PCA’s Change to the Hoosier Bias Ply Tire
by David Murry
Tire technology has advanced tremendously over the years. Tires that generate more grip result in lower lap times.
Conversely, advanced tire technology can be detrimental if it “outruns” the capabilities of the vehicle in which it is utilized. More grip results in much higher lateral and longitudinal G-loads. Problems arise when these stressors are applied to components originally designed for much less load. We have witnessed these problems with the older 911s vs. the Hoosier R7. The “youngest” 911 eligible for 911 CUP is 30 years old with the oldest being 41! The current Hoosier R7 generates more grip than any racing slick available 30+ years ago and FAR exceeds the capabilities of the street tires the cares were originally designed for. This leads to an accelerated wear rate on the aging tub/chassis and its components resulting in increased risk of failure at speed.
We recognized this type of issue when driving F-5000 cars with modern tires in recent years. While we were attaining much faster lap times than when the cars were originally campaigned, we experienced a significant increase in the failure rate of critical components.
The Hoosier “HOT D” bias ply generates grip at a much higher slip angle than the R7. This results in a more approachable and easier to control “edge” without the sudden drop off of the R7 at the limit.
Driving vintage cars should be authentic and that means tires as well. The additional control with bias ply, coupled with the greater slip angle delivers an experience that is more dramatic and fun to drive while delivering more driver feel as these cars were intended and designed to run. It also makes for better photos.