Rohloff FAT Bone for 180 mm rotors – for Postmount
The Rohloff FAT Bone 180 (8556) anchors the torque of an XXL SPEEDHUB (CC 190 mm / A12 197 mm, OEM2 axle plate) through a 160 mm post-mount brake mount and lifts the caliper for a 180 mm rotor – torque support and brake adapter in one.
Why the FAT Bone?
Two jobs, one part. It takes the hub torque via the OEM2 axle plate and carries the post-mount brake caliper. 
160 mm mount, 180 mm rotor. Fitted between frame and caliper, it converts a 160 mm post-mount frame to a 180 mm rotor. 
Bolts included. Supplied with M6x20 countersunk bolts for the frame mount (6–8 Nm); the caliper uses its original hardware. 
Strong anchoring. In low gears the hub passes very high torque into the frame – the FAT Bone is designed for exactly that.
Seatstay or chainstay mount
Rohloff allows the FAT Bone on frames with the post-mount brake mount on the seatstay or on the chainstay.
With a CC 190 mm axle, the anchoring point must lie on or behind an imaginary line through the dropout slot, so the torque cannot lever the axle out. With the A12 197 mm thru axle this does not apply.
Who is it for?
- Fat bike riders with an XXL SPEEDHUB. Year-round riding in snow and sand with 14 sealed gears.
- Frame builders. The standard Rohloff solution for 190/197 mm frames with post-mount brakes.
Compatibility
| Hubs | SPEEDHUB 500/14 XXL: CC OEM2 190 mm, A12 OEM2 197 mm |
|---|---|
| Frame brake mount | Post mount direct, 160 mm |
| Rotor size | 180 mm (Rohloff 4-bolt disc on the DB hub cap) |
| Frame bolts | M6x20 countersunk, 6–8 Nm (included) |
| Not for | Tandems; 140 mm or 203 mm post-mount frames |
Frequently asked questions
My frame has a 180 mm post mount – which FAT Bone do I need?
Then you need the FAT Bone 203 (8557), which takes a 203 mm rotor.
Can I use it on a tandem?
No. Rohloff does not permit the FAT Bone or the OEM2 axle plate on 190/197 mm tandems.
My frame has an IS brake mount – what then?
For IS2000 mounts on XXL hubs Rohloff offers the Monkey Bone -10 (8553-10 for 160 mm, 8554-10 for 180 mm).
About Rohloff
Rohloff AG designs and builds the SPEEDHUB 500/14 in Fuldatal, Germany: a 14-speed gear hub with a 526% gear range that has proven itself for more than 20 years on touring, tandem, cargo and e-bikes.
BoodaBike (Massive Bikes, Budapest) is an official Rohloff service centre, trained by Rohloff, and an official European distributor of Rohloff hubs and genuine spare parts. Not sure which part fits your hub? Send us the serial number and a photo of your hub and we will check it for you.