'P' to 'E' Tire Swap

[rvb]

I put E-rated BFG KO2s on my F150. LOVE 'EM.


Discount Tire said to run 38lb, which I thought sounded low, so I ran about 45. Started noticing a shade of center wear plus they seemed bouncy. Went to 38 and it rides perfect. When I tow I go to 40 front and 45-50 rear depending on load (only towing a 4k-lb trailer + firewood/coolers in the bed).


I also looked for, but couldn't find, load/psi tables...


-rvb

[s1njin]

Well I know for a fact that Ford is calling for 39 pounds in a Load 'C' tire for my exact tire size and for my exact axle ratings. We have a actual door placard to prove that much now. Given what I read from WMTire - I'll up the pressure 10 pounds if I'm towing. I just need to make sure my rim can take it now I suppose.

It sounds like 40F, 45R is going to work fine for non-towing for me, and maybe 50/55 for towing or 45/50 while towing. Lets see what my rim can handle.

[s1njin]

Originally Posted by rvb

I put E-rated BFG KO2s on my F150. LOVE 'EM.


Discount Tire said to run 38lb, which I thought sounded low, so I ran about 45. Started noticing a shade of center wear plus they seemed bouncy. Went to 38 and it rides perfect. When I tow I go to 40 front and 45-50 rear depending on load (only towing a 4k-lb trailer + firewood/coolers in the bed).


I also looked for, but couldn't find, load/psi tables...


-rvb

I believe the load tables are standard across the board - we have a link to them earlier in this thread.

[s1njin]

Originally Posted by wmtire

I think you are looking for exact math in an exact situation and thus ONLY considering the axle rating.

Vehicles turn, that changes the dynamic forces/loads applied to a certain side tire depending on speed and sharpness of the turn. There are other things too. Heavier tires require more energy to turn. Rolling resistance can be increased depending on air pressure, which thus takes more energy to turn. These may be little things, but if you are going to increase your safety margin with higher ply tires, why not take more advantage of what they can provide.

Your axle and tires are ratings, that have been determined to safely be used at. You may be exceeding either or both at certain times and not even know it.

Have you weighed your vehicle yet, with the trailer attached.... to see the back axle weights being applied to the tires?

You know, now that I think about this I think the 'add some extra air' might be a luxury for tires that have room to spare.

I drove a motorhome for 4 years, 16" Michelin MS2's. The door placard said 75/80, and the weight ratings for those numbers were pretty much right even with the axle ratings for my motorhome. There was no allowance beyond that as the tire's max pressure was 80 pounds. If you have a larger class 'C' (32'), chances are you're riding at max capacity on tires that are checking in right at the axle bearing weight. Lots of them on the road running like that.

[TexasZ71]

Granted i had a chevy with the tire size you had until i upped it to 275/70/18
Why not just run 60lbs in the tire, from personal experience 45 psi was under inflated, but at that psi it matched my load index of the factory tire. Truck road rough regardless.

[TaWiMa]

I don't know if you have the answer your looking for, I'm too lazy at the moment to read through this whole post. This is the sticker on my F250.

A load E @ 65psi on your F150 is going to feel very loose and your going to bounce.

I used to tow @ 40psi with my 1500 running P's. I also went slightly wider for more contact. That truck came with 245's and I went to a 265.

I hope this helps a little.

[s1njin]

Actually your numbers on a F250 make more sense to me. Its heavier, the axles are rated for more weight, etc. So 65s in your E's make sense, of course depending on your tire. I see my 18s carry more weight for PSI then the 17s, so you really need all the info.

Like I said for the guy who posted on the F150 forum, same axle ratings, same tires in 'C' load, and Ford says 39 pounds. So 40 pounds day to day, and maybe 45 in the back when towing to make myself feel better shouldn't be unsafe or a stretch.

My only outstanding question; Load C, Load E. As near as I can tell, its the same chart, same line, just the E's go up higher PSI and capacity. So a 45 psi Load C should carry the same wieght as a 45 psi Load E. Its just I have a lot more headroom in the Load E.

[LandPirate]

I swapped tires on my brand new truck because the P rated factory tires are crappola. I went from 265/65/18 to 285/70/18 in BFG KOII All Terrain with load range E. When empty I run them at 38 psi. When towing I run the fronts up to 42 and rear at 50 psi. No need to go higher with my small trailer. I run 70 to 75 mph all day while towing and without any issues at all.
I've also upgraded the tires on my trailer to LT tires (D load range) and run them at 65psi. One of the benefits of having a single axle trailer.
I know this doesn't give you numbers. Just tow with confidence knowing that you have a heavier, more capable tire. You don't need to run 80 psi with the trailer you're towing.