The small trailer tire guide: 4.80-8, 4.80-12, and 5.70-8

The short answer: almost every small utility and boat trailer that comes through the shop wears one of three tires — 4.80-8, 4.80-12, or 5.70-8. All three are 8- or 12-inch trailer sizes rated Load Range B or C, and the number stamped on your old tire’s sidewall tells you exactly which one to order. Read the sidewall, match the size, done.

I get some version of “what size does my trailer take” at the counter constantly from May through Labor Day, usually from someone standing in the parking lot with a flat tire and a boat still hooked up. Here’s the whole conversation in order: the three sizes side by side, which trailer wears which, the load and pressure numbers that actually matter, and the tube question that comes up every single time.

The three sizes, side by side

Every small trailer tire we sell a lot of boils down to three sidewall stamps, and the gap between them is bigger than the numbers suggest.

Notice 4.80-8 and 5.70-8 share the same 8-inch wheel but land in different load ranges — a wider, lower-ply tire against a narrower, higher-ply one, and it matters more than it looks like it should. We stock the 4.80-8 and 4.80-12 as the Deestone D901, and the 5.70-8 as the Kenda K397 Xtra Grip — two different brands doing the same job, and worth knowing if you’re trying to match what’s already bolted to the trailer.

Which trailer runs which size

4.80-8 is the size I see most — the default on small single-axle utility trailers, landscape trailers, and a lot of bunk-style boat trailers under roughly 1,500 pounds gross. It’s the “everything trailer” size for the same reason 4.80-8 shows up on carts and dollies too: it’s common, it’s cheap, and manufacturers default to it. If you want the full decode of what “4.80-8” actually means on the sidewall, we cover that in the 4.80-8 size guide.

4.80-12 shows up a size class up — slightly bigger box trailers and heavier landscape trailers that came off the factory floor on a 12-inch wheel instead of an 8. The tire itself isn’t dramatically different from the 4.80-8 (same load range, same 6-ply carcass); it’s built for the bigger wheel and carries a bit more weight as a result. The 4.80-12 size guide walks through that one specifically.

5.70-8 is the one people mix up with 4.80-8, because it mounts on the same 8-inch wheel — but it’s a wider, lower-ply tire, not a bigger version of the same thing. It’s common as original equipment on wider boat and pontoon trailers, and it’s a legitimate upsize off a 4.80-8 when the fender has the clearance for it. I run the actual differences, and the clearance-measuring procedure for upsizing, in the 4.80-8 vs. 5.70-8 guide.

If your axle needs more than any of these three carries, the D901 also comes in 5.30-12 — a step up in load capacity on the same 12-inch wheel family, and its own fender-clearance math. That’s outside what this guide covers; the size page has current stock.

Load ranges and real PSI

Load range is the number that actually decides whether a tire is right for your trailer, not the tread. Range C (6-ply-rated) carries more weight than Range B (4-ply-rated) at a comparable size — it’s why the narrower 4.80-8 (Range C, 760 lbs) outcarries the wider 5.70-8 (Range B, 715 lbs). If “ply rating” and “load range” have always sounded like two different things to you, the ply rating and load range guide clears it up start to finish.

The PSI column is the one people get backwards. Unlike a car tire, a small trailer tire isn’t inflated for ride comfort — it’s inflated to its maximum rated cold pressure, full stop, whether the trailer is loaded or empty. Underinflated trailer tires flex more in the sidewall, build heat, and fail on the highway with almost no warning. Check them cold before you hook up, and fill to the number stamped on the sidewall — not somewhere comfortably under it.

Why these fail before they wear out

Most small trailer tires age out long before they wear out — a boat or utility trailer might put a hundred miles a year on its tires and still need new ones. Tire manufacturers generally recommend replacing trailer tires around five to six years old regardless of remaining tread, because the rubber itself deteriorates from sun, ozone, and temperature swings while the trailer sits loaded in a driveway or storage lot — which is most of the year for most of these trailers.

The DOT code on the sidewall tells you the age: the last four digits are the week and year of manufacture, so “2321” means the 23rd week of 2021. Sidewall cracking — especially deep cracks or cracks that circle most of the tire — is the visual warning sign, and it means replace now, not “keep an eye on it,” even on a tire with plenty of tread left. Tread depth matters too, but on a trailer, the calendar usually gets there first.

Tube, tubeless, and the valve stem

All three sizes ship tubeless-capable on a clean rim and a good bead. Small trailer wheels don’t always stay clean, though — road salt and standing water eat at the bead seat on steel wheels, and once that starts, a tube is the standard, cheap fix for the trailer that goes soft every time it sits for a month.

We carry combo tubes for both D901 sizes: a 4.00/4.80-8 tube for the 8-inch tire and a 4.00-12/4.80-12 tube for the 12-inch, both built around a TR-13 valve stem. The 5.70-8 doesn’t have a dedicated tube on our shelf the way the two D901 sizes do — if your K397 needs one, call ahead so we can check what’s available, or ask about a tubeless repair instead. Not sure your rim even takes a TR-13? The TR-13 vs. TR-15 guide shows you how to measure the hole in thirty seconds. Current tube stock is on the inner tubes page.

How to check what’s on your trailer now

Confirm what’s actually mounted before you order anything — worn sidewalls make 4.80-8 and 5.70-8 look close enough from six feet away to burn a return shipping label.

1. Find the size stamped on the sidewall — it’ll read something like “4.80-8” or “5.70-8 LRB,” usually near the DOT code.
2. If it’s worn past reading, measure the tire’s width across the tread with a tape measure and compare it to the chart above — width alone separates 4.80 from 5.70.
3. Confirm the wheel diameter by measuring bead-to-bead across the rim (8-inch vs. 12-inch) — don’t assume it from how big the tire looks mounted.
4. Check the load range letter (B or C) stamped near the size — when two tires look nearly identical but one carries noticeably more, this is usually why.

Sidewall unreadable and none of this settling it? Bring the old tire in, or call — we size mystery trailer tires over the counter every week in season.