SN95 Autocross Springs and Setup

[electech]

Last event with the new springs putting in work. It was cold and damp all day. Front end kept sliding but the tires never got above 95 degrees even with a co-driver. I'm tempted to take some front compression out of the struts to see if that helps some.

 

[blacksheep-1]

Curious as to your tire pressures. If you can't get into the operating range, it just won't work. I used to run monster tire pressures to try and effect the temp range, slicks were much .ore amenable to this.

 

[electech]

Curious as to your tire pressures. If you can't get into the operating range, it just won't work. I used to run monster tire pressures to try and effect the temp range, slicks were much .ore amenable to this.

Typically, I start with 31 front and 29 rear. I'll make adjustments during the day if I need too. I didn't make any adjustments this event because I wanted a good data set for how the springs affected the handing. Next event, I plan to take some compression out of the front just to see what happens and I'll probably play with pressures some.

 

[blacksheep-1]

What tires?

 

[electech]

What tires?

RE71 tires. 295/35-18

 

[blacksheep-1]

Ok, are these Re71, Re71R, Re71rs or exactly which ones. Bridgestone love to confuse consumers almost as much as Porsche does with all of their numericals

 

[electech]

Ok, are these Re71, Re71R, Re71rs or exactly which ones. Bridgestone love to confuse consumers almost as much as Porsche does with all of their numericals

RE71RS -200TW tire.

 

[blacksheep-1]

so, it seems they recomend about 50 psi, I'm assuming that's a hot pressure but I cant find specific details on that. I would try running 50 psi hot, the 55 psi hot then 45 psi hot and see what it gets me. Normally the tire engineering group recomends a pressure, the RnD guys get hold of it and then add a pound or two for e"safety" reasons then the liability attorneys add at least one psi more to make sure they don't come off the bead on the outlap, There have been many tires out there that we run no place near the factory recomended pressures. So I would kind of hunt around in 5 psi increments to see where it goes. I wouldn't got too much under 45 psi (again, assuming these are hot pressures) because 200TDW tires kind of suck in that regard and tend to shed their carcasses. Slicks are much, much more forgiving at lower psi. This means you need to keep good notes and establish the difference between cold and hot pressure for each autocross layout. You wont get much time to do this since they probably limit your amount of runs. You could base it off ambient temps, see the amount of rise per tire and get close the next time. If it's a track, then it's much easier be ause you can putt it in every 5 laps or so and have someone check it. You seem to have a lot of mods on your car for a 200TDW class car.

 

[Dave_W]

You seem to have a lot of mods on your car for a 200TDW class car.

SCCA CAM autocross classes are very "run what ya brung" rules-wise. No limits on motor or suspension. The way they "control" performance is with the 200TW tire rule. Doesn't matter how much power you have if you can't put it to the ground.

 

[electech]

so, it seems they recomend about 50 psi, I'm assuming that's a hot pressure but I cant find specific details on that. I would try running 50 psi hot, the 55 psi hot then 45 psi hot and see what it gets me. Normally the tire engineering group recomends a pressure, the RnD guys get hold of it and then add a pound or two for e"safety" reasons then the liability attorneys add at least one psi more to make sure they don't come off the bead on the outlap, There have been many tires out there that we run no place near the factory recomended pressures. So I would kind of hunt around in 5 psi increments to see where it goes. I wouldn't got too much under 45 psi (again, assuming these are hot pressures) because 200TDW tires kind of suck in that regard and tend to shed their carcasses. Slicks are much, much more forgiving at lower psi. This means you need to keep good notes and establish the difference between cold and hot pressure for each autocross layout. You wont get much time to do this since they probably limit your amount of runs. You could base it off ambient temps, see the amount of rise per tire and get close the next time. If it's a track, then it's much easier be ause you can putt it in every 5 laps or so and have someone check it. You seem to have a lot of mods on your car for a 200TDW class car.

I've been experimenting with tire pressures for several years. Most of the fast guys in my class are running tire pressures similar to what I run. Typically, you only run higher air pressures if you have a summer or all-season tire. I don't have experience with hoosiers. This may be an autocross thing. I have limited experience with road racing (only one Lemons race). I have oval experience but that's no comparison.

The RE71's and most 200tw tires have an arrow on the sidewall that you can gauge roll over with. I'm right at that mark. There is a good chance that my current set have aged out.

Thanks for your post and I hope you don't take that as I think you're wrong. It's hard to convey "tone" in a forum post.

 

[electech]

SCCA CAM autocross classes are very "run what ya brung" rules-wise. No limits on motor or suspension. The way they "control" performance is with the 200TW tire rule. Doesn't matter how much power you have if you can't put it to the ground.

This is exactly why I love the CAM class. As close to outlaw as you can get but keeping you honest in the power and weight department. My car doesn't make a ton of horsepower but I can compete with guys with literally double the power I make.

 

[electech]

Just ran another event. I took out a total of 6 clicks of front compression. That helped out the car a lot. The push I experienced from installing the heavier front springs is all but gone. I will say that my current set of tires are toast. I'll probably have to make some adjustments once I get a new set hopefully next season. One more local event this year.

 

[electech]

 

[Dave_W]

Nice run. Good job looking ahead entering the 180.