Wheel centerbore question

[wludavid]

Sorry for the dupe for those of you who frequent the pelican parts boards, but here goes.

As I explained in this post (http://forums.bimmerforums.com/forum/showthread.php?t=207663) I bought a set of stock Mini wheels to put on my e30. I finally got around to doing that today only to find out that the hub on the car is too big for the centerbore on the wheel.

After doing the research I should have already done, I discovered that the hub is 57.1 mm and the centerbore on the wheel is 56 mm. Close only counts in hand grenades right?

Anyway, the way i see it I have 3 options:


Buy 8mm spacers and new lug bolts (or pony up to upgrade to lug studs and nuts). There is a 6 mm gap between the hub and the wheel, so 8mm would do it, and not change the suspension geometry much.


Have custom 6mm spacers made to disturb the suspension even less. I'd still have to buy longer bolts I think.


Have a machine shop bore out an extra 1.1 mm from each wheel. I like this option, but I haven't had much experience with machine shops, nor am I sure it's safe to go around machining wheels.


Would anyone like to weigh in on these options, or add one of their own?

David

[Conepunter]

Talk to the local BMWCCA clubracers and you can probably get a local machine shop reference. Boring out the centerbore is the right way to do the job.


Ed

[Bill]

All wheels have the center bore machined , thats how they change them for different models, and the same goes for the lugs. They get the wheels in as blanks (no lug) and do the machining to fit.

[randywalters]

Mini wheels have WAY too much offset for an E30, but i think if you have the centers machined to 57.1mm and get like 15mm or 20mm H&R double-hubcentric spacers you can make the wheels work. Awful lot of expense and trouble for skinny little Mini wheels though.

What size & width are the wheels, and what is the offset?

[wludavid]

Mini wheels have WAY too much offset for an E30, but i think if you have the centers machined to 57.1mm and get like 15mm or 20mm H&R double-hubcentric spacers you can make the wheels work. Awful lot of expense and trouble for skinny little Mini wheels though.

What size & width are the wheels, and what is the offset?


The wheels are 15x5.5 with an offset of 45 mm. The stock e30 wheels have are 14x6 with an offset of 35mm (as I'm sure you know). To minimize the change to the stock scrub radius, the offset of a 5.5 inch wheel should be about 41 mm (35mm + 6mm, aka 35mm + 1/4 inch).

I had a better explanation in my mind as to why that is, but apparently my mind is stuck on Friday mode and can't conjure it up. What I do know is that the bottlecaps came in 14x6 with a 35mm offset and the basketweave (also stock e30) came in 14x6.5 with a 30mm offset. So wheel width, scrub radius and offset are all interrelated.

[wludavid]

Eureka! I just called Tire Rack and the guy I talked to confirmed my suspicion. When you change the width of the wheel, you are effectively adding or subracting width from each edge. For example, a 15x7 wheel will have 0.5 inches extra on each edge as complared to a 15x6 wheel. So because you've moved the hub outward, in order to maintain the same scrub radius, the offset needs to be adjusted as I described in my post above - subtract half the added width of the wheel from the stock offset for a wider wheel and add half the subtracted width to the stock offset for a narrower one.