Autocross Tire Sizes for 89 C-4
05-17-2010, 02:56 PM
#1
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Autocross Tire Sizes for 89 C-4
Hi Guys,
Searched the forum, but I really didn't find a solid answer.
I am planning to autocross the C-4 this weekend and plan to use the stock 16 inch wheels for this duty. I have located the BFG R-1 in 205 /55/16 front and 225/50/16 for the rear.
My question is that the Kumho V-710 is available in the 225/50/16 for front and I could match that with a 245/45/16 for rear.
Will the Kuhmo fit within the wheel wells without rubbing. Does anyone have a better suggestion for a designated tire for the stock 16 inch rim.
Vehicle will be trailered to the event.
Thanks,
Ken
Searched the forum, but I really didn't find a solid answer.
I am planning to autocross the C-4 this weekend and plan to use the stock 16 inch wheels for this duty. I have located the BFG R-1 in 205 /55/16 front and 225/50/16 for the rear.
My question is that the Kumho V-710 is available in the 225/50/16 for front and I could match that with a 245/45/16 for rear.
Will the Kuhmo fit within the wheel wells without rubbing. Does anyone have a better suggestion for a designated tire for the stock 16 inch rim.
Vehicle will be trailered to the event.
Thanks,
Ken
05-17-2010, 04:42 PM
#2
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Unless there has been a very recent change, Porsche Parade AX rules allow tread wear rating of 140 and higher to remain in Showroom Stock class. And once you leave SS, any "R" tire is allowed.
A rule differentiating between a 30 wear rating vs. a 40 would be silly.
Brian
05-17-2010, 04:47 PM
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No problem running the 245 on the rear, and they are a good fit on the stock 8" wheel. The 225's may rub up front. If your region runs Parade rules, you are already in Production or higher.
On my '90 C2, I run 16x8's and 245's front and back. You will not complain about understeer with that setup. You will get a little rub at full lock, but that is of no serious consequence.
Brian
On my '90 C2, I run 16x8's and 245's front and back. You will not complain about understeer with that setup. You will get a little rub at full lock, but that is of no serious consequence.
Brian
05-17-2010, 05:08 PM
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The front V-710 225s may rub if the '89 stock 6mm steering stop washers haven't been retrofitted with 10mm washers, P/N 964 347 325 02. The retrofit is usually associated with installation of 17" wheels, but the wider 225s on 16" wheels could also rub. The rears should be fine.
For autocross performance, the Kumho V-710s in those sizes should be excellent. However, in PCA Z8 autocrossing, the V-710's wear rating of 30, awa the R-1's 40, will bump you out of stock classes into much more competitive improved classes, if that's important to you.
For autocross performance, the Kumho V-710s in those sizes should be excellent. However, in PCA Z8 autocrossing, the V-710's wear rating of 30, awa the R-1's 40, will bump you out of stock classes into much more competitive improved classes, if that's important to you.
Brian
05-17-2010, 05:19 PM
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No problem running the 245 on the rear, and they are a good fit on the stock 8" wheel. The 225's may rub up front. If your region runs Parade rules, you are already in Production or higher.
I think we are running the small region rules and I am already lumped in....wider wheels and tires would bump me up.
Follow up question I have a 3 position adjustable rear sway bar. If I want to reduce understeer the bar should be set softer?
Thanks,
Ken
05-17-2010, 05:30 PM
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Are we talking about the tires rubbing on the fender or just rubbing on the inside under full lock. Full lock I can deal with.....
I think we are running the small region rules and I am already lumped in....wider wheels and tires would bump me up.
Follow up question I have a 3 position adjustable rear sway bar. If I want to reduce understeer the bar should be set softer?
Thanks,
Ken
I think we are running the small region rules and I am already lumped in....wider wheels and tires would bump me up.
Follow up question I have a 3 position adjustable rear sway bar. If I want to reduce understeer the bar should be set softer?
Thanks,
Ken
Actually, my road wheels are 17 x 7.5 with 205's, and those will rub as well at full lock.
Being a C2 guy, I will have to let others answer your sway bar question.
Brian
05-17-2010, 09:30 PM
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I used to run my old C4 in AX, track events and Club Races. I'd defer to Brian on most AX tire or set up questions--lots of experiene--but I would suggest the Hoosier A6 as one other worthy compound to consider. As for rear bar, you want it set to full stiff or shortened. Attach the drop link to the adjustment hole furthest away from the bar ends.
Getting your cold pressure right will also be critical (no warm up laps!), so you may want to research that issue once you decide on a brand/model.
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05-17-2010, 11:09 PM
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Hey,
If I had only known I would have.....I've autocrossed the 928 for the last 10 years, but it requires a lot of setup changes from autocross to track days and I'm starting to get lazy.
I have looked at the Hoosiers and may go that route, there used to be a bigger price difference between the Hoosier A6 and the V 710 but not anymore. The only thing that I have read is that the Hoosiers seem to cycle out quicker and don't last as long?
Also looking at the 225 in the Kumho 710 it comes in a rounded shoulder and the 245 is the new square shoulder. That may present it's own little setup issue.
Thanks for confirmation on the sway bar....this one is on the wrong end of the car.
I do start with pretty high pressures for autocross. (Near where I want to be hot, since there is a shorter energy / time to raise the pressure.)
Ken
If I had only known I would have.....I've autocrossed the 928 for the last 10 years, but it requires a lot of setup changes from autocross to track days and I'm starting to get lazy.
I have looked at the Hoosiers and may go that route, there used to be a bigger price difference between the Hoosier A6 and the V 710 but not anymore. The only thing that I have read is that the Hoosiers seem to cycle out quicker and don't last as long?
Also looking at the 225 in the Kumho 710 it comes in a rounded shoulder and the 245 is the new square shoulder. That may present it's own little setup issue.
Thanks for confirmation on the sway bar....this one is on the wrong end of the car.
I do start with pretty high pressures for autocross. (Near where I want to be hot, since there is a shorter energy / time to raise the pressure.)
Ken