My trusty BFG tires are about worn out, and will be replaced before winter, so I've been thinking of tires. This truck is sprung a bit heavy, front and rear sway bars in good shape, everything maintained. It's my do all vehicle: grocery getter, mild fourwheeling rig, snowmobile hauler, road trips, and soon to be camper hauler. It's at gvwr when hauling and I want to make it do that job safer; I know gvwr can't be increased.

Currently running LT 33x10.5R15 load range C, max load 2600lbs. While 2600lbs is much more than needed already, I'm wondering if something like a LT255/80R16 or even LT235/85/R16 both in load range E would be substantially more stable in terms of sway/squirm when loaded.

I prefer skinnier tires for ice and snow but need some height for ground clearance in summer. No interest in anything over 265mm or 10.5", but are wider tires inherently more stable or is load range a better metric? Is a 235 load range E more stable than C rated 265 (same tread for comparison's sake)? I suspect yes but am interested in the knowledge of the more experienced.

Hate to jam up the forum with just another tire thread but most tire info I come across is based on looks or strictly the load capacity number.

 

If you had a good fitting 16" rim that was close or exact offset of the original 15s I think a 235/85r16 would be a good choice. They vary slightly between manufacturer, but generally are between 32" and 32.5. So, not far off from your 33s you are currently running.
​​​​​​​And yes a D or E can carry more but that is also partly because they can handle higher inflation pressure (55-80 psi vs 35 for a factory f150 tire) thus causing a substantially rougher ride.

 

What load index was stock?

It would be nice to have tires that can be aired up when fully loaded and run at less pressure for daily use ant not shake any fillings out of your teeth when going for groceries.

 

The root of my question is related to sidewall stiffness, and how that relates to tire stability, well below a tires max load.

33x10.5R15 C rated vs 235/85R16 E rated; same tread, will there be a big difference in how they handle 3500lbs on the rear axle in terms of side to side stability (sway/squirm/squish/whatever you want to call it)?

 

I'm no expert when it comes to this stuff, so all I can relate is my own experience.

My prior truck was a 1/2 ton Ram. From the factory it came with P275/60R20, and I had replaced them BFG Long Trails in the same size, still P size. Based on GVWR, the OEM tires exceeded the rating. I never felt "unsafe" towing with those tires, nor the BFGs. It seemed to do the job just fine, even when I had upwards of 12K behind the truck, which was considerably over the factory tow rating.

After blowing out one of the factory 20" wheels, I replaced them all with 275/75R17 BFG ATs, load range E. Not because I thought the E range would be better, rather because I got a screaming deal on the tires.

Holy crap..what a difference. I had no clue what I was missing. Those tires completely transformed towing with that truck. It suddenly went from controllable "mushiness" to rock solid stable, but at the cost of ride comfort. As others noted, the higher rated tires get their capacity from increased air pressure.

That said, 3500lbs on the axle? I'd be FAR more concerned about that much weight on the *** end of a 1/2 ton than I'd be over tire choice, mainly from an axle reliability issue.

 

Thanks (all) for the info. That is what I was wondering about stability.

GAWR for the 8.8" is 3777lbs so 3500# is no concern there. I'm talking 3500# total, truck with load, not just load.

 

You don't have to run load range E tires at 80 psi all the time; only when actually loaded or towing something. I drop mine to about 40 psi when the truck is empty.

You can calculate what pressure is needed for an unloaded truck by going backwards from the tire weight capacity at 80 psi. 40 psi is enough pressure to support about 6000lbs, 60 psi can support about 9250lbs, 70 psi can support about 10800lbs, and 80 psi can support 12300lbs. Your axles wont support some of these weights though; this is just what the tires themselves can support.

 

I originally had the stock 235/75-15 "Extra Load" (between B and C I'm told) tires on my '95 F-150. Those were OK with the truck (over)loaded with my camper. Then I lifted it and put 33/9.50-15 load range C BFG A/Ts. Those were terrible with the camper. Lot's of squirm / sway. Then I put LT235/85-16 load range E. It was a little too long between the stock setup and the lift / E tires for a direct comparison, but I'd say the E tires were at least as stable as the shorter stock tires, and probably better, even with the lift.

I had the 16" rims with 5 x 5.5" from my old Jeep.

 

I know for a fact that the 235/85/16 Firestone transforce on a 2002. 250 super duty will carry 28 square of shingles in the bed. And that's roughly 5980 pounds lol. Safe.... No. But we were working in flagstaff az and the wholesaler said if we didn't get them then and there he wouldn't hold them for us. That was a little squirmy so keep the bed load under 5k and you're good lol

 

Thanks for the input and pressure info. I doubt I'd ever be inclined to run 80psi. It sounds like the 235/85r16 should match my goals well. The axle bearings would likely catch fire with 6k lbs of payload, and then the 8.8" housing would split, lol.

NothingSpecial, I specifically was hoping you would chime in since your old truck is my trucks twin and I will be hauling a pop-up camper soon too. I knew you had 33x9.5r15 tires and found them unstable loaded, but I couldn't recall what size you went to. I won't be flat towing a jeep and my camper should be lighter with very forward center of gravity (fourwheel camper gutted and rebuilt). So if you felt the E rated tires suited your use well I think I'll be happy too.

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the biggest difference between "C" and "E" tires is
a "C" tire is 6 ply. 32 psi max.
"E" tire is 10 ply. 80 psi max.
so a load range "E" tire will be much more stable and hold a lot more weight than a "C" tire will.

on my 02 and 04 trucks with "E" rated tires, i run 35 psi rear and 55 front empty. i only air up if hauling heavy loads.

 

I did run 80 psi in my tires when the truck was (over)loaded. The tires didn't require 80 psi to hold the load, but it did make them more stable, and the half ton springs kept the ride from being too harsh. The main downsides to too much pressure are tire wear in the center of the tread and possibly traction. But play around with it and figure out what works best for you.

One other thing I felt I had to do to handle the camper in the F-150 was add air helper springs. Plumb them separately (otherwise air transfers from one side to the other and it doesn't resist roll very much). I ran them essentially empty most of the time and inflated them to bring the ride height back to normal after I put a load on it. That probably did more to make the truck feel like it could safely handle the camper than the tires (the two changes definitely addressed different symptoms).

For what it's worth, I think my camper was about 1200 lbs empty. It didn't have any tanks, so there wasn't a lot of extra weight when we were loaded up, but 4 people's clothes, food and other camping gear I'm sure added up. I never put the truck on a scale, but I guestimated around 7000 - 7500 lbs GVW.

 

Falken Wildpeak AT3W in E-rated 235/85R16 on Cragar Soft 8 steel wheels (16x7, zero offset, 5x5.5, 4.25"/108mm center bore, 2200lb capacity) are ordered. It will be interesting to see the difference, especially with fire wood hauling season starting. Fire wood weighs much more than snowmobiles or my little camper shell, and I often do my worst/best wheeling this time of year.

 

I found me some 16.5 rims and bought hummer tires. They are very durable . I did alot of reading before I jumped in and you can find an equal amount of people who love em as to hates em. I'm glad I bought mine and will continue to buy them. Good ground clearance and all I had to do was space my front bumper out about 2 inches. The tires are cheap and plentiful. Mine are 10 ply radials. They will balance and they are quiet on the road.

 

I'm not sure a military surplus tire would do what I want, though I'm glad you're happy with them. I run icy, snow packed roads a lot here in WY. Staying home is not an option, but I didn't want studs or a winter only tire at this time. I went with the Falken AT3W over Cooper ST Maxx specifically for the severe snow rating. Cooper AT3W were considered but I read many reviews highly critical of wear. This tire will hopefully be what I'm looking for: pretty good at everything all year, however, not perfect at any one set of conditions.