Two ways to mount aerobars to 25.4mm mountain bike handlebars:
Even though the industry has moved towards to 31.8mm sized handlebars, you might still own a mountain bike with 25.4mm sized bars and want to purchase aerobars for bikepacking. I’m sure you know now, all most, if not all aerobars are made to fit 31.8mm. So you are left with upgrading your cockpit or using shims to mount them. You are probably wondering if plastic/rubber shims or 26mm shims will work… They won’t. Don’t waste your time. Here are two ways to mount aerobars for bikepacking:
1. Using Metal Handlebar Shims ($12):
I found “25.4 to 31.8” metal handlebar shims like these on Amazon and used them to mount my Profile Design T3+ Aerobars. After cutting the shims in half to lay flush before the handlebar rise, the aerobars did not move after tightening them down. See video at the end of the post on how to mount the shims.
2. The Fred Bar by Siren Bicycles ($90):
Another way to mount aerobars to your mountain bike is to use the Fred Bar by Siren Bicycles. The bar attaches to your steerer tube like a riser. The Fred Bar raises your aerobars up slightly and shortens the reach to allow your body to sit in a more comfortable position. The bar diameter is 31.8mm and the clamps fits a 1 1/8″ steerer.
Video of mounting the handlebar shims: