Trailer Tire Maintenance: Pressure, Heat, and Wear

Why trailer tires fail

Trailer tires spend most of their lives parked, carrying a heavy load, and then run at highway speeds without the benefit of steering, braking, or suspension travel. That combination stresses sidewalls and bead areas far more than a passenger car tire. The Federal Motor Vehicle Safety Standards define ST (special trailer) tires as a distinct category, and they are built with heavier-duty materials to handle that duty. According to 49 CFR 571.119, ST tires are included in the specialty tire category, along with FI (farm implement) tires and tires with rim diameter codes of 12 or below, and they must meet the endurance, strength, and high-speed performance requirements of that standard.

The most common failure modes are heat-related separation, underinflation damage, and age-related cracking. All of these are preventable with regular inspection. The federal standards define the defects you are looking for: tread separation, sidewall separation, ply separation, cord separation, innerliner separation, chunking (pieces breaking away), cracking that extends to the cord, and open splices. When you inspect a trailer tire, you are hunting for these specific conditions.

Set pressure cold, check often

Use the pressure recommended by the trailer manufacturer on the placard or in the owner's manual, not the maximum pressure printed on the sidewall. The maximum permissible inflation pressure is a limit, not a target. Federal standards also require that the sum of the tire load ratings on an axle equal or exceed the axle's gross axle weight rating (GAWR), and that the load rating is based on the inflation pressure you run. If you drop the pressure, you drop the load capacity. For more on reading load ratings, see the tire load index rating guide.

Check pressure when tires are cold, meaning the trailer has not been driven for at least three hours. Underinflation is the leading cause of heat buildup. An underinflated tire flexes more, generates more heat, and can quickly exceed its temperature limits, which accelerates separation. If you carry heavy loads or tow long distances, consider increasing pressure within the range shown on the placard, but never above the sidewall maximum. The tire pressure basics guide covers this in more detail.

Heat: the silent killer

Heat is what kills trailer tires, and the hub is a good proxy for the tire's internal temperature. After the first 10 to 20 minutes of towing at highway speed, stop and place the back of your hand on each hub. The hub should feel warm, but not hot enough to be painful. If one hub is noticeably hotter than the others, something is wrong: a dragging brake, a failing bearing, or a tire that is underinflated or overloaded. The same check matters for the tires themselves. A tire that is hot to the touch after a short run is a warning sign.

The federal standards set temperature limits for tires under test, but those limits apply in controlled laboratory conditions. The practical rule for a trailer owner is simpler: any tire that is too hot to hold your hand on for more than a second or so is running too hot. Let it cool, check the pressure, and inspect for bulges or separations. If the heat comes back, replace the tire before the next trip. The tire temperature check hand guide has more detail.

Inspect before every tow

A quick visual inspection should take less than five minutes. Walk around the trailer and look at each tire, checking for cuts, bulges, uneven wear, and foreign objects. Then run your hand over the tread and sidewall to feel for bulges or exposed cords. The federal standards define the defects you are looking for: tread separation, sidewall separation, ply separation, cord separation, and cracking. Any of these means the tire needs to be replaced immediately, not patched.

Check tread depth as well. The federal minimum for passenger tires is 2/32 inch, but for trailers you want more margin. ST tires often start with deeper tread, and you should replace them when they reach the wear bars. For more on reading the indicators, see the tire treadwear indicators guide. If you see uneven wear, that points to an inflation or alignment problem. The tire tread wear causes guide explains how to read the patterns.

Pay special attention to the area between the tread and the sidewall. This is where trailer tires often start to separate, and a small bulge here can grow quickly at highway speed. Also check the bead area where the tire meets the rim, looking for cracks or bulges there.

Age matters more than tread on a trailer

Trailer tires age out before they wear out. The rubber compounds lose flexibility over time, and the sidewalls develop cracks that can lead to sudden failure. The best way to tell how old a tire is, besides the purchase date, is the DOT date code molded into the sidewall. The last four digits of the DOT code indicate the week and year of manufacture. For example, a code ending in 2419 means the tire was built in the 24th week of 2019. The tire DOT date code guide explains how to read it.

Most tire manufacturers, including those that make ST tires, recommend replacing tires that are six to ten years old, regardless of tread depth. For a trailer that sits in the sun, six years is a reasonable cutoff. Ozone and UV light attack the rubber even when the trailer is parked, so a tire can be dangerously aged even if it looks fine. Look for fine cracks in the sidewall and between the tread blocks. If you see them, replace the tire.

Load and speed: know your limits

ST tires have a maximum speed rating, usually 65 mph (105 km/h). If you tow faster than that, the tire may overheat even at correct pressure and load. The tire speed rating guide explains how to read the speed symbol. If you need to tow at higher speeds, consider using LT (light truck) tires instead, which are designed for higher speed service. The ST vs LT trailer tires guide compares the two.

Also check the load rating against the actual weight on each axle. The federal standards require that the sum of the tire load ratings on an axle equal or exceed the axle's GAWR. Weigh your trailer loaded for a trip to know the real axle weights. An overloaded tire is a blowout waiting to happen, no matter how new it is. For more on how to pick the right rating, see the tire load index for trailer guide.

What to pick for your trailer

If your trailer tires are more than six years old, show cracks, or have any separation, replace them before your next tow. Choose ST tires if you tow within the speed limits and want the extra sidewall strength and load capacity they offer. Choose LT tires if you need a higher speed rating or if you carry loads that exceed the ST tire's capacity. For a complete list of options, see the trailer tire buying guide with 15 picks by spec.

What to pick for your use

Questions

How often should I check trailer tire pressure?

Check cold inflation pressure every time you tow, and at least once a month when the trailer is parked. Temperature changes cause pressure to drop, and a slow leak can take a tire from safe to dangerous in a few weeks.

Can I use passenger car tires on a trailer?

You can, but federal standards require that you reduce the load rating by dividing by 1.10 when a passenger car tire is installed on a trailer. That means less load capacity than the sidewall suggests, and passenger tires are not built to handle trailer side loads. ST or LT tires are the safer choice.

How hot should trailer hubs get?

After a short drive, a hub should feel warm but not painful to touch. If you cannot hold your hand on it, the hub or tire is running too hot. Compare all hubs on the same axle; a significantly hotter one points to a dragging brake or bad bearing.

How do I know how old my trailer tires are?

Look for the DOT code on the sidewall. The last four digits indicate the week and year of manufacture. For example, 2419 means the 24th week of 2019. If the code is missing or you cannot read it, be suspicious and replace the tire.

Is it okay to patch a trailer tire?

A small puncture in the tread can sometimes be repaired with a plug-patch combi repair, but any sidewall damage, separation, or aging cracks require replacement. When in doubt, replace the tire. A blowout on a trailer can cause significant damage to the fender and trailer body.

What is the maximum speed for ST tires?

Most ST tires are rated for a maximum speed of 65 mph (105 km/h). Exceeding that speed causes heat buildup that can lead to failure. If you need to tow faster, switch to LT tires with a higher speed rating.