Trek IsoZone Handlebar Bar End Reinforcements for Bar End Extensions

UPDATE 2025-08-08:m     I uploaded version 3 models that print vertically. Both models are now oriented so that they can be printed with no supports.

NOTE:     The Trek/Bontrager IsoZone grips are notoriously prone to decomposing and delaminating. The grips have been discontinued. I happened to have a different pair of grips (Bontrager Satellites), so I replaced the IsoZone grips with those. These adapters make it possible to use non-IsoZone grips, as long as the replacement grips have a securing clamp system on the outside end of the grips. Securing clamps on bot end of the grips is even better. Additional Note: when I replaced the handgrips, I also replaced the Version 2 Bar End Reinforcements with Version 3 vertically printed reinforcements.

UPDATE 2023-06-29:     I redesigned the Reinforcement End Plug as follows:

• The Version 2 reinforcement end plug worked better than the version 1. However, I noticed that the bar end loosened up a bit and they rotated a small amount. This was caused by the plastic being deformed under the pressure of the bar end clamp, because the reinforcement end plug did not exactly match the surfaces of the crimped end of the handlebar. I traced the handlebar and modified the design to fit almost exactly with the handlebar. I use these models on my bicycle, which I ride regularly, so I will see how this new design holds up.
• I am 99.99% confident that this Version 3 design will work better, and be safer than the previous versions, so I am removing those older versions.
• Make sure that you check your bar ends regularly to make sure that they are sufficiently tight.
• A better design would be to mill the reinforcements out of aluminum, which would be far less likely to deform. Nonetheless, I think this new design will hold up well.
• Make sure that you print this model with 100% infill.

UPDATE 2023-06-17:    I redesigned the filler and the reinforcement pieces, as follows:

• I decided that the filler would add the most strength by not having the hole go through it, so I made it solid.
• With a solid filler piece, I reduced the height of the post that fits into the hole in the handlebar.
• The original reinforcement piece created a diameter that was slightly too small, which made it so that the bar end needed to be clamped down with a lot of force to secure it. I didn't like putting that much force on the bar end extension, so I increased the effective diameter of the version 2 reinforcement. The original design created a diameter of ~21.7 mm, while the version 2 created a diameter of ~ 22.7 mm. The typical bar end extension fits around a 22 mm handlebar. This means that you will need to spread the extension clamp a bit when sliding it over the handlebar end & reinforcement, or sand/file down the reinforcement a bit for a perfect fit for your extension clamp. I think that it is better to have the reinforcement a little bit on the large side, than it is to have it too small.
• For a better fit, I also shaved off a small portion of the apex of the V shape of the reinforcement that interfaces with the handlebar crimp.

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Certain models of Trek bicycles use IsoZone shock absorbing straight handlebars, which have an absorbing gel cushion built into the grip area of the handlebar. In order to accommodate this absorbing pad, the actual handlebar is crimped in the area of the pad. The hand grips then cover the pads. I regularly do long rides and I like to use bar-end extensions for various reasons. However, the crimped IsoZone handlebar ends are less accommodating for common clamp-on style bar ends, because there is less material to clamp around, and the handlebar end is no longer a complete circle. These reinforcement adapters convert the crimped IsoZone handlebar ends into a more traditional and sturdy round end, in the area where a clamp on extension would go. This assembly is designed to fit clamp-on style bar end extensions that fit handlebar ends with a 22mm diameter.

To use these adapters, you are required to trim away a portion of the absorbing pad, and to shift in the hand grip enough to accommodate the extension clamp (See photo). I am not worried about losing a little bit of the padding, because I ride with my hands on the extensions most of the time.

Note: the reinforcement adapters extend in farther than the width of a typical handle bar extension clamp because the IsoZone handlebar has a hole in it to help hold in place the padding. This hole introduces weakness to the handlebar, which isn't a problem if your are only using the stock handgrips. However, with the added torque on the handlebar end that extensions can introduce, I thought that it would be wise to extend the reinforced adapters in and beyond the hole (see photos). 

I printed the reinforcements with about 6 wall layers, which should make the reinforcements fairly strong. Just make the walls thick and print with 100% infill.

Note: when installing these adapters, the shift and brake levers, and the hand grips, AND the handlebar extensions need to be installed and slid in toward the handlebar stem enough to allow for the installation of the bar end reinforcement. Then, when the reinforcements are installed, the extensions, grips, and levers can be re-positioned and tightened in place. The extension clamp will tighten down nicely on the handle bar end and adapter. The fit is fairly tight, so you might need to loosen up component (brake and shift levers, and grips) clamp screws and spread the clamps a bit with a flat/straight slot screwdriver, by carefully wedging the screwdriver tip in the gap in the clamp.