[200q20v] Re: Tire Size for New Wheels on A8

[Greg Galinsky]

You are forgetting to check the load capacity of the tire.
The stock 225/60-16 is a 98 load index.  I don't have info what load index
the 255/45-17 is but best to check that is similar.  You could overload the
tires otherwise.

The other item that I didn't see is what the rim width is of the A6 4.2
rims.  Make certain that the rim width is one of the approved rim widths for
the 255/45-17 tire.

Since Nokian does not make a 255/45-17 I do not have the approved rim widths
or load capacity of that tire

Greg
----- Original Message -----
From: "Paul Waterloo" <pwaterloo at compuserve.com>
To: "A8 List" <a8 at audifans.com>; <quattro at audifans.com>; "200 list"
<200q20v at audifans.com>
Sent: Friday, December 21, 2001 10:11 AM
Subject: Tire Size for New Wheels on A8


> 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
>
>
>
>