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Quick answer: Ground pressure equals machine weight times 9.81 divided by the total contact area, and contact area is twice the contact length times the shoe width. Widening the shoes reduces pressure proportionally; lengthening the contact additionally reduces bulldozing resistance, which is what actually stops a machine sinking.
Ground pressure is the number that decides whether a crawler undercarriage can work on soft ground, and it is the number most often quoted approximately. It is also the number most often confused with track width, which is a related but distinct lever. This guide sets out the calculation properly, and then the practical question of which lever to pull.
The formula
Ground pressure (kPa) = Machine weight (kg) × 9.81 ÷ Total ground contact area (m²)
Total ground contact area is the sum of the contact patches of both tracks:
A = 2 × L_contact × W_shoe
where L_contact is the length of track actually touching the ground under load, and W_shoe is the width of a single shoe.
The two most common errors in this calculation are worth naming explicitly, because both make the number look better than it is:
- Using total track length instead of contact length. A track 3,500 mm long might only present 1,800 mm to the ground. Using the full length overstates the area by 40–50%.
- Forgetting that the machine's weight is not all on the tracks. A counterweight overhanging the rear, or a boom carried clear of the machine, changes the actual distribution between the front and rear supports.
A worked example
A 3-tonne mini excavator with 300 mm rubber track shoes, presenting 1,200 mm of contact length per side:
A = 2 × 1.2 × 0.3 = 0.72 m²
p = 3,000 × 9.81 ÷ 0.72 = 40.9 kPa
That is comfortably in the band for wet farmland and soft sand. Now widen the shoes to 400 mm, the same track length:
A = 2 × 1.2 × 0.4 = 0.96 m² → p = 30.7 kPa
A 25% reduction in ground pressure from a 100 mm shoe change. This is why shoe width is usually the first adjustment anyone reaches for — and why it is frequently not enough.
Contact length matters as much as width
Because contact length and shoe width enter the formula identically, a machine with a long, narrow track can achieve the same ground pressure as a short, wide one. But the two have different secondary effects that often decide which is better:
| Aspect | Longer contact length | Wider shoes |
|---|---|---|
| Ground pressure | Same effect as width | Same effect as length |
| Machine footprint length | Increases — stability improves, transport lengthens | Unchanged |
| Turning radius | Increases | Unchanged |
| Narrow passage access | Worse | Better |
| Stability on side slopes | Better | Better |
| Manufacturing cost | More chain, more rollers | Wider, heavier shoes |
| Weight penalty | Moderate | Moderate |
For a compact crawler undercarriage working between orchard rows or in a narrow trench, width is usually the better lever because it does not lengthen the machine. For a machine with stability concerns on a side slope, contact length is more valuable.
Reference ground bearing capacities
| Ground | Typical bearing capacity | Design ground pressure |
|---|---|---|
| Hard rock, concrete, asphalt | Over 2,000 kPa | No constraint |
| Compacted gravel, quarry floor | 400–800 kPa | Under 150 kPa |
| Firm, dry soil | 150–300 kPa | Under 100 kPa |
| Soft clay, wet sand | 50–100 kPa | Under 50 kPa |
| Marsh, peat, loose beach sand | 15–40 kPa | Under 25 kPa |
MAGEON designs to roughly half the ground's bearing capacity rather than matching it, because ground bearing capacity is measured in a test that does not represent the whole field, and because a machine that operates at the limit of the ground's capacity will sink in the first soft patch it reaches.
The steel versus rubber contribution
Ground pressure is independent of the track material — it is a purely geometric property. What the material changes is how the machine behaves in that pressure:
- Rubber track distributes the load over the whole shoe face rather than through the grouser contact line, and adds roughly 15–30% of effective area through a wider contact patch in soft material. It also shears rather than shears-and-tears, so a rubber track on soft ground deforms to follow the surface.
- Steel track contacts the ground along the grouser lines. On rock, the contact is a line on a hard surface and is extremely effective. On soft soil, the grousers punch into the ground and can actually increase the local stress.
For an agricultural undercarriage working in wet paddy fields, a rubber track on a low ground pressure chassis is the combination that works, because the low pressure stops the machine sinking and the rubber spreads the load while the machine transits.
How to reduce ground pressure on a custom undercarriage
In order of effectiveness, from MAGEON's experience:
- Extend the track length and the contact length — the frame is designed to place the roller groups further apart, and the tensioner travel is increased to keep the chain in contact over a longer span
- Widen the shoes — simple, effective, and usually the first change made
- Reduce machine weight — sometimes the chassis is fine and the machine is simply too heavy for the ground
- Choose a rubber track — adds 15–30% of effective area and behaves better in soft material
- Reduce ground clearance or bodywork drag — helps in soft ground by reducing the bulldozing effect of the machine's underside, which is a real and frequently overlooked contributor to sinkage
That last point is worth explaining: a machine sinking into soft ground is partly a ground pressure problem and partly a bulldozing problem. The soil in front of the track has to be pushed aside, and that resistance is what actually stops the machine. Reducing the machine's frontal profile and ground clearance can therefore matter as much as reducing ground pressure.
Common errors in practice
- Quoting the nominal machine weight when the working weight with attachments and full fuel is 15–25% higher
- Using the total track length rather than the loaded contact length
- Ignoring the grade — a machine on a 20% slope has a much higher effective contact pressure on the uphill track
- Forgetting that soil bearing capacity falls sharply when wet, and machines are often specified during a dry season
- Not accounting for the weight of the machine's own undercarriage, which in a custom build can be optimised
Conclusion
Ground pressure is a geometry calculation, but the engineering decisions that follow from it — contact length, shoe width, track material, machine weight, and body profile — are what a custom undercarriage is for. MAGEON calculates the ground pressure of the proposed configuration against your actual machine weight and the ground you work in, and shows the working, because a machine that sinks is expensive in a way that is difficult to argue with.
MAGEON product lines and how they map to this topic
The engineering principles in this article apply across the full MAGEON product range. Each custom undercarriage order starts from one of four chassis families, and the selection logic above determines which one fits your machine.
| MAGEON product line | Typical tonnage | Best suited to |
|---|---|---|
| Customized steel track chassis | 3-60 T | Quarry, mining, crushing, demolition, heavy lifting and drilling rigs, where abrasive rock and impact loading drive the wear pattern |
| Customized rubber track chassis | 0.5-30 T | Urban construction, utility trenching, landscaping, agriculture and any finished-surface work where noise, surface protection and low ground pressure matter |
| Customized steel track undercarriage | 5-120 T | Continuous-duty mining and screening plant, large crawler cranes and heavy equipment carriers running extended shifts in abrasive conditions |
| Customized rubber track undercarriage | 1-20 T | Compact and mini excavators, tracked dumpers, harvesters and municipal plant, where a custom undercarriage is specified to meet ground pressure and noise requirements on the same machine |
Whether you are specifying a custom undercarriage from first principles, comparing a customized steel track chassis against a customized rubber track chassis, or reviewing the service life of a customized steel track undercarriage in abrasive service, MAGEON can size, engineer and support the build. Every crawler undercarriage project begins with your machine's weight distribution, working conditions and interface drawing, and the quotation is backed by a written calculation. Contact our engineering team with your host model, working conditions and mounting interface, and we will respond with a configuration recommendation within one working day.