Load range letters and the ply ratings they replaced

Light-truck tires carry a letter — C, D, E, occasionally F — usually spelled out as LOAD RANGE E in small text on the sidewall. It is frequently accompanied by a ply rating: 10 PLY RATING, or on older markings simply 10 PR.

Neither is a count of anything you would find by cutting the tire open.

What the letter actually encodes

Each load range corresponds to a reference inflation pressure, and that pressure is the condition under which the tire's maximum load is stated:

Load range	Ply rating equivalent	Reference inflation
C	6	50 psi
D	8	65 psi
E	10	80 psi
F	12	95 psi

Passenger tires use a parallel two-step version of the same idea: Standard Load at 35 psi, Extra Load at 41 psi. XL and Reinforced markings covers that pair, which behaves differently enough to deserve its own treatment.

Where "ply rating" came from

On a bias-ply tire the number was literal. Strength came from stacking cotton, and later rayon, plies at opposing angles, so an 8-ply tire had eight layers and could be inflated harder and loaded heavier than a 4-ply one.

Radial construction replaced most of that stack with a small number of high-strength body plies running bead to bead, plus steel belts under the tread. A modern Load Range E light-truck radial typically has one or two body plies in the sidewall and two or more steel belts in the crown — and carries far more load than any ten-ply bias tire ever did.

The ply rating stayed in use as a strength equivalence, a way of telling a buyer familiar with the old scale roughly where the new tire sits. It is a translation, not a specification, and every current standard is written in terms of the letter.

What is physically different between the ranges

Going up a load range in the same size changes real things:

• Heavier cord material and more turn-up at the bead, so the sidewall resists deflection at higher pressure.
• Stiffer bead bundles to hold the higher pressure against the rim flange.
• Thicker sidewall and tread gauge, and consequently more weight — often several pounds per tire, all of it unsprung.

What it does not change is the tire's dimensions. A Load Range C and a Load Range E in the same size code are the same nominal geometry, so nothing on the size pages of this site moves when the letter changes.

The consequences people notice

• Ride. A stiffer casing transmits more of the road surface, and an unladen light truck on Load Range E tires at placard pressure is the classic complaint.
• Required pressure. The load table for a higher range starts lower per psi, so the same load needs a different pressure than it did on the original range.
• Fuel and acceleration. Extra rotating and unsprung mass is not free.
• Puncture behaviour. More material between the road and the air is exactly what the extra weight buys.

C is where most of the argument happens

On half-ton pickups and midsize trucks, the interesting choice is rarely between C and F. It is between a P-metric tire with no load range letter at all, a Load Range C light-truck tire, and a Load Range E one.

• The P-metric option is lightest, rides softest and has its capacity reduced by the standards divisor when used on a truck.
• Load Range C is the compromise that has quietly become the default for all-terrain fitments on unladen half-tons: LT construction, a 50 psi reference, and far less of the harshness that makes Range E unpopular on an empty truck.
• Load Range E buys capacity that most half-tons cannot legally use, at a cost in weight and ride that is paid on every mile whether the bed is loaded or not.

Flotation sizes carry the same letters — a 35x12.50R17 is sold in C, D and E in the same dimensions — so the notation of the size tells you nothing about which one you are looking at.

What a higher load range does not do

It does not raise the vehicle's ratings. Gross axle weight ratings and gross vehicle weight rating are properties of the vehicle — its springs, brakes, axles and frame — and they are unchanged by what is mounted on the wheels. A Load Range F tire on a half-ton pickup is a tire with a high ceiling on a vehicle whose ceiling is somewhere else entirely.

The door placard states the load and pressure the vehicle was certified with. Read the placard first and the sidewall second.

Reading it alongside the other load markings

Three separate markings describe capacity, and they are not interchangeable:

• The load index, a number in the service description, giving maximum load in kilograms from a standard series.
• The load range letter, giving the inflation the index assumes.
• The maximum load and pressure statement, in words, giving the same information in the units the market uses.

A tire marked LT285/70R17 121/118S Load Range E is telling you the same fact three times, in three notations, for three audiences. Where they appear to disagree, the service description and the load range are the specification and the words are the summary.

Trailer tires marked ST use the same letters on a different load and speed basis, and their sidewalls state it explicitly — a range letter alone never crosses categories. Pressure and load tables covers how load and inflation trade against each other once you are inside a given range.