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Quick answer: Crawler undercarriage load capacity is derived from a five-step calculation: contact length, frame bending moment, ground bearing pressure, roller and sprocket loads, and drive torque. MAGEON applies a 1.5 static safety factor, 2.0-2.5 on fatigue, and 3.0 on the track chain's rated breaking load.
Load capacity is the number every equipment buyer asks for first, and the number most often quoted without the context that makes it meaningful. "20-ton undercarriage" can describe a machine that will comfortably operate a 24-ton excavator in a quarry, or one that will be at its limit with an 18-ton machine on a 30% slope. The number is meaningless without the assumptions behind it.
Here is how MAGEON engineers calculate and rate the load capacity of a custom crawler undercarriage.
What "rated load capacity" actually means
For a crawler undercarriage, we use a rated load capacity defined as:
The maximum total machine weight the chassis can carry, expressed as a static vertical load distributed over the track contact length, at a specified operating condition and with a specified safety factor applied.
Four conditions always appear in that definition, and they are the four things a customer must confirm in writing:
- Machine weight including full ballast and attachments
- Slope and ground condition — the rating is not valid on a gradient
- Dynamic factor — how much the working load swings during a cycle
- Safety factor — the margin held against fatigue and overload
The calculation chain
Step 1 — Contact length and effective track length
The load path runs from the machine's mounting face into the frame, out to the track rollers, and through the track shoes into the ground. The critical section is the frame span between the front and rear roller groups, which behaves as a beam loaded at the machine's centre of gravity.
Effective contact length is the length of track actually in contact with the ground under load, typically 60–80% of the total track length, and it is a function of the machine's pitch attitude. On level ground with the machine's weight distributed evenly, use the full contact length; on a slope, the uphill track carries a disproportionate share and the effective length shortens.
Step 2 — Bending moment in the frame
With the load distribution known, the bending moment in the frame is calculated for the worst case:
M = W × a × b ÷ L
where W is the vertical load, a and b are the distances from the centre of gravity to the front and rear support points, and L is the effective contact length. The maximum moment occurs at the support point closer to the load.
The frame section is then sized against this moment, and the stress checked against the material's yield strength with a fatigue factor applied. This is where a custom undercarriage earns its value: a chassis designed to a specific load distribution can use a lighter section than a generic one carrying the same nominal tonnage at a worse distribution.
Step 3 — Ground bearing pressure check
p = W ÷ A, where A is the total contact area, being the contact length multiplied by the shoe width on each side. The pressure must satisfy the weaker of two constraints: the ground's bearing capacity, and the machine's permissible tip-over margin.
Step 4 — Roller and sprocket loads
The individual track rollers and the drive sprocket do not see a uniform share. The load concentrates at the ends of the track chain, and the sprocket sees the sum of the tensile forces in the chain plus the drive torque reaction. Each roller and sprocket is then checked for contact stress, bending, and bearing life at the expected duty cycle.
Step 5 — Drive torque and gradeability
Gradeability ties the load rating to the drive. The tractive effort required on a gradient is:
F = W × g × sin(θ) + F_rolling
and the drive must supply that force at the shoe-to-ground friction limit, which for a steel track is roughly 0.6–0.8 depending on ground condition. A custom undercarriage with insufficient drive torque is a machine that cannot work at its rated load, regardless of how well the frame is designed.
Safety factors MAGEON applies
| Check | Factor | Basis |
|---|---|---|
| Static frame stress | 1.5 | Yield with material variability |
| Fatigue, frame welds | 2.0–2.5 | Working load × dynamic factor |
| Track chain link | 3.0 | Manufacturer's rated breaking load ÷ 3 |
| Bearing L10 life | 1.5 | Rated life at 1.5× dynamic load |
| Tip-over stability | 1.33 | Standard static stability factor |
Why a wider track changes the answer
Track width affects load capacity through ground bearing pressure, not through the frame's bending strength. Doubling the shoe width halves the ground pressure, allowing the machine to operate on softer ground at the same rated load — but it does not increase the frame's load rating.
Where a customer needs more capacity, the levers are, in order of effect: increase the frame section depth; increase the contact length; increase the number and size of the track rollers; or reduce the distance from the centre of gravity to the support point by repositioning the machine's mass. Widening the track alone is a ground-pressure solution, not a capacity solution.
Rating conditions that must be stated on any capacity figure
Whenever MAGEON quotes a load capacity, we state alongside it: the assumed machine weight distribution, the slope, the ground condition, the dynamic factor, the safety factor, and the assumed track configuration. Without those six, the number cannot be compared against any other supplier's number, and it cannot safely be used to size a machine.
Conclusion
Load capacity is an outcome of a complete engineering calculation, not a single specification. When a supplier quotes tonnage without the conditions, ask for the calculation. MAGEON is happy to provide the full calculation basis for any custom undercarriage we quote, because a capacity figure you cannot verify is a capacity figure you should not rely on.
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.