From my book “Truck Nuts.” Understanding Truck and Trailer Tires (tire ratings, safety issues)
Tires are your first line of defense between you and the hard road. Another reason to read your truck and trailer owner’s manual. What allot of folks don’t understand is what’s printed in the truck owner’s manual, over-rides what is stamped on the side of the tire just like it over-rides the label on receiver hitches. The truck and trailer manufacture specifies to the tire company what they want in a factory tire sold with the truck when new. And the truck manufactures decide and takes responsibility for the load rating of the tire and tire pressure. So look in the owner’s manual and the safety compliance sticker in the driver’s door frame to see what your trucks tire pressure should be. Trailers also have a Safety Compliance Sticker which will show axle rating and tire weight rating and air pressure. (Trucks according to the government also means SUV’s and mini-vans, so when I say trucks, it covers the category.)
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.
You’re heard of the Lincoln head on a penny measuring tire tread depth. Stick the penny in the tread head first and if you see he’s whole head, the tire is illegally worn at 2/32 inch. Tires start at 10/32 or higher for snow tires. Truck tires need to be rotated every 5000 miles.
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.
Heat is the biggest enemy to trailer tires and under inflation which is related. Running a heavier ply tire at the maximum tire pressure using nitrogen helps. Load rating per tires is stamped on the sidewall of the tire.
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.
Trailer tires are basically the same as truck tires when it comes to proper air pressure. Look at the trailer owner’s manual. Trailer manufactures match tires like they do axles to be the proper combination for safety. With torsion axles like the majority of horse trailers use, a flat tire may not feel much different, it can hang in position. So you could drive for miles with a flat and not know it until it destroys the tire and pieces are flying off the trailer or when a flat tire tears apart and takes the trailer fender with it.
Newer trucks have tire pressure monitors as standard equipment as mandated by law. There are aftermarket tire pressure monitor systems for trailers to keep track of tire pressure on the go. Another value of having an onboard tire pressure monitoring system is being alerted that you have lost a tire or tire and wheel. It happens more often than you think. Tires will naturally loose air over time making if important to check your tire pressure often. Nitrogen instead of air is gaining popularity with over the road semi-trucks. It leaks less than air, collects less water inside the tire and may make the tires last longer. It’s used in most race cars. I use Tuson tire pressure monitor systems. Goes up to 203 psi and also tells your the heat in the tire. This can prevent blown tires, changing tires in the rain, snow and having hot horses while you change tires and fix the fenders. https://mrtrailer.com/tuson-tire.htm
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.
If you blow a tire and drive it awhile, the other axle tire on the same side, may have stressed. Watch it closely or replace it. Even if you don’t use your trailer much, 3 years in the sun may weaken the tires. I’ve towed 30,000 miles a year on trailer tires and got them to last 2 years. That’s not normal, I’m a test dummy. It’s more common for trailer tires to last less than 15,000 miles. The story is ST trailer tires are made heavier than even LT truck tires. Heavier cords, greater tensile strength. Better chemicals in the rubber compounds. That’s what tire companies will tell you. If that’s the case, why can’t you use them on trucks other than traction issues?
If you rarely use your trailer, you can put the axles on blocks to take the weight off the tires or put plywood under the tire, lower the air pressure and put covers on them. Don’t use the shinny stuff on tires, it has alcohol. A trailer tire sitting for a long time can get a flat spot. Just like boats, guns and engines, they last longer when they get used. That’s what she said.
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