Autocross and Wheel question

[sperry]

Originally Posted by dknv

I suppose it depends what kind of tires you are talking about. 2 top-level BS drivers at SD were on 285/30-18 hoosiers on 18x8 SSR's, one of them placed 2nd in class. Another back east is running 285/30-18 kumho's on 18x8 SSR's, he took 1st at the Dixie NT. We tried the 285 hoosiers last year, they look weird when mounted but they launched great. I did not think they handled transitions well, but I may just needed to have learned to handle them differently, or the car setup may needed to have been adjusted for them.

I don't know about r-compounds, but I know when I'm running 255's vs. 235's (Street Tires) on 8" wide rims, the 235's feel much better. I may have more overall grip (especially in a straight line or steady-state cornering) on the wider tires, but the transitional feeling is worse.

On a course with fewer transitions, or on a car with a very smooth driver, the wider tire may in fact be the faster tire, but I would think that the sidewall flex issues of such big tires on narrow wheels would make it much harder for a non-expert driver to get as close to the limit as properly sized tires especially if there are a lot of slaloms or other elements that require spending a long time on dynamic tire loads.

When my current set of 255 615's are worn out, I'll either be going back to 235/40's (or 245/40's if I can find 'em) or going to wider rims and new 255's, depending on budget and closeness of competition. In the meantime, I'm going to do my best to drive smoothly to minimize the sidewall bounce from the big tires.

[Kevin M]

Scott, out of curiosity, how does running greter and lesser tire pressure in your over-width tires affect the lack of precise feel? Which is worse in terms of affecting your times?

[sperry]

Originally Posted by BAN SUVS

Scott, out of curiosity, how does running greter and lesser tire pressure in your over-width tires affect the lack of precise feel? Which is worse in terms of affecting your times?

I've never played with tire pressure in terms of attempting to reduce the sidewall flex issue, so I don't know that I can specifically comment on that. Normally, if the event is warm enough to generate real heat in the tires, I adjust the front pressures to get a linear (if not even) I-M-O temp gradient. Then adjust the rears for handling purposes.

Running more pressure in the tires theoretically should lessen the transitional bounce, but I get the gut feeling that it would reduce overall grip under braking and steady state turning far more drastically than the benefits from "nicer" transitions. But I'm just guessing.

All I know is that over the years, I've found myself going lower and lower in my tire pressures and finding more and more grip. Going back to 50 psi in the tires seems like a step backwards.

[Kevin M]

Originally Posted by sperry

I've never played with tire pressure in terms of attempting to reduce the sidewall flex issue, so I don't know that I can specifically comment on that. Normally, if the event is warm enough to generate real heat in the tires, I adjust the front pressures to get a linear (if not even) I-M-O temp gradient. Then adjust the rears for handling purposes.

Running more pressure in the tires theoretically should lessen the transitional bounce, but I get the gut feeling that it would reduce overall grip under braking and steady state turning far more drastically than the benefits from "nicer" transitions. But I'm just guessing.

All I know is that over the years, I've found myself going lower and lower in my tire pressures and finding more and more grip. Going back to 50 psi in the tires seems like a step backwards.

I would concur with all of your conjecture. Higher pressures "feel" better, but as I gain experience I find that feel and grip are not in the same place, and grip is more important.

[MattR]

I've had real good luck with 245-40 R compounds with my Advan A048, the car feels great on those. My hoosiers are the same size and I think they'll work out nicely. Maybe next season I'll try for 18's.

[tysonK]

Originally Posted by MattR

I've had real good luck with 245-40 R compounds with my Advan A048, the car feels great on those. My hoosiers are the same size and I think they'll work out nicely. Maybe next season I'll try for 18's.

Speaking of the A048

Originally Posted by Tirerack Review gold

I have been driving on these tires for about 32000 miles now and they are just about worn out. The dry handling is far superior to my stock tires but they really lack when there is heavy monsoon rain like we get here in Phoenix. Also these tires have very stiff sidewalls and are not very comfortable. I have to say that these tires are pretty good but my next tires will have to be higher performance to match my 1987 Beretta GT

[Dean]

Originally Posted by tysonK

Speaking of the A048

OMG, that is teh funah.

[Kevin M]

That guy MUST be referring to the stock Advans...


plus, he is insane or thinks he's funny.

[sperry]

Originally Posted by BAN SUVS

That guy MUST be referring to the stock Advans...


plus, he is insane or thinks he's funny.

Um, I think he's referring to whatever the stock tires are on an '87 Beretta GT.

[Kevin M]

I can't see anybody getting 32,000 miles out of A048s on a Lotus, let alone an Evo.

[sperry]

Originally Posted by BAN SUVS

I can't see anybody getting 32,000 miles out of A048s on a Lotus, let alone an Evo.

What EVO, what Lotus? The review is from someone with a 1987 Beretta GT!