diy carbon (or fiberglass if you only want to use stuff you can get at lowes/home depot/auto zone)

- remove crank (with rings on)
- Find a flat surface to have the crank laying level. If it's like a shimano/etc (has a spindle connected) cut hole in a box (do not stick your junk in the box) to make a flat surface.
- Cover your now flat crank with a layer or two of saran wrap. (Just lay flat cut sheets over it. Be sure everything is covered +)
- Lay up your carbon/fiberglass on top of the saran wrap. Even just a single layer should be fine.
- wet the carbon/fg. Press down a little to make sure you've got the right shape.
- allow to cure.

After it's cured, do your rough cutting the outline of the chainrings. You want to end up with a circle shape that's roughly the same as the inner side of the chainring (so that the teeth with a chain on it will clear)
Then attach as you want. Hot glue, double sided tape, epoxy, etc.

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My Blog - http://leegoocrap.blogspot.com

I’ve thought about trying to design one and 3D print it.

How much more aero is it actually (other than looking cool!)? I haven’t really paid attention to any data or lack of data for aero cranks.

Where are the strain gauges located on this PM?
Are you sure you're not interfering with it's measurement? A crank based measurement outboard of your cover, or a spindle based measurement inboard of the chainrings hould be fine. However, if it's measured anywhere else, I'd be worried the cover is taking at least some structural load and thus distorting the power reading.

I'm going to be a pedantic turd and point out there is a front derailleur in that picture. While I realize that isn't the point of the topic, that just makes me twitch in my chair a little seeing that is a 2x with FD but has a custom aero cover.

welll.... back many years ago when I made it, David Millar's Prologue in the tour was still pretty fresh in our minds.

These days I don't have any derailleurs!

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My Blog - http://leegoocrap.blogspot.com