31x10.5R15 vs. P215 75R15

[1987 GMC Jimmy]

So what's the difference? Right now my Jimmy has dry rotted, flat, unevenly worn BFG 31x10.5R15 all terrains. I wanted to move to a Uniroyal tire that was quieter and more road friendly. I put my vehicle in the Uniroyal tire selector, but they don't recommend their P215 75R15 Laredo tire, and I don't know why, especially since that's the tire GMC put on it from the factory. The only tire they recommended was their more expensive 31x10.5R15 Laredo tire. I'd like to do the cheaper P215 version if I can. Can someone explain the differences and why the manufacturer is saying no? The combined load ratings for both models of tires are greater than the Jimmy's GVWR, by the way. Thanks.

 

[Georgeb]

Your 215/75-R15 is 27.7" tall and 8.5" wide for starters. Why they only list that one size is strange. What year?

 

[1987 GMC Jimmy]

Sticker date is 3/1987. 99% that's what it says about tire size because the sticker is faded and partially missing. Brochure also says P215 75R15. The tire site said it could have a P215, a P235 (both with the 75 aspect ratio and 15 rim diameter), or the 31x10.5R15, which is what it currently has. I always make sure whatever I'm doing knows that it's a V-Jimmy and not an S-Jimmy, but the stupid apps may not know the difference. I don't know. It sounds like the 31x10.5R15 is the only way to go, but it's two hundred more dollars for a set of those. At least the brand and model that I'm keen on, anyways. I wanted to buy them through Walmart because my mom has a 10% associate discount, and I'd have them mount the tires to the wheels, and I'd take them home and install them myself. I'll get someone to double check that sticker for me. I could be mistaken, but I usually have a memory for those identifications like that...

 

[77 K20]

Strange- I've never heard of running 215s on a full size. When I had my full size Blazer and a full size Jimmy I ran the 235 75R15 in winter (snow tires) and used 31x10.50s in the summer.
With the 8" wide rally wheels I had the 31" tires seemed to fit on the wheel better. Sidewalls were nice and square with the rim width. The 235s always looked a bit stretched on there. 215s would be even worse.
And technically if you do have the 8" wide wheels most shops will probably not even mount either of those tires to that rim.

What wheels do you have?

 

[Georgeb]

On a V truck it would not have been 215 in my mind 235/75-R15 is correct. Anyway thats what I would run. In Hankook Dynapro AT'M

 

[1987 GMC Jimmy]

What's the diameter of the 235?

 

[Georgeb]

What's the diameter of the 235?

~28.9" give or take.
This is handy:
https://tiresize.com/chart/

 

[1987 GMC Jimmy]

Thanks. That still sounds small, though. I always thought that for K-trucks and V-trucks 31 inches in diameter was what you started from with the stock setup, and people increased diameter from there be it slightly while maintaining the factory stance or more when adding a lift.

 

[yevgenievich]

Thanks. That still sounds small, though. I always thought that for K-trucks and V-trucks 31 inches in diameter was what you started from with the stock setup, and people increased diameter from there be it slightly while maintaining the factory stance or more when adding a lift.

At least according to factory sticker one my old v1500 suburban compared to current v2500, 3/4 ton and 1 tons had 31" tires and the 1/2 tons got the smaller ones. But was probably an option vs base as well

 

[Craig 85]

I would go with the 31's. The 235's are "P" rated which is passenger car. The 31's are LT (light truck) rated. The LT's have more sidewall belts which improve handling (less sidewall roll).

My guess is GM switched to P rated tires back then because more people where buying SUVs, but were used to the soft ride of passenger vehicle. The tires would have compensated for the stiffer truck suspension.

I think you would regret the P tires.

 

[1987 GMC Jimmy]

Yeah, I think I'm gonna go with the 31's, too. They're just more expensive.

 

[Georgeb]

I agree. The 31" tires will look better on a 4x4. I never ran P series on my trucks unless they were free. And it was only temporarily. I used to order the LT235/75-15 size for my heavy C-10.

 

[1987 GMC Jimmy]

Big mistake on my behalf. Mine did come with 31x10.5R15. The door sticker is mostly gone, but I was able to make out the first few numbers. I don't know why GM would have put P215's or P235's on these trucks, but the brochure and the tire outlets say so, at least on the Blazers/Jimmies. It's good news for me because the speedometer will read correctly, but it's bad because $$$. Thanks for teaching me about those tires, though. It's all about the knowledge.

 

[chevyzrule810]

My parts truck I bought the tag in the glovebox said 31x10.5R15 but the guy I got the truck from had 235/75R15s on.I put on a set of 31s.I would go with the 31s

 

[mikeh4848]

Big mistake on my behalf. Mine did come with 31x10.5R15. The door sticker is mostly gone, but I was able to make out the first few numbers. I don't know why GM would have put P215's or P235's on these trucks, but the brochure and the tire outlets say so, at least on the Blazers/Jimmies. It's good news for me because the speedometer will read correctly, but it's bad because $$$. Thanks for teaching me about those tires, though. It's all about the knowledge.

HI 87jimmy; I know this is a lot late but maybe I can help someone else. many 14in and 15in tires are hard to find. I have a 89 GMC 1500 4x4 suburban, couldn't find tires I could afford, so I found that some Toyota wheels will fit(16in) and Summit sells wheels that fit great. 6 hole, 16in x 8in , 4in c enter hole, 4in back-space you can find many tire sizes relitively cheap. I got 2 rims from Summit on my front and 2 Toyotas on rear. Hope this helps. mikeh4848