Rohloff FAT Bone for 203 mm rotors – for Postmount
The Rohloff FAT Bone 203 (8557) is the torque adapter for XXL SPEEDHUBs in fat bike frames with a 180 mm post-mount brake mount: it anchors the hub torque via the OEM2 axle plate and positions the caliper for a 203 mm rotor – maximum braking power for heavy fat bikes.
Why the FAT Bone 203?
Big rotor, strong brake. A 180 mm post-mount frame becomes a 203 mm rotor setup – useful for loaded fat bikes and long descents. 
Torque support built in. The OEM2 axle plate locks into the FAT Bone, so no separate torque arm is needed. 
Hardware included. M6x20 countersunk bolts for the frame (6–8 Nm) are supplied; the caliper is fitted with its original bolts. 
Rohloff-tested combination. Part of the official XXL mounting concept for 190/197 mm frames.
Who is it for?
- Heavy-duty fat bike riders. Bikepacking with luggage on snow or sand, where braking reserves matter.
- Builders of XXL SPEEDHUB bikes. The matching part for frames with a 180 mm post mount.
Compatibility
| Hubs | SPEEDHUB 500/14 XXL: CC OEM2 190 mm, A12 OEM2 197 mm |
|---|---|
| Frame brake mount | Post mount direct, 180 mm |
| Rotor size | 203 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
What if my frame has a 160 mm post mount?
Then the FAT Bone 180 (8556) is the right part, with a 180 mm rotor.
Is there anything to check with a quick-release (CC) axle?
Yes. With the CC 190 mm axle the anchoring point must be on or behind a line through the dropout slot. With the A12 197 mm thru axle this is not necessary.
Which axle torque does Rohloff specify?
CC axle 7 Nm, A12 axle 15 Nm. Afterwards always check that the brake works properly.
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.