut housing, and decided to mill 2.5mm off of the wheel mounting pad. I bought a set of five wheels so I did it on the spare to see if it would work. Well, it has. I'm sure you are all wondering about the strength of the wheel. Though I am a mechanical engineer, I have no finite element analysis to show what kind of forces the wheel can now withstand. I did examine the mounting pad design and took some measurements in comparison to other wheels that I have seen and felt that there was enough material left that it would not compromise the wheel for the stresses that my car would see. Though this is no gurantee that the wheel has enough remaining strength, I have taken my car to Portland International Raceway for a lapping day and have had no problems, so far. I plan to examine the wheel over several more miles before considering doing the others.

To mill the wheel I used a friend's CNC mill. I am very lucky to have a friend who has a Bridgeport CNC mill in his basement! It was actually very easy to do.

As a disclaimer, I don't recommend this to anyone but this is how I approached the fitment problem.

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