Determining safe tire load rating required

[YYC]

I posted this in General Modification but then thought I might get better first-had Tacoma knowledge in this forum.

I am trying to determine the appropriate load range tire for my setup and intended use. I have a 2012 Tacoma DCSB 4wd that will be hauling a FWC Falcon slide-in camper. Truck/camper usage will be about 60% on winding mountain highways, 30% on unimproved fire/gravel roads and 10% mild off-road. Fully loaded the rig will weigh 6500lbs. Given the truck's weight distribution, I could have about 3900 lbs on the most heavily loaded axle, or about 1950 lbs per tire.

If I de-rate a P or ISO-metric tire (265/70R17) with a 115 load rating by 10% for light-truck use (as is required) I get around 2430 lbs capacity per tire. "C" load LT tires are also about 2470 lbs. That works out to around a 25% safety margin when compared to the 1950lb load per tire.

So here is my question; I am not sure if that 25% is adequate or not? Does anyone know if there a standard tire capacity safety margin? When I compare the GVWR of my Tacoma vs. the OEM tire load rating, the safety margin (of max truck weight vs max tire capacity) is more like 50% and on my F150 it was 42%.

I'd like to avoid the weight and ride penalties of 10 ply LT tires on a lightweight Tacoma, however being safe is more important.

Thank you.

 

[J!m]

Not a direct answer but remember max load rating is at maximum tire pressure.

“xxxx lbs at 85psi” or some such will be on the side wall. In this example xxxx/2 at 42psi. So, you may want to go up to a D range to avoid riding on flintstone tires…

 

[skrypj]

My F150 has an empty(and I mean literally nothing in it except gas) weight of 6200 lbs. I run a topper full time which is probably another 200 lbs. So before I even put any gear or people in the truck im already at almost 6500 lbs. Offroading with the family im over 7000 lbs. When I hook up my trailer and go camping with the family my truck has close to 8000 lbs on the tires and I do get off pavement with the trailer.

I run load range C’s and its been totally fine.

 

[helenandtoby]

Short answer: Go with load range E tires.
Long answer: First, know that the load ratings on a tire are whatever the manufacturer wants to claim. There is absolutely no standard, testing, system, or anything objective behind those numbers.
So, where do those numbers come from? They sort of mean that most drivers won't see too many failures at that load. There is always a chance of failure at any load, of course. The quoted maximum load is the point at which the chance of a failure starts too get too high.
Not very helpful? First, go with an established manufacturer. Then, consider buying tires with a load rating well above your load.
On my 4runner, I run Michelin Defender LTX load range E tires, with a load rating of more than twice my actual load. Years of driving in Baja, never a tire problem.

 

[tlrols]

One thing to ponder is tire pressure. Load "rated" tires can take rather higher pressures but you really don't want to run them at maximums. Look at the manufacturer's recommended tire pressure and try that pressure out as your baseline. Then bang in more air if you wish and try that. I have a 3rd gen 4Runner with Coopers (rated E) and I roll at 29 pounds per the door sticker. I also have a 4th gen 4Runner (V8 heaven!) with C rated KO2s rolling at 32 pounds (per the door sticker). I have tried higher pressures and was very much unimpressed (poor traction, rough ride, and generally no point in running higher pressures).

 

[DaveInDenver]

You have to run tires at whatever pressure you need to achieve a load rating. The basic difference in load C, D, E is that the sidewalls are increasing stronger to allow a higher maximum pressure and to some extent be able to handle more heat as a result.

It's the air inside that is holding up the weight, not the tire directly. A typical load E gets it's higher capacity because it can hold 85 psi of air. Ride comfort aren't important considerations, handling and preventing a blow out are to the manufacturer.

But thing I've found is if you need 85 psi for your load the ride is probably not going to be that much worse carrying it than a lighter load on relatively lower psi was anyway. I run load range E but have never needed anywhere near the maximum load on small trucks. It's just that the tires I prefer tend to come in LT and LR E.

 

[97heavyweight]

I have a similar setup weight wise. Fully loaded i'm at 6500lbs. I have been running 34x10.5/R16 Load Range D for just over a year and done about 12k miles with no issues and I still rock crawl my truck like a delinquent. I would not run Load Range E tires they are overkill and the ride will be miserable. I have been super happy with the ride comfort of the D rated tires.

 

[rruff]

The basic difference in load C, D, E is that the sidewalls are increasing stronger to allow a higher maximum pressure and to some extent be able to handle more heat as a result.

I've heard that some (most?) manufacturers take the same E rated tire, and simply spec it for D or C... reduce max load and max pressure. No idea if that is true, or why they'd do that.

Temperature is the limiting factor, and will be a function of speed and hysteresis from tire deformation. Higher pressure capability certainly helps with load, as it reduces deformation at a given load.

I would not run Load Range E tires they are overkill and the ride will be miserable. I have been super happy with the ride comfort of the D rated tires.

Tires need to be inflated based on their specs vs the load you are actually carrying. The inflation spec for a E tire at a given load is no different than a C... so long as the max C load isn't exceeded.

For instance, my tires (325/65r18) are E rated and have a max psi of 65 at 3860 lbs. If I was loaded to 2500 lbs/tire, the correct psi would be 35... the same as a C tire with the same load. https://tirepressure.com/lt325-65r18-tire-pressure https://tirepressure.com/tire-pressure-calculator

It's likely that if the E tire has stronger and more robust sidewalls this will result in greater harshness during compression, though it should also contribute to greater damping during rebound; less bounce. But you need to verify that the C or D actually has lighter sidewalls.

Look at the manufacturer's recommended tire pressure and try that pressure out as your baseline. Then bang in more air if you wish and try that. I have a 3rd gen 4Runner with Coopers (rated E) and I roll at 29 pounds per the door sticker. I also have a 4th gen 4Runner (V8 heaven!) with C rated KO2s rolling at 32 pounds (per the door sticker). I have tried higher pressures and was very much unimpressed (poor traction, rough ride, and generally no point in running higher pressures).

You should not be following the door sticker if you've changed the tire size. Bigger tires mean less psi for a given load, not more. Actually if your truck is empty, you shouldn't follow the sticker even for the stock tire size.

And this is referring to street driving; offroad it best to reduce psi even more.

 

[bkg]

I've heard that some (most?) manufacturers take the same E rated tire, and simply spec it for D or C... reduce max load and max pressure. No idea if that is true, or why they'd do that.

Temperature is the limiting factor, and will be a function of speed and hysteresis from tire deformation. Higher pressure capability certainly helps with load, as it reduces deformation at a given load.


Tires need to be inflated based on their specs vs the load you are actually carrying. The inflation spec for a E tire at a given load is no different than a C... so long as the max C load isn't exceeded.

For instance, my tires (325/65r18) are E rated and have a max psi of 65 at 3860 lbs. If I was loaded to 2500 lbs/tire, the correct psi would be 35... the same as a C tire with the same load. https://tirepressure.com/lt325-65r18-tire-pressure https://tirepressure.com/tire-pressure-calculator

It's likely that if the E tire has stronger and more robust sidewalls this will result in greater harshness during compression, though it should also contribute to greater damping during rebound; less bounce. But you need to verify that the C or D actually has lighter sidewalls.


You should not be following the door sticker if you've changed the tire size. Bigger tires mean less psi for a given load, not more. Actually if your truck is empty, you shouldn't follow the sticker even for the stock tire size.

And this is referring to street driving; offroad it best to reduce psi even more.

I don't think your first statement is accurate, just based on looking at tire weight differences between most C's and E's that I've looked at.

 

[rruff]

I don't think your first statement is accurate, just based on looking at tire weight differences between most C's and E's that I've looked at.

I agree, if there is a significant weight difference then there is obviously something different. I looked at a few different models though and the weights were the same or 1lb different... so I don't know. Usually for the tires I'm looking at, there is no choice but E.