The_Mizarc

My understanding is that a staggered wheel setup could cause damage to the center diff/torsen if the rolling diameters were not within 2%-3% of one another. Now while I agree with not staggering could it be argued that since Audi is engineering Quattro toward a rear biased drive train is the damage concern any lessened or perhaps at the least is there more room for toying with the staggered idea? Just throwing it out there for discussion.

Vijay

A 255/35/20 front would require a 295/30/20 rear in order to maintain identical rolling diameters. I suppose, in theory, with a rear biased torque split you could do this, although it would still affect the distribution of power in slippage situations. You need a 10.5 to 11"wheel to properly seat a 295 tire. I am almost certain, it would rub in the rear.

DD1546

In general, larger rear tires cause understeer. Rear drive cars with high torque compensate for their inherent oversteer with larger rear tires that shift the balance somewhat, though not completely, to understeer. Do the host of Audi computers change this?

The_Mizarc

I would think the electronics and the torque vectoring would help but maybe not as effectively. If wider rears induce understeer then it would be a step in the wrong direction I think. Audis already understeer. The whole reason they engineered the vectoring in the first place was to compensate for it. Historically Audi platforms were based on a FWD architecture. That means the front wheels actually had a wider track than the rear. IDK if that's the same now with these new group wide platforms being put in service but I can't imagine it's gone away for some segments. I read on the 80/90 forum that early Audis in motorsport ran wider tires up front to improve the understeer and cornering. The majority of us won't ever push our vehicles to the steering limits anyway. So at the end of the day it's just a cosmetic change. For those that want a staggered look just get a custom forged set of wheels of the same width and just go with a lower offset for the rear pair. Same tire size used on all four corners and no fear of trashing the Torsen. You won't be rotating the tires though.

Jake-AudiUSAParts

+1
Rob Cheng's car looks fantastic and the wheels are, as you stated, at the limit, which is why it looks so fantastic, in my opinion.

Jake-AudiUSAParts

Same thing here, perfect fitment and it looks fantastic! I love how a car looks when the wheels fill the wheel well just right, well done.

RobC

Or run spacers in the rear so you can still rotate.

DD1546

I think you are right on target and the major reasons are cosmetic and the cars will never go 9/10ths. There is also the issue of tire "scrub radius" that nobody ever mentions. I've seen many racing front drivers with larger tires up front and agree that Audi is a modified front wheel design. Its one of the reasons that the engines are so far forward, though the new S6 seems an improvement in this regard. As an old "Showroom Stock" and Solo I SCCA racer, I always assumed that I would "bend" the car at some point so appearance was incidental. I bought the S6 for its performance not appearance and I don't understand much of what goes on in the forums with bling replacement parts and aesthetics. But its fine and occasionally interesting. However, I would never drive over NJ potholes with such low profile tires. Driving would be nerve-wracking! I guess my S6 has no bling. Even my wonderful Michelin Alpin A4 winter tires are on OEM Audi 19" wheels!

The_Mizarc

What is the scrub radius? Is that something related to sidewall flex?

DD1546

I found two impossibly obtuse definitions of scrub radius:
http://en.wikipedia.org/wiki/Scrub_radiushttp://www.hrsprings.com/technical/scrub_radius

Basically, it has to do with the contact patch the tire makes with the road. What I meant in my comment is that wider tires (and larger wheels) bring the center of that patch further out from the suspension and it changes the fundamental geometry. A couple of years ago one of the car mags did a piece on larger tires and wheels. While +1 had some slight benefit on handling (and negative effect on gas mileage), larger fitments produced poorer handling and real negative effects on economy.

Putting larger than 20" wheels on the S6 may adversely affect handling - it remains to be tested. It certainly affects ride quality. Then again, I think most folks put the larger wheels on because they like the look and will never press the car on a race course - other than a drag strip. That's fine, the car is at its best when going straight. Don't misunderstand - overall its the best handling "larger" sedan I've ever driven and I've tested many at the track. I did like the CTS-V but I like the Audi better in the wet and its a higher quality vehicle.

One last point. The weight of larger wheels and tires is also critical. Hopefully, the combo won't weight more than OEM. less is better.