Tire Air Pressures

[stevensmith2859]

This may seem like a dumb question, but when my tire says max load range of xxxx at 50 psi, that would mean 50 psi is the cold pressure my tires should be at correct?

[clarkbre]

Yes. Inflate them to the correct listed PSI in the morning before they get warmed up rolling down the road.

Trailer tires: Use the sidewall "Max PSI"

Tow vehicle tires: Reference the placard in the driver doorjamb for recommended PSI.

[Chuck_S]

What Clarkbre said. Check them every morning the rig moves. (Same for trailer lug nuts.)

Trailer tires should be at max pressure to minimize sidewall flex which builds heat and will eventually destroy the tire. Under-inflation is the main cause of blow outs on trailers.

Inflating the tow vehicle tires to a greater pressure than listed on the door-jam will not increase the carrying capacity of the vehicle but a little higher pressure on P-Metric rear tires will help minimize squirm back there.

-- Chuck

[CentralMePistol]

Short answer; Yes, cold pressure.

Which tires are you talking about? 50 psi sounds like trailer tire...

[Chuck_S]

Maximum tire carrying capacity on both cars at home today is at 51psi (cold).
Maximum vehicle carrying capacity using these tires is at 35psi for one car and 32psi for the other (cold).

Passenger car tires run well below their maximum capacity to provide a soft, smooth ride. Inflating passenger car tires beyond their "door jam" spec does not add vehicle capacity.

-- Chuck

[Airdale]

Originally Posted by Chuck_S

Maximum tire carrying capacity on both cars at home today is at 51psi (cold).
Maximum vehicle carrying capacity using these tires is at 35psi for one car and 32psi for the other (cold).

Passenger car tires run well below their maximum capacity to provide a soft, smooth ride. Inflating passenger car tires beyond their "door jam" spec does not add vehicle capacity.

-- Chuck

That will depend on the tire design. For instance, let's look at a chart for a P245/65R18 Extra Load tire. At a recommended cold inflation of 36 PSI it will provide 2149# of load capacity. Increase the cold inflation pressure to 42 PSI and it will provide 2337# of load capacity. (The load index for that tire is 107 for the standard load at 36 PSI and 110 for the XL at 42 PSI.).

XL tires normally have a maximum permissible inflation pressure of 51 PSI. However, there is no load capacity increase above 42 PSI. The higher optional PSI above 42 PSI will stiffen the sidewalls when carrying their heaviest loads.

[SeaDog]

Originally Posted by stevensmith2859

This may seem like a dumb question, but when my tire says max load range of xxxx at 50 psi, that would mean 50 psi is the cold pressure my tires should be at correct?

You are correct if you are talking about the st tires on your wildwood

[Chuck_S]

Tire capacity is directly linked to tire pressure regardless of vehicle or trailer application.

My point was on the tow vehicle tires are not the determining factor of vehicle capacity. Axles and suspension will have less capacity -- or else we couldn't run the tires soft for a nicer ride. Trailer tires are often what determines the vehicle capacity and inflating to anything less than maximum sidewall pressure serves no purpose and increases risk.

-- Chuck

[Airdale]

Originally Posted by Chuck_S

Tire capacity is directly linked to tire pressure regardless of vehicle or trailer application.

My point was on the tow vehicle tires are not the determining factor of vehicle capacity. Axles and suspension will have less capacity -- or else we couldn't run the tires soft for a nicer ride. Trailer tires are often what determines the vehicle capacity and inflating to anything less than maximum sidewall pressure serves no purpose and increases risk.

-- Chuck

I've tried to keep away from a long explanation about this but it's becoming unavoidable.

Your right, the vehicle GVWR is it's limiter. How the GAWRs and tire load capacities are determined by the vehicle manufacturer differs because of regulation factors. For the tow vehicle (FMVSS certified) the axles provide the vehicle's major load capacity reserves. If you will notice, your TV will have combined GAWR axle loads greater than the vehicle GVWR. That allows the axles to provide load capacity reserves. Tires fitted to those certified axles MUST provide a load capacity that supports the maximum axle load. Then the FMVSS throws the vehicle manufacturer a bone by saying it's their determination to insure the tires are appropriate for that fitment. They are free to advertise the vehicle any way they want to but they MUST follow FMVSS guidelines for they are minimum requirements.

For RV trailer tire fitments there is no provision in the FMVSS for the vehicle manufacturer to provide tires with more load capacity than the vehicle certified GAWR limits. Again, when the trailer manufacturer certified the trailer, they determined those tires on the trailer are appropriate.

For RV trailer model years 2017 and newer, you have a 98% chance of seeing tires on them with at least 10% in load capacity reserves, thanks to RVIA. Maybe in the next NHTSA tire rules committee meeting the issue of tire load capacity reserves for RV trailer fitments will be addressed and some action taken to insure a minimum load capacity reserve is provided for those tires..

[Chuck_S]

Trailer tires only support 90% of the trailer's weight the other 10% is on the ball. Moving up a tire size will add capacity if inflated to maximum sidewall pressure (and not under-inflating to the old capacity).

Radial tires on automobiles run soft deliberately and there's a little squish normally at ground contact. Those big semi-trailers are usually running radials with not a hint of squish and sidewalls as still as steel.

-- Chuck