Brakes and tires
What load does each trailer tire carry?
Trailer tires are the part of an RV most likely to end a trip, and they almost never fail from wear. They fail from heat, and the heat comes from being underinflated or overloaded, usually both, at a corner nobody is watching.
The load they carry is not the trailer weight. The tongue or pin weight goes to the tow vehicle, so the axle load is the loaded trailer weight minus that figure. Then add reserve, because trailers do not load evenly side to side and a tandem on a crowned road or in a turn puts more than its share on one corner.
Work out the load per tire
1,540 lb per tire. Look for load index 101 or higher to keep a real reserve.
| Figure | Value |
|---|---|
| Tongue weight to the tow vehicle | 840 lb |
| Load on the trailer axles | 6,160 lb |
| Load per tire | 1,540 lb |
| With 15 percent reserve | 1,771 lb |
| Minimum load index | 101 (1,819 lb per tire) |
Shown with the example figures above. Change any field to run your own numbers.
The working
Published standardaxle load = loaded trailer weight - tongue or pin weight per tire = axle load / (axles x tires per axle) with 15% reserve = per tire x 1.15 then pick a load index at or above that figure
The load index table and the load range to pressure mapping are published standards. The 15 percent reserve is convention. A published, traceable figure: a standards body, a federal regulation or a manufacturer specification states it.
Tires and monitoring for this load
Ranked by published maximum load per tire against the figure you calculated. A monitor is the only thing on the rig that warns you before a tire comes apart rather than after.
GUTA GT30 Trailer Tire Pressure Monitoring System, 10 sensors
$269.99Ten sensors, enough for a dually tow vehicle and a triple axle trailer together, which is the only configuration where the cheaper kits genuinely run out.
Best for: A dually and a large fifth wheel monitored as one rig.
Check price on Amazon
Goodyear Endurance Trailer Tire, ST205/75R15 107N
$182.35 Published ratingsThe 205/75R15 size, load index 107, which is 2,149 lb per tire.
Best for: A lighter tandem axle trailer on 15 inch wheels.
Check price on Amazon
Carlisle Radial Trail HD Trailer Tire, ST235/85R16 Load Range E
$170.99 Published ratingsA 16 inch load range E tire, which is what heavy fifth wheels and equipment trailers run.
Best for: A fifth wheel or a heavy equipment trailer on 16 inch wheels.
Check price on Amazon
Maxxis M8008 ST Radial Trailer Tire, ST205/75R15
$163.96The 205/75R15 Maxxis, for a lighter trailer.
Best for: A smaller trailer covering long distances.
Check price on Amazon
Maxxis M8008 ST Radial Trailer Tire, ST225/75R15
$149.12Maxxis M8008 has a long standing reputation among people who tow a great deal, and it sits between the Carlisle and the Goodyear on price.
Best for: High mileage towing where tire reputation is worth paying for.
Check price on Amazon Carlisle Radial Trail HD Trailer Tire, ST225/75R15 113M
$123.06 Published ratingsCarlisle has made trailer tires for decades and the Radial Trail HD is the value pick against the Endurance. Load index 113 is 2,535 lb per tire at a maximum 65 psi.
Best for: Replacing all four tires at once without the Goodyear price.
Check price on AmazonEvery rating shown is the manufacturer's own published figure. The rating on the part you receive is what governs, and your own door jamb sticker governs everything above it.
Load range and maximum cold inflation
Load range tells you the tire construction and, critically, the maximum cold inflation pressure. Here is the rule that catches car owners out: an ST tire carries its rated load only at that pressure. There is no door jamb placard telling you to run it softer, because this is not a car tire.
A Load Range E ST tire runs at 80 psi cold and a Load Range D at 65 psi. Most car tire gauges stop at 60 psi and cannot read either one.
Published standard A published, traceable figure: a standards body, a federal regulation or a manufacturer specification states it.
| Load range | Ply rating | Maximum cold inflation |
|---|---|---|
| Load Range B | 4 | 35 psi |
| Load Range C | 6 | 50 psi |
| Load Range D | 8 | 65 psi |
| Load Range E | 10 | 80 psi |
| Load Range F | 12 | 95 psi |
| Load Range G | 14 | 110 psi |
"Cold" means before the trailer has moved that day, not after a fuel stop. Pressure rises as a tire heats and you do not bleed it back down: that hot pressure is the tire doing its job.
The three things that kill trailer tires
Underinflation. The most common cause by a wide margin. A soft sidewall flexes, flexing generates heat, and heat separates the tread from the casing. Set every tire cold, before you move, every trip.
Speed. Most ST tires are built to an industry speed rating of 65 mph unless the sidewall says otherwise, and some newer ones are rated to 75 or 81. Exceeding it is a documented cause of tread separation, and it is a published limit rather than a rule of thumb.
Age. Trailers sit, so a trailer tire ages out long before it wears out. Replace at 5 to 6 years regardless of tread depth. Read the DOT date code on the sidewall: the last four digits are the week and year, so 2822 is the 28th week of 2022.
ST tires against LT tires
Some people fit LT truck tires to a trailer, and it is a real trade rather than a free upgrade. ST tires have stiffer sidewalls specifically to resist the lateral loads a trailer axle sees, because a trailer axle does not steer and the tire is scrubbed sideways in every turn.
An LT tire of the same nominal size usually carries less load at the same pressure and has a softer sidewall. If you go that route, the load capacity at your actual inflation pressure has to be checked against a published table rather than assumed from the size.
Frequently asked questions
Do trailer tires carry the tongue weight?
No, the tow vehicle does. That is why the axle load is the loaded trailer weight minus the tongue or pin weight, and using the full trailer weight overstates the tire load. Overstating it sends you to a heavier and more expensive tire than you need, which is the less dangerous error but still the wrong answer.
What pressure should I run in trailer tires?
The maximum cold inflation pressure printed on the sidewall, unless the trailer maker publishes something different. An ST tire carries its rated load only at that pressure, completely unlike a passenger car where the door placard sets a pressure below the sidewall maximum. Cold means before the trailer has moved that day.
How fast can I tow on ST trailer tires?
Most ST tires are built to an industry speed rating of 65 mph unless the sidewall states otherwise, and some newer ST tires are rated to 75 or 81 mph. This is a published limit rather than a convention, and exceeding it is a documented cause of tread separation. The sidewall and the maker specification are the authority for your specific tires.
When should I replace trailer tires?
At 5 to 6 years from the date code, regardless of tread depth. Trailers sit for months at a time, so the rubber ages out long before the tread wears, and ultraviolet exposure while parked accelerates it. The date code is the last four digits of the DOT number on the sidewall, giving the week and year of manufacture.
How much reserve should trailer tires have?
Roughly 15 to 20 percent over the calculated load per tire is the conventional target. Trailers load unevenly side to side, and a tandem axle in a turn or on a crowned road puts more than its share on one corner. That reserve is towing convention rather than a published standard, but the reason for it is real and measurable.
Can I fit LT truck tires instead of ST tires?
You can, and it is a genuine trade rather than an upgrade. ST tires have stiffer sidewalls specifically to resist the lateral scrubbing a non-steering trailer axle produces in every turn. An LT tire of the same size usually carries less load at the same pressure. If you do it, check the load capacity at your actual inflation pressure against a published table.
Free download
Get the complete tow rig setups emailed to you
Both ladders, conventional travel trailer and fifth wheel, at beginner, intermediate and expert budgets, every item priced and linked with a running total, plus a printable pre-trip weighing worksheet you can fill in at the scale.
One email with the setups. No sequence, no sharing your address, unsubscribe any time.
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.