The tire has two different labels, and they are not doing the same job. The sidewall says what that tire can carry. The placard says what the truck or the trailer was built to use.
The pressure to set
NHTSA's tire page says the proper cold inflation pressure is on the Tire and Loading Information label on the driver's side door edge, doorjamb, or the inward-facing surface next to the driver's seat, or in the owner's manual. NHTSA's own step says the correct pressure is the one the vehicle manufacturer listed, not the one listed on the tire.
NHTSA says to check every tire, including the spare, at least once a month when the tires are cold, meaning the vehicle has not been driven for at least three hours. If you have been driving and a tire looks low, NHTSA says to fill it to the recommended cold pressure on the placard anyway, then check it again when the tire is cold. A tire-pressure monitor is not a substitute. NHTSA says the monitor on passenger cars, light trucks, and vans from model year 2008 on warns when a tire is significantly underinflated, and that underinflated tires are hard to see.
A trailer has its own placard. Goodyear's tire care guide tells you to check a trailer's certification placard for the load limits, and to use the cold pressure on that placard. Goodyear's check for its special-trailer tires is cold when the trailer has been driven less than one mile. If you must check those Goodyear tires hot, that guide says to add 4 psi to the placard's cold pressure. That 4 psi step is Goodyear's instruction for those tires. It is not NHTSA's instruction for every tire. Set the cold pressure the placard names, and recheck when the tire is cold.
The door-sticker guide is the truck side of this. The trailer placard is a different piece of paper. Do not put the truck's door pressure into a trailer tire unless that same pressure is what the trailer placard prints.
Load range, ST, and LT
Goodyear defines a light-truck tire as a tire with "LT" in the sidewall size, and its example is LT245/75R16. It defines a special-trailer tire as a tire with "ST" in the sidewall size, and its example is ST235/80R16. The same guide says Goodyear ST tires are built for non-driven trailer axles, including travel trailers. An ST tire on a truck's steer or drive axle is outside that description.
The load-range letter, when it is printed, is part of that sidewall size. Goodyear's Endurance announcement says that trailer tire is offered in load ranges D and E. The letter is not a truck rating and not a placard pressure. The maximum load is molded on the sidewall of the tire. Goodyear says never to fit a trailer with new tires that have less load capacity than the trailer's tire placard shows. Match the size on the placard. If the placard also names a load range, match that letter. A lower load number on the sidewall is not a match.
NHTSA says to replace a tire when the tread is worn to 2/32 inch. The wear bars across the tread, and the penny test NHTSA describes, are the tread checks. Tread depth does not read the date code.
Age
NHTSA says the last four digits of the DOT tire identification number are the week and year the tire was made. If the number reads 0308, the tire was made in the third week of 2008. The full number may be on only one side, so look at both sidewalls.
NHTSA says you cannot see tire aging by looking. It names recreational vehicles, and other vehicles that are not driven regularly, as the ones where age matters before the tread is gone. It says some vehicle and tire manufacturers recommend replacing tires that are six to ten years old, regardless of treadwear. That is those manufacturers' recommendation, as NHTSA reports it. It is not a date this site can assign to your trailer. Read the tire maker's limit for the tire that is on the wheel, and read the date code.
A tire can also be recalled on its own. NHTSA's tire page points to the tire-recall search. The parts-recall answer is how a tire or an axle shows up separately from the coach VIN.
The towing check does not know your tire pressures. An overloaded tire will not show up as a math error on that page. The placard and a gauge will.
If the sidewall maximum and the placard disagree, set the placard's cold pressure. The number on the tire is the tire's maximum, which is what NHTSA says not to treat as the vehicle's pressure.
Questions people ask
- Do I inflate to the number on the tire?
- NHTSA says the pressure to use is the one the vehicle maker lists on the tire label or in the owner's manual, not the maximum molded on the tire.
- Where is the date code?
- NHTSA says the last four digits of the DOT tire identification number are the week and year. A code of 0308 was made in the third week of 2008. Look on both sidewalls.
- Can I judge a trailer tire by leftover tread?
- NHTSA says tires should be replaced at 2/32 inch of tread, and that some vehicle and tire makers recommend replacing tires at six to ten years regardless of tread. Looking at the rubber will not show age.