So I was thinking of running the 15" Bias tire for my FC, the same one that everyone runs for ITS. BUT, i was reading things about those tires and it seems that running V700's or radial DOT hoosiers may be the faster tire for what i do. Plus, the radials come in a lot more sizes...

Seems like all the new technology and developments are going into these radials...

Does anyone have enough experience to know which is the faster tire? I have a lot more experience with the radial DOT tires then with the bias tires.

 

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We did some testing on this. It depends on your driving style but it seems that the radials ended up a little quicker. Alignment and spring rates ended up changed to make the radials faster.

 

Everyone in ITS has to run a DOT radial tire. The EP cars can run a bias ply tire. Now there is a big difference between a slick radial and a DOT radial and then you throw in the bias ply slick as well.

 

WOOPS! sorry, i ment ITA.

 

What kind of differences were you seeing in time?

 

These were slicks on a tube frame car so its apples and oranges for your application but they gave us a consistant 1.5 seconds on about a 2:10 second lap around Sebring.

 

Everyone in ITx has to run a DOT tire.

 

what was the class that runs the hoosier cantilever tires? EP?

 

EP and GT3

 

Goodyear also makes a comperable tire.

Keep in mind that a radial and a bias ply will require somewhat different suspension setups and driving styles. Bias tires like somewhat more slip angle than a radial and take less camber. There's probalby more to it than that, but those are two of the big differences.

On the GT-3 BMW that I crew for when swapping between R's and cantilever bias slicks we have to take out most of the camber.

 

As far as I know radials have a bigger contactpatch, but take longer to heat up. So faster for the track, but not for short runs with cold tires.

 

radials are much faster than bias ply's with proper setup changes to the suspension. I found the braking performance was very noticeable and the radials were very consistant and tended to take more heat cycles. the bias ply's were only fast for 3-4 heat cycles and would drop off in performance after about 30 minutes of race time. for IT classes all DOT tires will be radials and for my own car I wont use anything but radial slicks. they last longer and work better. At the tracks I run the radials are about 4 sec's quicker on a 2 minute lap.

 

That would be assuming that you can get a similiar tire size though right? For example in GT3 and EP you're limited to a 15x7, so one of those bias cantilever slicks makes sense as you can get a lot more tire under the car because I don't think anyone makes a comperable radial, so you'd be stuck with a tire in the 225 sort of size range. If it was open then a similiar sized radial slick on a 15x10 or something like that would be faster. I'd think that the radial to bias difference would be more than made up for with the added width of the bias slicks in the case of an EP or GT3 type car, no?

 

IIRC from talking it over with someone who'd done experiments, with the Prod situation he found that the bias ply tires had more lateral grip, though the radials ended up faster down the straights. Less internal friction from the cords or something, I dunno.

YMMV.

 

I am running a smaller contact patch with the radials but the lap times are much faster. A fast lap time is not solely determined by lateral grip. I brake later and carry more speed through the turns and accellerated harder. I was night and day noticeable in my car. The setup of the car makes it turn faster and the tires perform at the limit longer.

 

The kind of tires you run and which tire is faster has allot to do with what the rules allow you to do.

For example in EP and GT3 the rules limit the cars to a 15X7" wheel however there is no requirement that the tires used on those wheels meet DOT specs. So in EP and GT3 the drivers have the ability to run any tire they want. They have continued to choose the cantilever bias ply tires because of the contact patch and the grip they provide DOT legal racing tires, while maybe faster in a straight line do not generate enough cornering force to allow the cars to properly maintain speed.

To me the bottom line is that no one that is fast or has won a Club Racing National Championship runs a DOT racing radial in a class where non-DOT racing tires are allowed. Given the money that is spent by the front runner I am sure that if a DOT Hoosier or Kumho was the hot setup they would run them.

 

Maybe not a DOT radial, but there's some other options, like there's Hankook, Kumho and Avon radial slicks that come in usable sizes. Of them Avon has the widest, then Hankook, then the Kumhos are the narrowest. Goodyear and Hoosier also make radial slicks, but not in sizes that would seem to be usable on the 15x7's.

Tims, care to share what wheels and tires you're running and what that's compared to in a bias tire? This is an interesting subject for me, as Spokane will be the closest track to where I'll be working post grad and it's a 2.5 mile 10 turn track with a 1.1 mile long front straight, so sacrificing cornering grip for straight line speed is probably a good tradeoff there, and it'd allow for smaller flares (or maybe even none) for less drag.

 

When I was involved in tire service at race tracks the whole issue with Radial racing tires (non-DOT racing slicks) was that they need negative camber at both ends of the car. Cars with IRS could use them - GT2 Porsches - but straight axle cars didn't use them.

At the Run Offs the faster GT1 cars were on Goodyear radials so apparently the rear camber issue has been solved. Still didn't see any production or small bore GT cars (GTL - GT3) on anything but Bias Ply cantilever slicks. That could be because only two tire brands could be found on any of the cars - Hoosier or Goodyear. Maybe some of the other brands will work - Avon has allot of saloon car fittments. However nobody is trying them and they are not cheap.

Ya Tims, what wheel are you running???