I was pretty sure that it would be impossible for any bike athlete to break a standard 1/2" pitch bicycle chain in a straight pull without some sort of assistance. There had to be something wrong either with the chain (worn, corroded, damaged etc), or the chain was being used incorrectly (power on while shifting gear for ex), or as a result of some other mishap (stick in the mech...).
So, assuming a chain in good condtion, with a straight pull, what is the pull required to break the chain?
Mr Google came to my rescue.
Question: "Breaking strength of a standard half-inch pitch bike chain?"
Answer: A standard half-inch pitch bicycle chain typically has a minimum breaking strength of approximately 8.2 kN to 10 kN, which is equivalent to about 1,800 to 2,200 pounds of force (lbf) or 830 to 1,000 kilograms of force (kgf).
The answer went on to say...
Key points regarding the breaking strength: (the highlights are mine)
- Standards: The German Industrial Standard sets a minimum breaking load of 8,200 Newtons for standard bicycle chains and 10,000 Newtons for derailleur chains.
- Real-world vs. Tensile Strength: This figure refers to the straight-line tensile strength under a controlled, one-time load. In real-world use, chains rarely fail due to pure tensile force, as no human can generate enough power to snap a good quality chain in a straight pull.
- Failure Modes: Chain failures in real-world riding often occur due to wear, improper maintenance, or sideways twisting force, such as during a high-torque, poor gear shift.
- Working Load: The actual working load a strong rider puts on a chain can be up to around 2 kN during a sprint, which is well within the chain's safety margin. Industrial applications typically recommend a working load of only 1/6 to 1/9 of the ultimate tensile strength to prevent fatigue failure.
- Chain Type: Single-speed and fixed-gear chains (typically wider, 1/8" inner width) may have slightly different strengths compared to narrower multi-speed chains (e.g., 11 or 12-speed chains are narrower), but even the narrowest modern chains are designed to be strong enough for powerful riders.
In summary, a standard bicycle chain is remarkably strong in tension and engineered with a significant safety margin for normal riding conditions. Then came the ebike and that was OK, but then the Amflow!!
Note from the above Google quote, that the actual working load that a strong rider can exert is up to around 2kN during a sprint. I
assume that is on a non-assisted bike. Many ebikes boost the riders power by x4 (the Amflow by x8!). Even at x4 that is getting close to exceeding the design of the chain. ie 2kN x4 = 8kN, when the minimum breaking load for derailleur chains is 10 kN. If the chain is sub-optimal and the chain is not straight at peak load, then a break could be on the cards. I have broken two chains but only on my emtbs, never on my regular bikes.
For the Amflow in Turbo (at x8) that would be 16 kN, which is well above the minimum breaking load for derailleur chains. But how often do we hear of Amflow riders breaking chains? Maybe the bikes and chains are all too new? Maybe there is a rash of broken chains about to be reported? Or maybe Amflow riders just accept it as a feature of their powerful motor, almost like a badge of honour, but keep quiet about it?
Note: A kilogram is a mass, a kg force (kgf) is the weight exerted by that mass under the force of gravity. A Newton is the Systeme International unit of force (N). The acceleration due to gravity is 9.81m/sec2. Therefore one kgf is the same as 9.81 kilo Newtons (kN). 10,000 kN is equivalent to 1019 kg hanging on the chain, which is a small fraction over a ton for those used to the Imperial system.
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