From my book “Truck Nuts.” Understanding Truck and Trailer Tires (tire ratings, safety issues)
Trucks span the country for what tires suits your use. If you’re on the dry highway the majority of the time, simple highway tread works well as with most truck tires. But if you’re on snow, ice down pouring rain, you look at all-season tires, all-terrain tires and mud-terrain tires in order of severity. If you are a rock climber and sand jumper, then you’re looking at wide tires with bead locks.
Are you confused yet? Some people inflate under what the safety compliance door sticker states for tire pressure for a softer ride. Low tire pressure causes the tire sidewalls to flex more and build up heat. Not a good thing. It works on an empty truck but not under a load. I would say to stick to the air pressure ratings in the owner’s manual and safety compliance door sticker, that’s what’s been tested to be safe. The maximum tire pressure is cold inflation. In the sun or after you’re driven awhile is hot inflation which will show 5-10 psi higher which is fine.
Some manufactures have a different rating for the front truck tires and rear tires. A couple years ago, Ram had a lower tire pressure setting you could use when empty on heavy duty trucks. It would just lower the Tire Pressure Monitor to not beep or flash a warning in the dash. You still had to manually add or subtract air from the tires.
½ to trucks can have a P-rated tire for “passenger tires.” Some have LT tires for “light truck.” The Nissan Titan XD trucks have LT tires. All heavy duty trucks as in ¾ ton and one ton have LT tires. LT tires can be 6-ply (C-rating), 8-ply (D-rating), 10-ply (E-rated), 12-ply (F-rated) and beyond.
On my rear wheel drive truck, I replace tires on one axle at a time. Of course it’s better to replace all 4 tires but I loose tires to road conditions and I hate to buy 4 tires each time I blow one tire. So logically I like to put the new tires on the front (steer axle) for better steering. But that would be a mistake. With good tires on the front and worn tires on the rear, if you hit bad road conditions on a curve like water, snow, ice, the rear of your truck would break loose before the front ones, that’s called a skid. Or for you enthusiast, drifting. That’s good on a track, but bad on a road.
Trailer tires are ST for “specialty tire.” ST tires have the same ply rating as truck tires. Something new is speed rating. My last 3 new trailers for 2016 have a speed rating on the side wall of the tire. My toy hauler RV trailer has L rating for 75 mph, my tilt trailer has a M rating for 80 mph. For decades all ST trailer tires were speed rated for 65 mph. Commercial tires can also be used where ST tires are recommended.
In olden days, bias-ply were touted as the best trailer tires. They did have stiffer sidewalls but flexing side walls helps the poor suspensions on trailers ride better. Radials produce less heat than bias-ply. Now radials rule just like they do in the truck world. Trailer tires are close together, throwing nails at each other. Steel belted radial tires can take lots of abuse from the road and nails before going flat. I use Slime in my trailer tires for even more protection. Eventually when trailer tires have mandatory Tire Pressure Monitoring, available in aftermarket now, I’ll have to quite using the thick slimy stuff. Slime says they are safe for TPMS, tire repair shops don’t like working with Slime in the tires.
Back on the farm, when trucks had the same size tires and trailers, I would wear out tires on the truck and then run them on the trailer. Now truck sizes have grown larger. And with my CDL and DOT number I have to follow the rules. That means to be legal, I use ST or commercial trailer tires.
All tires need to be balanced. Trailer tires can be aligned and axles re-arched, if you see excessive wear showing excessive toe in or toe out or wear on the inside of the tire. Over inflation will wear the middle of the tires and under inflation will wear the outsides. Some of you don’t use your trailer often and after a few years, the tires have great tread but the side walls have dry rot from the sun and crack. You can buy covers for tires.
Get a good tire pressure gauge. These are the long ones sold at better auto parts stores and truck stops. Cheap short air pressure gauges are not accurate or not accurate for long. If your truck has a factory tire pressure monitoring system and has individual pressure readings, it’s interesting to watch the pressure go up when the tires warm up. You can even tell air pressure difference from the sunny side of your truck and the shady side. That tells you that heat expands the tires to increase air pressure. This is why you want to check the air pressure before you drive when the tires are cool. You want to check the tires air pressure at sitting still air temperature. If you check the tires when they are hot and let some of the air out to get the correct pressure, then when the tires cool, they can be under inflated.
If you blow one tire, it’s usually better to replace both tires on the same axle. Of if you don’t, the new tire will wear down to the other tire on the axle. Don’t use different size of tires on your trailer. Tire capacity on the axle must equal or exceed axle weight rating. All the tires on the trailer should exceed the trailer GVW by 20%. Keep your trailer as level as possible for even wear on your tires and better braking.
ST tires can be 6-ply (C-rating), 8-ply (D-rating), 10-ply (E-rated), 12-ply (F-rated) 14-ply and 16-ply are now common on heavy trailers and beyond just like truck tires. On their large 30 ft. Big Tex test trailer I used with TFLtruck.com on the IKE, they have 16-ply H rated tires. Triple axle tires on a trailer take special attention. Not just because the front and rear axle bearings can loosen up from all the tire flexing on corners, but the tire beads can lose air and tire side walls can crack early. watch this video