13" Radials

[B17overhead]

I am still in the process of building a lightened FA for SCCA Solo2 (1020# with driver) and am very interested if anyone knows anything about the new Hoosier 13" radial tires.

The tires are the ones that are 23" and 23.5" diameter front and rear, about like the 15's, just with taller sidewalls outside the rim diameter.

I'd love to speak to someone who has tried them before I buy any.
For the foreseeable future, I'm stuck with 13" rims.

Hoosier is recommending about -3 degees negative front and about -1 rear.

Do they come on as fast from cold as the Hoosier C3000 Bias plies in the equivalent cmpound (R25A vs the Radial R25B)

....and how is the feel in terms of control? Do they have a more wicked breakaway characteristc than the bias plies? In other words.... any thoughts on how they should behave vs. 15" rim size equivalents?

Broader range of slip angles in a 13" rim and perhaps easier to drive at the limit in a more qualifying-like scenario as my type of racing is?

Or worse when trying to make big steering corrections with more windup and release by the slip angle twist of the carcass?

Chuck

AZ

480-837-4531 H
480-892-8200 x2365 W

[Charles Warner]

Chuck,

All of those questions will need a unique and personal perspective (read "your perspective") to answer. The only way you can know these answers is to buy a new set of these tires and test.

[B17overhead]

Charlie,
I'd STILL love to speak to someone who has tried them before I buy any.:->

[Rennie Clayton]

Chuck,

Have you spoken with Bruce Foss at Hoosier Tire yet with regard to the driving characteristics information for these tyres? Unfortunately, I was not in a position to be in on the testing cycle with these tyres because my car was not complete, but Bruce is the first guy I'd talk to about getting driver comments.

Give him a call if you haven't already, and tell him I sent ya.


Cheers,
Rennie

[B17overhead]

Rennie,
Thanks for the suggestion. I do pester the Hoosier guys pretty often and haven't got much feedback from them on these tires 'cept vague stuff like "well, they won the runoffs last year in FA"

I still get the impression that no one has actually tried the 13's. I reckon the FA at the the 06 runoffs running Hoosier radials were on the 15" versions anyway.

I'll have to find someone who is still serious with a RT41 and hasn't switched to 15's, I guess.

The local hot dog in the Phoenix area here is running a 014 for club and a 016 for Pro racing. All 15" stuff-and Yok Advan Radials on the 016

Chuck

[Rennie Clayton]

Chuck,

Guys that are serious with their RT-41 won't be switching to 15's, but that's another issue altogether. Unfortunately, the 13 radials were not available for the Runoffs, or I suspect that you'd be able to find more information out there.

Best bet in the absence of being able to track down a serious competitor on 13's is to obtain a set and go testing. As soon we're ready to do testing on the new tyres, I'll report back with my own observations.


Cheers,
Rennie

[John Robinson II]

Contact the current FA champ, he uses Hoosiers and is a member of theis board... Mirl Swan

[Paul LeCain]

He's using the 15" radials.

[B17overhead]

Thanks, I'll try to contact Mirl anyway, even if he is on 15's.

Rennie, why is switching to 15's" a problem for the RT41?
A local shop converted a RT40 to 15" wheels quite a few years ago. They changed the pickup points and that was it.

I suppose to take full advantage of 15's, one would also change rotors and inboard close-off plates.

All told, wheels, PU points, rotors, close off plates..not cheap.

Are there other issues, like not enough strength in the tub PU point area or in the original A-arms that makes it more expensive still ?

Chuck

[MirlSwan]

The basics with the 15" Hoosier Radials that I have been running on the swift is... We run 3.5 degrees front camber and 2.4 degrees in the rear. The radials haven't given any bad or quirkie handling issues. The radial does take about a lap, on average, more to get up to full temp/bite compared to the bias ply. Once up to temp, the car has so much more potential with the radials. The steering correction movement went down noticably with radials, particulary in fast corners. With the bias ply there was always very small (and occaisionally very enormous) correction movement of the steering wheel in fast or long corners as the bias tires grip then give. The radial was also more consistent over the duration of the race. Not that that is of too much concern for solo. Basically, they're fast. And, the setup info that Hoosier has for the tires will get you very close on setup. Hope this helps.

[Rennie Clayton]

Chuck,

Running the 15's on an RT-41 is not a problem in terms of fitment - in fact I believe we were among the first to do it in SCCA. We were disqualified from a National Race win at Phoenix International Raceway in 1999 for using them, despite the fact that the rules quite clearly stipulated a 13" minimum tyre diameter. In any case, the problem is simply a matter of performance. Why pay so much to go slower?

Changed roll centre locations, rotating assembly weight, rolling resistance and aero drag are the main drawbacks of using the 15's on an RT-40 or -41. The braking advantage of the newer cars is offered by advances in caliper technology, not in the rotor diameter, although one might argue that modulation becomes slightly easier at higher speeds with a larger diameter rotor. Certainly not a real consideration for autocrossing.

Bottom line, in my experience you give up somewhere in the neighborhood of 4-6 tenths on an average road circuit by using the 15's on an RT-41

FWIW, my sentiments about the superiority of the 15" radial compared to bias plies echoes Mirl: they are clearly superior on a lap to lap basis, and have much better longevity.


Cheers,
Rennie

[B17overhead]

Mirl,
Were those R25B's in a radial that came in slower than R15A bias plies?

Thanks,
Chuck

[MirlSwan]

Yes, 25 radial to 25 bias. The radial "currently' takes about half a lap longer to come all the way in compared to the bias, but then it's much better. Perhaps that will change this year as Hoosier continues to develope the radial including it's compounds?

[B17overhead]

Mirl,
Thanks-I probably should talk to Hoosier again before getting my contingency tires.

Might be better to wait if they say they are going to diddle the compound.

Even R25A in a bias ply actually has not been soft enough in the cold weather events. This is why many solo people sipe the tires like a dirt track racer to try to build heat faster as well as using co-drivers.

GY unfortunately eliminated their really soft E070 FA radial compound from about 2 years back. The Solo guys who ran those instead of the Hoosier R25A bias ply FA tires liked the soft GY radials better (while the availability lasted). They came in even faster than the R25a bias ply.

Chuck