For over 100 years, bicycles have had a chain ring fixed to the right hand crank as part of their drive train. The External Disk Brake (EDB) standard employs the same proven strategy but with an ingenious difference: the chain ring is replaced by a disc brake rotor, and the derailleur by a disc brake caliper. This innovation provides the smooth and secure stopping power of a disc brake for unicycles.

KH Spirit cranks with External Disc Brake (EDB)

The Advantages


Mounting the rotor on the crank permits a wider flange spacing on the hub. This results in a stronger wheel at minimum weight, with no change in hub width.

Weight Saving

The disc rotor mount add just 2 grams to the right hand crank, and no weight to the hub.


Works with a standard width hub for every wheel size from 24” to 36”, using a standard hydraulic bicycle disc brake and rotor.

Proven Track Record

The EDB was tested for both on- and off-road unicycling. It simply reverses the purpose of the front chain ring on a bike, which has already been proven on billions of bicycles over more than a century.

Photo: Markus Greber Riders: Lutz Eichholz & Stephanie Dietze on Cima Ombretta Orientale in Italy

The KH Spirit EDB Crank Line-up

Kris Holm Unicycles offers EDB compatible Spirit double-hole cranks in several different lengths. Click for details.

Frequently Asked Questions on the EDB Standard

Am I likely to hit my ankle on the disc rotor while pedalling?

No. The rotor is in the same location as a bicycle front chain ring. A 160 mm or 180 mm disc brake rotor is also smaller than most front chain rings. We recommend that shoelaces and loose pant legs be tucked away regardless of whether a disc brake is used on a unicycle.

Is the disc rotor susceptible to damage from ground impact?

It's rare but damage can happen. The EDB rotor is similarly vulnerable to ground impact than hub-mount disc rotors on bikes or unicycles. However, disc rotors are widely available and inexpensive to replace. KH frames are also rim brake compatible if this proves to be an issue.

Is the EDB standard compatible with all disc brake models?

Mostly, yes. The EDB standard works with hydraulic disc brakes containing International Standard (IS) mounts or IS adaptors. Mechanical disk brakes may not be compatible due to the larger size of caliper.

What unicycles contain the EDB standard?

The EDB standard is available on 24” or larger Kris Holm unicycles produced after June 2012. These unicycles contain a disc caliper mount on the frame and Spirit Disc Cranks.

Can other unicycles be retrofitted to accept the EDB standard?

Potentially, yes. The EDB standard requires an IS brake mount on the right fork blade or bearing housing, 20 mm or narrower bearing housings (to ensure clearance of disc rotor bolts), and a standard unicycle hub with 154 mm or longer axle. A Nimbus brand D'brake disc mount works with Spirit cranks on many unicycles. Older (pre-2012) KH frames contain 22 mm wide bearing housings, and will likely require filing the bearing housing to prevent the disc rotor bolts from rubbing on the frame. User frame modifications void the KH warranty.

Does the EDB standard work with the KH/Schlumpf geared hub?

The latest model (2016 and later) KH/Schlumpf geared hub is fully compatible with the EDB standard.

KH/Schlumpf geared hubs produced before 2016 are not compatible with the EDB standard, due to insufficient clearance between the installed crank and frame. Some riders have chosen to modify their KH equipment to allow for EDB usage. User modifications to KH equipment void the KH warranty and are done so at the riders own risk.

Click here for additional notices regarding use of the KH/Schlumpf hub with disc brakes.