Foam fill — weight and cost

Enter the size as it appears on the sidewall — 8.25-15, 12.00R20, 10.00-20, 405/70R20. Fill work is concentrated in industrial, materials handling, quarry, telehandler and skid steer sizes, and those are mostly imperial markings.

The fill rate is the price per litre of the fill material. Enter your own trade rate to get a cost, or leave it blank and you will still get volume and weight. Quantity multiplies the weight and the cost across a set.

What comes back: fill volume in litres per tyre, added weight in kilograms per tyre and for the set, and material cost per tyre and for the set.

Take 8.25-15, the standard heavy forklift and industrial size, four tyres, at an assumed rate of £3.20 per litre:

• Fill volume: 49 litres per tyre
• Added weight: 52 kg per tyre, 208 kg across four
• Material cost: £155.57 per tyre, £622.27 for four

Consider the added weight carefully. Two hundred kilograms added to a machine that may only weigh four or five tonnes changes its axle loads, its floor loading and how it has to be transported. Filling typically adds two to three times the weight of the tyre itself.

The added weight increases with tyre size. A 12.00R20 comes out at around 141 litres and 151 kg per tyre. On a four-wheel machine that is roughly 600 kg of polyurethane, before you have loaded anything.

There is no lookup table of cavity volumes behind this. The calculator builds one geometrically, and there are three approximations in the chain.

The cavity is modelled as a ring of elliptical cross-section. The section width and the section height — width multiplied by aspect ratio — are treated as the two axes of an ellipse, and that ellipse is swept around the wheel at the radius from the axle centre to the middle of the section. That gives a gross cavity volume from nothing but the size marking. Imperial sizes state no aspect ratio, so 92% is assumed, exactly as in the sidewall decoder.

A flat 0.85 fill factor is applied. The real air space is not a clean ellipse. The rim well and the bead seats take volume out of the bottom of the section, the tread band and the belt package are not part of the cavity, and a fill is deliberately not taken right to the theoretical brim. Multiplying by 0.85 accounts for all of that in one number, applied identically to every size. A deep-well wheel, an unusually shaped industrial casing or a tyre with a flap and tube will sit either side of it.

Weight is calculated at 1.07 kg per litre. That is a typical cured density for polyurethane tyre fill. Products vary by grade — softer, lower-density grades exist for ride comfort and heavier grades for maximum stability — so the weight moves with the material the fitter actually uses.

The volume and weight are approximate planning figures. Actual fill requirements vary with the tyre, rim and material used. Confirm these details with the fill contractor before ordering or assessing assembly weight.

The cost is material only, at the rate you typed in. It excludes labour and machine time, the tyre itself, valve conversion and wheel preparation, any tube or flap, delivery, and disposal of the tyre that is coming off.

Include disposal in the cost assessment. A filled tyre cannot be deflated, repaired or handled through the normal casing route at end of life. It has to be cut off the rim as a solid and disposed of accordingly, which costs more than scrapping a conventional casing and needs to be in the whole-life sum from the start.

This calculator answers how much and how heavy. It does not answer whether you should fill at all, and that is the bigger question.

• Check the machine before the tyre. Added weight affects rated capacity, axle and wheel ratings, floor and ramp loading, trailer weights for transport, and on some machines the manufacturer’s approved tyre specification. Confirm with the machine maker rather than assuming.
• Fill is a low-speed, short-cycle solution. There is no air to cushion the load or carry heat away. Deflection drops, the machine and the operator take more shock, and heat generated in the fill has nowhere to go. Fill products carry speed and duty limits, and none of them are for highway use.
• It is not always cheaper than the alternative. On many applications a solid resilient or press-on tyre is the better answer than filling a pneumatic. Puncture-prone sites with genuine pneumatic ride requirements are where fill wins.

Use the output for initial planning only. It cannot establish load-limit compliance or approve a fitment. Confirm the actual assembly weight, the manufacturer’s approved machine and wheel specifications, and a written quotation with the fill contractor.