Hi yall

I am assuming my track performance is being limited by my current (nice and light, but narrow) Rota Slipstream 15x6.5 wheels (12 lbs jobbies)

This because I have to pump up my tires to near max to minimize roll on the sidewall. Its gotten alot better since the eibach springs and RSB, I can run now at about 38-40 PSI (cold) whereas before I had to run around 48 (front)

Things that make me go hmm:

1) If I go to racing rubber ever what will the effect be of a wider rim? Any different than a street tire?

2) Will I be able to run lower PSI (like near optimal grip PSI, say, of 30 cold warming up to 40 hot) on a wider rim w/o scrubbing the sidewalls? (Im assuming so)

3) How much of a difference will I see / feel I wonder - and will the difference be majorly different with a 15x7.5 rim compared to the easier to find 15x7 rim? And what sort of difference will it be? Steering response mainly?

4) Running a lower PSI probably means more grip, but shorter tread life on the track, right? Or will a wider rim do anything at all to help tire treadlife (I doubt this but... ive been suprised plenty b4)

Any comments are very welcome and appreciated! Thanks in advance!

 

when it comes to track tires, wider is always better.

what tires are you running at the track anyway? brand, type, size, etc.
If you're running the balloon sized factory tires, you're doing to have problems with them rolling over. even if you stick with the 15" wheels, get something wider and more low profile- remember, you could care less if the speedo is accurate at the track, and it's the only thing that changes by changing tire size. every other aspect of the change is better- lowers the car to the ground slightly, without FUBARing your alignment, ABS isn't affected since all 4 wheels are still the same size, you have slightly shorter gearing so that you will accelerate better, and less rotational mass to accelerate and slow down.

when you get into the corners, the wider tires will definitely help. I can't say for certain on pressures and such because I don't have personal experience with your car, setup, tires, tracks, etc but I would be fairly certain that you can lower your tire pressures a lot if you get rid of the sidewall flex by other means (wider tires, shorter sidewall, different tires that work better on heavy cars).

As I've said in a few other threads, the Toyot RA-1 work GREAT on lighter cars like civics, miatas, SE-Rs, etc.. but they're not too hot on my car because the front end is so heavy. airing them up to 60psi hot and I still have problems rolling the sidewalls over on hard corners.

http://www.mattblehm.com/pics/track_...s/188%2012.jpg
(2.1MB pic, but you can very obviously see the sidewall flex in a 1G corner)

 

Erjan, like Matt said - definately go as wide as your classing rules allow.

Moving from a 6.5" to 7.5" wide rim offers 15% more sidewall support and increases section width .2". Provides for lower pressures and greater grip. Treadlife might improve actually as you carve corners instead of sliding on them. The whole gotta-go-slow-to-be-fast thingy.

I auto-x 215 and 225 widths on a 7.5" rim with success. Street is a 225 on an 8" rim of all things (little overkill and wouldn't do that again)

 

Thanks Brian and Matt-

A question - what does section width refer to.. Tire Tread Sections?

I like the idea of more sidewall strength. I guess if I decide to take the plunge and buy yet another aftermarket set of wheels I will look for 15x7.5 or 15x7 at least.

 

Section width is the width at the sidewall (widest point I believe). It's very different from tread width which actually makes contact with the road surface. Published section widths are pretty accurate between tire mfg's. And they change with the rim width. Tread widths vary from mfg to mfg as they all measure differently. Who's to say how far towards the sidewall you'll wear on a hard corner.