Posted at: Feb 13, 2022
There are two types of front derailleurs, "top-route" and "down-route", depending on how the frame is routed. Here is a summary of the differences between the two, how to tell them apart, and what to look for when choosing one.
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A “top-route” front derailleur is a type of derailleur where the shift wire that pulls the front derailleur comes through the top of the derailleur.
In the case of a top-route front derailleur, the shift wire goes through the top tube as well as the rear brake, so it can be the furthest from the ground, which provides protection against mud.
In MTB and cyclo-cross bikes, there is a high possibility of mud from the ground, and if the shift wire is close to the ground, there is a possibility that the mud will clog the shift wire and prevent it from shifting gears.
However, today’s MTB and cyclocross bikes have more and more interior frames, so even with a lower pull, the shift wire is less affected by mud, etc. Therefore, a lower pull is increasingly being adopted.
The front derailleur “down-route” refers to the type of shifting that is done by pulling the shift wire that comes through from below.
In the case of down-route, the shift wire from the STI lever passes under (or in) the down tube, and then passes through the wire from under the BB to the top to pull the front derailleur.
This method is mostly used for road bikes because they are designed to be ridden on paved roads, so there is no need for mud protection.
Whether to use a top- or down-routed front derailleur depends on the frame.
Even if you buy a top-route front derailleur for mud protection, you cannot use a top-route front derailleur if the frame does not allow the shift wire to be routed through the top tube.
On the other hand, if you mistakenly buy a top-pull front derailleur for a bottom-pull frame, you will not be able to shift gears.
For example, the top images in this article are both of the band type FD-CX70, but the left one is the “top route” and the right one is the “down route. You can see that not only the position of the metal fittings that hold the shift wire is different, but also the structure that pulls the derailleur is completely different.
Most of Shimano’s current line of front derailleurs for road use have a downward pull, but be aware that some front derailleurs for cyclocross, which have “CX” in the model number, have a top pull.
Be careful when using the following two models of recent CX series front derailleurs.
MTB front derailleurs differ from product to product as to whether they have a top or bottom pull, so be sure to check the manufacturer’s official website.
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