Recommended Tire Pressure for ST Trailer Tires and Load Rating Capacity

Updated 03/23/2021 | Published 12/09/2017

Question:

Your QandA states - The correct tire pressure for a trailer tire will be indicated on the tire sidewall. Trailer tires should always be inflated to the full cold psi pressure noted on the tire. They should never be run under- or over-inflated since this can reduce their load capacity and lead to overheating. But tire manufactures put out inflation charts based on weight load and say you should adjust the pressure based on actual load. So, Which is correct and why?

asked by: Ray

Expert Reply:

The trailer tire manufacturers we work with all have recommended the information you have seen given in our online answers. The max PSI from most manufacturers the listed capacity at the highest load capacity rating of the ST tire.

There are charts as you stated to give you a variable psi level from certain manufacturers, like Goodyear and Maxxis for instance, that have their primary business in automotive tires. They have testing of these levels built into their system where most ST specific trailer tire manufacturers do not. The reason why they do not do as extensive testing on their tires is because of the function. Trailer tires have a stronger sidewall because they are not used for turning in the same way as the front axle of a vehicle tire is. Also, it is very rare for a person with a trailer to weigh their load each time and adjust the pressure accordingly and tire failure is most of the time attributed to not having enough or having too much air in the tires for proper use. The max psi is the safest place to keep the tires inflated whether traveling empty or fully loaded to give you best traction with an ST tire and that is the majority of the reason why we recommend it.

One is not right and the other wrong, they are simply different approaches based on manufacturer.

If you have further questions, please let me know.

expert reply by: Jason S

George L.

5/28/2020

Unfortunately, both are kind of misleading. If a trailer has a max gross of 2000lbs (this is the combined weight of the base weight of the trailer AND cargo and should NEVER be exceeded per mfcr), then if I'm running ST175/80*13 tires with a load rating of 1360lbs at 50psi, that means, per tire, I have a loading of 1000lbs per tire. Based on the Load Limit at various pressures table supplied by the mfcr, I should inflate my tires to around 30psi (not to exceed 50psi). The further away from 30psi I get, the more likely i will have over inflation wear. If I go under 30psi I could risk under inflation wear.

Wil Y.

8/22/2020

@GeorgeL I'm with you, George. My two-wheel trailer max weight is 3500 lbs. I've got ST225/75R15 load range D tires. Max load 2540 @ 65 psi. I know, way over tired, but that's what was on it when I bought it. The data plate on the trailer specifies the tire size but not load range. The inflation is listed as 50-65. That's load range C and D max respectively for that tire size. Goodyear, Maxxis, and Power King all have inflation charts (all the same chart [DOT standard?]) that show that this size tire can carry 1760 lbs at 35 psi, right on my weight. What should I use? Various "experts" on various fora have argued about this ad infinitum. Jason here says go for max because it gives you the best traction. I would take exception with that. For my weight and tires that would be grossly over inflated, almost 2X, causing the tread to "bulge", carry most of the weight in the center treads, and have less rubber on the road. Typical wear pattern for over inflation is center treads worn thin and shoulders still deep. Less rubber on the road - less traction. So I split the difference and go for 50 psi. That's max for load range C, but I've got D. Still over inflated by 50% according to the charts. I'm not full timing so the tires will probably rot before I get to see the tread wear pattern. Especially if COVID keeps us close to home another summer.

Jim H.

3/23/2021

Just like with automobile tires, correct inflation give the best preformance and wear of the tire. The max inflation listed on a trailer tire will put the tread flat on the found st the maximum load the tire is rated for. Less than full load on the tire requires inflation pressure adjustment to keep the tread flat. If you have trailer breaks, the is especially important for proper beaking. I have a 3 horse trailer and when fully loaded, is about 8000 lbs. I get 18,000 to 20,000 miles on a set of tires. During the life of the tires, I check wear patterns and fine tune inflation accordingly.