Just purchased a 2022 TTS with 20" wheels and 255 30 20 tires. It has summer tires and living in New England I need all seasons. I have reviewed threads in various forums in advance that identified Conti Extreme Contact all season 245 35 20’s as not causing rubbing/clearance issues. There will be a speedo tweak, but the .8" diameter difference seen here, combined with a .5" reduction in tire width appears to work: 255/30 R20 vs 245/35 R20 Tire Size Comparison Table with Graphic Visualization (inch difference) Any info/direction/help would be appreciated.
I live in Wisconsin, my snow-covered driveway is over 1/4 mile long, and over the last 30 years have experimented with under-sizing winter tires and believe it does no good other than increasing the speed at which tires hydro-plane of snow-plane. I have and old 2002 TT and a 2016 A6.
The larger the contact patch, the larger force vector that the tire can perform before slippage. So, for my winter tires both the TT and the A6 they are full width.
The key issue for me is to increase ground clearance so as get the car from bottoming on a layer of snow and then the car turtling. So, for my A6 I raise the suspension about 20 mm which gives me a bit mor ground clearance. The tires have to sit on top of the snow. If they sink into the snow, the car can turtle.
In any case, for highway use, whether full width or reduced width, you still have to monitor speed to prevent hydro/snow-planning.
Most experts agree that a narrow tire is better on snow. I’m not sure what you mean by a “force vector” but the laws of physics say the smaller the contact patch, the more pounds per square inch downward force you have which means better traction in snow. Also, a narrower tire reduces the tendency to “ski” over snow for the same reason. That said, I doubt that a 10mm change in width will make much difference either way so I wouldn’t bother unless you are also looking for better pot hole protection. To get significant benefit of snow traction you have to go to a smaller rim so the tire can be much narrower. There is a downside since a narrower patch reduces traction in all other road conditions; ice, rain, dry.
Thanks for the feedback. I passed on the TTS given I would not be able to put on all seasons and moving down to 19" was not possible given there is only 1 of the stock Audi wheels I wanted in the USA. Took delivery of a 22 TT with 19’s and installed Conti Extreme Contact DWS all seasons. Fantastic tires.
I have been using the Conti Extreme Contact DWS all seasons for years on my C6 Audi A6. The Conti’s really are very good tires. I am very satisfied with the Conti’s. However, we don’t get very much snow in my area. Next time around I may consider the Michelin Pilot Sport all seasons because they seem to be so highly rated. We’ll see (lol).
A couple points. If the TT weighs 3,000 pounds, and assuming a 50%/50% front rear and left-right weight distribution. On a flat surface, each tire is loaded at rest with 750 pounds.
If the tire has 40 PSI inflation pressure; then, the tire contact area = force (weight pounds) ÷ 40 pounds per square inch = 18.75 square inches independent of tire width. During accleration/deceleration the weight of the car shifts and can produce greater loaded weight thus producing a larger contact area.
If you get one of the race engineers from one of the tire manufacturers that is big in racing Bridgestone, Michelin, etc. they will tell you the one size smaller is folklore that the corporation has no interest in disproving the lore. (Check out a glacier bus.)
Generally, there are one or two logical conclusions to any math problem. An infinitely wide tire will produce infinite traction as will an infinitely narrow tire. Somewhere in the middle is the practical solution.