The old-vs-new tractor tire size chart (and why your size “doesn’t exist” anymore)

The short answer: most old two-number tractor tire sizes didn’t get bigger — they got re-measured. A 10-28 became an 11.2-28, an 8-24 became an 8.3-24, and a 12-28 became a 13.6-28, all still the same tire on the same rim. If your tractor’s original size “doesn’t exist” at a tire shop anymore, that’s why — not because the tractor got orphaned, but because the industry changed what the number on the sidewall was measuring. Twice.

We built this chart from our own antique fit pages, not a guess — every pair below is cross-checked against an independent farm-tire conversion table and the tractors we actually document fitments for.

The three real renames on our fit pages

Three old-style rear sizes that show up on our antique fit pages got renumbered decades ago, and here is exactly what each one became. None of these are upsizes — they’re the same tire, relabeled.

One more that trips people up but isn’t actually a rename: the Farmall Super A rear is sometimes written “9-24” on old sidewalls and sometimes “9.00-24.” Those are the exact same tire — someone just dropped the trailing zeros when they stamped the mold. Don’t confuse that with the genuine renames above; nothing needs converting there.

Why your size “doesn’t exist” anymore

Your tractor’s original tire didn’t vanish — the industry changed what the size number measures, and it did it twice. Early rubber tractor tires were sized off an 8-inch rim, and the number reflected that. When wider rims proved to spread the bead and flatten the tread for better traction, manufacturers renumbered to match the new recommended rim width — same tire, new number, first shift. Then, in the late 1950s and into the ’60s, they renumbered again, this time to reflect the tire’s overall carcass width instead of just the tread-to-tread width across the shoulders. A former Goodyear tractor-tire-plant technician walked through this exact progression in a Farm Collector piece: an early 11.25-24 (built for an 8-inch rim) became a 13-24 once wider rims took over, then became a 14.9-24 once the industry switched to measuring overall carcass width — some old tires from the transition are literally stamped with both numbers. Two renumbering events, same physical tire.

That’s the trap restorers fall into: they read the original owner’s manual, see the old number, and order what looks like the modern match — except the manual’s number predates one or both renumbering events, so the “obvious” modern size is actually too small.

The fronts that never got renamed

Not every antique tractor size got a new number — the front tires on our own fit pages prove it, because we sell them today under the exact size stamped on a tractor built seventy-plus years ago. The three-rib front sizes never went through the carcass-width renumbering that hit the big rear drive tires, so 5.50-16, 5.00-15, and 4.00-12 are the same designations now as they were on the original parts list.

One size up the same three-rib family, 6.00-16 is just as unchanged and just as common on this era of row-crop tractor. All four are stocked here under the Deestone D401 Tri Rib name — the same tread pattern this class of front tire has run for decades, in the size that’s always been on the tag.

Check rim width before you trust the equivalent

A size conversion only holds if the rim width matches too, and that’s the detail restorers miss most. The renumbering that turned old rear sizes into today’s designations happened alongside a shift to wider recommended rims — the same history that explains why an old 11.25-24 became a 13-24 before it ever became a 14.9-24. If your tractor still wears its original, narrower rim, the “correct” modern-equivalent tire may be built for a rim a couple inches wider than what’s actually on the axle, and the fit won’t be right even though the size number matches the chart.

Before you order, measure the rim across the bead seat rather than trusting the tractor’s age or the manual’s original number. It takes thirty seconds and it’s the difference between a tire that seats correctly and one that fights the bead the whole time you’re airing it up.

The letter matters as much as the numbers

A dash means bias-ply construction and an “R” means radial, and that distinction runs independent of the size renumbering entirely. Every size in the charts above — 11.2-28, 8.3-24, 13.6-28, 5.50-16, and the rest — uses the dash format, meaning bias-ply, which is the correct, period-appropriate construction for these antique fitments. If you ever see the same numbers written with an “R” instead — 11.2R28, for instance — that’s a radial tire, a different carcass structure built for a different class of modern tractor, and not a straight swap even though the width and rim numbers look identical.

For the two-number system itself — what the width number and rim number mean on a single tire, no history involved — our guide to reading tire sizes covers that from scratch. And if the tire you’re chasing is going back on a tube-type wheel, our upcoming TR-13 vs. TR-15 valve stem guide covers the other number that trips up antique restorations.