Tire Buying Guide: Size, Type & Load Rating
How to read tire size codes, load index, and speed ratings — and where to find your vehicle's correct specifications before buying replacement tires.
Tire sizing and rating codes look cryptic, but they encode genuinely important safety information — here's how to actually read them and buy the right tire for your vehicle.
Reading a Tire Size Code
A code like P215/65R16 95H breaks down into specific components: P indicates passenger vehicle (LT indicates light truck), 215 is the tire width in millimeters, 65 is the aspect ratio (sidewall height as a percentage of width), R indicates radial construction, 16 is the wheel diameter in inches, 95 is the load index, and H is the speed rating.
Load Index Explained
The load index number corresponds to a specific maximum weight the tire can safely carry — a higher number means higher load capacity. Never go below your vehicle manufacturer's specified load index, even if a lower-rated tire is available in the correct physical size, since this directly affects safe load-carrying capacity.
Speed Rating Explained
| Tier | Price Range | Best For |
|---|---|---|
| S | 112 mph | Standard passenger vehicles, economy focus |
| T | 118 mph | Family sedans, standard daily driving |
| H | 130 mph | Sport sedans, performance-oriented daily drivers |
| V | 149 mph | Performance vehicles |
| W/Y | 168+ mph | High-performance and sports cars |
Match or exceed your vehicle's original speed rating specification — going below it isn't just a performance limitation, it can affect handling characteristics the vehicle was tuned around.
Finding Your Vehicle's Correct Specifications
Your vehicle's specified tire size, load index, and speed rating are printed on a sticker in the driver's door jamb — not the tire sidewall itself, which shows the currently installed tire's specs rather than necessarily the manufacturer's original specification. Always reference the door jamb sticker when buying replacement tires.
All-Season vs. Summer vs. Winter: Quick Overview
All-season tires balance year-round usability at the cost of not excelling in any single condition. Summer tires maximize warm-weather grip and handling but perform poorly or unsafely in cold and snow. Winter tires use a specific rubber compound that stays flexible in cold temperatures for genuine ice and snow grip that all-season tires can't match. See our All-Season vs. Summer vs. All-Weather Tires comparison for the complete breakdown.
Don't Guess on Fitment
A tire that physically fits your wheel but doesn't match your vehicle's specified load index or speed rating isn't a safe substitute, even if it seems like a reasonable size match. Always confirm against your door jamb sticker specifications.
Plus Sizing: Going Up a Wheel Size
Some drivers choose to "plus size" — moving to a larger wheel diameter with a shorter sidewall tire to maintain the same overall tire diameter while improving handling and appearance. This requires careful calculation to maintain correct overall diameter (which affects speedometer accuracy and clearance) and generally trades some ride comfort for sharper handling, since a shorter sidewall flexes less and transmits more road harshness.
UTQG Ratings: Treadwear, Traction, Temperature
Beyond size and load rating, tires carry a Uniform Tire Quality Grading rating covering treadwear (a comparative wear rating, not a mileage guarantee), traction (wet braking performance, graded AA through C), and temperature resistance (how well the tire dissipates heat at speed, graded A through C). These ratings help compare tires within a similar category, though they're not directly comparable across different tire types or manufacturers using different testing baselines.
When to Replace Rather Than Repair
A puncture in the tread area, away from the sidewall, is often repairable if caught before the tire has run significantly underinflated. Sidewall damage, however, generally means replacement rather than repair, since sidewall flexing under load makes a repair in that area unreliable regardless of how it's performed.
Frequently Asked Questions
Can I use a tire with a higher load index than specified?
Yes, a higher load index than your minimum specification is safe and sometimes preferred for towing or heavy load use. Going below your vehicle's specified minimum load index is not safe.
Where do I find my vehicle's correct tire specifications?
Check the sticker in your driver's door jamb, not the tire sidewall itself. The door jamb sticker lists your vehicle manufacturer's specified size, load index, and inflation pressure.
Do I need to match my original tire's speed rating exactly?
You should match or exceed it, not go below it. A lower speed rating than specified can affect handling characteristics beyond just top-speed capability, since the vehicle was tuned around the original specification.