ZRace RX crankset - broken

[Linsook]

I wouldn't go as far as expert but I have a little bit of knowledge of this kind of things. If you could get some good close up photos of the two faces if you can get them apart that might be helpful. Make sure to indicate which side is the pedal side.

Non-drive side.  Had to grab a monkey wrench to bend the piece off- you can see where I just broke it off.  Aluminum shavings probably from me trying to get pedal off - pedal extender threads are perfectly fine. 

Before anybody says it first- it's time to cut my nails.   

[TidyDinosaur]

I would say yes, a larger moment is being exerted on the connection point because of this.

When I was looking up info about putting shims between my pedal and crank it looked like the consensus is that 3mm of shims is OK. This one shim should not ne a problem. The difference of wattage between different people will be a far greater variable than this shim...

[electrolux]

I've just noticed the 20mm extensions, wonder what effect that would have?

[Linsook]

Ya, maybe my extenders taken it beyond the tolerances it was built for.

Chatgpt:

User
How much additional stress is caused to crank arms by using pedal extenders?

ChatGPT
Using pedal extenders can introduce some additional stress to crank arms compared to using standard pedals. This stress is primarily due to the increased leverage created by the extended distance between the pedal and the crank arm. The amount of stress can vary depending on several factors:

Extender Length: The longer the pedal extender, the greater the additional stress on the crank arms.

Rider's Weight and Power: Heavier riders or those who apply significant power while pedaling may put more stress on the crank arms.

Crank Arm Material and Design: The material and design of the crank arms play a significant role in their ability to withstand stress. High-quality, durable materials and designs are better equipped to handle the additional stress.

Proper Installation: Ensuring that the pedal extenders are correctly installed is crucial. Improper installation can exacerbate stress on the crank arms.

It's essential to follow the manufacturer's guidelines when using pedal extenders and to periodically check for wear and stress on both the extenders and the crank arms. If you have concerns about potential damage or wear, it's advisable to consult a professional bike mechanic for an assessment.

[TidyDinosaur]

I've just noticed the 20mm extensions, wonder what effect that would have?

OK, I did not see those 

[AzureEssence]

Re: pedal extenders

I tried using some from AliX and they broke on my MTB, and JUST after I finished a hectic descent. Could've caused a massive crash. Although I love the wider Q being a tall dude, I will never run them again on any bike. I just wish companies would introduce cranks with variable Q-factor.

[Pedaldancer]

On the first photo on the right side of the crank the surfaces do show lines that look like characteristic fatigue lines.
If the pattern is not something from the alloy manufacturing process, that's probably the hint you wanted. The orientation of the lines and the torque from the pedal are in agreement.

Are these lines also on the left side (on photo 1)? To me this surface looks very rough not showing lines. This would give at least a complete story.. fatigue lines until the remaining material  can't resist any longer and then sudden breakage.