We have been running our V8 Miata on track for some time now and have found the Hoosier R6 275-35 R15 (HR6) to be the tire of choice for our car on both 9” and 10” rim widths. There is really only one major negative issue with the HR6 275 tire and that is cost at $288 each.
I have therefore been looking for some time for an alternative tire that would perform as well as the R6, provide similar longevity and be of similar size and at a price point that was more in line. After reviewing every tire manufacturer site, racing sites, call asking around and reviewing and testing the alternatives, I have finally now found an alternative.
American Racer makes a tire for Formula and Modified cars in the 23.5-10-R15 (http://www.americanraceronline.com/Asphalt-Track/modified.html). These tires are available in 2 compounds (similar to the Hoosier A6 and R6). The specifics on the American Racer (AR) tire when compared to the Hoosier R6 (HR6) are as follows:
AR 23.5/10.0-15, width 10”, section 11”’ diameter 23.8”, Circ. 75” Cost $115 Two compounds available M28 (soft) 131 (Medium)
HR6 275/35 R15, width 10.1”, section 10.8”, diameter 23”, Circ. 72.2”, Cost $288 Two compounds available A6 (soft) R6 (Medium)
So after reviewing all the details, making a few calls, I ordered 2 sets of the AR tires in the 131 compound from Day Motor Sports (www.daymotorsports.com). Shipping was significantly cheaper as Day Motor Sports will ship up to 24 tires on a pallet for a flat fee (in my case $100) vs. the shipping price per tire when I have order the HR6 tires at as much as $18 each.
Upon receiving the AR tires we took numerous measurements, reviewed the sidewall stiffness and then mounted and test fitted on the car. While the circ. is approx. 3” larger on the AR vs. the HR6 we had already mounted a body kit and flared fenders to fit the R6 so no further modifications were necessary.
We then scheduled a two-day testing session and loaded up the car on the trailer and filled the tirerack with the HR6 and the AR tires.
Hoosier tires recommend the R6 tire be heat cycled and then laid up for up to a week to gain the best performance. In contrast the AR recommended initial heat cycle process is not as onerous. AR recommends the following process. Run a few laps to get the new tires up to temp (we were looking for 180 – 190 degrees F). This should be done with an initial lap at a slow pace, then increasing lap speed in subsequent laps so that at lap 4-5 we were running the car at about 80% pace.
We then pulled into the hot pit and checked tire temps. When certain we had reached the targeted heat range we immediately returned to the pits raised the car and pulled the air out of the tires. The tires were then allowed to cool (out of the sun). This allows the cords in the tire to shrink and bond together and also makes the tire more resistant to graining.
The initial feel of the AR tire when being heat cycled was not as crisp at initial turn-in as compared to the HR6, however overall grip levels were very similar. We next mounted a se of the HR6 tires on the car and set out to establish a lap time baseline.
We then remounted the heat cycled AR tires and ran 8 or so laps (heat race length) and reviewed tire pressures and temps at the end of the session. The first AR tires session lap times were just off (almost a full second slower) the HR6 lap times. We found that my initial guess on tire pressures in the AR’s was too high. Once the tires cooled off we lowered our air pressures and set out for another 8 lap session. These lap times were in line with the HR6 tire lap times. Driver feedback was also positive, as the initial sloppy turn in feel was gone and overall grip levels gave the driver a heightened level of confidence when compared to the HR6.
We then made a few chassis and further pressure adjustments and topped off the tank and then set out on a long run on the AR tires. We were able to match the lap times of the HR6 tires for almost 20 laps before running out of fuel. Temps were now close to even across the tire surface and handling degradation from 1st lap to last lap was in line or a little better than the HR6.
So after 4 heat cycles (initial heat cycle, 2 short lap sessions and one long lapping session) the tires were showing even wear, no flat spots, and have many more laps left in them. Time will tell just how many sessions / heat cycles we can get out of these tires before they heat cycle out, so far no noticeable heat cycle degradation has been identified.
So if you are looking for a reasonably priced low profile 275 15” track tire available in auto cross (soft) and road race compounds, this may very well be an alternative for you too.
Mark
Hope to hear tomorrow.
