Audi Vader

I had an earlier thread asking about Michelin replacement tires for my 2015 Q7 and I decided on Michelin Premier LTX. To improve ride quality, I am considering 275 /50/20 (50 series) instead of the 45 series that came with it. Does anyone have experience with using a higher profile tire? Any issues?
For exmple, I would like know if there will be any tire rub on sharp turns or significant speedo problems.

snagitseven

It's best to stay with a tire that has the same circumference as OEM. Besides any clearance issues, your speedometer will be off if they don't closely match. If you want more sidewall, you would have to go to a smaller wheel to compensate for the taller sidewall.

superswiss

At 60 mph, your actual speed will be 62.2 mpg with the 50 series vs the 45 series tire. Following is a good website to compare tire sizes and their effects.

https://tiresize.com/calculator/

Audi Vader

Thank you for the responses. I am going to stick with the specified 45 series tire. The only problem now is the wait for the next couple weeks until they release the 45 series version (the 50 is already available).

cuatrokoop

Problem is, factory speedo is optimistic at speed. I've verified with a GPS on both Q7's. I fitted slightly taller tires on the 3.6 with no issue, and my speedo is now correct in the 60-80mph range against the GPS on flat ground. I downgraded the 3.6 from factory 20's to factory 18's with the aforementioned slightly taller tire to get an improved ride quality, which I did achieve.

Ljn21

We upsized from 295/35/21 to 295/40/21 and also noted our speedometer is now dead on with the larger tires. We did notice the dead reckoning in the GPS is off a little though, it takes longer when getting off on an exit ramp for example for the GPS to pick up that you are not driving on the highway anymore, it seems to want to hang onto the previous track longer. We also noticed that even the track that shows in the gps wants to wander a little diagnally a little, hard to explain but its like to the icon moves one pixel straight ahead and then one right, then one straight ahead, then one right. I think its because of the change in rotations per mile, the GPS doesn't track correctly. Would love to know if there is a VAG setting to correct for wheel rotations as the ride with the 40 series is soooooo!!!!!! much better and less harsh than the 35 series.

superswiss

That actually makes sense. The navigation doesn't just use the GPS to lock the position of the car, but it uses wheel speed, steering angle, travel direction etc. to estimate its current position and then correct it with the actually GPS coordinates when it gets a signal. So, yes it would make sense that with different rotations per mile, it would throw off the calibration and if you drive without line of sight to the satellites for a while (thick forest, tunnels, tall buildings) it may soon put you in the wrong place. As far as I know yes, the system can be calibrated, but I don't know what it takes.

iconoclast

you can change the tire size circumference through vagcom which should put things a bit more in line with factory specs.

snagitseven

I wasn't aware that you could do that with VCDS. I know that you can change the computer to compensate for the fuel mileage consumption in the DIS from different tire sizes but not change the tire circumference. Can you provide the Vag-Com module location and coding for that?

Ljn21

Any idea how to do that?