Autocross Tire sizes

[AOlimon]

I bought a used (slightly, only 6000 miles and in great condition!) 2015 Audi s3 at the end of October, and just did my 2nd autocross with it last weekend. The outer shoulder of my front tires were in really bad shape after the first autocross, so i rotated them for the second and wore out the other ones. Im thinking i might flip them on the wheels and rotate them around to get one more use out of them, but I'm looking for a more permanent solution in terms of getting a set of wheels and tires for racing.

I was thinking of getting the cheapest 18" wheels i could find off tire rack, but i was curious how wide you could go with the tires. Im looking at getting potenza re-11s, but they don't have them in the proper size for the car on 18" wheels. I know 245/40/18 are very close in outer diameter to the 235/35/19s, but i don't know how to check if they will rub when turning. I would appreciate any advice or other suggestions from people more experienced with tire fitments or auto crosses. Thanks!

some pictures:





and the damage

[onequick4door]

To save you some serious coin next time, bump up your tire pressures. Those tires were under inflated, hence the extreme sidewall damage/rollover.

[AOlimon]

To save you some serious coin next time, bump up your tire pressures. Those tires were under inflated, hence the extreme sidewall damage/rollover.

Yeah, i was experimenting with the tire pressures throughout the event & i did more harm than good. I started the day off with 40 psi on all corners and it felt alright, but when i checked my pressures after the first set of 5 laps they had jumped up to 50 (!). I got a bit worried about the extremely high pressures so i let them cool off a bit and bled them to 39/36 thinking that they would rise back up after a few laps, but i had definitely let out too much. Ill stop taking peoples advice that "lower pressure gives you better traction" cause its just not worth the money

[onequick4door]

The kicker with the less is more theory is, the traction compound ends right below( 1 or 2mm, maybe 3) below where the tread pattern ends on the sidewall. Any rollover beyond that and your not gaining a thing, just resulting in the above.

[will13k7]

might be helpful:
http://www.willtheyfit.com/

[S3in15]

Yeah, i was experimenting with the tire pressures throughout the event & i did more harm than good. I started the day off with 40 psi on all corners and it felt alright, but when i checked my pressures after the first set of 5 laps they had jumped up to 50 (!). I got a bit worried about the extremely high pressures so i let them cool off a bit and bled them to 39/36 thinking that they would rise back up after a few laps, but i had definitely let out too much. Ill stop taking peoples advice that "lower pressure gives you better traction" cause its just not worth the money

It's normal for tire pressure to rise with temperature, and you should not release air from hot tires thinking they're over-inflated. Your baseline should be the recommendations on door-jam; 44 PSI cold for the 19-inch tires, front and rear. For autocrossing this car, you'd probably want to add some air (2-4 PSI?) especially to the fronts.

[onequick4door]

At the road course I ran 45 - 46 and the rollover was perfect. I still owe the forum from this thread and another a picture to show that the tires didn't chunk or wear excessively after 8 sessions of 25 mins - 4 in the rain however - 4 in the dry and pounded on. As a side note, I was very impressed with the stock Conti's in the wet. In the dry - for being a five year old design that slots into the max performance category they had a pretty high level of grip. I'm used to extreme summer and R compounds, so I have a good perspective.

This is off topic - but I took the car bone stock to the track to get a baseline except for yellow stuff front brake pads, high temp brake fluid and a 034 db insert and I was very, very pleased with how the car ran. Very neutral unless you just over cooked the corner entry. It also confirmed that with some tweaking this car has a lot potential and my "to do" list is very long for the car.

[onequick4door]

Here's the pics I finally snapped of my left side tires. It was run 4 - 25 mins in the rain, and 2 - 25 mins on the left front in the dry, then I rotated it back to left rear for 2 more 25 min sessions in the dry. I pounded on them in the dry. The event was Nov 7 - 8, so the feathering has been worn down from the street, but they handled the torture pretty well.

[CbutterK]

I ran 245/45/17 NT01 on 17x9 TSW Bathurst wheels for the track on My S3 on H&R Supersport springs. No rubbing, no issues. I have the wheels/tires for sale, as I no longer have the S3. They have total of 4 20 minute sessions on them and still looks new.