Here is a mistake we see constantly. Somebody puts load range E tires on a half-ton truck, runs them at the 80 psi printed on the sidewall because that is the biggest number they can find, and comes back three months later complaining the ride is terrible and the centers are wearing out. All of that was avoidable, and every clue was molded into the rubber they were already looking at.
A tire sidewall is a spec sheet - a badly designed one, written in abbreviations nobody has updated in fifty years, but a complete one. Here is what each marking means, and which ones should actually change what you buy.
The size code is three different systems pretending to be one
Start with the biggest text on the tire. You will see one of two formats.
Metric: 285/70R17
- 285 is the section width in millimeters at the widest point of the sidewall, measured on a specified rim width. It is not tread width, and it is not what the tire measures on your wheel.
- 70 is the aspect ratio - sidewall height as a percentage of section width. So the sidewall here is about 200 mm tall. Lower number, shorter sidewall.
- R means radial construction. Almost everything is radial now. A D here means bias-ply, which you will only run into on trailer tires and some purpose-built rock crawling tires.
- 17 is the rim diameter in inches. Yes, the width is metric and the diameter is imperial in the same code. Nobody defends this, it is just how it is.
Flotation: 33x12.50R17LT
The imperial format is easier to read: 33 inches tall, 12.5 inches wide, 17-inch wheel. Both formats describe the same thing. A 285/70R17 and a 33x11.50R17 are close cousins.
The important caveat: the size on the sidewall is a nominal figure, not a measurement of your tire. Two 33s from different brands can differ by half an inch in real diameter, and every tire loses height under load and more as it wears. If you are calculating clearance or gear ratios, use the manufacturer's published specs.
The letters before and after the size matter more than people think
- LT (Light Truck) - built with heavier construction and rated for higher inflation pressures. Standard for anything that sees trail use.
- P or no letter (P-metric / Euro-metric) - passenger construction. Lighter, softer riding, better on fuel, less puncture resistant.
- ST - Special Trailer. Never put these on a vehicle you steer.
- C after the rim diameter (as in 235/85R16C) - a European commercial designation, roughly equivalent to a light LT tire.
Here is the part that trips people up. An LT tire carries less load at a given pressure than a P-metric tire of the same size. That is why you cannot take the pressure off your door placard - which was calculated for the P-metric tires the truck shipped with - and apply it to a new set of LT tires. Do that and you will be running the new tires underinflated for the load, which cooks the shoulders and kills them early.
Load range and ply rating: the most misread numbers on the tire
You will see something like LOAD RANGE E or 10 PLY RATED stamped near the bead. These mean the same thing, and neither means what it sounds like.
| Load range | Ply rating | Max cold inflation (typical LT) |
|---|---|---|
| C | 6 | 50 psi |
| D | 8 | 65 psi |
| E | 10 | 80 psi |
| F | 12 | 95 psi |
"10 ply rated" does not mean the tire has ten plies. It means it carries the load a ten-ply tire carried back when tires were actually built that way. A modern load range E tire typically has two or three body plies of polyester and two steel belts under the tread. The rating describes capacity, not layers.
So what does a higher load range buy you? Higher maximum inflation pressure, and therefore higher maximum load. That is it. It does not automatically mean a tougher sidewall, better puncture resistance or longer life - those come from construction details that are not printed on the tire.
Why heavier is often the wrong answer
Load range E has become the default request at tire shops, and for a lot of rigs it is more tire than the truck needs. Consider what you actually give up:
- Weight. Stepping from a load range C to an E in the same size can add several pounds per corner. That is unsprung, rotating weight - the most expensive kind. It hurts acceleration, braking, steering response and fuel economy all at once.
- Ride quality. A stiffer carcass at a given pressure transmits more of every road seam straight into the cabin.
- Airing down behavior. A heavier carcass resists deforming. At 15 psi, a load range C tire will bag out and wrap around rocks noticeably better than an E in the same size. That contact patch is the entire point of airing down.
The honest guidance: if you are hauling near your payload rating, towing regularly, or running a three-quarter-ton or heavier truck, buy the load range the vehicle's placard calls for. If you have a half-ton, a midsize truck, a Bronco or a 4Runner that mostly carries you, some gear and a fridge, load range C or D is very often the better-driving choice - and it is a lighter, cheaper tire. Browse what is available in each range in our tires collection and compare the listed weights before you decide.
The service description: load index and speed rating
After the size you will see something like 121/118Q. That is the service description, and it is more precise than the load range letter.
The numbers are load indexes, which map to a maximum weight per tire at the tire's maximum pressure. LT tires carry two: the first for single-wheel applications, the second for dual-rear-wheel setups, where each tire carries slightly less because heat builds between the pair. You do not need to memorize the table - just know that higher is more capacity, and that comparing load indexes between two candidate tires is far more meaningful than comparing load range letters.
The speed rating letter
The letter at the end is the speed rating - the sustained speed the tire was validated to under a standardized test.
- Q - 99 mph
- R - 106 mph
- S - 112 mph
- T - 118 mph
- H - 130 mph
Most aggressive all-terrains and mud terrains land at Q or S. Nobody is running 99 mph on a mud terrain, so the temptation is to ignore this. Do not. Speed rating is a proxy for heat tolerance, and heat is what actually destroys tires. A heavily loaded rig with a rooftop tent and a full rack crossing the desert at 80 mph on hot pavement is generating real heat, and a Q-rated tire has less margin than an S. If your rig is heavy and your trips involve long, fast, hot highway stints, treat a higher speed rating as cheap insurance. Worth noting too: dropping below the speed rating your vehicle originally specified can matter for insurance and inspection in some places.
Snow markings: M+S and the mountain snowflake are not the same
Nearly every all-terrain and mud terrain wears an M+S stamp. This is close to meaningless. M+S is self-certified by the manufacturer based on tread geometry - void ratio, block edges - with no traction test required. A tire earns it by looking the part.
The 3PMSF mark - the three-peak mountain with a snowflake - is different. That one requires the tire to hit a measured acceleration threshold on medium-packed snow against a reference tire. It is a real test with a real pass/fail line.
Two things to keep straight. First, 3PMSF is a snow test only - it says nothing about ice. Second, it is not the same as a dedicated winter tire, which uses a much softer compound that stays pliable below freezing. A 3PMSF all-terrain is a useful compromise for someone who sees occasional snow, not a substitute for winter tires if you live somewhere with real winter. Our other wheels and tires writeups cover how tread choice interacts with pressure and traction.
UTQG, and why it disappears on truck tires
On P-metric tires you will find three ratings: Treadwear (higher lasts longer), Traction (AA, A, B, C) and Temperature (A, B, C). Two caveats. Treadwear grades are self-assigned by each manufacturer against their own control tire, so they are only loosely comparable between brands. And the Traction grade measures straight-line wet braking on asphalt and concrete - it says nothing about grip in dirt, on rock or in mud.
LT-metric tires are exempt from UTQG entirely. If you cannot find these markings on a truck tire, nothing is wrong; you just have to lean on published mileage warranties and real-world reports instead.
The DOT code, and the four digits that matter most
Somewhere on the sidewall, usually on one side only, is a string starting with DOT followed by a mix of letters and numbers. The last four digits are the manufacture date: week, then year. 2325 means the 23rd week of 2025.
Check this before you pay, every time. Tires age out whether or not they are driven - the oils in the rubber migrate and the compound hardens, which shows up as fine cracking in the tread grooves and sidewall flex zones. A tire that sat in a warehouse for three years is three years into its life before you ever mount it.
Most manufacturers suggest inspection after five years and replacement by ten regardless of tread depth. For a rig that spends time on sharp rock, that is conservative guidance, not paranoia - an aged sidewall is a brittle sidewall. If you are buying used wheels and tires, or a "new old stock" deal that seems too cheap, the date code is where the catch usually hides.
The markings that are not on the sidewall
The single most useful number for offroad durability - how many plies are in the sidewall itself - is almost never printed on the tire. Some use two-ply sidewalls, some use three, and that third ply is the difference between a sharp rock scuffing the tire and a sharp rock ending your day. You have to dig it out of the spec sheet, and it is worth doing.
A few other things worth checking while you are there:
- Rotation arrows. Directional treads must go on a specific side of the vehicle. Mixing this up costs you wet and snow performance.
- "Outside" / "Inside." Asymmetric treads have a required orientation. Easy to get wrong, and shops do get it wrong.
- Max load and max pressure. These are a ceiling, not a target. The number on the sidewall is the pressure at which the tire achieves its rated load - not the pressure you should run.
Finding your actual pressure
Once you are on aftermarket sizes, the door placard no longer applies. Two workable approaches:
- Load inflation tables. Weigh each axle at a scale, divide by two, then look up the pressure that supports that weight for your tire's load range and add a few psi of margin. This is the accurate way.
- The chalk test. Draw a chalk line across the tread, roll forward a few feet, and read the wear. Worn only in the middle means too much pressure; worn only at the edges means too little. Even wear across the line is your number. Cruder, but it works.
Do this with the rig loaded the way you actually drive it. A truck weighed empty and the same truck carrying a rooftop tent, fridge, water and recovery gear are different vehicles, and correct pressure follows the load rather than the sticker.
The short version
Standing in front of a tire, four things are worth reading: the size and whether it is LT or P-metric, the load range and whether you actually need it, the speed rating as a heat proxy, and the date code. The rest is informational or marketing.
And once you have picked the tire, remember the wheel behind it decides whether that tire clears anything - width, offset and backspacing all change how a new size sits in the well, so work through wheel fitment and tire size together rather than one at a time.
Ready to spec a set? Compare load ranges, weights and construction across our full wheels and tires selection, and check that date code when the box shows up.