Steve Baur
Former Editor, Modified Mustangs & Fords
January 1, 2009

Speed Rating
The United States government grants speed ratings when tires meet a minimum standard for reaching and sustaining a specified speed. Generally, a higher speed rating will result in better car handling. Downgrading the speed rating of your tires is not recommended, as poor handling and unpredictable steering may result. However, if you want better cornering response, you can install a higher speed rated tire on your vehicle. Tire manufacturers recommend not mixing and matching tires with different speed ratings on your vehicle. Remember, the speeds are test speeds, not recommended speeds.

  • Q- Up to 100 mph
  • R- Up to 106 mph
  • S- Up to 112 mph
  • T- Up to 118 mph
  • U- Up to 124 mph
  • H- Up to 130 mph
  • V- Up to 149 mph
  • W- Up to 168 mph
  • Y- Up to 186 mph
  • Z- 149 mph and higher

Reading the Sidewall
The following is a breakdown of the components of the size of the tire: Example P205/65/R15.

P=Passenger car tire. If there is no "P" before the size it would indicate it's a European metric tire. An LT before the size would designate a light truck tire.

205=This is the section width in millimeters. This measurement is taken from sidewall to sidewall.

65=This number refers to the height of the sidewall, or the aspect ratio, as it's a percentage of the section width. In this example, you would take 65 percent of 205 millimeters and this would give you the sidewall height.

R=Radial tire construction.

15=Wheel diameter in inches.

Heat Cycling
Like any high-performance component, competition tires require careful break-in to achieve the full benefit. Competition tires are capable of sustaining traction throughout a much wider temperature range, but they are also very sensitive to the first heat cycle of use.

A proper break-in and heat cycling results in a tread compound that lasts longer and provides better traction. However, if the first cycle is not performed correctly, the tread may develop irregular compounding, leading to poor wear and inconsistent traction. Manufacturer's instructions should be followed for proper break-in.

This service costs $15 per tire. All competition tire manufacturers recommend heat cycling service. To learn more about Discount Tire's heat cycling service, or the process involved, contact them at

Spec Tire Special
Toyo Tires is an official contingency sponsor of the 2008 The Tire Rack SCCA Solo National Tour. Competitors must use Toyo Proxes R1R tires on all four wheel positions during all runs to qualify. Classes include STS, STSL, STU, STUL, STX, STXL, STS2, and STS2L. Cash awards are presented to the First, Second, and Third Place drivers per event in the 2008 SCCA Solo National Tour competition only. There must be five or more competitors in a class to be eligible for awards. Toyo's R888 is the spec tire for the Speed World Challenge, both touring and GT class.

In the NASA Pro Racing series, the Toyo Proxes RA1 is currently the spec tire for both Camaro/Mustang Challenge classes, and will be replaced by the R888 for the '09 season. In the American Iron categories, the RA1 is currently the spec tire. American Iron Extreme allows for any size readily available commercially sold DOT-certified tire. Be sure to check with NASA regarding tire and wheel size for each class.

The Drag Radial and Factory Stock classes of the National Mustang Racers Association run off of a spec tire list, which allows for BFGoodrich Comp T/A or g-Force Drag Radial, Nitto NT555R Drag Radials, or any approved radial-construction tire with a DOT treadwear rating of 180 or greater that fits all other criteria and sizing.