Temperature Resistance
The temperature grade measures how effectively a tire resists and dissipates heat build-up during continuous high-speed testing. Sustained high temperatures are the primary cause of tire degradation and failure. Heat breaks down rubber compounds over time, reducing structural integrity and increasing the risk of catastrophic blowouts.
The evaluation involves running a tire against a 67-inch rotating steel drum at increasingly high speeds. The assigned grade corresponds to the highest speed the tire can sustain for 30 continuous minutes without heat-induced failure. This rating is displayed alongside other grades in the Uniform Tire Quality Grading (UTQG) system on tire sidewalls. All passenger car tires sold in the United States must meet a minimum Grade C rating.
Speed Step Test Procedure
Testing involves running the tire at increasing speeds, with each stage lasting 30 minutes. The tire’s grade is assigned based on the highest speed it reaches before showing signs of thermal breakdown.
250 rpm
2 hours
375 rpm
30 min
400 rpm
30 min
425 rpm
30 min
450 rpm
30 min
475 rpm
30 min
500 rpm
30 min
525 rpm
30 min
550 rpm
30 min
575 rpm
30 min
Low speed (cooler)
Medium speed
High speed (hotter)
A
Over 115 mph
Excellent heat resistance for sustained high-speed driving. Best for performance vehicles, heavy towing, and hot climates.
B
100 - 115 mph
Moderate heat resistance suitable for most driving conditions. Best for daily drivers, family sedans, and mixed city/highway use.
C
85 - 100 mph
Minimum legal requirement for all U.S. passenger tires. Adequate for normal driving speeds and everyday conditions.