Re: 255/40 R19s on A6 55 reg SE, 2.0 tdi –
21-12-2009,10:03 AM

Originally Posted by
paul b
According to the calculator I use at 65mph indicated on the speedo you'll be doing nearly 71mph. That's quite a large difference.
An indicated 65 with 255/35/19s would be 68mph.
Surely 255/40/19s are what is used on S6/RS6s? They'll be geared differently, by my calculations to get your speedo accurate on your car you'd need to fit 255/30/19s which would not only break your wallet but probably your back too. That's if you can even buy them!
If I remember rightly, the Le Mans spec cars come with 235/40/18s which would be safe to put on, or whatever size the Le Mans' come with.
Hi Paul,
Standard fit for the Le Mans is 255/35/19, and the S-Line models come as standard with 245/40/18. S6 comes with 265/35/19s and is indeed geared differently.
I did my calculations based on the difference between the 255/35/19s on my car and the 255/40/19s Nick fitted to his. Given that both the 205/55/16s on the SE and the 235/35/19s on the Le Mans are standard fit (and 19s of this size are available as an optional extra for the SE), I'd say the difference in radius between these two is within tolerance for the speedo calibration, but 255/40/19s are not.
You're correct though that the speedo in Nick's car will now suddenly read a lot slower than it did - by a rather bigger margin than my calculation - because of the jump from 16s.
Cheers!
MF.
Gone: 2016 A6 Saloon BE Ultra S tronic - Floret Silver, Tech Pack Advanced, Parking Pack Advanced, Heated F+R Seats & Wheel, Electric Seats, Matrix LED, Ambient Lighting, Speed Limit Display, Twin Spoke 20", Folding Memory Mirrors
Now: E 53 AMG 4MATIC / Q5 2.0TFSi Prestige