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Trailer Tire Tips

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During the course of last year, I had a number of racers stop by my trailer to change out failed trailer tires. Here are a few things to do to reduce your highway shoulder time on your way to the track.


If your "ST" metric trailer tires (i.e. ST225/70R15) do not have a Speed Symbol or Speed Rating, then the following inflation pressure and load adjustments apply (per The Tire and Rim Association):


Operating up to 65 mph - No inflation pressure change and no load change

Between 66 mph and 75 mph - Add 10 psi cold inflation pressure and no load change

Between 76 mph and 85 mph - Add 10 psi cold inflation pressure and reduce tire load 10%

Above 85 mph - you probably should have left earlier as these speeds are not recommended for towing


If you read the fine print on the tire sidewall, you will notice that a maximum load is stated along with a corresponding inflation pressure. That inflation pressure is not the maximum that can be used for the tire. It's the inflation pressure for the stated maximum load. So, as you're tooling down the highway in the Buckeye state, you should be starting off with 10 psi more in your trailer tires. As an example if you have Load Range D tires without a speed rating, the inflation pressure for the max load is 65 psi. You should be starting out at 75 psi if you are planning to drive above 65 mph at max load. If you're driving at anytime between 76 and 85 mph, then you need to also have 10% less load.


And before you start adding air, be sure that your rims can handle the increased inflation pressure. Some rim manufacturers (usually the better quality ones) stamp a max load and/or max inflation somewhere on the rim.


If you're not running the max load, then you should be adjusting your inflation pressures that correspond with the load you are carrying. Don't know your trailer tire loads, well you should. Running at an inflation pressure higher than what is necessary will make the trailer tires too stiff and may bounce all over the road behind you and decrease your braking distance. I think you know what happens when your tire contact patch gets smaller. Your trailer tire manufacturer should have tables showing loads and inflation pressures.


It's also a good idea to have an infra-red temp gun in your tow vehicle. I'll shoot the trailer hubs, rims and tires when I hit a rest area or fuel stop making sure that temps are consistent. This will let you know if you have a problem coming either tire, brake or bearing related.


If you want to know what's happening in real time, then install a TPMS system for your trailer tires to get pressure and temp data on the fly.


Thanks for reading and see you at the track!


Rudy's Racing Services


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Sterling Doc

Good info, thanks - didn't know about pressure adjustments for speed.

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