How ground pressure is calculated from track width and contact length, what each surface will carry, and how rubber and steel tracks compare on wear, surface damage and cost per hour, with real figures for 1 to 3 tonne machines.
Ground pressure, not machine weight, decides whether a machine travels or sinks — and track type decides ground pressure. Rubber tracks spread load over a wider, longer footprint and leave asphalt and turf intact; steel tracks take impact, cut into hard ground and tolerate heat and abrasion that destroys rubber. The trade is not preference, it is arithmetic: divide the machine's weight by the contact area and compare the answer to what the surface can carry.
Most buyers order the undercarriage last, after engine and bucket size. That is backwards. The undercarriage decides where the machine can go at all, and retrofitting it later costs more than the difference between two models at purchase.
How do you actually calculate ground pressure?
The formula is simple and worth doing yourself, because suppliers quote "low ground pressure" without numbers.
Ground pressure = machine weight ÷ (2 tracks × track shoe width × ground contact length).
Worked example on a real machine. The YH-1000 mini dump truck has an 880 kg net weight, 180 mm track width and 1000 mm track ground contact length.
Contact area = 2 × 0.18 m × 1.00 m = 0.36 m². Empty, 880 kg → 24 kPa (0.24 kg/cm²). Loaded to its 1000 kg rating, the machine weighs 1,880 kg → 51 kPa (0.51 kg/cm²).
Now the same arithmetic on a bigger machine. The ME30A is 3000 kg on 230 mm tracks with 1700 mm ground contact length: 2 × 0.23 × 1.70 = 0.782 m², giving 38 kPa. That is with the empty bucket; add spoil and you are near 45 kPa.
| Surface | Roughly what it carries | Practical note |
|---|---|---|
| New asphalt, hot weather | Below 30 kPa to avoid rutting | Steel tracks will mark it regardless of pressure |
| Concrete slab, 100 mm | 40–60 kPa if the sub-base is sound | Point loads from a steel grouser matter more than average pressure |
| Firm dry clay | 150–300 kPa | Almost anything travels here |
| Wet silt or paddy | 20–50 kPa at best | Wide rubber shoes or you bog down in the first pass |
| Lawn, turf, golf course | Below 25 kPa to avoid visible rutting | Rubber only; steel is not an option |
Why do rubber tracks have lower ground pressure?
Two reasons, and only one of them is obvious. Rubber track shoes are wider at the same machine weight — 180–300 mm is normal on compact machines. And the rubber track runs on a flat contact patch with a continuous belt, so the whole ground contact length actually touches. Steel track links sit on individual shoes and the effective bearing length is shorter than the nominal track length, especially on crowned ground.
The second effect is why two machines with identical nominal dimensions can behave completely differently in wet ground. A rubber track machine that publishes 30 kPa may in practice disturb less ground than a steel track machine publishing 35 kPa, because the steel only bears on maybe 70% of its nominal length.
What does each type do well?
Rubber tracks. They travel on finished surfaces without tearing them up, they are far quieter, they do not spark (which matters in some demolition and utility environments) and they give a much smoother ride, so the operator's back survives a full shift. They also grip on sealed surfaces, which steel does badly. On a 1.5-tonne machine such as the GW16 — 1500 kg, 0.04 m³ bucket, 1520 mm ground contact — the machine is small enough that rubber is the default choice, and the factory ships it that way.
Steel tracks. They survive rock, slag, demolition rubble and heat. They do not tear on rebar or broken concrete. They tolerate being run over sharp aggregate all day. And they can be re-shod rather than replaced in one piece, which matters on large machines. On drilling rigs working blasted rock, steel is standard — which is exactly why the HQZ-220L pneumatic drill rig is offered in both rubber-track and steel-track versions with otherwise identical specifications: 130–254 mm drilling diameter, 220 m depth, 17–31 m³/min air consumption and 4000–4600 N·m rotation torque.
What is the real cost per hour?
Rubber tracks on a compact machine typically run 1,500–3,000 hours in mixed ground and cost USD 900–2,500 per set depending on size. That is roughly USD 0.40–1.20 per hour. On abrasive ground — sharp crushed stone, slag, quarry floors — expect the low end of that life, maybe 800–1,200 hours.
Steel tracks on the same size machine cost more up front, but the links and shoes are replaceable individually. In rock, a steel undercarriage commonly outlasts two or three rubber sets. In soil with no rock, steel wears faster than people expect because soil abrasion polishes the pins and bushes, and the chain stretches until it jumps the sprocket. That failure has nothing to do with the shoes.
The hidden cost with rubber is not the belt, it is what the belt does to the rest of the undercarriage. Rubber tracks demand correct tension. Run them loose and the belt walks off the idler on a turn. Run them tight and you wear out the idler bearings, the drive sprocket and the final drive seals. Either way the belt is not what fails first.
What maintenance actually decides the life?
Three habits, all cheap:
Tension. Check it weekly, cold, on level ground, using the manufacturer's sag figure — typically 10–20 mm on compact rubber tracks. A track that has been run loose for a month usually needs a new idler before it needs a new belt.
Cleaning. Packed soil between the sprocket and the belt grinds the drive lugs away. On machines working in clay this is the single largest cause of premature belt failure, and it costs nothing to prevent.
Turning practice. Counter-rotate on the spot only when the ground allows it. On asphalt in summer, a full counter-rotation scrubs a black circle into the surface and takes the tread with it. On a 3-tonne machine doing municipal work, an operator who turns with the machine rolling instead of pivoting can add 30–50% to belt life.
When is the conventional answer wrong?
Two cases where the standard advice leads people astray.
"Buy rubber because it is gentler." On abrasive ground and demolition sites, rubber is not gentler on your wallet. A rubber belt in sharp rubble can be finished in a few hundred hours. If the machine works in broken concrete or blasted rock, steel is the cheaper answer over the life of the machine even though it costs more on day one.
"Buy steel because it lasts longer." On turf, on indoor floors, on asphalt and in orchards, steel simply cannot be used — not because it wears out, but because it destroys the surface it crosses. A machine that cannot perform the job lasts a long time doing nothing.
What should you specify in the order?
Ask for the ground pressure in kPa or kg/cm², calculated at operating weight including a full bucket, and confirm whether the figure includes the dozer blade. Ask for the track shoe width and the ground contact length as separate dimensions — a supplier who can only give you the belt length is guessing. Then ask about availability of aftermarket belts or steel shoes in your region, because a 20% cheaper machine with no track supply within 3,000 km is not cheaper.
Frequently asked questions
Can I swap rubber tracks for steel on the same machine? Sometimes, if the undercarriage is offered in both versions from the factory, as the HQZ rig is. Retrofitting onto a machine built for one type requires changing rollers, idlers and often the drive sprocket, and it is rarely economic below 3 tonnes.
Do rubber tracks work in snow? Worse than steel. Rubber hardens and loses grip below about −15 °C, and on packed snow a steel grouser bites where rubber slides. If the machine works in a permanent cold climate, look for a winter compound belt or choose steel.
Are over-the-tyre tracks worth it for wheeled machines? On a wheeled skid steer working in mud, yes — they roughly halve ground pressure for a fraction of the cost of a dedicated track machine. They are not a permanent solution and they wear the tyres, but for seasonal wet work they are the cheapest answer.
Does track type change digging performance? No. Digging force comes from the boom, stick and bucket cylinders. Track type changes travel, flotation and lateral stability with a load, not breakout force.
How do I know if the ground will carry the machine? Do the division. Take the machine's loaded weight, divide by the contact area from the track dimensions, and compare with the figures in the table above. If the answer is close to the surface capacity, walk the route first or lay plates.
Next step
Name the ground the machine will cross and the surface it must not damage. Those two facts decide the undercarriage, and the undercarriage decides which models are even eligible. Everything after that — engine, bucket, attachments — is a choice within a range that is already fixed.
Tell us the surface, the working weight and whether the machine will be turning on finished pavement, and we will come back with the ground pressure figures for two or three undercarriage options. Browse the mini excavators and loaders and handling equipment ranges, or read how to choose mini excavator tonnage if the machine class is still open.