top-swing, down-swing, low clamp, dual pull: front derailleur nomenclature
02-19-16, 01:48 PM
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top-swing, down-swing, low clamp, dual pull: front derailleur nomenclature
top-swing, down-swing, low clamp, high clamp, dual pull: what do these mean? I think I have a high clamp: can I use a low clamp?
What's 'chainline'?
How well do adaptors that allow one to mount a braze-on model to a clamp work? Shims, if I want a 34.9 model on my 31.8 seat tube?
What's 'chainline'?
How well do adaptors that allow one to mount a braze-on model to a clamp work? Shims, if I want a 34.9 model on my 31.8 seat tube?
Last edited by RandomTroll; 02-19-16 at 02:06 PM. Reason: Added question.
02-19-16, 02:36 PM
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RT- I see this is your second or third thread started about ft ders. I take it all the replies to the other threads haven't been of enough help yet for you to understand better. Follows is my reply to one of these previous threads trying to explain the aspects of ft der design, in case you missed it.
"Already mentioned is the direction of cable pull, bottom or top. But also mentioned is that some Shimano ders have both capacities. The next design aspect is whether the parallelogram is above or below the cage as in bottom swing or top swing. This is more about the interference with frame designs like suspension pivots, seat tubes that get non round at the shell or bottle bosses located where the der clamp might be. The there's the obvious aspect on mounting interface. What tube diameter for a clamp around one (and again some ders have shims for the common tube sizes), braze on mounts, E bracket and now direct mounts are the usual versions issues. A factor not often mentioned is that some ft ders have different cage movement for the same cable pull movement. Road and mountain ft ders can be different in their cable pulling needs as well as the cranks can have different ring spacing (center to center) between road and mountain cranks. There's the cage shape. Double rings usually have an inner cage plate with less height then triple ders have. Some cages are curved along their lower edges to better follow smaller rings. Lastly there's the cage width. Wider chains or a lack of ft shift controller trim functions mean wider or more sculpted cages. Andy"
So to try again- Top swing is when the der's frame clamp is below the cage, the parallelogram works above the clamp. This is also sometimes called low clamp. Bottom swing is when the clamp sits above the cage and the parallelogram extends below the clamp, and sometimes called high clamp. Dual pull is when the der's cable routing can be from either above the der or from bellow. As in the cable descending from the top tube or the cable raising up from the BB.
As long as the section of the seat tube is round, consistent in it's diameter and has no interfering bits (like suspension pivots, bottle bosses, pump pegs) either a top or bottom swing der could be interchanged.
See my fuller list of other design and fit aspects for the complete picture as to what you need to spec right to have a different der be the correct choice.
Chain line is the term given the dimension from the frame's center plane to the center of either the rear cog set or the ft rings. As example at the rear on a common/current road bike (the one hanging in my bike room) has the center of the rear cog set about 24mm from the end of the axle (or inside of the dropout). Since the rear hub is 130mm wide (axle lock nut to axle lock nut) this places the rear chain line at about 41mm. (130/2 - 24 = 41). The center of the 3 front rings is about 28mm from the side of the seat tube. So that chain line is about 42.3mm. (28.6/2 + 28 = 42.3. In an ideal world the front and rear chain lines should be the same. But real life of a bike's set up make this often not the case. That my bike has a difference of 1.3mm is no big deal. The non measuring way to visualize this is to place the chain on the cog and ring that are closest to being in the middle of the front or rear and sighting from behind the cog set along the chain as it travels to the front. It should be easy to notice the chain's being in a perfectly straight line or if is has some side ways offset between the rear and front.
As to using adapting shims in a clamp on design to allow for different seat tube diameters- they can work very well if set up well. Of course like any mechanical situation a good assemble or set up can have bad results. I install ders with shims at work often and our customers don't have issues with the der not being secured tight enough or in the correct position. I have a tandem with over 25,000 miles on it that uses a home made shim under it's ft der clamp.
Does this help you understand better now? Andy.
"Already mentioned is the direction of cable pull, bottom or top. But also mentioned is that some Shimano ders have both capacities. The next design aspect is whether the parallelogram is above or below the cage as in bottom swing or top swing. This is more about the interference with frame designs like suspension pivots, seat tubes that get non round at the shell or bottle bosses located where the der clamp might be. The there's the obvious aspect on mounting interface. What tube diameter for a clamp around one (and again some ders have shims for the common tube sizes), braze on mounts, E bracket and now direct mounts are the usual versions issues. A factor not often mentioned is that some ft ders have different cage movement for the same cable pull movement. Road and mountain ft ders can be different in their cable pulling needs as well as the cranks can have different ring spacing (center to center) between road and mountain cranks. There's the cage shape. Double rings usually have an inner cage plate with less height then triple ders have. Some cages are curved along their lower edges to better follow smaller rings. Lastly there's the cage width. Wider chains or a lack of ft shift controller trim functions mean wider or more sculpted cages. Andy"
So to try again- Top swing is when the der's frame clamp is below the cage, the parallelogram works above the clamp. This is also sometimes called low clamp. Bottom swing is when the clamp sits above the cage and the parallelogram extends below the clamp, and sometimes called high clamp. Dual pull is when the der's cable routing can be from either above the der or from bellow. As in the cable descending from the top tube or the cable raising up from the BB.
As long as the section of the seat tube is round, consistent in it's diameter and has no interfering bits (like suspension pivots, bottle bosses, pump pegs) either a top or bottom swing der could be interchanged.
See my fuller list of other design and fit aspects for the complete picture as to what you need to spec right to have a different der be the correct choice.
Chain line is the term given the dimension from the frame's center plane to the center of either the rear cog set or the ft rings. As example at the rear on a common/current road bike (the one hanging in my bike room) has the center of the rear cog set about 24mm from the end of the axle (or inside of the dropout). Since the rear hub is 130mm wide (axle lock nut to axle lock nut) this places the rear chain line at about 41mm. (130/2 - 24 = 41). The center of the 3 front rings is about 28mm from the side of the seat tube. So that chain line is about 42.3mm. (28.6/2 + 28 = 42.3. In an ideal world the front and rear chain lines should be the same. But real life of a bike's set up make this often not the case. That my bike has a difference of 1.3mm is no big deal. The non measuring way to visualize this is to place the chain on the cog and ring that are closest to being in the middle of the front or rear and sighting from behind the cog set along the chain as it travels to the front. It should be easy to notice the chain's being in a perfectly straight line or if is has some side ways offset between the rear and front.
As to using adapting shims in a clamp on design to allow for different seat tube diameters- they can work very well if set up well. Of course like any mechanical situation a good assemble or set up can have bad results. I install ders with shims at work often and our customers don't have issues with the der not being secured tight enough or in the correct position. I have a tandem with over 25,000 miles on it that uses a home made shim under it's ft der clamp.
Does this help you understand better now? Andy.
02-19-16, 02:37 PM
#3
Constant tinkerer
I'm not great at top swing versus down-swing but I think I can answer the rest of your questions.
High/low clamp: relative location where the FD clamps onto the seat tube. You might need low clamp if you have water bottle bosses low on the seat tube. You might need high clamp if your seat tube tapers to a funny shape near the BB. Often times you can use either.
Dual pull: indicates the cable can come from the top or the bottom. ***Note: most FDs are either top pull or bottom pull. Meaning the cable must be routed to either come across the top tube or down the downtube.
Shims work fine. I've never had an issue. Adapters also work fine.
High/low clamp: relative location where the FD clamps onto the seat tube. You might need low clamp if you have water bottle bosses low on the seat tube. You might need high clamp if your seat tube tapers to a funny shape near the BB. Often times you can use either.
Dual pull: indicates the cable can come from the top or the bottom. ***Note: most FDs are either top pull or bottom pull. Meaning the cable must be routed to either come across the top tube or down the downtube.
Shims work fine. I've never had an issue. Adapters also work fine.
02-19-16, 06:17 PM
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