Biggles

I'm driving a '11 FX4 SCREW , and have recently replaced the SR-A's with LT BFG A/T's 275/65-18 KO2's. I'm towing a 24ft TT , operating weight about 5800lbs , hitch weight about 650 lbs. I'm wondering what tire pressure range I should be using. I'm presently using 60 PSI when towing. The ride feels firm but okay, and tire wear appears to be okay.

brulaz

That's what I use with my Michelin LTX LTs
Nice and crisp ride. Even wear.

acadianbob

Depends on your Load Range

C = 50 pounds
E = 80 pounds

If you have C, run 50 pounds.
If you have E, you do not need to run 80 with that load. 50 to 60 sb fine.

smokeywren

Not enough info. You need to know the weight on each axle when wet and loaded on the road. The CAT scale will tell you the weight on each axle. Divide that weight by the number of tires on that axle. Then apply the TRA load/inflation table to determine the proper PSI you need to support that load.


At 60 PSI cold inflation pressure, your LT275/65R18 tires will support a max of 2,825 pounds on each tire, or 5,650 pounds on each axle. So you are overinflated by a bunch.


At 40 PSI, your tires will support 2130 pounds on each tire or 4,260 on each SRW axle. Your front and rear GAWRs are probably less than 4,260 pounds each @ground, so the most air you ever need is 40 PSI cold.


Here is the TRA load/inflation table for LT275/65R18 tires:


PSI . Max weight on each tire (lbs)
-- .. --------------
35 . 1940
40 . 2130
45 . 2310
50 . 2535 (max for load range C)
55 . 2660
60 . 2825
65 . 3000 (max for load range D)
70 . 3150
75 . 3305
80 . 3415 (max for load range E)


So you bought a lot more tire than you need.


TRA = Tire and Rim Assn. They are the official group that sets the specs for tires and wheels sold in the USA. Tire companies often quote the TRA load/inflation tables for the tire sizes they sell, but TRA is the source.

DieselDawg

Problem with the "inflate only to the STATIC weight that your axle is carrying" is that your truck/trailer is DYNAMIC.


When you start moving, accelerating, turning, swaying and braking....the load of each tire varies between that "static weight" to higher and lower "dynamic weights". Saying that you are "over tired" can be a bit simplistic. When you have to apply (or even slam) on your brakes, you will have much more than the static weight on your front axle. When you turn, your tires on either side of your axle will have varying forces/weight to manage/carry. There is also the factor of construction...all brands are not created equal. Some tires ,E rated or not, will handle differently than other similar rated tires.


If you had no way to measure psi, what you would usually aim for is equal amount of tread as a contact patch on the ground as when you tires are properly inflated unloaded and go from there. This means you would be increasing psi until your tires appear normal under normal conditions. Of course, you really want to know what psi works and feels best for you.

smokeywren

The Professional Engineers (PEs) at TRA understand that, and allow for it in their weight ratings in the load/inflation tables If you go by the load/inflation table, you'll be golden.


But you also need to be well-informed as to how to use the load/inflation tables. Look it up at TireRack or Toyo dot com. Basically, you can increase the max inflation by up to 10 PSI for high-speed, long-distance towing. But more than 10 PSI is over-inflated.


ST trailer tires are a different ball of wax. Most trailer tire manufacturers say to inflate the trailer tires to the max on the sidewall of the tire. However, Maxxis includes a load/inflation table for their ST tires on their website.
http://www.maxxis.com/trailer/traile...nflation-chart

1wayhighway

I run a load E range tire and run 50lbs in them while towing and air them down to 40 when not. I pull a 32 ft trailer and am near my payload max when towing so that is part of the reason why I went to a higher load range tire. It is more than needed but I will get more wear out of them than the SRA's that come on the truck.

brulaz

Beside their weight rating, LT-E tires have two other "positives" IMHO.
1) A stiffer side wall with less squirm.
2) A tougher tire overall, because of the additional belts, giving greater protection against road debris and potholes.

Run the Lt-Es on my truck at 60psi all the time.
Run the STs on my trailer at 70psi all the time.

raisin

I just installed Michelin LT275/65R18's on my '14. Not for load carrying, but stiff sidewall. If Michelin had "C" or "D" rated I would have got them.

I'm replacing a "F250LD" that has Michelin LT tires. Needed LT tires, Hellwig sway bar and Rancho 9000XL rear shocks to do it. I've set at 55 psi for now. Its been said on here that Michelin LT's should run min. of 47 psi to prevent sidewall cracking.

Biggles

Thanks for all the replies. I bought E rated tires because the KO2's do not come in C or D ratings. Besides towing, the KO2's are also a winter rated tire, which is a good thing in Calgary.