How to measure a mower tire when the sidewall is unreadable

The short answer: if the sidewall is too worn or cracked to read, you can recover the size with a tape measure — overall diameter and width from the inflated tire, rim diameter from the wheel. The one place everyone goes wrong is the rim: measure where the tire bead seats, not across the outer flange lip, or you’ll order a tire one size too big. And if you know your machine’s make and model, you can skip the tape measure entirely.

Tire sizes are stamped in raised rubber, and thirty years of sun and mowing will erase them. Happens constantly on older garden tractors. Here’s how we work it out at the counter, in the order we actually try things.

Easiest first: look it up by machine, not by tire

Before you measure anything — if you know what the tire is bolted to, the size question is probably already answered. Factory fitments for common riding mowers and garden tractors are well documented, and our fitment guides list stock sizes by make and model, paired with what’s on our shelf. One caveat, and it’s the reason the rest of this article exists: previous owners swap wheels. If the tire you’re replacing looks out of proportion to its partner, or the machine’s had three owners, verify with the tape measure anyway.

The three numbers you’re solving for

A mower tire size like 23x10.50-12 is three measurements: about 23 inches tall, about 10.5 inches wide, on a 12-inch rim. (The full decoding system — including the older two-number sizes — is in our how-to-read-tire-sizes guide.) So measuring a mystery tire is just filling in those three blanks.

Measure with the tire inflated if it holds air at all — a flat tire squats, and a squatting tire measures short and wide. If it won’t hold air, expect your diameter number to read an inch or so under the true size, and lean on the rim measurement instead, because the rim never lies.

The rim trick: bead seat, not flange lip

Here’s the mistake behind most wrong-size orders. A wheel’s stated diameter — the “12” in 23x10.50-12 — is the diameter of the bead seat, the shelf inside the rim where the tire actually sits. The outer flange lip, the shiny edge you’d naturally hook a tape measure over, stands taller than the seat on both sides. Measure lip-to-lip and a 12-inch wheel reads close to 13 inches. Then a “13-inch” tire shows up and won’t go anywhere near the rim.

1. With the tire off (or pushed aside), find the flat shelf just inside the flange.
2. Measure straight across the wheel from shelf to shelf, through the center.
3. You should land almost exactly on a whole number — 6, 8, 10, or 12 on most mower wheels. If you’re reading a half-inch over a whole number, you’re on the lips.

Our version of this rule, after telling it at the counter for 22 years: “Measure where the tire lives, not where the wheel shines.”

Round to a real size — don’t chase your tape measure

Tires only come in certain sizes, so your job isn’t precision — it’s getting close enough to recognize the answer. A worn tire measures smaller than it started: tread wears down, rubber shrinks a little, and a tire that began life at 23 inches might tape at 22 and change. So if you measure 22.5 tall, 10.25 wide, on a 12-inch rim, you’re not hunting for an oddball — you’re holding a worn 23x10.50-12. Match your three numbers to the nearest standard size, and when you’re between two, the rim number and the width are more trustworthy than the worn diameter.

Still stuck? Send us photos

Some tires defeat the tape measure — odd old sizes, homemade wheel swaps, sidewalls with just a ghost of lettering left. For those, take three photos: the whole wheel and tire straight-on, the sidewall up close in angled light (raised lettering often shows up in a photo when it’s invisible in person — shoot it with the sun raking across), and the tire on the machine so we can see what it’s attached to. We identify mystery tires from photos every week; it’s honestly one of the more satisfying parts of the job.