What does the P on a tire mean?

P means P-metric: a passenger car tire rated against the North American Tire and Rim Association's load tables. Fitted to a light truck, SUV, pickup, van or minivan, its load capacity is divided by 1.10 before it counts.

What is the difference between LT and P tires?

An LT tire is built and rated for light truck duty and takes no derating on a truck. A P-metric tire of the same nominal size does. That is why a P-metric size cannot simply stand in for the LT size a truck was built around, even though the numbers look identical.

Can I use ST trailer tires on a car?

No. ST tires are built for trailer axles, which neither steer nor transmit drive torque. They are not appropriate on a vehicle.

What is the difference between XL and load range E?

They are different scales. XL, also marked Reinforced, is a passenger tire whose load index is certified at a higher reference pressure than a standard load tire. Load range E is a light truck rating. An XL passenger tire is not a load range E tire and is not interchangeable with one.

Service type prefixes

The letters before the width, what each one means, and why the absence of a letter is a reading rather than a missing one.

The one that costs people money

No prefix is a reading, not a missing one. An unprefixed size such as 225/65R17 is Euro-metric, rated against the European tyre and rim organisation's load and inflation tables; P225/65R17 is P-metric, rated against the North American Tire and Rim Association's. The two are the same nominal shape and are commonly cross-fitted, but their rated load at a given pressure is set by different tables and can differ. Treating a missing P as a typographical detail is the mistake this page exists to stop.

Every prefix

Tire service type prefixes and what they mean
Prefix	Means	In one line	Where it sits
P	P-metric (passenger)	A passenger car tire rated against the North American Tire and Rim Association tables.	Immediately before the section width.
none	Euro-metric (no prefix)	No letter at all. The tire is rated against the European tyre and rim organisation tables.	Nothing precedes the section width.
LT	LT-metric (light truck)	Built for light truck duty, and rated for it without any derating.	Immediately before the section width, or after the size on flotation sizes (33x12.50R15LT).
ST	ST (special trailer)	For trailer axles only. Not for a vehicle that steers or drives.	Immediately before the section width.
T	T (temporary spare)	The space saver spare. Restricted speed and restricted distance.	Immediately before the section width.
C	C (commercial or van)	A commercial van tire. The C sits after the rim diameter, not before the width.	After the rim diameter, at the end of the size.

The 1.10 factor

A P-metric or Euro-metric tire fitted to a light truck, SUV, pickup, van or minivan has its rated load divided by 1.10. A tire rated 3086 lb is worth 2805 lb in that service. Both manufacturer bulletins cited attribute the factor to federal motor vehicle safety standards, and both apply it to Euro-metric as well as P-metric. An LT tire takes no such reduction.

An LT tire fitted in duals carries 9 percent less than it does singly, to account for the effect of road crown on a twinned pair. That is why a dual-rated tire prints two load indices, for example LT235/85R16 120/116S: 120 singly, 116 in duals. Read the second index off the load index table rather than applying the percentage yourself - the printed pair is the rating.

Worked example: a tire rated 3086 lb, divided by 1.1, is worth 2805 lb on a light truck. Both manufacturer bulletins cited use that same example.

Construction letters

The letter inside the size, between the aspect ratio and the rim diameter. Not the same alphabet as the prefix, and not the same as the speed symbol that follows the size.

R: Radial. Body plies run radially, across the tire from bead to bead, under a belt package. Effectively every passenger tire sold new is radial. The R here has nothing to do with the speed symbol R, which sits in the service description after the size.
D: Bias ply (diagonal). Body plies run diagonally, crossing each other. Still found on trailer, agricultural and some motorcycle tires. Sometimes printed as a dash instead of a D.
B: Bias belted. Diagonal body plies with a belt added under the tread. Uncommon on modern passenger tires.

Standard load, extra load and the rest

These describe the reference pressure a passenger tire's load index is certified at. They are a different scale from the light truck load range letters.

Passenger tire reinforcement designations
Marking	Name	Reference pressure	What it means
SL	Standard Load	35 psi	The default. An absent marking means standard load. The load index is certified at 35 psi (36 psi for Euro-metric sizes); inflating beyond that adds no rated capacity.
XL	Extra Load (also marked Reinforced or RF)	41 psi	The load index is certified at 41 psi (42 psi for Euro-metric sizes), so an XL tire carries more than an SL tire of the same size - but only when it is actually run at that higher pressure. An XL tire at 35 psi carries no more than an SL tire at 35 psi. XL is not a step on the LT load range scale and is not equivalent to load range E.
LL	Light Load	not published	A lightly loaded passenger construction. Only one of the sources consulted gave a reference pressure for it, so no figure is published here.
HL	High Load	not published	A newer designation for heavy battery electric vehicles, certified at a higher reference pressure than XL. The prefix appears in the size itself, as in HL275/50R22. One of the sources consulted puts the reference pressure at 50 psi and none of the others state one, so no pressure is published here.

A blank pressure is a stated gap, not an oversight. See the sources block below.

Common questions

What does the P on a tire mean?: P means P-metric: a passenger car tire rated against the North American Tire and Rim Association's load tables. Fitted to a light truck, SUV, pickup, van or minivan, its load capacity is divided by 1.10 before it counts.
What does it mean when a tire size has no letter in front of it?: No prefix is a reading, not a missing one. An unprefixed size such as 225/65R17 is Euro-metric, rated against the European tyre and rim organisation's load and inflation tables; P225/65R17 is P-metric, rated against the North American Tire and Rim Association's. The two are the same nominal shape and are commonly cross-fitted, but their rated load at a given pressure is set by different tables and can differ. Treating a missing P as a typographical detail is the mistake this page exists to stop.
What is the difference between LT and P tires?: An LT tire is built and rated for light truck duty and takes no derating on a truck. A P-metric tire of the same nominal size does. That is why a P-metric size cannot simply stand in for the LT size a truck was built around, even though the numbers look identical.
Can I use ST trailer tires on a car?: No. ST tires are built for trailer axles, which neither steer nor transmit drive torque. They are not appropriate on a vehicle.
What is the difference between XL and load range E?: They are different scales. XL, also marked Reinforced, is a passenger tire whose load index is certified at a higher reference pressure than a standard load tire. Load range E is a light truck rating. An XL passenger tire is not a load range E tire and is not interchangeable with one.

Where these figures come from

Published values here were read from 5 independent sources:

Tire code - Wikipedia, revision read 27 August 2026 (read 2026-08-27)
Service type letters, construction letters, load range letters and ply ratings, sidewall marking glossary
Application of Load Inflation Tables, version 20170203 - Nitto Tire (Toyo Tire group) technical bulletin, version 20170203 (read 2026-08-27)
P-metric against ISO/Euro-metric load tables, the light truck derating factor, dual fitment reduction, standard load against reinforced
Tire Safety Bulletin: Replacing Tires of P-metric or metric tire on Light Trucks - Nexen Tire USA technical bulletin, undated safety bulletin (read 2026-08-27)
The 1.10 light truck derating factor with a worked example
Load Index & Weight Ratings - rimlist, undated reference article (read 2026-08-27)
LT against P-metric fitment, ST trailer tires, SL, XL and HL reference pressures
Tire Load Ranges: Complete Guide (B Through F) - TireGrades, updated 24 June 2026 (read 2026-08-27)
Load range letters with ply rating equivalents and maximum inflation, LT against passenger designations

These are independent publishers, not independent measurements. Each one reproduces a table originally set by a standards body, so agreement between them shows a value was transcribed correctly, not that the underlying table is right. Where a figure is safety relevant, check it against the tire manufacturer's own data before relying on it.

Whether Euro-metric tires take the 1.10 light truck derating: yes - the bulletin's heading and text both read 'P-metric or metric tire' (ST-NITTO) against yes - 'When P-metric or metric tire are installed on light trucks' (ST-NEXEN). Retail and forum sources are split, with several stating that the derating applies to P-metric only. Both tire manufacturer technical bulletins consulted state it applies to metric (Euro-metric, also called hard metric) as well, and both attribute the rule to federal motor vehicle safety standards. This site follows the two manufacturer bulletins and flags the split, because the conservative reading is also the one the primary-facing documents give.

Left out on purpose

The Light Load (LL) reference pressure appears in only one of the sources consulted, so no pressure is published for it.
The High Load (HL) reference pressure appears in only one of the sources consulted, so no pressure is published for it. The designation itself is confirmed by two.