# Tire size difference + Quattro **URL:** \ **Category:** Shift518 Automotive\ **Created:** [July 15, 2010, 1:54pm UTC](https://forums.speedlife.net/t/tire-size-difference-quattro/253277 "2010-07-15T13:54:10Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Ender](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/ender/32/6367_2.png) [@Ender](https://forums.speedlife.net/u/Ender)\ **Post date:** [July 15, 2010, 1:54pm UTC](https://forums.speedlife.net/t/tire-size-difference-quattro/253277/1 "2010-07-15T13:54:10Z")
I have done my research on this and I just need some clarification and opinions. I’ve got 225 40 18 on the front and 255 35 18 on the rear of a quattro car. Everything I’ve heard about this usually says any variation will make my diff explode and the world to end. Running those numbers through a tire size calculator yields a 0.24% diameter difference with an extra 2 revolutions per mile. Circumference: 78.79 in 2001.2 mm Circumference: 78.60 in 1996.4 mm Revs per Mile: 829.3 Revs per Mile: 831.3 Actual Speed: 60 mph 100 km/h Speedometer1: 60.1 mph 100. km/h Speedometer Difference: - Speedometer Difference: 0.241% too fast Diameter Difference: - Diameter Difference: 0.24% **this is from tire rack:** Audi - As published in their vehicle owner’s manual, “rolling radius of all 4 tires must remain the same” or within 4/32-inch of each other in remaining tread depth. (4/32) in = 3.17500 millimeters My difference (4.8mm) - 3.2mm = 1.6mm The extra 1.6 mm outside of factory tolerance doesn’t sound like it would cause a problem. I’m assuming factory tolerance is slightly lower than what is safe as well to protect Audi from a legal standpoint… I plan on getting 225 40s for the rear anyway, but I have run into some other expenses so I am putting it off for a bit. **My question is is this difference negligible and can I compensate the difference by running slightly lower pressure in the front?** ---
**Author:** ![TurboTravis](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/turbotravis/32/6406_2.png) [@TurboTravis](https://forums.speedlife.net/u/TurboTravis)\ **Post date:** [July 15, 2010, 2:00pm UTC](https://forums.speedlife.net/t/tire-size-difference-quattro/253277/2 "2010-07-15T14:00:45Z")
LOL@4/32"