15" wheels & tires on a Ralt RT 41?

[John B]

Has anyone tried or thought of mounting the 15" radials on a Ralt RT-41 instead of the 13"?
I know it would take some special wheels & different set up but that wouldn't be that hard.

[KevinFirlein]

john , i know John Dole tried them a couple of years ago and Jacek Mucha is currently running them.

without having had a chance to do the measurements i wonder the affect on geometry with the slightly larger circumference. The tire companis went to 22" fronts to get the right circumference so it matched the way the car was designed on the pro radials. So it would seem that putting 15" wheels on would screw that all back up. that and the cars are over braked as it is so i cant see putting larger rotors and calipers on. But take it all with a grain of salt since i havent measured a car with 15" wheels installed.

Kevin

[Adair]

I'm far from an expert, but it appears it was done when the series went to Yoks in '97. It appears the tire itself is of a lower profile and may offest the larger rim size with regard to total height.

[P.W. LeCain]

That car looks familiar (Doc1.doc).


If I remember correctly, John D wasn't overly impressed with the 15" setup. I have never driven an RT-41 with 15's, but he didn't like them too much at Lime Rock.

[Drivers Services]

Actually the Pro series was on yok's before 97 but they were 13 inch yok's.
When the 008 was introduced in 97 it came with 15's and a host of problems including not getting enough of the cars delivered in time.
Two make sure of full fields they let us run 41's (w/15's as yokohama wasn't interested in bringing 2 sets of tires to the tracks) in what was supposed to be a spec class. Well, all hell broke loose ,as the Ralt's that many teams had just sold were faster than the new "spec" 008. The series started handicapping the Ralts, Teams started scrambling for Ralt's (Some buying back or renting the cars they had just sold). It was a real mess. Certain teams with ties to Indy teams and autoclaves suddenly had faster 008's. Couldn't blame them as some looked at the improvements as purely a safety issue. Yeah those early 008's reminded me of my childhood, I had a favorite sled, the brand was "Flexible Flyer". But I digress.
I put the 15's on J.Doles car, we were always faster on the 13's.

Jim Little

[Paul LeCain]

One thing you have to remember with the 15" tires is that their spring rate is nearly double that of the 13" tires. If you don't compensate for that, you'll likely rattle your teeth out, especially on unpaved tracks like Lime Rock.

[Drivers Services]

Paul's right

If you wish to try the 13's and 15's back to back, the set-up change over is very time consuming. Especially at VIR in August in 100 degree heat.

Jim Little

[Drivers Services]

Just re-read your post Paul, I think you describe Limerock perfectly, and in only one word too.

Jim Little

[Stan Clayton]

Boy, does this thread bring back memories...!

We bought our 41 from Bill Fickling at the end of the '97 season, just in time to switch to the 15" wheels in the pro series. Even though nobody had more than a few days of testing Ralts on the new tires and wheels, the Ralts absolutely clobbered the Swifts. After qualifying at Long Beach, where IIRC no Swift made it into the top ten, CART called all the Atlantic team owners into an auditorium and announced that CART had a contractual obligation to Swift to ensure that the 008 was 'competitve' with the Ralts, and that we should anticipate 'competition adjustments' to ensure that happened. However, even after imposing a 5/8" bottom plank, 50 lbs extra weight, and a minimum 14-degrees on the upper rear wing element, Ralts still gathered 9 of the top ten spots in the race.

Even though the spring rate of 15" tires is nearly double that of 13's, teams figured them our pretty quickly. If you are a corner-rate kind of guy, 5 minutes with a calculator will give you your new coil spring rates, and damping isn't much tougher. But as Jim says, converting between the two tire sizes is like rebuilding the car...

Furthermore, at least at the pro level, there is no such thing as "too much braking". One of the factors that allowed the 008 to overtake the Ralts towards the end of the '98 season was teams figuring out how to exploit its demonstrably better brakes. If you are enthralled with your Ralt braking, try a Swift. I don't have the torque figures to hand, but I assure you that the Swift's high-speed braking has to be seen to be appreciated.

As for John B's question about wheel availability, the 15" BBS spec'd for the Swift 008 fits the Ralt perfectly, as some aspects of the Swift's outer suspension geometry is a clone of the older car. Usable wheels are routinely sold by the pro teams and are quite reasonable in price. IMO however, it'd be a waste of money unless one is prepared to install larger brakes and engage in an extensive testing program -- and was already exploiting ALL of the car's potential. Of course, my opinion is worth exactly what you paid for it...

Cheers! Stan

[John B]

Great input guys, thanks.

John Burke

[bsunier]

John, you can try 15" wheels off the 008.
Bernie Sunier