Many people wonder why you can’t use these two tires interchangeably. They’re both tires, after all – what harm could there be?

Quite a bit of harm. The casual observer might mistake them at first glance, but trailer tires and passenger tires are very different. Once you know what you’re looking for, they’re easy to differentiate. 

First, most passenger tires will bear a code of P for Passenger, or LT for Light Truck in front of the other numbers on the tire. Trailer tires have a code of ST. 

Second, trailer tires have thicker sidewalls, and narrower tread width. When side by side with a car tire, it’s easy to tell them apart.

Different designs for different needs

When outfitting your trailer for tires, you may see that they share a common size with your passenger vehicle. The temptation may even arise to use the spare from your vehicle on your trailer.

Don’t. Trailer tires and passenger car tires have different structures to respond to different stresses. Using a trailer tire on your car, or a car tire on your trailer, could lead to disastrous consequences.

Passenger vehicles interact with the road through their tires. The tires transfer the power back and forth through acceleration and braking. They morph in response to turns, to continue gripping as best they can. They have longer tread life, and can usually see more use than a trailer tire.

Load bearing capacity and towing are the top priority in trailer tire construction. They have stiffer sidewalls, with less priority on the tread life. There are two types of trailer tire construction, both designed for the stresses caused by towing. Not to transfer power to the road, and not to steer.

 

Trailer Tires

Trailer (ST) tires come in either bias or radial ply, each having its own advantage. In general, though – they’re designed for towing.

The material that makes up the sidewalls of trailer tires is thicker than that of passenger tires. Trailer tires don’t need to handle sharp turns, so their tread focuses mostly in the middle of the tire to help with heavy loads.

Radial trailer tires share the same basic design as car tires and tend to have a longer tread life – a definite buy for long hauling. Bias ply trailer tires have a shorter tread life, but are built with a different construction method intended for heavier loads. For more info, check out the best trailer tires.

 

Vehicle Tires

Your average passenger car (P) or light truck (LT) tire is a radial design. These tires are designed for different purposes than trailer tires. Depending on the classification that could be for load bearing capacity, long distance driving, or a combination of both.

No matter which design though, the base construction is similar.

There are three major factors in mind during their construction:

  • Acceleration: When speeding up, a car tire must both deliver traction and endure the stresses caused by the acceleration.
  • Braking: When braking, the car tire must endure the stresses incurred and stop the vehicle.
  • Turning: When a vehicle tire makes a turn, the tread and overall construction of the tire deforms to provide better grip.

These three factors are of the utmost importance when designing a car tire. The materials and construction respond to the vehicle’s needs. They’re even designed to respond to weather conditions based on these needs.

These tires can have tread life capacities upwards of 80,000 miles with proper maintenance. It can be tempting to toss them on a trailer.

 

Can I use regular car tires on my trailer?

While it may be tempting, this is a dangerous practice. Unless the owner’s manual for your trailer states this is an option, you should avoid doing this.

 

Different designs

 

Trailer tires have a thicker side-wall design that has a few different purposes. First, the thicker sidewall allows for heavier load bearing capacity. Second, the thicker sidewall helps to avoid trailers swaying as they travel down the road and through turns at high speeds.

While LT tires may have thicker sidewalls and seem to make sense as an option, they still are not designed to respond to trailer specific issues. The load bearing capacity listed on an LT tire is designed based on the frame of a truck – not the frame of a trailer.

Trailer frames can vary greatly from model to model. ST tires are designed with this in mind when they list their load bearing capacity.

 

The dangers

When a car or truck tire is used on a trailer, it causes stress that the tire wasn’t designed to handle. The tread of the tire begins wearing differently than it was designed. The tire’s actual weight capacity is different from the load rating shown because of the different frame designs.

A car tire’s thinner side walls won’t be able to reduce the trailer’s swaying as well either.

A blowout can happen much more easily under these conditions, especially on the highway. Trailers in general are not intended for use above 65 mph. Going at these speeds with tires not intended for the trailer is a ludicrous proposition.

The tires may not blow-out during this trip – or during the next one. But the stresses they are enduring will not produce the typical signs of wear. The tread-life might look healthy, but there could be unseen damage to the sidewall.

 

Can I use my trailer tires on my car?

If you didn’t get a spare with your car when you bought it, you may be tempted to get a rim and toss a trailer tire on it. If you’re not on it long, what’s the worst that could happen?

Well, a car accident that totals your car is bad.

Using a trailer tire on a vehicle focuses stress on areas where trailer tires are weakest. Vehicle tires keep traction and grip in mind during their construction, while trailer tires do not. This increases the risk significantly, especially at highway speeds or in poor weather.

We don’t recommend using a trailer tire on your vehicle.

Conclusion

Trailer tires and regular car tires might seem the same based on casual observation, but they’re very different. Using them interchangeably is a recipe for disaster, even if the intended use is short.

Car tires transfer power from the vehicle to the roadway and respond to sharp turns while maintaining traction and grip. Trailer tires carry heavy loads and have strengthened sidewalls to help with swaying during operation.

If ever in doubt, consult the owner’s manual for the trailer or vehicle in question.