Winter storage for mower tires: stopping dry rot before it starts

The short answer: mower tires don’t die over the winter from cold — they die from sunlight, ozone, big temperature swings, and sitting flat for four months. Store the machine out of direct sun, top the tires up to their normal operating pressure before you park it, and either roll it a foot or two once a month or take the weight off the tires entirely. That’s the whole program. Everything else is detail.

Every March we sell a round of tires that didn’t wear out — they cracked out, sitting still. Dry rot is the quiet tire killer in Northeast Ohio, and it’s mostly preventable. Here’s what actually causes it, one stubborn myth included.

What actually kills a parked tire

Rubber doesn’t rot like wood — “dry rot” is the rubber’s protective oils and compounds breaking down until the surface loses flexibility and cracks. Four things drive it:

• UV light. Sunlight is the big one. A mower parked beside the garage all winter is getting a slow sunburn on whichever sidewall faces south.
• Ozone. Electric motors and some furnace and welder equipment give off ozone, which attacks rubber. If the mower shares a wall with a running freezer or your shop compressor, give it a few feet.
• Temperature cycling. It’s not the cold itself — it’s the repeated freeze-warm-freeze swings that work the rubber as it stiffens and relaxes. An unheated shed that tracks the weather is still far better than outdoors, because it removes the sun and the wet.
• Sitting flat. A tire that loses air over the winter ends up parked on a crease. Months of that folds the sidewall at the same spot, and the crease is where the first cracks show.

Notice what’s not on the list: age alone. A tire stored dark, dry, and inflated stays usable a surprisingly long time. The sidewall cracking you see on a ten-year-old mower tire is a storage record, not a birthday.

The concrete floor myth, handled honestly

You’ve heard it — “never store tires on concrete, it leaches the life out of them.” There’s a kernel of history in it: decades ago, rubber compounds were more vulnerable, and a cold, damp slab was a genuinely bad neighbor. Modern tire compounds don’t much care about concrete itself. What the slab can still do is hold moisture against the rubber, and a persistently damp contact patch is a slow, real problem — more for the steel rim than the tire, honestly, and rusty bead seats are their own leak factory.

So here’s the fair verdict: a piece of plywood or a scrap of old carpet under the tires costs nothing and keeps the damp off, so do it if your floor sweats. But if your garage is dry, the bare slab is fine — spend your worry on the sun instead. A mower stored outdoors under a clear sky is aging faster than one parked on the dampest floor in Cleveland.

Jack stands, or the monthly roll?

The gold standard is taking the weight off entirely: machine on jack stands or blocks, tires just kissing the floor or clear of it. No load, no flat spot, no creased sidewall. If you’re storing a machine you care about — say, a restored garden tractor wearing period-correct rubber — do this and don’t think about it again until spring.

For the daily-driver mower, the honest alternative is the monthly roll: once a month, push or drive the machine forward a foot so the tires rest on a fresh spot. Thirty seconds, no jack. It doesn’t protect quite as well as stands, but the difference is the tire resting on a rotating cast instead of the same patch for 120 straight days — which is most of the battle. Our take, for what it’s worth: “Nobody regrets the jack stands, but nobody who did the monthly roll ever came in with a flat-spotted tire either.”

Top up before you park — then again in January

Air pressure drops as temperature drops, and small tires bleed pressure faster than car tires to begin with. A tire parked soft in November is parked flat by February, folding its sidewall the whole time. Before storage, set the tires to their normal operating pressure — the number in your operator manual, never above the sidewall max — and then hit them once more with the gauge in mid-winter. That January top-up is the most skipped step on this page and the one that saves the most sidewalls. If you’re not sure what that number should be, the mower tire pressure guide walks through it.

The five-minute spring checklist

• Pressure first. Set all four to operating spec before the first mow — a winter of slow leaks makes every tire suspect.
• Read the sidewalls. Flex each one and look for cracking in the folds. A web of fine surface checking is a warning; cracks deep enough to catch a fingernail mean replacement, because a sidewall fails all at once, not gradually.
• Check the valve stems. Rubber stems dry-rot too. Wiggle each one and soap-test for bubbles.
• Watch the first hour. A tire that lost air over the winter and “seems fine” after a fill often has a rim or bead issue. Recheck pressure after the first mow.

If a sidewall failed the fingernail test, the mower tires page has replacements on the shelf, and the fitment guides confirm your size by machine if the sidewall’s too far gone to read.