A rim does not have “one” maximum load. It has as many as there are ways of using it: the same 25 mm internal rim takes 200 kg under a cargo bike and 130 kg under a mountain bike, and that is not a contradiction. The two figures on our sheets each answer a different question.
Two figures, two questions
System weight — max load
What the whole bike is allowed to weigh, everything included: the bike, you, the luggage, the child, the shopping, the battery. This is the figure you check first, because it is the one you can put on a scale.
Axle load
What <em>one</em> wheel actually takes. This is the physical value: it is the one put on a test rig, because a wheel only knows what passes through its axle. It is always lower than the system weight, since two wheels share the load.
Going from one to the other is not a division by two. It depends on how the weight is split between front and rear, and that split changes completely from one type of bike to another. That is the whole difficulty, and it is why the manufacturer publishes both.
Why it is not half and half
On a road bike the rider sits roughly centred: each wheel takes about half. Load the same bike with two rear panniers and you move to 40% front, 60% rear. On a longtail with a passenger on the rack, the rear wheel can reach 70% of the total. It therefore works harder than both wheels of a road bike put together, at the same overall weight.
The calculation, in one line
Axle load = system weight × the share carried by that wheel. A cargo bike rated at 250 kg whose rear wheel takes 60% needs a rim good for 150 kg on the axle. The same rim, under a 130 kg city bike with an even split, only sees 65 kg: it is very largely over-specified.
It is also why a published system weight does not carry over from one bike to another. Two bikes of 180 kg — one an urban e-bike, the other a rear-loaded longtail — do not ask the same thing of their rear wheel.
Why the same rim changes figure with the use
On our sheets a rim often shows several lines: cargo, longtail, e-trekking, e-MTB. The values drop while the weight itself does not necessarily move. The reason is not the weight: it is what comes on top of it.
- Impacts. A kerb taken at 25 km/h puts several times the static load through the rim, for a few milliseconds. A cargo bike rides slowly and loaded; an e-MTB rides fast and jumps.
- Torque. A hub motor does not push the bike through the chainset but through the spokes. The spokes take the acceleration and the braking, on top of the weight.
- Duration. A permissible load is not a breaking point, it is a load the wheel must take tens of thousands of times without cracking. It is a fatigue figure, not a failure figure.
A wheel almost never gives way all at once. It cracks around the spoke holes, slowly, long before letting go. Riding above the rating breaks nothing on the first day — which is exactly what makes the mistake so common.
What the figure does not tell you
The rim is only one link in the chain. Three limits are beyond it, and they often come first:
- The tyre. No bicycle tyre today goes much beyond about 140 kg per wheel. A rim rated higher is of no use if the tyre caps out first.
- The frame and the hub. The bike maker publishes its own maximum total weight. That one always wins: a more capable rim does not raise the bike's limit.
- The build. A permissible load assumes an evenly tensioned, properly dished wheel. A poorly tensioned wheel loses part of its capacity, whatever the rim.
What the standards say
The ISO standard for bicycles certifies each wheel for only 65 kg on the axle — a standard city bike, no more. For carrying loads, the reference is the German DIN 79010 standard, written for cargo bikes and far more demanding. A rim announced as “cargo” with no reference to a test protocol remains a marketing claim.
How to read our sheets
In the selector, every rim carries a “Maximum permissible loads” table with one line per use, the axle load on the left and the system weight on the right. Three steps are enough:
- Find your use in the first column. If your bike is not there, take the most severe line, not the most flattering one.
- Compare your real weight, you and the load included, with the system weight on that line.
- Look at the axle load if your bike is clearly loaded on one side — trailer, longtail, rear child seat. That is where the margin is decided.
A cell marked n.c. means the manufacturer does not publish that figure for that use: we would rather say so than estimate it. And if no value reassures you, call the workshop — we assemble 170,000 wheels a year, the question has been asked before.
Not sure which rim to choose?
Tell us your bike, your use and your load: we pick the rim and the tension that go with it. New rim, spokes and nipples, back within 48 to 72 h.
