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Stieber CSK Backstopping Clutch for High Speed Bicycle

Every year, engineering teams from around the world come to compete at the World Human-Powered Speed Challenge held in Battle Mountain, Nevada. The current speed record stands at 133 Km/h (83 mph). Team AeroVelo, comprised of professionals and engineering students from the University of Toronto, brought “Eta”, their newly designed, high-speed aerodynamic bicycle or “Speed Bike” to the 2014 competition.

Most bicycles have a freewheel which allows the wheel to rotate even when the pedals and chain are stationary. However, Eta’s front-wheel-drive design could not utilize an off-the-shelf bicycle freewheel. Instead, an overrunning clutch solution was required.

After careful research, the team contacted Formsprag in Warren, Michigan to request a Stieber Model CSK25 PP overrunning clutch, which was donated as part of Formsprag’s Student Support Program. While other clutches were considered, given the size and loads involved, the CSK was the clear choice. The clutch was press fit onto the front wheel hub body, and pressed inside of the sprocket. It is responsible for driving the wheels up to 145 Km/h (90 mph).

CSK units feature ultra-hard Formchrome® sprags which provide extra-long life, maximum wear resistance and lower maintenance costs. Formchrome sprags — exclusive with Stieber/Formsprag — are made by diffusing chromium into the surface of hardened high carbon alloy steel to form a chromium-carbide alloy.

With the help of the Stieber clutch, Team AeroVelo’s Eta speed bike achieved a top speed of 126 Km/h (78 mph) at the 2014 World Human-Powered Speed Challenge.

Stieber CSK Backstopping Clutch Flat View


  • 77.5 lb.ft. (105 Nm) torque capacity
  • Sprag type backstopping clutch
  • Keyway on both the inner and outer race
  • 5,000 RPM maximum overrunning speed
  • Formchrome┬« sprags for long life

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69126 Heidelberg - Germany
Phone: +49 6221 3047-0
Fax: +49 6221 3047-31

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