Shimano SM-AD91 braze-on front derailleur clamp

The SM-AD91 Shimano is an adapter clamp designed to mount a braze-on front derailleur on a frame that does not have a dedicated mount. It thus transforms a frame intended for direct mounting into one compatible with a clamp-on derailleur, offering a neat, reliable and fully adjustable solution.

Developed by Shimano, this adapter is used on many modern road and gravel groupsets (Dura-Ace, Ultegra, 105, Tiagra and certain Di2 models), ensuring broad compatibility and a precise finish. In particular, it allows for the correct adjustment of the angle, height and positioning of the front derailleur to ensure optimal gear shifting.

Available in sizes to suit the seat tube diameter (28.6 / 31.8 mm or 34.9 mm depending on the version), the SM-AD91 provides a stable and rigid mount, which is essential for fine-tuning the front derailleur on modern drivetrains.

Technical specifications

• Brand: Shimano
• Model: SM-AD91
• Type: solder-on front derailleur adapter clamp
• Compatibility: Shimano -road front derailleurs and certain mountain bikes (depending on assembly)
• Available diameters: 28.6 / 31.8 mm or 34.9 mm (depending on version)
• Material: aluminium
• Installation: on frames without a soldered derailleur hanger
• Use: road, gravel, cyclo-cross

Key features

• Allows a brazed-on derailleur to be fitted to a frame not designed for it
• Precise adjustment of derailleur height and alignment
• Wide compatibility with modern Shimano s
• Rigid construction for reliable support under load
• Simple and clean installation
• Standard solution used in workshops for frame conversions

FAQ

What is the SM-AD91 Shimano used for?

It allows a solder-on front derailleur to be fitted to a frame that does not have a dedicated mount, converting it to a clamp-on fitting.

Is it compatible with all Shimano derailleurs?

It is compatible with most recent Shimano road front derailleurs (Tiagra, 105, Ultegra, Dura-Ace, depending on the generation), provided you choose the correct frame diameter.

How do I choose the right size?

The size depends on the diameter of the frame’s seat tube:

• 28.6 mm (slim frames, often steel or older standards)
• 31.8 mm (modern road/gravel standard)
• 34.9 mm (oversize frames)

Is this essential for a brazed derailleur?

Yes, if your frame does not have a brazed-on mounting pad, this adapter is required to fit the derailleur correctly.

Can it be used on a mountain bike?

Yes, in some cases, but it is primarily designed for road/gravel standards with brazed mounts.