Santos Balbuena

I recently bought my first set of wheels for my 8V Audi S3 Prestige Sedan Quattro. Stock brakes, stock suspension.
I bought WCI SB10's:
(2) 18x8.5 ET40 Fronts
(2) 18x9.5 ET38 Rears

My question is... does anyone know if I will have any diff or transmission issues? Will I have any traction ctrl issues? OR Am I going to be okay? I am doing a lot of research, and people are saying different things, such as if my diameter is the same i will be alright and etc. I found out about this the day that the wheels shipped (Thursday) and the wheels just arrived today (Monday). I tried to contact WCI about correcting the rears and just sending a square setup but it was too late. On the bright side, I haven't opened my REAR wheels, which are the ones I am worried about.

Sinister#4

As long as the overall tire diameter is the same, you will be fine, they can be 17,18,19,20 and any width at all long as the overall (with tire) is the same diameter

Spinnetti

slight clarification - the tires can be bigger or smaller as long as they are the same diameter front to rear - there's about a 4% tolerance, and various on-line calculators can figure that out for you. If tires are bigger or smaller, it does affect the speedo, but generally not more than a couple mph either way.

Sinister#4

Interesting that it will tolerate 4%, Porsche is about 1.5% max difference (996)

Spinnetti

Dunno if that 4% is gospel, but a former engineer on "haldex" (now Borg Warner?) posted something to that effect. If you plug in the RS3 staggered set into one of the wheel calcs they are close to 2% different front to rear, and if you think about it, when you turn corners and what not, you are generating different wheel speeds right to left and front to back even if they are all exactly the same diameter, not to mention wheel slip etc. Its not an exact thing and not something to get hung up on unless they are way different