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Hey guys

just curious...I'm interested in learning more theory behind sidewall flex, and how it affects cornering.

I bought 17" rims with small tires because I thought the less the sidewall, the less sidewall flex you have when punching it in a corner.

what's the best rim size to compete in Solo II? is a medium sidewall (16") better?

weight aside, what rim size would be the best?

I have a set of 15" rims that are a mildly OK weight, and I have some heavy 17" rims.

If anyone can point me in the right direction (I've searched, and didn't come up with anything), I'd greatly appreciate it.

thanks!

 
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Based on my limited autocross knowledge, I'd have to agree with you that the thin sidewall helps under hard cornering. However, a wheel is unsprung weight, so you'd want the lightest wheel you can run without falling apart.

Some people run smaller tires over a smaller wheel so they get the light weight AND the thin sidewall. This combo also adds a gearing advantage so you get better acceleration. However, the shorter gearing will force you to get into higher gears on the course, and the extra shifting might not be desireable.

You also have to remember different wheel and tire sizes might throw you into a class you don't want to run in...

 
Rep Power: 317

excellent point about the wheel and tire sizes putting me into a different class.

I hadn't thought of that.

hrm.

Excellent points about the sizes, though. Thanks for the input!


I wish there was some sort of definitive guide
Actually, have you read "The secrets of solo racing" (not sure if thats the exact title)? I wonder if it has any goodies in it? You can get it at www.soloracer.com, and most other book stores. Perhaps I'll buy it and give it a read.

 
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Wheel sizes for autocross.........

easy...
run the smallest possible wheel diameter that will fit around your brakes

and run the widest possible wheel width that will fit without rubbing the uprights and not completely destroy your wheel bearings.


then Run the widest possible tire you can with the shortest side wall you can find.

the reasons behind this, simple. Smaller wheels are lighter, wider wheels allow you to run wider tires, and short tires give you a gearing advantage over stock, and thus impoves acceleration. Smaller tire diameter also lowers the vehicle

For autocross I run a set of 15X6.5(I shoud have waited for the 15X7s) Rota slipstreams, wraped in Falken Azenis Sports (205/50R15) that are 5% shorter then stock. I'd run shorter tires if I could find some stickys that were legal for my class (STS) something like a 225/45ZR15 would work. Unfortunatly the Hoosiers that come in that size ar not legal for STS


As far as having small Sidewalls to help cornering, yes thats true. But with a compititon tire, the sidewalls are much More Rigid then your street tires. you can tell the difference just by compairing tire PSI between them. example. when I started to autocross my civic I had a set of 17's with 205/40R17 Falken 512 tires on them. durring that time I ran my PSI's like this, 48 Front 34 rear. I currenty run my Falkens(205/50R15) at 42 front and 32 rear.

So By just haveing a tire with a MUCH stiffer side wall, you have the same(if not better) effect as if you had a very short side wall.

Oh ya, I have and read the Secrets of Solo Racing. Most excelet book on Autocross its a MUST read!!

 
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I've been running 17's this year cuz I have better tires on them that the stock shitstones. Next year, I'm buying some supersticky STS legal 15" and slapping them on my Si rims. If you need more incentive... a sticky 15" tire is about $65, a sticky 17" tire is about $150. You can get 15" tires with stiff sidewalls. A lot of 17" tires actually don't have super stiff sidewalls as a consequence of those granny drivers who like "comfort". Damn lazy bums... get a better pad for your seat.

As far as rims go... Lighter is better. But since we can't all afford 8.5lb SW388s, Rotas usually make people happy at about 12 lbs. Konig Heluim and Greenlight are about the same weight and price. Kosei K1's go for a hair more. Wanna step it up a little more and 15" OZ Superleggeras are 11 lbs (my 17's are still only 15 lbs) for about $200. Go for $300-400 and you can score some Volks, Advans or Racingharts, but you really don't need them or want them for autocross... you'll mess em up.
Go cheap... no one cares unless you win anyways.

 
Rep Power: 317

Thanks for the info, guys!

I think I'll try to find some nice and sticky tires for my 15's, then.

the 17's don't really have a sidewall at all! 205/40/17...not exactly comfortable.

I think I'll testout the weight of the rims (I have steelies and the enkei 5 spokes for the sport sedan thing from last year), and then slap a set of sticky tires on the lighter of the two.

If things work out (read: I get better), I'll buy some nice and lightweight rims.

no sense in investing in it if i still suck anyways hehehe

thanks again guys!

 
Rep Power: 382

Flaken Azenis Sports and Kumho Ecsta MX are the top 2 tires in STS right now.

 
Rep Power: 317

"Kumho Ecsta MX"...interesting.

I've heard of the supra 712's, but not the MX's. I'll look into those!

Thanks ZzyzX!