It's the "crank shaft" of your bicycle, the small part that helps direct the power from your legs to the drivetrain. It's the bottom bracket, which our resident expert Tim Laflin addresses in this issue of Tech Talk:

What is the difference in bottom bracket design? Shimano and Campy both offer sealed cartridge bottom brackets. What is the big deal? Campy makes a typical design for their philosophy and so does Shimano. The Shimano bottom bracket is a very easy to install piece that seems to work as well as the Campy unit. The one advantage that Shimano has in design over Campy is that the bottom bracket bearings are all sealed in the cartridge as a unit. Campy uses individual sealed bearings (3 to be exact, two on the drive side and one on the non-drive), and if water is allowed to collect in the bottom bracket shell it will enter the Campy bearings before draining out the threaded areas in the bottom bracket. The only exposure to contamination that Shimano worries about is on the exterior of the bottom bracket where the spindle meets the crank arm. On the exterior, the plastic bearing seal is all Shimano uses were Campy goes to an extra step of putting a seal on the fixing cups to seal out dirt and water.

I have not seen early failure of either companies bottom brackets. If your frame collects water in the bottom bracket shell the Shimano bottom bracket might work better for you. The difference comes in the way the bottom brackets are made. The Campy design allows the user to replace the bearings where Shimano makes the entire bottom bracket as sealed unit which must be replaced in its entirety--the old one is then thrown way. The really neat thing about the Campy design is that you can get the bearings from almost any local bearing distributor and you can change the characteristics of the bottom bracket. It is possible to substitute faster low drag bearings or full contact metal sealed (high drag) bearings if you ride in the wet a lot. I have a friend who lives on board a sail boat who ruins bearings like crazy on his bike that he keeps on the ship. The answer was a set of stainless steel-cased full-contact sealed bearings. There is nothing special about the Campy bearings to force you to use their bearings.

Installation is very typical to Shimano thinking. They use a special bottom bracket tool, which is heavy enough to kill somebody if you drop it on them. Campy took a more elegant approach and reused the lock ring tool for the cassette to install the bottom bracket; it is very small and light. If you tour and carry tools this is an important fact.

Campy uses a 103mm bottom bracket for Record and Chorus and the rest of the gruppos use the 111mm and 115mm bottom brackets for all the other cranks including the Racing Triple. That means you can replace the crank on a non Record or Chorus bike with a triple and not have to swap the bottom bracket. Lots of Florida racers use a triple front and rear derailleurs and when they go to the mountains just pop on a triple up front. All the Campy shifters can handle the triple so you don't have to change much. Shimano uses a 103mm bottom bracket for the super low profile Dura-Ace crank and 115mm for the standard Dura-Ace. The Ultegra uses a 115mm bottom bracket for every thing. The 105SC super low profile takes a 107mm bottom bracket, 105SC low profile takes a 115mm bottom bracket, 105SC triple takes a 118mm bottom bracket and the standard 105SC takes a 107mm bottom bracket. It is a little easier to remember the Campy numbers if nothing else.

The only note to watch out for is the 105 bottom brackets come with plastic fixing cups on the non-drive side. This is a cheap piece and care should be taken installing it. The Dura-Ace and Ultegra as well as the Record, Chorus and Athena bottom brackets come with aluminum fixing cups.

Tim Laflin

We created this page on April 7, 1997

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