Trailer tires
How do you choose the right trailer tires?
A trailer tire has three things to get right, and none of them is simply "the same size as what came off." The load index has to cover your actual per-tire load with a real reserve, because a tandem axle in a turn or on a crowned road routinely puts more than an even share of weight on one corner tire. The tire's age matters as much as its tread depth, because rubber degrades from ultraviolet exposure and ozone whether or not the trailer is moving, and a trailer that sits for months at a time ages out well before the tread wears down. And the speed rating is a real published limit, not a suggestion, because exceeding it is a documented cause of tread separation at highway speed.
Work the actual load first on the trailer tire load calculator, using the loaded trailer weight and the tongue or pin weight the tow vehicle carries, rather than assuming the trailer's brochure dry weight tells you what the axles are actually seeing.
Step by step: choosing the right tire
- Find the load on the trailer axles, not the whole trailer. The tow vehicle carries the tongue or pin weight, so the axles only carry the loaded trailer weight minus that figure, divided across every tire on the ground. Using the full trailer weight overstates what each tire actually sees.
- Add roughly a 15 percent reserve. Trailers load unevenly side to side, and a tandem axle in a turn or on a crowned road puts more than its even share on one corner. A reserve over the bare calculated load is the conventional target for exactly that reason.
- Find the smallest load index that covers it. Published load index tables map an index number directly to a maximum load in pounds per tire. Round up to the next published index if your figure falls between two.
- Check the load range matches your inflation setup. A tire's load rating is only valid at its load range's maximum cold pressure. Confirm you can actually reach and maintain that pressure before buying a higher load range than you can properly inflate.
- Confirm the tire size matches your wheel. The size stamped on the old tire and the wheel diameter both have to match the new tire exactly. A load index upgrade in the wrong size does not fit.
- Check the speed rating against how you actually tow. Most ST tires carry an industry speed rating of 65 mph unless the sidewall says otherwise. If you regularly tow faster than that, look specifically for a tire rated to 75 or 81 mph rather than assuming a premium tire automatically covers it.
- Check the DOT date code before buying. The last four digits of the DOT code on the sidewall give the week and year of manufacture. New-looking tire stock that has actually sat in a warehouse for years has already used up a meaningful share of its 5 to 6 year service life before it ever touches the road.
Load index to pounds per tire
This is a published table from the tire industry, the same one printed in reference form on every sidewall's load index chart. It is not an estimate.
Load index 117, common on ST225/75R15 tires, carries 2,833 lb per tire, more than double what index 90 carries.
Published standard A published, traceable figure: a standards body, a federal regulation or a manufacturer specification states it.
| Load index | Maximum load per tire |
|---|---|
| 90 | 1,323 lb |
| 95 | 1,521 lb |
| 100 | 1,764 lb |
| 105 | 2,039 lb |
| 110 | 2,337 lb |
| 115 | 2,679 lb |
| 117 | 2,833 lb |
| 126 | 3,748 lb |
Published tire industry load index table. Round up to the next published index rather than down when your calculated per-tire load falls between two figures.
Two ST tires that cover most travel trailers
The Goodyear Endurance ST225/75R15 is the tire most commonly recommended by owners replacing whatever a trailer shipped on, at load index 117, which is 2,833 lb per tire. The Carlisle Radial Trail HD in the same size covers a lower budget at load index 113, 2,535 lb per tire, for a full set replaced at once without the premium brand price. Both are radial ST tires in the same load range; the choice between them is largely price and brand history rather than a meaningful capacity difference at the same size.
ST tires exist for a reason
ST, Special Trailer, tires have stiffer sidewalls than a passenger or light truck tire of the same nominal size, specifically to resist the lateral loads a trailer axle sees in a turn that a driven vehicle axle does not. Some owners fit LT truck tires instead, and it is a real trade rather than a free upgrade: an LT tire of the same size usually carries less load at the same pressure and has a softer sidewall built for a different job. See ST tires against LT tires on a trailer for the full comparison before making that swap, and load range D against load range E if you are deciding between the two most common ratings on a mid-size travel trailer.
Frequently asked questions
What load index do I need for my trailer tires?
Find the load each tire actually carries, the loaded trailer weight minus the tongue or pin weight, divided across every tire on the axles, then add roughly a 15 percent reserve and find the smallest published load index that covers that number. A trailer weighing 7,000 lb on two axles works out to a few hundred pounds per tire less than a naive total-weight-divided-by-four calculation would suggest, once tongue weight is correctly subtracted.
Should I use ST tires or LT tires on my trailer?
ST tires are built with stiffer sidewalls specifically for the lateral loads a trailer axle sees, which a driven vehicle axle generally does not experience the same way. An LT tire of the same nominal size usually carries less rated load at the same pressure. Either can work, but the actual load capacity at your real inflation pressure has to be checked rather than assumed if you go with LT.
How do I read the DOT date code on a trailer tire?
Look for the DOT code on the sidewall; the last four digits give the week and year of manufacture, two digits each. A tire stamped with a code from several years before you bought it, even brand new, has already used a real share of its 5 to 6 year service life sitting in inventory before it ever touched a road.
Do I need to replace trailer tires that still have plenty of tread?
Yes, once they reach 5 to 6 years from the date code. Trailer tires sit unused for long stretches, and the rubber ages from ultraviolet exposure and ozone regardless of mileage or tread depth. Waiting for visible wear misses the actual failure mode on a tire that mostly sits, which is aged rubber cracking or separating rather than a worn-out tread.
What speed rating do ST tires have?
Most ST tires carry an industry speed rating of 65 mph unless the sidewall specifically states a higher figure, and some newer tires are rated to 75 or 81 mph. This is a published limit rather than a rule of thumb, and towing faster than a tire's rating is a documented cause of tread separation, so check your own tire's sidewall rather than assuming a premium price implies a higher rating.
What is the difference between load range D and load range E?
Load range D tires max out at 65 psi cold and load range E at 80 psi cold, with E carrying more load per tire at that higher pressure. Moving up a load range only helps if you can actually reach and maintain the higher pressure with a gauge and inflator rated for it, and it does not substitute for correctly sizing the load index itself.
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Researched, not professional advice. This page is compiled from published standards, manufacturer towing guides and product specifications, and owner-review consensus, not hands-on testing. Figures described as a rule of thumb are towing convention rather than published standards, and they are labelled that way wherever they appear. Nothing here overrides your own ratings. Work your payload sum before your tow rating, because payload is the limit that actually binds on most half ton trucks and nearly every SUV. Load a conventional trailer to 10 to 15 percent tongue weight and a fifth wheel to 15 to 25 percent pin weight, and never lighter: a tail heavy trailer is what starts sway. Weigh the rig loaded rather than trusting a brochure dry weight. A weight distribution hitch and a set of air bags both restore ride height and control, and neither one raises a single rating. Trailer brakes are required by state law above a threshold that varies by state, and a breakaway battery that has quietly gone flat is the normal condition of most trailers on the road.