Trailer tires are often much smaller than a truck's, yet they're engineered to safely carry heavy loads. The real secret isn't tire size... it's matching the tire to the trailer.
Rated trailer tires rarely match the size of the tires on the towing vehicle. A tow vehicle must accelerate, steer, brake, and provide a comfortable ride. A trailer simply follows behind, carrying its load while resisting sway and enduring tremendous side forces during turns.
Because many trailer tires are considerably smaller in diameter, they rotate far more times over the same distance. A typical light-duty trailer tire can make nearly 50% more revolutions than a 31-inch O.D. pickup tire at highway speeds. Those extra rotations mean the wheel bearings, grease, seals, and tire casing all work harder, making heat a big enemy.
Trailer tires marked ST, for Special Trailer, are engineered specifically to carry vertical loads and maintain stability. Their stiffer sidewalls reduce sway and withstand the sideways scrubbing that occurs because trailer axles do not steer. Tire diameter alone says very little about how much weight a tire can safely carry. Load range, construction, and inflation pressure determine its true carrying capacity.
While larger trailer tires generally rotate more slowly, roll over bumps more smoothly, and often run cooler on long highway trips, smaller trailer tires perform exceptionally well when they're the correct size and load rating for the trailer. Proper cold inflation pressure, staying within the tire's speed rating, maintaining wheel bearings, and avoiding overloads contribute far more to safe towing than simply installing larger tires.
Another overlooked factor is trailer attitude. A trailer that rides level distributes weight more evenly across its suspension and tires, improves stability, and can reduce sway. Adjusting the hitch height so the trailer travels as close to level as possible is one of the simplest improvements a trailer owner can make.
For a deeper look at why trailer tires require higher air pressure, what the ST designation means, how speed ratings affect heat buildup, and why trailer tires fail, watch our companion HIPS episode: https://youtu.be/wW-YfJBilzE
Sometimes the smallest tires on the highway are doing the hardest work.
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This video explains how to choose the correct tires for a trailer, emphasizing that while tire size affects performance and wear, the tire's rating and proper maintenance are the most critical factors for safety and efficiency on the highway.
You have a trailer. You want to put the right tires on it.
But does size matter? That's the age-old question. Let's break it down and find out.
We've all seen it. We're going down the highway. Here's a truck towing a trailer. Truck,
big tires. Trailer, little tires. Does it matter? Do they need to be the same size?
Well, there's a couple factors you need to know. What's more important than the size is whether or
the trailer tire is rated for its use. Is it truly a trailer tire? It's not an agricultural tire.
It's not something for a wheelbarrow or lawn equipment. It's truly rated to be on a trailer
and operate it at highway speeds. That's designated with an ST mark on the side
of the trailer tire, meaning special trailer. The second thing is what you're asking that
tire to do, no matter what the size. Is that tire rated for its load? So number one,
will it carry the load correctly? Number two, is the inflation pressure correct?
If you've got those two things and it's truly an ST tire, then you're on the right track.
The third thing to just keep in mind though is the diameter of the tires between the tow vehicle
and the towed trailer. They have different responsibilities. But also,
if there's a big size difference, it's kind of like the gait of people. How long you walk. Now,
I remember when I had my little sons, they struggled to keep up with me. Why? My step
was longer than theirs. And so every one of my steps, it was like two or three of their steps.
And the same way with a tire. One rotation on a larger tire goes a lot further than one rotation
on a smaller tire. Therefore, the tire, the smaller tire has to take extra steps,
rotations to catch up. This translates into higher rotation speed, higher heat buildup
in the spindle and the bearings. And if the tire is not properly inflated,
also heat buildup in the carcass of the tire. So you need to keep that in mind that you keep
it at the right speed rated for the tire. The tire is properly inflated and the grease
in the bearings is all fresh and ready to go to work. As for me, my opinion is to use larger
diameter trailer tires just to reduce the spindle rotation or the bearing rotation around the
spindle. But also they ride a bit smoother. They'll go over obstacles, less rolling resistance,
that sort of thing. So the larger tire is my vote. But as long as it's a correctly rated tire,
ST, doing what it should do with smaller tires, fine. Now, the other thing that can be overlooked
is the trailer attitude. No, not whether it's thinking you look nice today or insulting you.
I'm talking about whether the trailer bed is level or it's tilted up or down. And that is
all adjusted at the trailer hitch level on the tow vehicle. So you want that so that the level
is this way. If the tow vehicle's here, it's not diving, nor is it doing this, being pulled upwards.
That affects the sway of the trailer, the stability and where the load is being distributed on the
tires. So get the attitude correctly. The last and most important thing you need to know
is that trailer tires are made entirely differently than light truck
and passenger tires. Check out this video and I'll tell you all about it.
