Tire load index rating

Spangled · April 20, 2020

I'm looking to put a bit beefier tire on a Sierra 2500 (not a dually) but the local tire shop tells me the tire will need to have a rating of at least 126 (3,748 lb) since that is what the OEM tire is, or it would be unsafe to drive, so they will not mount a new tire with a lower rating, say 121 (3,197 lb).

I haven't found the info yet personally but I understand the implications, that the max load capacity would be slightly diminished, but barring any heavy towing, would it really be unsafe for normal driving or average towing?

KCJackson1 · April 20, 2020

Will it be unsafe... maybe, maybe not. if the truck is empty 99% of the time, it may be just fine.

BUT...

Using tires less than the OEM-specified load rating voids not only your warranty, but your auto insurance coverage as well if something goes wrong. That's why the tire shop won't do it... they do not want to be on the hook for any liability of installing sub-rated tires.

newdude · April 20, 2020

The tire shop is not only watching their a$$ but yours as well.

What size where you trying to go to and what type of tire are you looking at?

Spangled · April 20, 2020

5 hours ago, newdude said:

The tire shop is not only watching their a$$ but yours as well.

What size where you trying to go to and what type of tire are you looking at?

It sounds like I may want to choose a different tire then.

It's a Cooper Evolution M/T All-Terrain 35x12.50R20 121Q 10 ply

Tampa_HD · April 20, 2020

I'm surprised they are giving you issues with another load range E tire. I would have guessed you were going from E to D like a lot of people do, but a lower rated E range tire seems somewhat surprising they wont mount it.

That is quite a drop though, 550lb per tire is no small number. Check out Ridge Grapplers, they are usually rated higher for most sizes.

KCJackson1 · April 20, 2020

There will very likely be a de-emphasis of the old letter ratings - which evolved from the ply count (each letter was 2 plies) - in favor of the more universally recognized load index number. The letters are just too broad in scope... for example, my 96 Ram dually came with LT215/85R16E tires and my 05 Ram dually has LT235/80R17E tires. The "E" rating is consistent, but the load index isn't even close - 115 (2680 lb) vs 120 (3085 lb). The benefit of the load index is that it takes various dimensions out of the picture... a 126 load index tire will do the job whether it's a 17-inch rim, 18, or 20. So if you like bigger rims, you can more easily find tires that fit without compromising load ratings.