Foam filling: what it costs, what it weighs, when it is worth it

Foam filling replaces the air in a tyre with cured polyurethane, so it cannot puncture. It buys uptime on slow machines working in debris, and it costs you weight, ride quality, speed and a more expensive disposal at the end. It is the right answer on a scrap yard loader and the wrong answer on almost anything that travels.

The decision is nearly always about downtime, not about tyres. If a puncture costs an hour, fill is hard to justify. If it costs a shift and a low-loader, the sums change completely.

The fill is a two-part polyurethane elastomer. The components are metered and mixed as they are pumped, and go in as a liquid through the valve with the tyre already mounted on its rim, displacing the air as the cavity fills. It cures over hours to days depending on volume and temperature, ending as a solid but resilient mass filling the whole cavity.

The filler works to a target that corresponds to the tyre’s normal inflation pressure, so a filled tyre sits at roughly the same deflection under load as a correctly inflated one. What it no longer does is act as an air spring. Air compresses; cured polyurethane does not, in any useful sense. That single difference is behind every advantage and every drawback below.

The fill is a little heavier than water, litre for litre, and it occupies essentially the whole air cavity. On a large plant tyre that is a great deal of material. Expect a filled tyre to weigh in the order of two to three times what the tyre alone weighs — more on a large, wide section, less on a small one — and put a real number on it before you commit.

Where the weight matters:

• Machine capacity and load charts. A lift truck or handler is rated with a specified tyre. Adding several hundred kilograms in front of the fulcrum changes the machine’s stability, and adding it behind changes it the other way. The rated capacity on the plate belongs to the machine as configured — take it up with the machine manufacturer or its dealer, not with the tyre fitter.
• Axle, bearing and final drive limits. The extra weight is permanent, unsprung and there whether the machine is loaded or not.
• Transport. A filled machine can push a low-loader over its plated weight. Work it out before it is on the trailer and at a weighbridge.
• Fuel. Every cycle now accelerates and stops that extra mass.

Fill earns its money where punctures are constant, speeds are low and downtime is expensive. In practice that is a fairly short list, and it is a familiar one:

• Scrap and metal recycling yards — swarf, offcuts, banding, plate. The classic case.
• Demolition sites, especially anything with reinforcement or nails in the arisings.
• Waste transfer stations, tip faces and landfill.
• Quarry loading shovels working a face where sidewall damage is routine.
• Steel plants, foundries and anywhere with a hot or sharp floor.
• Port and airside equipment where an unplanned stop blocks an operation.

The common factor is not the material on the ground. It is that the machine works slowly, over short distances, in one place, and that stopping it costs far more than the tyres do. A loading shovel shuttling 50 metres all day is an ideal candidate; the same machine sent down the road twice a week is not.

Air carries heat out of a tyre. Polyurethane does not — it insulates, and it generates heat internally as it is worked. On a machine that runs continuously, or at speed, the temperature climbs, the fill degrades, and what follows is a separation inside the tyre rather than a puncture. Not sudden in the way a blowout is, but the tyre is finished.

Every filler publishes a maximum speed and a duty limit — a continuous running time, or a distance per shift. They are low. Treat them as hard limits, get them in writing for the specific machine, and check them against the machine’s verified operating duty. Where a machine occasionally exceeds them, fill is the wrong product.

The rim. Shock loads that an air-filled tyre absorbs are now passed straight into the wheel and the bead seat. Rims on filled assemblies work harder and fatigue faster, and corrosion under the bead cannot be inspected because the tyre never comes off until it is scrapped. Fill only onto a sound wheel with the correct, matched components — the multi-piece wheel safety points in the OTR codes and star ratings guide apply here too, and they apply at the point of fitting the tyre before it is filled.

The machine. Everything the tyre used to absorb now goes into the axles, the boom, the chassis and the welds. On a machine kept ten years that cost is real, and it turns up as cracked structures rather than as a tyre bill.

The operator. The ride is noticeably harder over dock plates, kerbs and potholes, and whole-body vibration exposure rises — worth measuring rather than assuming on a machine worked all day.

Fill is priced by volume, so it scales with tyre size, and on a large plant tyre the fill can approach or exceed the price of the tyre itself. Get a current quote for the exact size rather than working from a rate you used last year; both material prices and haulage move.

The end of life is where the sums usually go wrong. A filled tyre cannot be casing-graded or retreaded and cannot go into the normal part-worn or casing stream. It has to be cut off the rim, it weighs several times what an empty casing weighs, transport is charged by weight, and not every processor will take filled tyres at all. Ask your disposal route what it will charge for that size before you fill it. The cost per kilometre calculator does the same arithmetic if you feed it machine hours instead of kilometres, which is the right unit for plant — use it to line the whole-life cost up against a conventional tyre changed more often.