Yes, every trailer should carry a spare tire. Roadside assistance trucks rarely stock trailer sizes, so a flat can strand you for hours. A correct spare matches your bolt pattern, wheel diameter, and load range, mounts on a dedicated bracket, stays inflated to the sidewall pressure, and gets replaced every three to five years.
Why trailers need a spare more than cars do
Roadside services stock common car sizes, and most cars carry a compact spare. Trailers get neither. Special Trailer (ST) sizes such as ST205/75R15 are not standard inventory on a service truck, and many shops keep only a handful of trailer sizes. Go down on a rural highway and the nearest matching tire may be a long tow away.
Tandem axles do not remove the risk. When one tire blows, the remaining tire on that side carries load it was never rated for, and heat builds fast in an overloaded trailer tire. A second failure on the same side is a real possibility if you keep driving. The spare lets you stop, swap, and continue.
The three things your spare must match
A spare only works if it bolts on and carries the weight. That comes down to three checks: bolt pattern, wheel diameter, and load range. The load range letter (B, C, D, E) is molded on the sidewall with the maximum load and required pressure, and the spare's letter must be equal to or higher than your current tires, never lower. If you are unsure how to read your bolt pattern, our bolt pattern measuring guide walks through the measurement.
| What to match | Why it matters | How to check |
|---|---|---|
| Bolt pattern | The wrong pattern will not bolt onto your hub at all | Count the lugs and measure the circle diameter, or read the spec stamped on your current wheel |
| Wheel diameter | A different diameter changes clearance and will not fit your tire size | Read the size on the current tire sidewall, e.g. the 15 in ST205/75R15 |
| Load range | A lower rating can overheat and fail under your trailer's weight | Find the load range letter on the sidewall; the spare must be the same letter or higher |
| Construction (R or D) | Radial and bias tires flex differently and should not be mixed on an axle | R in the size means radial, D means bias-ply |
The simplest route is a pre-mounted spare: a tire already seated on a wheel in your bolt pattern. Our trailer wheels collection and trailer tires can be filtered by all three specs.
Radial or bias: keep construction consistent
The letter in the size tells you the construction: ST205/75R15 is a radial, ST205/75D15 is bias-ply. Radials generally run cooler on highway trips; bias tires have stiff sidewalls suited to short, heavy, off-pavement work. Whichever your trailer runs, the spare should match, because mixing radial and bias on the same axle is not recommended. The two constructions flex and track differently under load.
Where to mount the spare
Three placements are common. An upright bracket on the tongue or front wall is the most popular: the tire is visible, easy to reach, and easy to inspect. An under-frame carrier keeps the tire out of the cargo area but leaves it in road spray and is harder to work with at the roadside. Carrying the spare inside an enclosed trailer also works if it is strapped so it cannot shift. Whatever the location, use a locking attachment.
A spare ages even if it never rolls
Rubber degrades from time, UV, and ozone, not just miles. A spare that has hung on the tongue for years can look fine and still be brittle. A common industry guideline for trailer tires is replacement at three to five years regardless of tread. Check the DOT date code: the last four digits are the week and year of manufacture, so 3221 means week 32 of 2021. A vinyl cover slows UV damage, and a pressure check belongs in every pre-trip walkaround.
FAQ
Should the spare be kept fully inflated?
Yes. Inflate it to the maximum pressure shown on its sidewall, because ST tires only carry their full rated load at that pressure. Spares lose air slowly over months, so check it before every trip, not just when you need it.
Can I use the tire I just took off as my spare?
Only if it came off with life left in it. Check the DOT date code and the sidewalls: if the tire is past the three-to-five-year window or shows cracking, it was removed for a reason and should not be your backup plan.
My single-axle trailer blew a tire. Can I drive slowly to the next exit?
No. Stop as soon as you can do so safely. A single-axle trailer has no second tire to lean on; driving on a flat destroys the wheel, can damage the hub and fender, and can pull the trailer out of line.
Do I need a full wheel-and-tire assembly, or just a tire?
Carry a mounted assembly. A bare tire cannot be seated on a rim at the roadside, so an unmounted spare only helps once you find a shop, which is the problem the spare was supposed to solve.
When you are ready to add a spare, Cheap2Go Tires ships mounted trailer wheel and tire assemblies from Florida with free shipping.