I had to replace my trailer tires while on the road. I upgraded from load range C to load range E (shop only had Es). The sticker on the trailer recommends 50 PSI on load range C. The new tire’s sidewall says 80 PSI. The trailer is two axles (4 tires) and weighs 8560 lbs. loaded. GVWR is 8760. Tongue weight is 1100 (if it matters). These are actual weights via scale.
Which number should be used? Is there a difference in the contact surface area* with the higher inflation (80 lbs.)?
*unsure if that’s the right term, referring to the amount of tire in contact with the road.
I can’t tell you which number to use, but all else being equal, the higher the PSI, the less surface in contact with the road. It’s [a reason] why people reduce their tire pressure when driving off road.
IIRC, the area (in square inches) of tire, in contact with the road, times the PSI, should equal the weight of the vehicle, which makes sense. What that in mind, higher tire pressure necessarily means less contact with the road.
[ETA, just to head off the nitpicks, instead of saying they’re equal, let’s say there’s a direct relationship between the two numbers]
Is the number the trailer manufacturer specifies still applicable when using tires with a different load rating than the OEM tires?
My gut says to use the number on the trailer, but I’m not sure here. Maybe it’s worth contacting the company that makes the trailer. However, I suspect you’d get a non-answer telling you to use the correct tires and/or ask the tire manufacturer).
A few minutes of poking around online and I think if I did what the OP is doing, I’d probably start with the pressure listed on the trailer and go for a test drive. Then increase the pressure if things feel squirrelly.
Here’s a few things I saw. I did not read these carefully. I’m not vouching for them. They might be entirely incorrect. However, it’s just enough information to make you even more confused.
For tires with no material stiffness (i.e., stiffness only due to the air inside), they’d be exactly equal. For real-world tires, the material stiffness is much less than the pneumatic stiffness, so they’re very close to equal. One can always find finer levels of detail, in physics, but it’s fair to say that they’re the same.
I kinda think the tire proclaims it can handle a maximum weight at a maximum inflation. The vehicle recommends an optimum pressure for comfort, traction, handling, efficiency, tire life, and maybe other considerations, and it’s typically negotiable. You can go higher if you want better fuel efficiency and lower if you want less vibration on rough road surfaces, for example, but it’s on you to figure it out.
Thanks everyone, especially for the links/tables. My concern with the lower pressures was whether the E range tires would heat up at some value lower than 80 psi.
I looked at my truck tires, and they’re E as well, with 80 psi on the sidewalls. The truck’s placard says Load range E at 60 psi, and that’s how it came from the factory. So I’m going to assume that at least 60 psi carries no worries about heat buildup. It’s my understanding that underinflated tires are much worse than overinflated, as the flexing will eventually cause a failure.
One problem I didn’t mention is the ride quality. Believe it or not, with strong weight-distributing bars, the trailer’s ride is actually transmitted to the truck. It’s noticeably worse with the E range tires. Not unbearable, but after a few thousand miles it begins to wear on us. Lowering the pressure will help some.
For now I’ll go with 60 psi and check the trailer tires frequently to see it they’re getting hot. I don’t have an actual temp gauge, but my ballpark is whether I can lay my hand on a tire without burning (and jerking away). Anything I can touch is probably OK, heatwise.
The inflation rating on the tire is generally the maximum for the tire itself, while the vehicle inflation listed on the door jamb is for the vehicle itself.
So if you have a tire with a max PSI of 45 psi, that means that within the load limits of the tire, it can be safely used at 45 psi. It doesn’t have to be used at 45 though.
However, your vehicle’s inflation rating may be something like 30 psi, which is the rated tire inflation for the desired and/or safe handling characteristics as manufactured.
As far as making your decision goes, the door jamb inflation is the one to pay attention to, provided the tire’s own rating is as high or higher. If you somehow got those flip-flopped, that would be bad.
Yeah, the pressure ratings on tires are maximum. Take temperature into account too-- if you fill the tires to maximum on a relatively chilly summer morning at, say, 50 degrees, and a couple days later it’s a high of 90+, you’ve exceeded the max rating. I usually go a little more than 3/4 of the max, give or take depending on the drive conditions, and just make sure all tires are evenly inflated.
All tires heat up when being driven, regardless of their PSI. That’s why there’s a consistent distinction made between “cold” inflation and hot, and why the cold numbers are considered the controlling ones.
