Load index question

Assuming :

Payload capacity 1300lbs
Truck weight 4000lbs
Tire load index 116 or 2756lbs

2756x4=11024lbs total load capacity of the four tires or 5512lbs per axle. For sake of argument let's say 75% of the weight of the truck is in the front. That leaves 1000lbs for the weight of the back of the truck distributed to the rear axle. 5512lbs-1000lbs= 4512lbs of load capacity left that the rear tires can safely carry. In general is this a correct way to look at this?

If so, then the tires could carry over three times what our payload could ever be which leads me to my question... Besides better sidewall puncture protection is an SL rated tire with a 116 index just as good as a C rated tire with a 116 index with regard to carrying a load in the bed or towing a camper with a tongue weight of 357lbs? Thanks for any input.

@Discount Tire are the calculations in the first paragraph the correct way to look at this, and can you please give your opinion in general on SL vs C in this situation. Thank you...

 

Biggest thing that comes to mind for me is sidewall flex. When running higher loads in a weaker tire, you get more of the sidewall stretching/deforming in turns and as loads shift. Can make a big difference in how the vehicle feels while driving down the road. Stiffer sidewall=more control vs flexing sidewall=wallowing tires. How noticeable? that would depend on load and tires.

 

Thanks Ryan that makes sense.

 

And sorta disclaimer

And just to add, I've done a lot of towing miles with an open car hauler with ATV+UTV on SL tires. Even with a pretty heavy truck bed load. I always felt pretty good. I now run E-load, but only because of the heavy weight of my current camper (and yes, I still tow). Having never run with the camper on the SLs, I can't give an apples to apples comparison, but moving to the E range tires I definitely have a stiffer ride. MUCH stiffer, lol.

 

Some additional food for thought: I have been told you need to reduce the rated load capacity, for SL/P rated tires, by ~10% if used on a truck. I believe the logic for this is the loads that the tires sees are potentially higher than on other vehicles due to the higher COG of a potential load up in a truck bed. Even so, you 116 load index tire would now be 2756 * 10% reduction = 2480 lb/tire. This is still well in excess of any realistic load for a Tacoma.

I have hauled an in-bed camper around for quite a few miles on 116 load index tires (wildpeaks) with good success. It feels stable and I am well under the rated load per tire. The one thing I will say, is that the stability is only there at proper pressures (~45 psi in my case) and begins to feel unstable (side to side movement) with lower pressures. I would imagine a E range tire would do much better at lower pressures in this regard.

 

What kinda Camper you running?

 

How do you figure that when the tires supplied by Toyota are SL rated? Even on my Tundra they're SL rated.

edit: Or do you mean the rated load of the tire itself and not the rated payload of the vehicle? Either way, I have my doubts on that claim.

 

The SL tire typically is manufactured with shallower tread depth compared to the C-rated tire, so it will have shorter lifespan. The SL tire will also be lighter because there's less solid rubber in the tread.

 

I had never heard of the 10% thing, but a quick google search found some stuff on it referencing RMA (Rubber Manufacturers Association) suggesting this. Can't find anything more official though, like on the actual RMA website.

Quote from article: "Notice that, in Case One, a P-metric tire was installed on a light truck. According to the RMA, the load capacity of a P-metric or euro-metric tire installed on a light truck has to be reduced. Divide the load capacity of the P-metric or euro-metric tire by 1.1 to determine the load capacity for a light truck application."

https://www.tirereview.com/double-jeopardy-right-size-wrong-load-index-can-mean-liability-risk/

 

Same thing stated on here about dividing by 1.1 when installing on a Truck/Van/Crossover/SUV.

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=70

 

There is little or no difference in how much weight you can haul between C rated tires and P or SL rated tires. All of them are going to be rated for more than any Tacoma and virtually all 1/2 ton trucks. There MIGHT be a little better sidewall protection. IMO C rated, even D rated tires are a waste of money. If you need a tougher tire than a standard SL or P rated tire go straight to an E rated tire.

 

Seems to be the conclusion I'm coming to. Ironically a Toyo at3 has an index of 116 in a C and a higher 117 in the SL. 285 /70 /17.

 

Oh, i meant the in-bed camper you mentioned. Curious what you had.

 

I meant load of the tire itself. If anything, its just a bit of buffer.

It's an earthcuirser mod shell. I have been meaning to weigh it recently but probably in the 850-900 lb range for context on the tire topic

 

You mean 1200lbs? Lol. I was on the process of ordering one when they said 900 was their goal weight and it was really 1200 ish. I bought my AT habitat a couple days later lol

 

I believe you are thinking of their built out camper that they used to make (is GZL the name of it?). Either way I will let you know when I weigh it but the documentation on it says 611 lbs but that is likely for just the shell.

 

Oh, you musta got the ... Mod camper was it called? Yeah, it was the fully decked out GZL we were gonna be ordering. Was extremely disappointed, but o well, it all worked out!