Load Rating vs. Load Index

[drury]

Could someone explain the difference between the letter rating and the number rating to me? The stock tires on my 2500 are load rated "E" and have a load index of 121. I've seen other tires that also have a load index of 121, but are only "D" rated. This is confusing to a newbie such as myself. The FAQ's on the tire sites haven't been of much help.

 

[GaryCarter]

The letters C-D-E etc are related to 'ply rating'. Ply rating arose from the even older system of just counting the plies (e. g. 10-ply) when the mfrs. figured out how to make tires stronger with fewer plies than original. Basically this all relates to how thick the tire sidewall is and how much inflation pressure it is designed for. Higher rating means more air pressure.



The load index tells how much weight a tire can carry. This is a product of tire size and pressure. More pressure = higher load capacity. Larger size = higher capacity.



So it's quite common for a smaller high pressure tire e. g. 265 "E" to have similar or identical load index to a larger low pressure tire e. g. 315 "D".



Don't forget to look at the speed rating too. IMO a 121S is likely a better tire than a 121Q for example. If you're ever going to run heavy and fast, that is.



Gary

 

[drury]

OK, Thanks for the info. Sounds like I don't really care about the D & E then, as long as I keep the load index up.

 

[J&LRam]

Drury

just to add to Gary's reply, a "E" load range tire has thicker/heavier plies than a "D" load range tire so you should care if your into hauling heavy such as commercial/hotshot folks. A "E" tire is heavier in actual weight than a same size "D" tire. Most hotrodders find the "D" rated tire better suited as they are lighter and less unsprung weight.

JIM