staggered setup, strange diameter?
 

Sorry to post this without doing some research first, but I just picked up a set of 19" staggered 63's, and when I was showing my wife we realized that A) the diameter of the fronts (255/50) was about .5-1" wider than both the backs (285/45), and the stock 17" on the car now.

The rears, the tires are shot, and the fronts the tires are relatively new, so could that PLUS tire pressure (not sure what they are set at), cause that discrepancy, or is something awry?

I'm going to assume that you haven't grasped the full meaning of "staggered" wheels & tires yet....or you haven't grasped the calculation & interplay of tire width & tire aspect ratio in the overall diameter/circumference of a wheel/tire set up when the wheels have different widths but the same height. :)

Since this is slightly complex...and already written very well...check out a site like http://www.tirerack.com/tires/tirete...jsp?techid=200 ...they do a great job in explaining width/height/aspect ratio etc of staggered wheels and/or a set of wheels/tires that are the same size on all 4 corners.

Staggered Style 63 wheels have fronts that are 9"x19" & rears that are 10"x19". As written on the chart on your door and the owners manual...BMW lists the recommended tire sizes for a straight or staggered set-up. As the tire gets wider...the aspect ratio gets smaller so that it retains the same rolling diameter/circumference. That's why the front & rear tires are different.

You can also input the tire sizes into a tire size calculator (try Tire Size Calculator - Tire & Wheel Plus Sizing ) and get the specs for various tire sizes (input your regular 17 set-up as the base, then input the staggered 19" tire sizes...then compare).

Good luck, I hope this makes sense. :)

In addition to what Qsilver has posted, I suggest you look up the meaning of "diameter" and then "width". You have used the terms interchangeably, and they have far from the same meaning.

255-50 and 285-45 are the same diameter, 255-50 has a sidewall height that's 50% of 255mm, 285-45 sidewall height is 45% of 285mm.

Doh... I totally meant height not width. I'm stupid, but not that stupid. The new set is TALLER

Are you asking why the rears wore more quickly than the fronts? You have the proper tire size.

If your rears are wearing quicker you have worn suspension in the resr

never mind - I'll play with them tomororow. I think the fronts are way over inflated. It just threw me for a loop when the rears were the same height as the existing tires, but the fronts were noticeably higher. Granted, a fully worn vs brand new tire would have a nearly half inch in diameter of wear (right?) and so that might be part of it as well.

Now I need to find a set of matching rears that wont break the bank.

then a little wheel work, maybe some plasti-dip, a balance, and we are good to go.

scratch that. the idiot I bought these from put 255/55!!! not 50 on here. that 100% explains it. Christ this just got complicated....

The closest staggered size you can get is 285 50 19 which has a sidewall height of 5.61", vs 5.52" for the 255 55. I dont know if the difference is within allowable specs.

Or maybe you can put 255 55 on the rears too, I see some people here doing that (putting same size front and rear tires on staggered wheels). I dont know if the stretch on wider wheels appreciably affects rolling diameter and any effect on the drivetrain though. Just some less expensive avenues to consider.

Yeah, I just might flip these on to someone who's willing to buy 4 new tires. That size doesn't exist. The fronts are worn, so I'll go out and set the correct pressure then measure the actual diameter. Maybe the wear on the tire offsets the difference against a brand new rear tire.