what are you serious racers running for wheel and tire sizes for the FC? I run mostly autoX and open track events. There is a class system, but with the mods I have done to my car, i doubt ill be in anything else other then a race class. Normally I would run a v700 or the hoosiers, but now that im going to be in a full race class, i dont have to run a DOT tire, and my wheel/tire size is unrestricted (except by the fenders). I was looking at some of the bias ply tires that hoosier offers, is this the way to go? what do you guys run?

 

You probably will get 1 answer from 95% of those who have a serious FC race car (not just an autocrossed street car), and that's 15x7. That's all that's allowed in both ITS and EP, which is where most of the cars fit in. They'll use either a 225/45/15 or 225/50/15 in ITS, or a 23x9x15 (Goodyear) or 23x9.5x15 (Hoosier) cantelever slick in EP.

 

Plus 1 for the above answer. 90 RX7 E production- 15x7 with Hoosier 23x9.5 slicks.

 

Since your peak torque will be inthe 150 ft-lb range, the 225-wide rears should be fine for road course use. The FC chassis is prone to understeer when you put staggered tires on it, so unless you are dialing out wheel-spin, I would recommend against the stagger.

 

You can fit the 8.5" wide slicks under your stock fenders on 15x7's. We run the 9.5's with flared fenders. Just go with some R45 Hoosiers to start with. Check around, you can find them used through a few people in the back of mag's like Grassroots or Sportscar. They will ship them and if you don't like the looks of them you just refuse them from UPS and they send them back with no cost to you.

 

15x7's eh? hmmmm... I saw some wedssport 16"s that seemed really attractive and light, i was thinking about those, but the smallest tries were something like 10" wide, to big for stock front fenders.

So, you guys would run 15's even if you werent restricted by rules to run that size?

I use to run 235's in front and 255's on the rear on 17x8's! Those wheels are too damn heavy though.

 

The availability of slicks is the issue. Tire companies build racing tires to fit specific classes and weight of cars. Usually you go with the smallest rim you can fit over the brakes you're allowed to run but allowed suspension mods also comes into play(lowering the outer lower ball joint is one mod sometimes allowed).

The next issue is rubber compounds. You can fit a tire for a formula car on some smaller sedans but you will overheat it from the car weighing twice as much.

So, for your relatively unmodified car you probably have about 6 tires to choose from when it comes to slicks in this country.

 

I remember reading in an old book about suspension design about taller wheels having the benifit of stiffer sidewalls and was thus better. Is this benifit still founded these days? It seems like they would compensate with modern sidewall technology.

 

I've run 225 50 15 Toyo RA-1's on 15x8 rims and a staggered setup of 235 40 17 out front and 275 40 17 out back. I would agree, for the money it will be hard to beat the goodyear bias ply slicks for the money. the cantilevered 23x8 up front and the 23x9 out back. I'm going to try the hankook F200 slicks this year in a 240 625 17 (the 625 is height in mm). Should be fun. The taller tires really make it hard to get the FC low enough though

-Trent

 

Yes, you will get a shorter sidewall with a slick for the most part. There are new street tires that have shorter sidewalls than slicks but that doesn't mean they will be better. The wide slicks have very stiff sidewalls to support the contact patch that is wider than the rim itself. The rules stating a maximum width of rim led to the special tire design.

Making slicks is still a 'by hand' procedure. I saw the BFG facility a while back when they were making them for some series. The rubber for the tread would come out of a machine and was hand cut to length for whatever dia tire carcass it was going on. That was the only part of the process I was able see when we were picking up some tires but I think there was only a few people making all the race tires.

 

what is the item number at hoosier for the cantilevered tires? It doesn't say what is cantilevered or not.

 

The tires on the 17s i ran were no taller then the oem tires. They just had less side wall. There was some tarmac rally tires i was thinking of getting which would fit 17s on our cars perfectly. The tire was the Silverstone S585. There was a company that had some in stock, but their website is down. Heres the manufactures website http://www.silverstone.com.my/tyre_s585.asp

I thought this might do good on some of the less-than-perfect asphalt autoXs i do.
The price was right on these too! I think $125 a tire.

One other question on the hoosier cantilever slicks, will they fit on an 8" wide wheel? i found some people talking about the goodyears, and apparently goodyear even confirms they will work better on 8s than 7s.

 

Hoosier #'s 43375 for the 8.5
43385 for the 9.5 wide

Just look at the tread width a lot wider than the rim. These tires are mainly use in Prod and GT because of the rim width limits.

 

15x7 baby!