Originally Posted by
79pmooney
I cut a piece of narrow inner tube so 18" long, wrap it around the HB, try the mount on it and just keep cutting an inch or two at a time until the fit is good.
I'm not just saying this. All my HBs are 25.4 or 26.0. Nevgr owned a 31.8. I've got an Element Bolt on my good bike right now. (This trick works for all oversized HB mounts. I just keep that length of tube with it's computer, light or what-have-you. For a neater look, you can cut the tube into a narrow strip just the width of the clamp. but that required more than twice the wraps. I used to do that but no longer.
I just bought a Wahoo bolt 2 and I need a mount for a 25.4/26.0. The stem mount works with zip ties so it won't be easy to transfer from one bike to another. The out front mount is easy to move from bike to bike but it is compatible with 38.1 handlebars. This is a 2 year old thread but it is a good solution.
Post 5 above has some solutions as well as there are 3d party mounts with shims like this but may not be compatible with version 2 of the bolt,
https://www.amazon.com/Wahoo-Elemnt-...01G35DLQ0?th=1