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Do Washers (Spacers) for Pedal Offset Create a Risk for Crank Arm Fatigue?

The crank arms on my Moots Vamoots RSL are the Cannondale Hollowgram with SRM power meter). My other bikes are using Shimano DuraAce.

I am researching the following question:

This is a reasonable question to ask: using a 1mm washer means that there is one screw thread less insertion of the pedal spindle into the crank arm so that pedal force is acting on a slightly smaller portion of the crank arm.

My particular concern? I ride at least 10,000 miles per year on my road bike. That’s a lot of pedal force over a lot of time. Crankarms are aluminum, and aluminum has a limited fatigue life. The last thing I’d want is to have a year’s hard effort go up in smoke by having a crankarm break during the Everest Challenge.


Maybe this is a realistic concern, maybe not, but I want to hear from the manufacturer yeah or nay.

Most opinions seem to be of the form that “1mm ought to be just fine”. And some cranksets apparently come with washers. But every design is different, and it doesn’t seem defensible to assume that design 1 of material A can be assumed to have the same tolerances as design 2 of material A or B.

I have sent a message to Cannondale asking this question, and I also hope to hear directly from a Cannondale representative.

My question:

1. For the Cannondale Hollowgram crankarms, is it acceptable to use a 1mm washer (for pedal offset).

2. Is there an official spacing specification on this matter, e.g., no washers allowed, up to 1mm, up to 2mm, etc.

Email answer from Hollowgram:

Hollowgrams aren't designed to be used with pedal washers. It is not recommended.

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