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How-to guide · Michigan City Ford · Michigan City, IN
How to Read Tire Size, Speed Rating and DOT Codes
A passenger tire's sidewall usually carries a size code, a load and speed rating, a DOT number with a date code and, on most passenger car tires, grades for treadwear, traction and temperature. Here is how to read each one, from the National Highway Traffic Safety Administration (NHTSA) and the federal tire rules in 49 CFR.
P215/65R15type, width (mm), aspect ratio, radial, rim size (in.)
95Hload index and speed rating
Last 4 digitsof the DOT code: week and year the tire was made
AA to Ctraction grades on passenger car tires
The short answer
In a size like P215/65R15 95H, P means passenger vehicle, 215 is the width in millimeters, 65 is the height-to-width ratio, R means radial, 15 is the rim diameter in inches, 95 is the load index and H is the speed rating (130 mph in NHTSA's table). The last four digits of the DOT code give the week and year the tire was made, so 0109 means the first full week of 2009.
How to read a tire size: P215/65R15 95H
NHTSA uses P215/65R15 95H as its example of a tire size code. Here is what each part means:
| Code | Part | What it means |
|---|---|---|
| P | Tire type | The tire is for passenger vehicles. An LT at the start instead means the tire is for light trucks. |
| 215 | Width | A three-digit number giving the width of the tire in millimeters, from sidewall edge to sidewall edge. |
| 65 | Aspect ratio | A two-digit number giving the tire's ratio of height to width. |
| R | Construction | The R stands for radial. |
| 15 | Rim diameter | A two-digit number giving the wheel or rim diameter in inches. |
| 95 | Load index | A two- or three-digit number that measures how much weight each tire can support. NHTSA notes it may not appear on all tires because it is not required by law. |
| H | Speed rating | The speed at which the tire is designed to be driven for extended periods of time (see the table below). |
From NHTSA's Safety First: Basic Tire Maintenance brochure (DOT HS 809 361), read November 10, 2026.
Tire speed rating letters
The speed rating is the letter at the end of the size code. NHTSA lists these ratings:
| Letter | Speed |
|---|---|
| Q | 99 mph |
| R | 106 mph |
| S | 112 mph |
| T | 118 mph |
| U | 124 mph |
| H | 130 mph |
| V | 149 mph |
| W | 168 mph |
| Y | 186 mph |
NHTSA adds that for tires with a maximum speed capability over 149 mph, tire manufacturers sometimes use the letters ZR, and for those with a maximum speed capability over 186 mph, they always use the letters ZR.
From NHTSA's Safety First: Basic Tire Maintenance brochure (DOT HS 809 361), read November 10, 2026.
How to read the DOT code and find a tire's age
The tire identification number (TIN) starts with the letters DOT, which NHTSA says indicate that the tire meets all federal standards. Under federal rules (49 CFR 574.5), the TIN on a new tire has 13 symbols in three groups, and it must be permanently marked on one sidewall:
| Group | Symbols | What it tells you |
|---|---|---|
| Plant code | 3 | Identifies the tire manufacturer or retreader. NHTSA assigns it on request. |
| Manufacturer's code | 6 | Can describe significant characteristics of the tire or identify the brand name owner. |
| Date code | 4 numbers | The week and year the tire was made: the first two digits are the week, the last two are the year. |
Reading the date code. The week number counts full calendar weeks, Sunday through Saturday, with 01 for the first full week of the year. The regulation's own example: 0109 means the tire was made in the first full calendar week of 2009, the week of January 4 to January 10, 2009. NHTSA's brochure gives another: 3197 means the 31st week of 1997.
Older tires may show a two-symbol plant code: the regulation allowed previously assigned two-symbol codes until April 13, 2025. A retreaded tire carries a shorter seven-symbol TIN and is marked with the letter R, which is not part of the TIN.
From 49 CFR 574.5 (eCFR, current as of November 6, 2026) and NHTSA's Safety First: Basic Tire Maintenance brochure, read November 10, 2026.
Other markings on the sidewall
Federal motor vehicle safety standard No. 139 (49 CFR 571.139, S5.5) requires these markings on tires it covers:
| Marking | Where |
|---|---|
| The symbol DOT, a certification that the tire conforms to federal motor vehicle safety standards | Each sidewall |
| The tire size designation | Each sidewall |
| The maximum permissible inflation pressure | Each sidewall |
| The maximum load rating, and for LT tires, the letter for the tire load range | Each sidewall |
| The generic name of each cord material used in the plies | One sidewall |
| The number of plies in the sidewall, and in the tread area if different | One sidewall |
| The term tubeless or tube type | One sidewall |
| The word radial, if the tire is a radial ply tire | One sidewall |
A snow tire may also show a mountain-with-snowflake (alpine) symbol, at the manufacturer's option. NHTSA describes the maximum load as the most weight in kilograms and pounds the tire can carry, and the maximum inflation pressure as the greatest amount of air pressure that should ever be put in the tire under normal driving conditions.
From 49 CFR 571.139, S5.5 (eCFR, current as of November 6, 2026) and NHTSA's Safety First: Basic Tire Maintenance brochure, read November 10, 2026.
Treadwear, traction and temperature grades
Uniform Tire Quality Grading (49 CFR 575.104) applies to new passenger car tires. It does not apply to deep tread, winter-type snow tires, space-saver or temporary spare tires, tires with rim diameters of 12 inches or less, or limited production tires. Except for a new tire line in its first six months of production, the grades must be permanently molded into the sidewall.
Treadwear
A comparative number based on wear on a government test course. A tire graded 150 would wear one and one-half times as well on that course as a tire graded 100. Real-world wear depends on driving habits, service practices, roads and climate.
Traction: AA, A, B or C
From highest to lowest. The grades represent the tire's ability to stop on wet pavement in straight-ahead braking tests; they do not include cornering, acceleration or hydroplaning.
Temperature: A, B or C
A is the highest. The grade shows resistance to heat on a laboratory test wheel. C is the level all passenger car tires must meet under FMVSS No. 109; A and B are higher.
From 49 CFR 575.104 (eCFR, current as of November 6, 2026), read November 10, 2026.
Where to find your tire size and correct pressure
NHTSA says to look at the tire information placard, the owner's manual, or the sidewall of the tire you are replacing to find your tire size. Placards and vehicle certification labels are permanently attached to the vehicle door edge, door post, glove-box door, or inside of the trunk lid. You can also find the recommended tire pressure and load limit in the owner's manual.
The pressure molded on the sidewall is the tire's maximum permissible inflation pressure, not your vehicle's recommended pressure. NHTSA says the vehicle manufacturer, not the tire manufacturer, determines the correct tire pressure for the tires on your vehicle. That figure is the recommended cold inflation pressure on the placard, certification label or owner's manual.
From NHTSA's Safety First: Basic Tire Maintenance brochure (DOT HS 809 361), read November 10, 2026.
Tire checks at Michigan City Ford
The Works® at Michigan City Ford includes a synthetic blend oil change, tire rotation and pressure check, brake inspection, Multi-Point Inspection, fluid top-off, battery test, and a filter, belts and hoses check. See our tire care advice and tread depth guide.
Schedule service online and see our service specials first. Michigan City Ford is at 3930 Franklin St. in Michigan City. Get directions.
Michigan City Ford service hours
| Days | Hours |
|---|---|
| Mon-Fri | 7:30 a.m.-5:30 p.m. |
| Sat | 8 a.m.-3 p.m. |
| Sun | closed |
From Michigan City Ford's website, November 10, 2026. Holiday hours can differ.
Tire size FAQ
What do the numbers on a tire mean?
In NHTSA's example P215/65R15 95H, P means a passenger vehicle tire, 215 is the width in millimeters, 65 is the aspect ratio (height to width), R means radial, 15 is the rim diameter in inches, 95 is the load index and H is the speed rating.
How can I tell how old my tires are?
Find the tire identification number that starts with DOT. Its last four digits are the date code: the first two are the week and the last two are the year. Under 49 CFR 574.5, 0109 means the first full calendar week of 2009. Federal rules require the TIN on one sidewall of a new tire, so if you do not see it, check the other side.
What does the speed rating letter mean?
NHTSA says the speed rating is the speed at which a tire is designed to be driven for extended periods of time. Its table lists Q (99 mph), R (106 mph), S (112 mph), T (118 mph), U (124 mph), H (130 mph), V (149 mph), W (168 mph) and Y (186 mph).
What is the tire load index?
The two- or three-digit number after the size is the load index, a measurement of how much weight each tire can support. NHTSA notes it may not appear on all tires because it is not required by law. The maximum load in kilograms and pounds is also marked on the sidewall.
Should I inflate my tires to the PSI on the sidewall?
No. The sidewall figure is the maximum permissible inflation pressure. NHTSA says the vehicle manufacturer determines the correct pressure, shown as the recommended cold inflation pressure on the tire information placard, certification label or owner's manual.
What do treadwear, traction and temperature grades mean?
They are Uniform Tire Quality Grades under 49 CFR 575.104. Treadwear is a comparative wear number (150 wears one and one-half times as well as 100 on the government course), traction runs AA, A, B, C for wet straight-ahead braking, and temperature runs A, B, C for heat resistance.
What does LT mean on a tire?
NHTSA says LT indicates the tire is for light trucks. Federal rules also require LT tires to show the letter for the tire load range along with the maximum load rating.
Need a tire check?
Bring your vehicle to Michigan City Ford, or read our tire pressure light guide.
Sources
Tire size, speed rating, load index, placard and pressure details are from NHTSA's Safety First: Basic Tire Maintenance brochure (DOT HS 809 361), read November 10, 2026. Tire identification number, sidewall marking and quality grading rules are from 49 CFR 574.5, 571.139 and 575.104 on the eCFR, current as of November 6, 2026, read November 10, 2026. Service details, address and hours are from Michigan City Ford's own website, checked the same day. Photo is illustrative.
- NHTSA, Safety First: Basic Tire Maintenance (DOT HS 809 361), National Highway Traffic Safety Administration, read November 10, 2026
- 49 CFR 574.5, Tire identification requirements (eCFR), Electronic Code of Federal Regulations, current as of November 6, 2026, read November 10, 2026
- 49 CFR 571.139, FMVSS No. 139, S5.5 Tire markings (eCFR), Electronic Code of Federal Regulations, current as of November 6, 2026, read November 10, 2026
- 49 CFR 575.104, Uniform tire quality grading standards (eCFR), Electronic Code of Federal Regulations, current as of November 6, 2026, read November 10, 2026
- General service: The Works, Michigan City Ford, November 10, 2026
- Address and service hours (structured data), Michigan City Ford, November 10, 2026