Fitting a chainguard to a bike and its effective operation have been a source of constant frustration for me and apparently others, including manufacturers and bike shops. At some point I bought a lot of 12 or so guards from a Geman bike shop that were apparently misfitting customer bikes and taken off. Out of that variety of guards, I managed to fit one to one of three bikes I could use them for. The variety of frame details, derailleurs and cranksets challenges the guard design.

With that frustration, I went ahead to come up with something custom for my main bike. I started with a Driveline ring off Ebay that had its center though open. After a while I decided to fill it and I acquired alu sheet. The sheet was large, though, and after cutting the fill circle, I was left with quite a bit of material and then went to add the back and front using left-overs and L and flat bars left from other projects. Since this has been holding solid for over a week, I thought I'd share it. The guard works so effectively that there is now no difference in the appearance of the left and right legs of pants. I further completely ceased to care on which side of the bike I am standing.

That is awesome! I wonder if you can use that as a template to turn out carbon fiber copies, or do you have to custom design it for the bike?

The outline is just a product of using the combination of a compass and tape measure . Aside from this, I tried to stay away from what I perceived to be mistakes in commercial designs. As to the carbon fiber for material, sure alu is heavier but it is still pretty light. The alu sheet is quite thin. I was afraid it might deform and get in the way of the crank, but after I gave it a bit of arch it has been holding its shape in a set it and forget it kind of manner. Overall, my guard could be a bit more robust than many commercial guards I know, but some customization might be unavoidable under the best of circumstances to get this level of fit I now have.

Is that a jockey wheel just behind the chainring?
Also, my own experience with aluminum, is that uncoated such as on normal crank arms, it turns my pant legs black. It's the reason I've taken to wearing straps around both my pant legs when riding in long pants.
Did I mention that you made one heck of an impressive chainguard!

That is a wheel that is adapted from a recumbent. It acts effectively as an extra tensioner when the chain is ran around it, allowing me to boost the gear range beyond what the standard tensioner of a derailleur would allow.

You presumably have a good point there. I still had a bit of darkening in the leg, source of which I had a hard time tracing down - of course it may also be a combination of things.

Thanks .