Moving to tires with a lower load index

[TheNotoriousTRD]

It is my understanding that one should "never" change to a tire with a lower load index than stock. However, when overanalyzing an upcoming move to a different profile (255/75 from 265/70), I've encountered a few well-known AT options with lower load indexes than my stock all-season Dunlop Grandtreks at 113. I assume that the slight geometry change could affect this but I have four LT C-rated 255/75 options on my list with load indexes of 111. I'm not especially concerned as the actual difference in max weight looks to be ~100lbs, I am not modifying my truck with anything of substantial weight, and I mostly drive it solo and empty (also, it's obvious that all of these popular options with 111, including KO2, have been used by many truck owners for years without any issue) but I'm curious if anyone has thoughts about why more durable tires would have lower load ratings and whether it's worth even pausing to consider.

 

[fkheath]

It is my understanding that one should "never" change to a tire with a lower load index than stock. However, when overanalyzing an upcoming move to a different profile (255/75 from 265/70), I've encountered a few well-known AT options with lower load indexes than my stock all-season Dunlop Grandtreks at 113. I assume that the slight geometry change could affect this but I have four LT C-rated 255/75 options on my list with load indexes of 111. I'm not especially concerned as the actual difference in max weight looks to be ~100lbs, I am not modifying my truck with anything of substantial weight, and I mostly drive it solo and empty (also, it's obvious that all of these popular options with 111, including KO2, have been used by many truck owners for years without any issue) but I'm curious if anyone has thoughts about why more durable tires would have lower load ratings and whether it's worth even pausing to consider.

The difference between 113 and 111 load index is insignificant. But why do you want to go with a narrower tire (255 vs 265)? Most people want to go with a wider tire (275 or 285) although the 285s can have clearance problems. A wider tire gives you a larger contact patch on the road, hence more traction.

 

[patkelly4370]

A narrower tire can "cut" through slick slop to terra firma underneath.


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[TheNotoriousTRD]

The difference between 113 and 111 load index is insignificant. But why do you want to go with a narrower tire (255 vs 265)? Most people want to go with a wider tire (275 or 285) although the 285s can have clearance problems. A wider tire gives you a larger contact patch on the road, hence more traction.

Thanks. I assume it's not a big deal but I am curious about the underlying factors. As far as size, that's been debated ad nauseam so I don't want to open that up here as it's ultimately a personal preference (for me, it's primarily due to weight) but many people would disagree with the last part of your statement around traction in most conditions.

 

[BlueRidge77]

I’m not taking the bait of wider tires vs narrower...

The actual load rating for a 113 is a little over 2500lbs and a 108/111 is around 2400lbs. Either provides well over the rating needed. Even an overloaded 4Runner won’t get close to 9,600lbs... (6300gvwr...) You would be losing some safety factor I guess. You will overload your axles well before any of those tires...

 

[Ripper238]

I had the same concern when i went to my C 112Q rated Duratracs. But in reality at ~38 PSI i meet the technical/actual weight per tire needed with no load, and at the max 50 psi i meet the full required load index.

RGAWR = 3439 lbs /2 = 1720 lbs per tire and since 112 = 2469ea at 50psi i can run the C 112Q rated Duratracs at 38+ psi and exceed the actual RGAWR still. If i need additional weight capacity i just bump up the air pressure to 50 and get the full 2469 at max capacity of each tire exceeding the stock required load index.


The matching of stock required load index is extremely important for higher speeds as well as with heavy loads/towing capacity as i understand it. Not so much at slow off road driving like when we run 10psi for better traction or when the vehicle is empty/no load.

I was also told by a Goodyear tech that going with a C rated tire with the extra air is better then going with a heavier E rated tire and running it way under its capacity like 20psi all the time.

 

[97BlackAckCL]

OP I love your screenname!

 

[TheNotoriousTRD]

Thanks. Long-time lurker but I finally pulled the trigger last fall on an ORP and it came to me. ¯\_(ツ)_/¯

 

[TheNotoriousTRD]

I had the same concern when i went to my C 112Q rated Duratracs. But in reality at ~38 PSI i meet the technical/actual weight per tire needed with no load, and at the max 50 psi i meet the full required load index.

RGAWR = 3439 lbs /2 = 1720 lbs per tire and since 112 = 2469ea at 50psi i can run the C 112Q rated Duratracs at 38+ psi and exceed the actual RGAWR still. If i need additional weight capacity i just bump up the air pressure to 50 and get the full 2469 at max capacity of each tire exceeding the stock required load index.


The matching of stock required load index is extremely important for higher speeds as well as with heavy loads/towing capacity as i understand it. Not so much at slow off road driving like when we run 10psi for better traction or when the vehicle is empty/no load.

I was also told by a Goodyear tech that going with a C rated tire with the extra air is better then going with a heavier E rated tire and running it way under its capacity like 20psi all the time.

Thanks. I knew PSI was important for the actual performance but I hadn't thought about how the possible PSI range of a tire factors into a load index. I just equate heavier, thicker tires with being more "heavy duty" and therefore inherently capable of supporting more weight so the logic of this threw me.