Timm's Fitting replica alloys to the BMW E31, E32 and E38
You can't beat the look
of an M-Parallel on just about any BMW. The problem is that they are very
expensive, new ones fitted with tyres will set you back £2k at the very least.
The good thing is that there are loads of replica m-pars that look very close to
the real thing:
A set of these, staggered, 8.5J x 18" and 9.5J x 18" complete with tyres can be had for around £600.
However, what they don't tell you is that they don't directly fit the E31 (or the E32 and E38). Replica's nearly always have a centre-bore of 74.1mm, this is so that they will fit the E39. Fitting these wheels to any other BMW will require spigot rings to decrease the bore to 72.6mm. Here's the rings that are usually supplied:
They are made out of plastic and are pretty useless. After fitting the m-pars to the E31 using these spigot rings all was OK for a while until some 'spirited driving'. After that, the dreaded 50MPH shimmy was noticeable. I measured the rings after they had been used a while, they had distorted and the thickness of the wall varied by 0.1mm - 0.4mm. They were obviously not man enough for the job.
The other measurement of the replica alloys that is not spot-on is the offset, the replica's are usually 20mm. The E31 needs a 10mm - 15mm offset. So, I bought these, SP86 spacers along with 10 x longer bolts:
They are 10mm thick hub-centric spacers, they have a 72.6mm hole in the middle and a 74.1mm nose. They do two things, they space the front wheels outwards to change the offset from 20mm to 10mm, they also increase the effective bore size from 72.6mm to 74.1 to suit the replica's.
I checked the fit of these spacers on both the hub and the alloys. Both fitting showed a reasonably loose fit. In particular, I reckon that the bore of the replica's is around 74.3mm and that is just too floppy for me! To make sure everything was an perfect fit I decided to use a shim to increase the bore diameters. Here's the shim material, it is 0.002" or 0.05mm:
I also bought some Kapton tape, this a bit like Sellotape but can withstand very high temperatures and will not compress. I cut a strip of shim material with a pair of scissors and stuck it to a length of Kapton tape:
.....and wound it onto the spacer:
......and squished the top over:
I then made sure it was a good fit in the alloy, I used some grease on the inner-bore and it twiddled in nice and tightly:
The hub needed just two turns of Kapton tape:
I removed the wheel
centre cap to make sure everything went together properly, it all fitted easily
That sorted the front wheels out nicely. I went for a spin to make sure there were no problems and it was absolutely perfect.
For the rear wheels, I did not need spacers, instead I used metal spigot-rings:
Again, these were not a tight fit so I increased the hub diameter with one turn of Kapton and then fitted the ring:
Two more turns of Kapton over the ring:
....and on with the wheel:
The results were excellent, not even a trace of shimmy or vibration.
All done, time for a cup of tea!