Post by dasaint on Mar 31, 2004 16:00:18 GMT 8
After a recent accident in Australia in which a cyclist was injured when her front brake pulled away from the fork, road bike riders are being urged to check that the front brake is properly fitted to their bikes.
Almost all modern road bike brakes are mounted to the fork using a cylindrical hex key nut that inserts into the back of the fork crown and engages the brake center bolt. The depth of the fork crown varies between bikes, and carbon fiber forks in particular can have quite deep crowns. These crowns require a longer nut to properly engage the centre bolt. If a nut is used that's too short, then it's possible for the brake to become detached from the bike with potentially hazardous results.
While this problem seems to be rare, it's straightforward enough to check for it. The nut should turn at least six times before it disengages from the centre bolt - if it unscrews with fewer turns, then a longer nut is needed.
According to our local Shimano office, centre bolts for Shimano brakes are available in four lengths: 10.5mm, 12.5mm, 18mm and 25mm. Dura-Ace brakes for aftermarket use come with 12.5mm, 18mm and 25mm, and the fitting instructions say, "For sunken nut type brakes, use sunken nuts of the appropriate length which can be turned six times or more; when re-installing, apply sealant (locking adhesive) to the nut threads."
By the way, we're emphatically not implying that Shimano has a particular problem here - but there are a lot of Shimano brakes out there, so the parts situation is a useful illustration, and Shimano's instructions apply to just about any safety-critical threaded fastener on a bike.
Almost all modern road bike brakes are mounted to the fork using a cylindrical hex key nut that inserts into the back of the fork crown and engages the brake center bolt. The depth of the fork crown varies between bikes, and carbon fiber forks in particular can have quite deep crowns. These crowns require a longer nut to properly engage the centre bolt. If a nut is used that's too short, then it's possible for the brake to become detached from the bike with potentially hazardous results.
While this problem seems to be rare, it's straightforward enough to check for it. The nut should turn at least six times before it disengages from the centre bolt - if it unscrews with fewer turns, then a longer nut is needed.
According to our local Shimano office, centre bolts for Shimano brakes are available in four lengths: 10.5mm, 12.5mm, 18mm and 25mm. Dura-Ace brakes for aftermarket use come with 12.5mm, 18mm and 25mm, and the fitting instructions say, "For sunken nut type brakes, use sunken nuts of the appropriate length which can be turned six times or more; when re-installing, apply sealant (locking adhesive) to the nut threads."
By the way, we're emphatically not implying that Shimano has a particular problem here - but there are a lot of Shimano brakes out there, so the parts situation is a useful illustration, and Shimano's instructions apply to just about any safety-critical threaded fastener on a bike.