The last letter in a tire size — like the H in P225/45R17 92H — is the speed rating. It tells you the maximum speed the tire is rated to sustain. For most U.S. drivers it never matters... until you put the wrong rating on a fast car.
The chart
- M — 81 mph (temporary spares)
- Q — 99 mph (winter tires, light trucks)
- S — 112 mph (basic passenger)
- T — 118 mph (most family sedans)
- H — 130 mph (performance sedans, common upgrade)
- V — 149 mph (sport sedans, performance coupes)
- W — 168 mph (high-performance and exotic)
- Y — 186 mph (supercar)
- (Y) — 186+ mph (uncapped, with engineering review)
Where speed rating matters
Speed rating isn't really about top speed — almost nobody drives at the limits these ratings imply. It's about how the tire is built. Higher speed ratings mean stiffer sidewalls, better heat dissipation, and more responsive handling.
An H-rated tire on a car designed for W will feel mushy and may not be safe at sustained highway speed in summer. A W-rated tire on a car designed for H will give a harsh ride but is otherwise fine.
Going up vs going down
Going up in speed rating is always safe. Going down compromises the handling characteristics the car was designed for, and on a sports car can be genuinely unsafe at speed. Match or exceed what's on the door jamb.
Mixing speed ratings on one car
Don't. The handling difference between an H tire and a V tire on the same car causes unpredictable behavior in emergency maneuvers. If you have to mix, put the lower-rated tires on the rear and drive to the speed rating of the lower.
Winter tires are special
Most winter tires carry Q or R ratings (99 or 106 mph) even when fitted to V-rated cars. This is accepted practice because winter tires are used in conditions that limit speed anyway. Your insurer typically considers this acceptable as long as you switch back to summer/all-season tires in the warm months.
Above 100 mph the speed rating stops being a marketing letter and starts being a safety spec.