How To Choose Trailer Tire Size

How to choose trailer tire size 1

If you have been towing for a long time you will know how important choosing the right kind of tire is for trailers. Putting on a wrong kind or the wrong size of tire on your trailer can cause faster wear, uneven load distribution and cause your trailer to sway. This is dangerous to both you and the people around you. Buying tires online or looking at catalogs can confuse you on the size. I have put up a complete guide to choose the correct size of trailer tires.

1. Choose The Right Kind Of Trailer Tire

Many people make the mistake of thinking that trailer tires and truck tires are the same. They are not, trailer tires are specially made for trailers. They are stiffer and have a greater load capacity.

Check for the serial number on the tire. 

It will look something like this- ST215/65R15 95H

While looking for trailer tires, see the series number embedded on the tire surface. Trailer tires usually have LT or ST written in the serial number. LT stands for Light truck while ST stands for Special trailers. If a tire has P in the start it means the tire is for ‘passenger cars’. An Ideal trailer tire should be ST marked, they are strong enough to hold heavy weight, and flexible enough to move around.

2. Load Capacity

The number ‘95’ in the sample serial number above is called the load index. You can determine the amount of load the tire can carry and work in optimal condition. Higher number indicates higher capacity to carry weight.

Load Index






Load LBS






Determine the weight of your trailer from a local garage. Calculate what could be the maximum weight your trailer will acciqure when fully loaded, once you have got the number divide it by 4 to determine what load index your tire should be. 

If you are planning to replace one of the tires in your trailer see what is the load index for the other tires of your trailer and match it with the new one. Never get a replacement tire with a lower load index than the original one. 

3. Choose The Correct Rim Diameter

In the sample serial number, ST215/65R15 95H, the number ‘15’ is considered the rim diameter. While replacing old tires with new ones, check the wheel or rim size. Match this rim size with your tire rim diameter to get a perfect match. 

4. Radial Or Bias Ply Construction?

The letter ‘R’ before the number ‘15’ in serial number gives the internal construction of tires. R stands for Radial tires and B stands for Bias ply tires. 

Ideally trailer tires should be Radial construction, however some trailers originally have Bias tires. Match the tire type with the original tire or with the rest of the tire for an even weight distribution. Since, Radius and Bias tires wear differently, and touch the ground in a different manner, it is recommended not to mismatch the types of tire on your trailer.

5. Take A Look At The Speed Rating.

The number ‘H’ in the serial number indicates the speed rating.

Speed Rating










Miles / Hour










Match the speed rating with your original tire. Speed rating unlike Load rating is not high for trailer tires. Trailers not usually acquire a high speed. Just make sure the speed rating on the new tire is same as the original one and it can withstand the maximum speed your trailer can aquire. 

6. Temperature Ratings

If you are operating cargo, RV trailers, make sure to look at the temperature rating. A, B and C, from most heat resistant to least . Heavy duty tires carrying heavy weight usually get heated up much faster, it is recommended to get either A or best B temperature rated tires. 

7. Treadwear Rating

Many tires have ‘Treadwear’ rating embedded at the side wall. The number is usually around 100. Industry standard is 100, so anything more than 100 or very close to 100 is considered best for trailer tires. 

Ideally you should replace tires every 3 to 4 years, or at least get it professionally checked for wear.