Quote:
Originally Posted by GregW / Oregon
Well, 125/70-80 is, as I calculate it, 2 x.70 = 1.4 x 125 = 175/25.4 = 6.9 = 18 = 24.9" OD. Stock 19" PS2s are 25.8"F & 26.3"R (18s are 25.7"F & 26.3"R). So, that's 1.4" smaller than rear, a little worrisome for the diff.
135/80-18 calcs at 2 x .80 = 1.6 x 135 = 216/25.4 = 8.5 + 18 = 26.5" OD. That's closer on both front and rear than the 125/70s (only 0.2" off in rear). I would go for the Caddy size, myself.
I am not 100% sure of the CB and ring. Ben at Tire Rack says, "I would guess that the X6 spare may not be machined in such a way as to accept a centering ring, but have not tried it myself to find out. My database has the X6 listed as a staggered centerbore (!), so BMW may have some kind of ring to use if the spare is going on the "small" hub. I do have part # 72.56RING which goes from 74mm to 72.56mm. I have no guarantee that this would work, but if I had to try something, that is what I would use."
With a steel wheel, as Ben says, a standard alloy wheel ring may not work. Worst case is you may get a slight vibration without the ring, but hey, it's an emergency, right? Rings are cheap, though, so you could try one.
So, jury is out. Care to be a test case?!!
Edit 3/3: My parts guy says the wheel is $165.
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Dear Greg,
I think you may be right: the 135/80-18 size might be a better overall fit. On the other hand, I asked Mike Miller about the effect of the smaller size on the dif and he assured me it's not a problem. I'll try the plastic centering ring and let you know how it works.
Godspeed,
Tom