What's the story with 20" alloys?

[Dave]

I have read some posts that the RS6 won't take the 20" alloys, but I also notice that the Abt car is wearing some georgeous 20" alloys.. have they had to do anything with the suspension or do they fit straight on??

I presume that if I went for the 20" I would have to use a thinner profile tyre to compensate.. is that correct??

Cheers
Dave

[jconley]

Yes, you would need a thinner sidewall. I think you have 255/35/19s. You would need 255/30/20s for your speedometer to be accurate. Even with the smaller sidewall your spedomer will be off 0.015%

[Dave]

I can live with that I think.. does that mean that the speedo will read over or under....

hang on.. don't tell me.. gives me an excuse for the cops

[Mr. Fru-T Pants]

Hi Dave,

To answer your questions in a nutshell("Help, help, I'm in a giant nutshell"):

The increase in rolling diameter will make your speedo read under
your actual speed, though .015% will hardly affect much of a change.

The hypothetical increase means your rolling radius(measured from the
center of the wheel to the outer edge of the tire), also increases. Therefore,
the total distance(circumference), your tire has to travel increases.
Subsequently, it takes more revolutions of the crankshaft to completely
turn each wheel one revolution. This can decrease your acceleration by effectively
changing the gear ratios. So you end up going slower off the line.

As I said, this is a hypothetical...the small change noted above will hardly have
an impact, fwiw. Many ricers, ahem, 'scuse me..., Japanese automotive enthusiasts
in my area put rather smallish wheels and low aspect tires on their cars to decrease unsprung weight
and lessen the rolling diameter(you know, those folks with a barge-load of fender gap)
, thus giving them a lower gear ratio and increasing wheelspeed.

For what it's worth...
Cheers,
Fru-T