[200q20v] Tire Size for New Wheels on A8

[Paul Waterloo]

I purchased some summer wheels for my 97 A8. They are the forged five spoke
wheels off of the A6 4.2 quattro. After determining what the OD of the tire
will be with the stock tire for the wheel (the ones that come on the A6
4.2), I see that it is smaller than the stock A8 (16", 17" or 18" stock
wheels). The offset is also different from the 17x8" polished wheels or
18x8" S8 wheels. Those have an offset of 48mm, my new wheels have an offset
of 35mm. I don't think that's a big deal though, the wheel will sit out 1/2"
(13mm) further.

Here are the details:

STOCK 16" WHEELS (A8 7.5 width)
Tires are 225/60/16, therefore:
Wheel OD 406.4 mm (16")
Sidewall (225)(.6)(2) = 270mm
OD = 676.4 mm

STOCK 17" WHEELS (A8 five spoke polished 8" width)
Tires are 225/55/17
Wheel OD 457.2 mm (17")
Sidewall (255)(.55)(2) = 247.5mm
OD = 679.3 mm

STOCK 18" WHEELS (S8 8" width)
Tires are 245/45/18, therefore:
Wheel OD 457.2 mm (18")
Sidewall (245)(.45)(2) = 220.5mm
OD = 677.7 mm

As you can see, all three wheel/tire combos are within 2mm OD of each other,
makes sense to me.

So the stock tires on the A6 4.2 are:

A6 4.2 Quattro Stock Tires
Tires are 255/40/17, therefore:
Wheel OD 431.8 mm (17")
Sidewall (255)(.4)(2) = 204mm
OD = 635.8 mm

This is significantly less than the stock OD of 678 mm for the A8 series.
It's actually 93.8%. That would not be good (at least that's what I think).

QUESTION:

Is there a problem going with a 255/45/17 tire? If I did that:

Tires are 255/40/17, therefore:
Wheel OD 431.8 mm (17")
Sidewall (255)(.45)(2) = 229.5mm
OD = 661 mm

Therefore, the tire OD would be 661mm, stock A8 would be 678, or 97.5% of
the stock size.

I imagine my engine is going to have to turn a little faster and my speedo
will read a little high, but I might be able to recalibrate that with my
ross-tech software.

Is there a problem putting the 255/45/17 on the stock A6 4.2 wheel? I've
learned a lot about offset and tire sizes recently, and I know these wheels
will look totally hot on my car. Considering the offset is 13mm further out,
and the tires will be slightly less in OD, I don't think I'll have any
problems with the tires rubbing. I have plenty of room right now in the
wheel well.

TIA

Paul

_____________________________________________________
Paul Waterloo
Applied Energy Services
Phone 708-524-9464
Fax 708-524-0079
Cell 312-961-2523
pwaterloo at compuserve.com