Audi S6 tires

[Aaronl4903]

Anyone know if running 255s up front and putting 265s in the rear will work? Or would I have to put 265s on all 4 corners?
I’m just more concerned on messing up the Spedo if I do it.

[Gravy Train]

No, same tire spec on all four corners, since the car has a Torsen-style center differential.

265/35-20 matches the factory calibration of the speedo on the S6-- 255 was a compromise and doesn't make for an exact GPS match.

[Aaronl4903]

No, same tire spec on all four corners, since the car has a Torsen-style center differential.

265/35-20 matches the factory calibration of the speedo on the S6-- 255 was a compromise and doesn't make for an exact GPS match.

Thank you I appreciate it

[tdietro]

No, same tire spec on all four corners, since the car has a Torsen-style center differential.

265/35-20 matches the factory calibration of the speedo on the S6-- 255 was a compromise and doesn't make for an exact GPS match.

And yet, on my S7, the speedometer was always a little ahead of GPS when I had the stock sized 265/35/20's. A few weeks ago I went with 275/35/20's and now my speedometer is dead-on with GPS.

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[Audisthesia]

No, same tire spec on all four corners, since the car has a Torsen-style center differential.

265/35-20 matches the factory calibration of the speedo on the S6-- 255 was a compromise and doesn't make for an exact GPS match.

Compromise meaning? Audi put 255 because 265 dont fit the rim or what?

[Gravy Train]

The geometry and body lines on the 6, when compared to the far deeper wheel wells on the 7, provided for only a 8.5" wheel barrel on the S6 with a 255mm tire.

A 9" wheel (with 35-40mm of offset) and 265/35-R20 tire is ideal on the S6.

[Audisthesia]

The geometry and body lines on the 6, when compared to the far deeper wheel wells on the 7, provided for only a 8.5" wheel barrel on the S6 with a 255mm tire.

A 9" wheel (with 35-40mm of offset) and 265/35-R20 tire is ideal on the S6.

Ahh, now I understand, thanks for the reply sir. I've often wondered why audi didn't a different ET to allow for a 9" wheel. Folks put spacers on the s6 at 20mm and the stance is dam near perfect. So if stock is ET45, then I would go for an ET25-30 9" if I were getting new wheels... That would be sweet.

[Alabama]

265/35-20 matches the factory calibration of the speedo on the S6-- 255 was a compromise and doesn't make for an exact GPS match.

The standard tire for the 2014 S6 is 255/40-19. The 20" is the "+1" equivalent. Per the "1010tire" website the difference in circumference between 255/40-19 and 255/35-20 is 0.01 inches (but reduces sidewall height from about 4 inches to about 3.5 inches). By contrast, the difference in circumference between 255/40-19 and 265/35-20 is 0.87 inches, roughly a 1% difference. Isn't that why Audi uses the 255/35-20, an almost exact match in circumference?

[Gravy Train]

Ahh, now I understand, thanks for the reply sir. I've often wondered why audi didn't a different ET to allow for a 9" wheel. Folks put spacers on the s6 at 20mm and the stance is dam near perfect. So if stock is ET45, then I would go for an ET25-30 9" if I were getting new wheels... That would be sweet.

a 35mm offset for a 9" wheel is ideal on the S6 body, so long as you want a 265mm tire to fit fully within the fender line. 20-25mm offset would provide a little too much poke and the very outside of the tread block shoulder would appear in line or just outside the sheetmetal fender arch.

[Gravy Train]

The standard tire for the 2014 S6 is 255/40-19. The 20" is the "+1" equivalent. Per the "1010tire" website the difference in circumference between 255/40-19 and 255/35-20 is 0.01 inches (but reduces sidewall height from about 4 inches to about 3.5 inches). By contrast, the difference in circumference between 255/40-19 and 265/35-20 is 0.87 inches, roughly a 1% difference. Isn't that why Audi uses the 255/35-20, an almost exact match in circumference?

Yes, the math checks out, until you try to make a GPS-based comparison at 80 MPH, where you'll notice the speedometer reading is 2MPH off on the 255mm tire geometry. The 1% difference is trivial compared to the benefit to a slightly wider tire contact patch, given the weight of the S6, and realizing that 265/35mm size is where the S7 started from the factory.

[Audisthesia]

a 35mm offset for a 9" wheel is ideal on the S6 body, so long as you want a 265mm tire to fit fully within the fender line. 20-25mm offset would provide a little too much poke and the very outside of the tread block shoulder would appear in line or just outside the sheetmetal fender arch.

Ahh yeah, that half inch width extra is at least 12mm...

[gk1]

It is also probably better to think in terms of contact patch area.
(Calculations based on 4600 lbs with 60/40 weight distribution.)
Front
255/35/20 97Y on 8.5"@44PSI (Audi recommended normal load) = 47.24 sq in
265/35/20 99Y on 9"@40PSI (to maintain load rating) = 52.76 sq in
Rear
255/35/20 97Y on 8.5"@39PSI (Audi recommended normal load) = 38.01 sq in
265/35/20 99Y on 9"@36PSI (to maintain load rating) = 41.98 sq in
So 170.5 sq inches of rubber on the road vs. 189.48 sq inches. About 19 sq in. (11%) larger or about half the size of a standard #10 envelope.
Obviously these are only theoretical calculation there is probably so much variance just between tire models and brands to make it difficult to compare, but if comparing exact same tire model just in different sizes it should be accurate enough.

[Valpo A7]

The Quattro system needs tires that are similar in diameter and thus circumference. If you want to run staggered then you need to find tires that wind up with the same diameter and circumference. I am not sure you can match them up to achieve that which is why everyone says same tire spec front to back. I think I read the system will handle about 3/32nds difference in tread depth which would be 6/32 diameter or 3/16ths. Not very much.

[Alabama]

It is also probably better to think in terms of contact patch area.
(Calculations based on 4600 lbs with 60/40 weight distribution.)
Front
255/35/20 97Y on 8.5"@44PSI (Audi recommended normal load) = 47.24 sq in
265/35/20 99Y on 9"@40PSI (to maintain load rating) = 52.76 sq in
Rear
255/35/20 97Y on 8.5"@39PSI (Audi recommended normal load) = 38.01 sq in
265/35/20 99Y on 9"@36PSI (to maintain load rating) = 41.98 sq in
So 170.5 sq inches of rubber on the road vs. 189.48 sq inches. About 19 sq in. (11%) larger or about half the size of a standard #10 envelope.
Obviously these are only theoretical calculation there is probably so much variance just between tire models and brands to make it difficult to compare, but if comparing exact same tire model just in different sizes it should be accurate enough.

We had this discussion in thread "Widest wheel and tire fitment". One post was "Some people (not saying you OP) are under the illusion that a wider tire increases contact patch or traction, while this is not the case. The wider tire spreads out the force horizontally instead of vertically treadwise, and can actually hurt your traction and handling if taken too far. Only way to increase contact patch is a larger circumference tire, or decreased pressure, or both." A further caution was that a larger contact patch redistributes weight so may affect handling in lower traction situations. As you suggest, another thread noted that contact patch size and shape may vary significantly between manufacturers for the exact same tire size. At least there is agreement that all four tires should be the same size.

[choy188]

It also depends what brand of tire you are getting, for example michelins tread tends to usually be the widest as they minimize the rounding off of their tread blocks where as continental and pirelli both round off the tread a little more. When it comes to cornering, usually a wider tire is better as a lot more load is being generated on the outside tire, increasing it's contact patch. If you do some research on tire rack, they actually measure the actual tread width on tires under their specifications so you can take a closer look there.

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[gk1]

We had this discussion in thread "Widest wheel and tire fitment". One post was "Some people (not saying you OP) are under the illusion that a wider tire increases contact patch or traction, while this is not the case. The wider tire spreads out the force horizontally instead of vertically treadwise, and can actually hurt your traction and handling if taken too far. Only way to increase contact patch is a larger circumference tire, or decreased pressure, or both." A further caution was that a larger contact patch redistributes weight so may affect handling in lower traction situations. As you suggest, another thread noted that contact patch size and shape may vary significantly between manufacturers for the exact same tire size. At least there is agreement that all four tires should be the same size.

Handling aside...
That implies that if I went with a significantly narrower tire say 195/45/20 (if it existed) I'd have the same contact patch area and traction as the 255?
Somehow I am dubious as I know from experience 235's do not have nearly as much dry traction as 255's and an S6 would liquify a 195 on launch.
I understand the physics concept, but tires are much more complex than the theoretical physics of perfect balloons.

And this from a Physics university only confuses it more...
"Tire Width
Intuitively, increasing the size of the tires would also, in theory, increase the size of the contact patch and thus improve traction. In reality, this isn’t the case: changing the dimensions of the tire, with tire pressure and car weight held constant, does not increase the size of the contact patch. Changing from a high-profile, narrow tire to a low profile, wide tire simply changes the shape of the contact patch from long and narrow to short and wide with the area remaining constant. "
"Conclusion
As discussed, the magnitudes of normal force and coefficient of friction dictate the maximum amount of traction, regardless of tire size, with a given vehicle and appropriate tires. Of course, the real world does not abide perfectly to the laws of kinematics and other physical characteristics come into play such as the size of the contact patch. A larger contact patch increases the chances of the maximum coefficient of friction being achieved between the car tire and the uneven road surface. Thus, with this concept in mind, a wider tire with a larger contact patch perpendicular to the direction of travel does, in fact, improve traction."

[choy188]

Handling aside...
That implies that if I went with a significantly narrower tire say 195/45/20 (if it existed) I'd have the same contact patch area and traction as the 255?
Somehow I am dubious as I know from experience 235's do not have nearly as much dry traction as 255's and an S6 would liquify a 195 on launch.
I understand the physics concept, but tires are much more complex than the theoretical physics of perfect balloons.

And this from a Physics university only confuses it more...
"Tire Width
Intuitively, increasing the size of the tires would also, in theory, increase the size of the contact patch and thus improve traction. In reality, this isn’t the case: changing the dimensions of the tire, with tire pressure and car weight held constant, does not increase the size of the contact patch. Changing from a high-profile, narrow tire to a low profile, wide tire simply changes the shape of the contact patch from long and narrow to short and wide with the area remaining constant. "
"Conclusion
As discussed, the magnitudes of normal force and coefficient of friction dictate the maximum amount of traction, regardless of tire size, with a given vehicle and appropriate tires. Of course, the real world does not abide perfectly to the laws of kinematics and other physical characteristics come into play such as the size of the contact patch. A larger contact patch increases the chances of the maximum coefficient of friction being achieved between the car tire and the uneven road surface. Thus, with this concept in mind, a wider tire with a larger contact patch perpendicular to the direction of travel does, in fact, improve traction."

Math aside, I think 265s are fine since that's the stock size on 20inch a7/s7. Also basically you have to strike the balance where the contact patch is large and the force applied (pressure) is also high to have the greatest coefficient of friction. My physics is a bit muddy but basically I doubt 265s go beyond the width where you're actually reducing the pressure applied to the ground to the point where you're losing grip relative to having a higher pressure with less area on 255s. It's also late and my brain is wracked so I may have said something wrong or just been confusing

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[Alabama]

At least I can blame my lack of knowledge on the tire manufacturers, as per Wikipedia "Since the wear characteristics of tires is a highly competitive area between tire manufacturers, a lot of the research done concerning the contact patch is considered highly proprietary and, therefore, very little is published on the subject." If stock S7 would be acceptable on an S6, would 275/30-21 be acceptable (if OP wanted to spring for new wheels) as these became a stock option in newer S7s? Gravy Train notes differences in the wheel well size; is that a published figure or something one has to ask at the tire store?

[choy188]

At least I can blame my lack of knowledge on the tire manufacturers, as per Wikipedia "Since the wear characteristics of tires is a highly competitive area between tire manufacturers, a lot of the research done concerning the contact patch is considered highly proprietary and, therefore, very little is published on the subject." If stock S7 would be acceptable on an S6, would 275/30-21 be acceptable (if OP wanted to spring for new wheels) as these became a stock option in newer S7s? Gravy Train notes differences in the wheel well size; is that a published figure or something one has to ask at the tire store?

So at the tire store I work at, the c7 a6 is listed at being able to fit up to a 275 on a 9.5 inch rim. I believe there are others who have gone to a 10 inch rim without rubbing but regardless 275s will fit on our cars on a 9-9.5inch rim

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[Alabama]

So at the tire store I work at, the c7 a6 is listed at being able to fit up to a 275 on a 9.5 inch rim. I believe there are others who have gone to a 10 inch rim without rubbing but regardless 275s will fit on our cars on a 9-9.5inch rim

Thanks! Looks like Michelin has a Pilot Sport 4S in 275/30-21 for a 9.5 inch rim. But their new Pilot Sport All Season 4 has 255/35-20, the original size (and no 265/35-20). Decisions, decisions.

[choy188]

Thanks! Looks like Michelin has a Pilot Sport 4S in 275/30-21 for a 9.5 inch rim. But their new Pilot Sport All Season 4 has 255/35-20, the original size (and no 265/35-20). Decisions, decisions.

I'm personally going with a 275/40-19 P Zero PZ4 BMW spec tire, it's the oem front tire on the new m5

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