Decode a tire speed rating
The letter at the end of a tire size — the H in 225/65R17 98H — names the maximum speed the tire is certified to sustain, defined in km/h with the mph figure derived from it.
| Letter | mph | km/h |
|---|---|---|
| L | 75 | 120 |
| M | 81 | 130 |
| N | 87 | 140 |
| P | 94 | 150 |
| Q | 100 | 160 |
| R | 106 | 170 |
| S | 112 | 180 |
| T | 118 | 190 |
| U | 124 | 200 |
| H | 130 | 210 |
| V | 149 | 240 |
| W | 168 | 270 |
| Y | 186 | 300 |
Getting a number you can act on
- 01Find the letter after the load index
In a size like 225/65R17 98H, the H is the speed rating — the last character before the end of the designation.
- 02Decode it against the published table
Each letter maps to a specific sustained speed capability, not an approximate range.
- 03Never fit a lower rating than the vehicle specifies
The rating on the vehicle's placard reflects what the vehicle was engineered around, particularly relevant on anything with genuine high-speed capability.
- 04Understand what 'sustained' means here
The rating describes a speed the tire can hold continuously under laboratory test conditions, not a hard cutoff — but it is also not a rating to casually exceed.
Why the ratings are defined in km/h, not mph
Tire speed ratings originate from an international standard (ISO/ETRTO) written in km/h, in round 10 km/h increments — 120, 130, 140 and so on. The mph figures published everywhere are conversions from those defining values, which is exactly why they land on numbers like 149 and 168 rather than clean round figures.
This also explains a detail that surprises people: an H rating (210 km/h, 130 mph) sits between U (200 km/h) and V (240 km/h) alphabetically out of order — H was assigned later, after the alphabetical sequence up to U was already established, to fill a gap in the middle of the range as tire capability evolved.
What speed rating actually certifies
- The maximum speed a tire can sustain continuously, at its rated load, under standardised test conditions
- It says nothing about handling, grip or braking performance at that speed — only structural integrity
- Higher-rated tires generally use stiffer, more heat-resistant constructions, which is a separate and real handling benefit
- A tire rated below the vehicle's actual top speed is a genuine limitation, not just a technicality
- All four tires on a vehicle should carry the same speed rating unless the manufacturer specifically permits otherwise
Tire Speed Rating Decoder FAQ
What does the H rating mean on a tire?+
H-rated tires are certified to sustain up to 130 mph (210 km/h) continuously at their rated load, under standardised test conditions.
What is the highest tire speed rating?+
Y is the highest standard letter, certified to 186 mph (300 km/h). Some tires with capability beyond that carry a (Y) rating in parentheses alongside a ZR designation.
Can I mix tires with different speed ratings?+
Not recommended without manufacturer guidance — mismatched speed ratings on the same vehicle can create uneven handling characteristics, particularly under hard driving.
Why is H out of alphabetical order in the speed rating sequence?+
H was added later to fill a gap between U (200 km/h) and V (240 km/h) as tire capability at that specific speed became common enough to warrant its own rating.
What speed rating do I need?+
At minimum, match the rating specified on the vehicle's tire placard. That figure reflects what the vehicle was engineered around, particularly relevant for anything with genuine high-speed capability.
Standards and references behind these figures
The arithmetic on this page is fixed, but the boundaries and conventions around it come from published standards and manufacturer guidance. These are the documents they come from, so you can check them rather than take them on trust.
01UN Regulation No. 39 — speedometer and odometer equipmentThe regulation requiring that an indicated speed never falls below true speed, and capping the permitted positive error.↗02The Tire and Rim Association — standards filing (NHTSA docket)TRA has been the US standardising body for tire and rim interchangeability since 1903; this filing sets out dimensional practice.↗Nominal sizes, not measured ones. Every figure here is calculated from the size marked on the sidewall. Real tires vary from nominal by a few millimetres between manufacturers, and more as tread wears or pressure changes. Use these numbers to plan and to sanity-check a quote — measure the actual tire before committing to a tight fitment.