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The Firestone Roadster Tires

Posted on October 17, 2009 at 7:28 PM

The Firestone Roadster Tires

As I was writing the previous blog about the Firestone test cars, I got off on a tangent, and found myself gathering some information about the Firestone tires, used throughout the roadster era. I decided that there was enough interesting stuff to write a separate blog about these tires.

 I still have some unanswered questions, but the guys I talked to, who were there, including A.J. Watson, Bob Clidinst and Bill Spoerle gave me a lot of information that told most of the story.

I will keep digging for the few missing bits of info. If any of you guys have anything to add, please do!


Some comments about the Firestone racing tires "of the day".

During the prime years of the roadster era, from 1952 through 1962, Firestone was the exclusive tire supplier for the Indy car series.

The sizes available were 760X16 on the front and 800X18 on the rear.

The front tires measured approx, 29" diameter, 6.5" wide and 4" tread width.

The front wheels were Halibrand magnesium measuring 16" diam. X 6" wide.

The rear tires measured approx. 31.5" diameter, 7.75" wide and 5.25" tread width.

The rear wheels were Halibrand magnesium measuring 18" diam. X 7" wide.

The tires were bias ply construction and recommended pressures were 35 PSI.

During the roadster era, Firestone designed and built two distinct types of pavement tires.

The "Indy" tire

The "Indy" tire tread surface was smooth on the left half with circumferential grooves on the right half, two grooves on the front tires and three grooves on the rears. These grooves provided some cooling effect and, also, were used to measure tread wear. The tires were always mounted so that the grooves were on the right side. These tires also had "notches" across the corners of the tread, angled across the right corner and straight across the left corner. These "notches" provided some heat dissipation.

   The "Indy" tire was used at Indianapolis, Milwaukee and Trenton. Unlike today, with different rubber compounds and sidewall constructions for each track, the roadsters ran the same tire everywhere. Of all of the original roadster tires, I have never seen any, obvious molded in numbers or letters, indicating that any of the tires were for different tracks. I have talked to some of the guys who worked on the roadsters and none of them knew of any differences.

   They, also, used the same tire on the right and left side of the car.... no right and left compounds and no "stagger".

   I'm sure that Firestone did a lot of development and made many improvements to their "Indy" tires between '52 and '62, but, sizes, profiles and overall appearance did not change very much during the era from 1952 to 1961.

  A couple interesting comments by the drivers "of the day".

    First was about driving until the "white" started to show on the tires. The"white" was, actually, the light colored nylon structural fabric of the tire. When the driver saw the "white", he had about 2 or 3 laps, to pit for new rubber, before the "blowout".

    Another great comment was about the "Voice of Firestone". The "Voice of Firestone" was a musical variety TV show sponsored by Firestone in the 50s... but the Indy roadster drivers adopted the term, "Voice of Firestone", to describe the squealing and screeching the tires made when they were spinning, skidding and sliding down the track during a crash. Hearing the "Voice of Firestone" was not a good thing.

Things began to change, in late '61 and '62, when Firestone used some slightly different tread patterns and different compounds at Trenton and Milwaukee. I have even seen some 1962 photos from Trenton showing some version of the "Monza" tire, being used.

   Some guys were, even, attempting to create a little "stagger" by overinflating their new "right rears" and leaving them in the hot sun to "stretch" out a little. Firestone was also allowing the cars to run lower "left rear"tire pressures to reduce circumference.

The "Monza" tire

   The roadsters, in the 50s, ran on, relatively, flat speedways at Indy, Milwaukee and Trenton, but in 1957, a race was scheduled at the incredible Monza, Italy high bank, 2.64 mile oval.

   It was necessary for Firestone to design and build a totally different tire to cope with, not only the increased vertical and centrifugal loading, but also the bumpy concrete surface of the banking.

   Firestone came up with a tire, featuring stiffer sidewalls and a symmetrical, intricate tread pattern.

  This tire was successfully tested at Monza, in excess of 170MPH, prior to the 1957 race, using the KK500C-Chrysler test car, and, also, successfully raced there in 1957 and 1958.

     The next "high bank" race for the roadsters was scheduled for April, 1959 at the new 2.5 mile Daytona International Speedway.  Compared to Monza, Daytona was brand new, super smooth ashphalt, but exerted the same kind of vertical and centrifugal forces on the tires,

    The "Monza" tire was successfully tested at Daytona, using the Kurtis SPL-3 - Pontiac roadster, and used in the race with no problems.

   Unfortunately, the Daytona race and associated events turned into a disaster with one driver killed during testing and another killed in the race.

  Following the Daytona race, the roadsters were deemed unsuitable for high bank racing and never again returned to race at either Monza or Daytona.

     The "Monza" tire was, also, used at Daytona, in 1961, by the Mad Dog IV on its record 180+ MPH lap.

The Indy Roadsters -1963 to 1966

    In 1963, everything changed when Lotus showed up at the Indianapolis Speedway with their specially built low profile, wide tread Firestones, mounted on 15" diam. wheels.

   Top roadster drivers, Parnelli Jones and A.J. Foyt, who had showed up at the track with the standard 16 and 18 inch wheels, "protested" the fact that Lotus had access to Firestone tires that they didn't have. Firestone said that they had built the tires to Lotus specs and Lotus had paid for the development of the tires.

    After more "discussion", Firestone agreed that they could produce more tires for the roadsters that wanted them....

      But, that wasn't the main problem.

  There were no 15" wheels that would fit on roadsters. Roadster wheel supplier, Halibrand, scrambled up some existing 15" wheels that he was building for Shelby Cobras and other sports cars, that he was able modify to fit on the roadster hubs.

   Other problems included brake clearance problems, ride height problems and torsion bar lever & radius rod geometry problems.  

    Apparently, the advantages of the 15" tires were greater than the problems they created because Parnelli was able to win the '63 "500" with the new wheel & tire setup along with the top four finishing roadsters. About half of the roadsters in the '63 field were, eventually, able to get the new "15s" with no apparent tire related problems in the race.

    The tire sizes on Parnelli's '63 winner were 7.40 X 15 fronts and 8.00 X 8.20 X 15 rears

      They measured:

Fronts- 27"diam. X 7.5"wide X 6"tread mounted on 6" wide wheels

Rears- 29"diam. X 9"wide X 7.5" tread mounted on 8" wide wheels

By '64, the "16s" & "18s" had disappeared and Goodyear came sniffing around the Speedway. Tires became lower and wider.

By '65, Goodyear came in full force and the tire war was on

. In '66. the last standard front engine roadster started the Indy 500, ironically, on Goodyear tires.

I have posted pix of the roadster tires in an album titled "Firestone Roadster Tires" in the "Photo Gallery"..

Have a look at:

mac miller in Indy

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Reply dave agosti
10:20 AM on July 22, 2013 
Did the lotus Fords that Clark and Gurney ran at Indy in 64 have Dunlop tires? Didn't they chunk and destroy the light suspension links?

Reply ★ Owner
1:20 PM on July 22, 2013 
Yes,... On lap 47, while leading, Clark's RR Dunlop started throwing its tread,coming down the front straightaway, causing a catastrophic suspension failure. Fortunately, he was able to guide the car safely to a stop inside of turn one.
On lap110, Gurney's Dunlop equipped Lotus was withdrawn due to tire problems.
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