What P and LT mean
P (P-metric) marks a passenger car tire. LT marks a light truck tire, built for heavier loads. You can tell them apart on the sidewall by the letters in front of the size: P265/70R17 against LT265/70R17. Inch sizes put LT at the end: 33x12.50R15LT. The sidewall decoder reads every other marking.
Load index, single and dual
A P-metric tire has one load index. An LT tire usually shows two, such as 121/118: the first is the load for single mounting, the second for dual mounting, where two tires sit side by side. The load index is converted with the standard load index table, then to pounds:
load (lb) = load (kg) × 2.20462Worked example: P265/70R17 113T against LT265/70R17 121/118S. Load index 113 is 1,150 kg (2,535 lb) per tire. Load index 121 is 1,450 kg (3,197 lb) per tire single, and 118 is 1,320 kg (2,910 lb) per tire dual. Single against single, the LT tire is rated for 300 kg (661 lb) more per tire. The size is the same, so the size maths gives the same 31.61 in (803 mm) diameter for both. The tire maker's published dimensions for the exact tire can differ.
Load range and ply rating
LT tires also carry a load range letter. It maps to a ply rating: C is 6, D is 8, E is 10, F is 12. The ply rating is a strength rating, not the number of plies in the tire. A tire marked LRE or LOAD RANGE E is ply rating 10.
Can you swap one for the other?
This page does the load maths only. A P-metric tire used on a light truck may carry a reduced rating. The vehicle placard (door sticker), the owner's manual and the tire maker decide what your vehicle needs.
Questions
What is the difference between LT and P tires?
P-metric tires are passenger car tires. LT tires are light truck tires, built for heavier loads. In the same size, P265/70R17 113T is rated for 1,150 kg (2,535 lb) per tire and LT265/70R17 121/118S for 1,450 kg (3,197 lb) single.
What does 121/118 mean on an LT tire?
Two load indexes. 121 is for single mounting, 1,450 kg (3,197 lb) per tire. 118 is for dual mounting, two tires side by side, 1,320 kg (2,910 lb) per tire.
What does load range E mean?
Load range E is ply rating 10. The ply rating is a strength rating, not a count of the plies. The load index on the same sidewall gives the load in figures.
Can I put P-metric tires on my truck?
A P-metric tire used on a light truck may carry a reduced rating. The vehicle placard and the tire maker decide what applies, so check both before you change tire type.