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How to Determine the Right Air Pressure to Fill a Trailer Tire

Question:

Hello, i just bought a pop up camper and ive been going crazy trying to find out how much air pressure i should fill the tires too, everybody tells me that i should fill them out to 35 psi but the tire says max 60 psi. the tire also says that its load rate is 1,360 lbs and according to my calculations that comes out to 2,720 lbs but the weight of the trailer without weight is 2200 lbs and i could add an extra 700 lbs, that comes out to 2900 lbs. that exceeds the both tires together? so i was thinking that i should buy a bigger tire, a whopping 14inch tire. i feel so lost. i just want to be able to feel safe pulling the trailer and not put my family in any danger weaving threw mountain grades. what would be the proper psi for the tire? and should that be with the weight of the trailer on the tire or with the tire off the ground or off the trailer ? should i put a bigger tire? size ST205/75R14, i wonder if they would fit?

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Helpful Expert Reply:

I can end this debate for you real fast! Trailer tires, which will have an ST in front of the size, should always be inflated to the maximum psi indicated on the tire. Trailer tires usually do not have a recommended and maximum psi indication so I am curious if the tries on the camper are ST tires or regular passenger vehicle tires. On a regular trailer tire you would inflate it to the max psi indicated on the tire because trailer tires are built with a thicker sidewall to handle more vertical load.

If a trailer tire is under inflated, because of the thicker sidewall it will generate excessive heat and that is what leads to failure.

Check the camper frame and there should be a sticker or plate that lists what tire size should be on the trailer. It could also be in the owners literature. That is the size you will want to stick with.

Any given size tire can have different load ranges. For example an ST175/80-13 load range B will have a capacity of 1,100 pounds at 35 psi. But a load range D in the same size, # AM10210, is rated for 1,610 pounds at 65 psi. So you do not need a larger size, you just need a higher load range.

The wheel also has to be rated high enough. Tires and wheels are not always rated the same. There should be a sticker on the back of the steel or possibly stamped into the metal and indicates the wheel capacity and psi rating.

If you are not sure then the safe bet is to replace the tires and wheels. To do that I would need to know the bolt pattern of the wheel. I have linked a help article that shows how to measure for bolt pattern. I have also included a link to our informational article on trailer tires for you.

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Follow up Questions

Michael S.

I have a 2018 Thor Windsport 34J. The sticker in the RV says to inflate tires to 90 PSI but the tires say 110 PSI. Which one is correct?

Etrailer Expert
Reply from Jon G.

For trailer tires we always recommend going with what's printed on the sidewall of the tire. For a motorhome like what you have it would be better to treat that like a passenger vehicle and inflate the tires to the 90 psi that the sticker states (provided these are the exact same size and load range).

Reply from Ryan K.

@JonG Hello, I have a 2009 Jayco Jay Feather x213. It had load range C tires on it with a 50 PSI. It also says that on the trailer itself (Sticker with weight ratings, etc.). The trailer now has tires on it that are load range D saying "inflate to 65 PSI for max load" on the tires. We never fully load the trailer with gear. Do I keep the cold tire pressure at 65 PSI or at 50 PSI as it says on the trailer itself? Thank you.

Etrailer Expert
Reply from Jon G.

@RyanK Great question! Since my post above we have actually been getting some different feedback from the manufacturers and they are a little more okay with PSI ratings being adjusted per load. What I would do in your situation is check with the tire manufacturer to see if they have a progression chart for different weight ratings and if they do then go by that. If they don't then I would just say to go by the PSI rating on the tire just to be safe.

Reply from Rhiannonr

@JonG I have a tpms system for my trailer. I have to set the low pressure alarm for my tires, which are CastleRock ST ST225/75R15 (D rated, 65PSI cold). Any idea where to find out what I should set the low pressure alarm to?

Etrailer Expert
Reply from Victoria B.

The owner's manual for your TMPS system may have outlines for the best way to set your high and low pressure alarms. If not, a good general rule is to set the high alarm 20-25 percent above your Max PSI and to set the low alarm 10% below the PSI that you run.

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