mopar bob

So I bought a new set of Rival S tires since there are no RE71r's to be had. I also bought some OZ racing 11x18 rear wheels. My stock 11x19 is 67et and these are 63et so thats good. 245x40x18 front and 315x30x18 back and dam these things are large. So my question is what are a good starting point for air pressure. I was thinking 34 front and 36 rear to start. I have a test and tune on Friday and the tour this weekend.

sjfehr

If you're at a T&T, you can tell US! Start high and bleed down. Chalk will get you in the ballpark, but skidpad is the best way to do it. Andy Hollis has a nice write-up of how he does GRM skid-pad testing on his racing facebook page you might want to look over beforehand, too.

mopar bob

Yep that is what I'm thinking also. I may have to run the rears higher to keep from under steering. I will find out tomorrow.

mopar bob

So I ran a test and tune today with my new Rival S tires and I was surprised on the pressures. I was down to 29.5 in the front and still wasn't going to the edge. In the back I was at 32 and I was using the whole tread block. OH and it was 97 deg. out. I may try 28 in the front tomorrow. I ran 3-24 second runs back to back then came in for a 1/2 hour and did 3 sets. Pressures were only going up about 1 1/2 lbs after each set. I need to buy a temp gun to see my temps across the tires.


Edit I was hitting 1.2 g

sjfehr

If you can swing it, this thermal camera is friggen awesome compared to a spot IR thermometer:
http://www.flir.com/instruments/c2/

There's a $250 one that attaches to a smart phone, too.

mopar bob

Whats the mater with you sjfehr telling an Engineer to look at a cool toy like that. I can think of a dozen things I can use that for off the top of my head. Are you an instigator, I just bought wheels and tires, MUST RESIST. As for the smart phone device if you are already using your phone for a lap timer connected to your GoPro you want to break the link after each run. Thats going on my shopping list for later in the year.

sjfehr

Why, I would NEVER instigate

sjfehr

Never!

mopar bob

Well all I can say is they sure feel different. At low pressure the car squirms around but sticks well. After the first day I was .78 seconds down from the winner. The squirm unsettled some, now the RE71r always felt planted. The second day I screwed up and started to play with the tire pressure. Yep not a good thing as I went another 1.1 seconds down. I just drove bad but I ended up second. I will go and try the lower pressure this Saturday.