Bicycle Mechanics - Top Swing vs Bottom Swing

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ronbridal
12-03-05, 04:01 PM
I understand the difference between top pull/down pull, but I don't understand the difference between top swing and bottom swing. I am building a cross bike that will have 39/46 chainrings. Would I be at an advantage by using one or the other? The frame is a Ridley Crossbow and has a cable guide on the back of the seat tube. I guess that makes it so I need a bottom pull. Not sure about that either. I also see that Shimano has dual pull derailleius. What do you think would be best to put on the bike? Thanks for any help. Ron

Sheldon Brown
12-03-05, 04:23 PM
I understand the difference between top pull/down pull, but I don't understand the difference between top swing and bottom swing. I am building a cross bike that will have 39/46 chainrings. Would I be at an advantage by using one or the other? The frame is a Ridley Crossbow and has a cable guide on the back of the seat tube. I guess that makes it so I need a bottom pull. Not sure about that either. I also see that Shimano has dual pull derailleius. What do you think would be best to put on the bike? Thanks for any help. Ron

If you have a cable housing stop on the back of the seat tube above the rear derailer, you need a "top pull" because the cable comes down from above.

If the cable runs under the bottom bracket and comes up to the derailer from below, you need a "bottom pull" unit.

The "top swing" vs "bottom swing" distinction is not important in most installations. These have to do with the internal construction of the derailer's pivots.

On some frames there might be a low mounted water bottle braze on that would get in the way of the mounting clamp for a "bottom swing" unit.

On some frames, the lower end of the seat tube is ovalized so much that it interferes with installing a "top swing" unit.

However, for most frames either type works. I have a slight preference for top swing, but both types work well.

Sheldon "Bottoms Up" Brown


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