What do the numbers on a tire mean?

Take the tire code 225/65R17 as an example: 225 is the tire width in millimeters; 65 is the aspect ratio (the sidewall height as a percentage of the width — 65% of 225mm = 146mm); R means radial construction; 17 is the wheel/rim diameter in inches. You may also see a load index (e.g., 98) and speed rating (e.g., H) after the wheel size.

Where do I find my car's correct tire size?

Your car's correct tire size is printed on a sticker inside the driver's door jamb, in your owner's manual, and on the placard attached to the door. You can also look up the OEM tire size on a tire retailer's website by entering your year, make, and model. The size on the door jamb sticker is the manufacturer's recommended specification.

Can I put a different size tire on my car?

Within limits, yes. Going up or down one aspect ratio (e.g., 225/60R17 instead of 225/65R17) has a small effect on ride height, speedometer accuracy, and handling. Changing the wheel diameter requires matching the tire diameter to avoid affecting speedometer readings and clearance. Always stay within the range listed on your door jamb or consult a tire professional before deviating from OEM specs.

What is the speed rating on a tire?

The speed rating indicates the maximum sustained speed the tire is certified for. Common ratings: S = 112 mph, T = 118 mph, H = 130 mph, V = 149 mph, W = 168 mph, Y = 186 mph. Never replace tires with a lower speed rating than the OEM specification, especially on performance vehicles.

What does 'P' or 'LT' mean at the start of a tire size?

P stands for Passenger — tires designed for cars and light SUVs. LT stands for Light Truck — tires designed for trucks, vans, and heavier SUVs with higher load capacity. Some tires have no letter prefix, indicating they meet European metric standards. LT tires are stiffer and have higher load ratings than P-metric tires.

How to Read Tire Sizes 2026 — Decoding the Numbers on Your Sidewall

The number printed on your tire sidewall — something like 225/65R17 98H — contains everything you need to buy the correct replacement. Each part tells you the width, sidewall height, construction type, wheel size, load capacity, and speed capability.

Decoding a Tire Size: 225/65R17 98H

$$\underbrace{P}{type}\underbrace{225}{width\ (mm)}/\underbrace{65}{aspect\ ratio}\underbrace{R}{radial}\underbrace{17}{wheel\ (in)}\ \underbrace{98}{load\ index}\underbrace{H}_{speed}$$

Code Part	Example	Meaning
Tire type	P	P = Passenger; LT = Light Truck; no letter = Euro metric
Section width	225	Tire width in millimeters (tread face to tread face)
Aspect ratio	65	Sidewall height = 65% of width (225 × 0.65 = 146 mm)
Construction	R	R = Radial (virtually all modern tires)
Wheel diameter	17	Rim size in inches
Load index	98	Maximum load capacity (98 = 1,653 lbs per tire)
Speed rating	H	Maximum sustained speed (H = 130 mph)

Aspect Ratio: What It Affects

The aspect ratio tells you how tall the sidewall is relative to the width.

Aspect Ratio	Sidewall Feel	Handling	Ride Comfort
70+ (tall sidewall)	Cushioned	Less precise	Comfortable
55–65 (standard)	Balanced	Good	Good
40–50 (low profile)	Stiff	More precise	Harsher
35 and below (ultra-low)	Very stiff	Sport feel	Rough

Lower aspect ratios generally come with larger wheel diameters. A 225/35R20 and a 225/65R17 cover approximately the same total wheel+tire diameter — the difference is how the diameter is split between the wheel and the sidewall.

Common Speed Ratings

Letter	Max Speed
S	112 mph
T	118 mph
H	130 mph
V	149 mph
W	168 mph
Y	186 mph
(Y)	Over 186 mph

Always match or exceed the OEM speed rating. Never install tires with a lower speed rating than specified by your manufacturer.

Load Index Chart (Common Values)

Index	Max Load per Tire
85	1,135 lbs
91	1,356 lbs
95	1,521 lbs
98	1,653 lbs
103	1,929 lbs
108	2,205 lbs

Your four tires combined must be rated to carry the car’s GVWR (gross vehicle weight rating). Never replace tires with a lower load index than OEM.

Where to Find Your Correct Tire Size

Driver’s door jamb sticker — most reliable; lists OEM tire size and inflation pressure
Owner’s manual — lists approved tire sizes and any approved alternates
Glove box or fuel door — some vehicles list tire specs here
Tire retailer website — enter year, make, model for OEM size lookup

Can You Change Tire Sizes?

Small deviations from OEM size are common when upgrading wheels or tires:

One aspect ratio step (e.g., 65 → 60) — minimal effect; check overall diameter
Wheel diameter change — compensate with aspect ratio to keep overall diameter within 3% of OEM (beyond this, speedometer reads incorrectly and wheel arches may rub)

Use an online tire size calculator to verify overall diameter before buying non-OEM sizes.

Written by WealthVieu

WealthVieu researches and writes data-driven personal finance guides using primary sources including the IRS, Bureau of Labor Statistics, Federal Reserve, and Census Bureau.

The content on Wealthvieu is for informational purposes only and should not be considered financial, tax, or investment advice. Consult a qualified professional before making financial decisions. Full disclaimer · Editorial policy