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Ask Dr. Tire – Trailer Tire Pressures?

Have questions? Dr. Tire has answers! What pressure should trailer tires be inflated to? What happens if they are under-inflated?

Doctor TireI was told not to fill my trailer tires to the full PSI rating on the tire. Then another person said I had to. Does this effect how my tires will work or will it cause any problems? Every person you ask has a different answer?!

Please help!

RVBikerHDLady

Hi RVBikerHDLady!

Happy to share some direction on the air pressure information maze! Answers are in the gold font!

Correct Air Pressure:

Let’s get you set in the right direction first! You trailer tires should be set to the full rated pressure that is called out on the sidewall of your tire. This pressure should be set “COLD”, meaning at general ambient outside temperature before you set off on the road.

To find your operating inflation pressure visit: https://www.tredittire.com/tires/ and select your tire!

Why? Science!

Fun fact: Tires are a “top-loaded” support structure! Think suspension bridge next time you are looking at them!

Tires are an elastic hysteretic system that see forces load up (tension) then unload in loss of extension (compression). When you stretch and compress a rolling tire, the work is being converted into elastic energy. That energy is working to keep the tire in its original shape and support the load; some of that energy is dissipated as heat. 

Stress-Strain Diagram

Tires = Suspension Bridge. This means the weight of the load is carried by the tension in the ply of the tire at the 12 o’clock position. A common misconception is that the weight of the load is being supported by the bottom of the tire; that area is in compression. As the tire rolls, the tension is constantly being transferred to the next ply cord as you move down the road. NEAT!

The “ST” in trailer tires stands for Special Trailer. These tires may look like passenger or light truck tires – but that is where the similarities end! Trailer tires are designed for one of the most extreme service requirements – high loads, highway speeds, and long storage periods.

Trailer tires are designed to operate and carry their maximum load at specific “COLD” inflation pressures. The rise in pressure as the tire reaches operating temperature has been accounted for by the tire manufacturer. They have built in this expansion to how the carcass reacts (supports tension) and footprint changes. Giving you the best towing service environment – cooler running carcass and best wearing tread.

Under-inflated?

Back to that “top-loaded” elastic hysteretic structure!

When you lower the air pressured from its optimal state (aka designed air pressure OR “COLD” inflation pressure), then you create a tire that sees higher forces and extension in the material. That means more heat build-up!

Heat (and pinch of sulfur) is the magic that vulcanizes rubber to make tires. Its also what can be used to take a tire apart. A hotter running tire may work for a short period…but its service life will be significantly decreased and could lead to an air-loss event and possible trailer damages! Remember, tires cannot repair themselves after damages or over-heating!

Under-inflated also affects the tires’ footprint and wear. As the pressure is decreased the footprint increases, causing more drag on the road surface and an uneven loading of the carcass at the inner and outer tire ribs. This will cause higher tread shoulder wear rates and more heat build-up! Prolonged operation may cause the rubber between the belts and tread cap to separate. Again, leading to an air-loss event and possible trailer damages!

All aspects of your trailers handling will be affected too! Braking distances increase due to the trailer being “bouncier” with under-inflated tires. Left-right handling will be softer and slower since the tire carcass is not as stiff. And your gas mileage will decrease since the tires are dragging more going down the road.

Recap: Run your trailer tires at the recommend maximum “COLD” inflation requirements to get the optimal towing experience your ST trailer tires have to offer!

To find your operating inflation pressure visit: https://www.tredittire.com/tires/ and select your tire!

Thanks for writing in!

Dr. Tire

(And if you have a question for Dr. Tire, write us at askdoc@tredittire.com and maybe we’ll answer your question next!)