lt265/70/17 upgrade to lt275/65/18 worthwhile

SoCalDesertRider wrote:

brian91 wrote:

SoCalDesertRider wrote:

brian91 wrote:
I wonder who decides on the ratings or how they are determined...
265/75/16 3415 31.7x10.4
265/70/17 3195 31.7x10.4
265/65/18 3306 31.5x10.4

All 3 tires above are the nearly the exact same dimensions, but vary in load capacity.

It depends on how the individual brand and model of tire shell is constructed. More plies and/or thicker side walls means greater load capacity, generally.

If you compare all E rated tires, you will notice the same rating across all brands for a given size. I have yet to see an E rated tire with one brand having a higher rating then another. Every 265/75/16E will have a rating of 3415, etc. Correct me if I am wrong but have been looking for higher rated 265/70/17 tire and every brand is 3195, regardless if its a $250 Michelin or a $100 Chinese tire.

I get what you're saying. I think the key there is the 'E' load rating, which is also expressed by a number, like '123', etc. Same size tire in a 'C' or 'D' rating (which also have lower numbers) have lower weight limits.

In the olden days, 'E' used to mean 10 plies. C and D meant other numbers of plies. Now days, there are not actually 10 plies in an E radial tire, but they are constructed such that they meet a standard that equates to 10 plies.

For the same width and diameter tire, a tire with greater side wall height can hold more air. For otherwise equally constructed tires and equal air pressures, a tire that can hold more air volume, can hold up more weight.

It remains a mystery to me why the 17" tires have unusually low weight ratings, out of step with the other 2 wheel sizes. One would expect them to be half way between the 16" and 18" weight ratings...

Even LT275/70/17E is still 3195... Odd but i am sure there is some reasoning behind it. My guess its just the way the ratings were set and maybe at the time there was not much for 17s? who knows.

For me it will likely come down to make do with the 17s even though i would like to have a larger safety margin. Probably easier to put the 5th wheel on a diet and try to lower its weights a bit. Right now kicking myself for not keeping the new set of 16s with lt265/75/16 off my old truck. Did not even cross my mind at the time. Tires and wheels only had about 5k miles on them...