Front derallieur compatiiblity

The compatibility info at si.shimano.com is a great resource for Shimano compatibility questions. You can also find the specification handbook (including current models on the web version and pdf archives of the handbook going back to 2004), as well as service documents by model (dealer manuals, exploded views, etc)

The parameters that need to be compatible for a front derailleur are:

Front speeds: triple or double

Top gear teeth: the number of teeth on the large chainring. an FD outer cage plate meant for a 38T will not sit low enough on a larger chainring like a 44.

Rear speeds/chain: different numbers of rear cogs require different chains, and both the width and the profile of the FD cage are designed to match a specific chain. 6, 7, and 8 speeds all use the same chain width.

Shift family: how much cable does the shifter pull? When it comes to switching front shifters, the front drivetrain compatibility chart is not quite exhaustive. I believe all Shimano MTB 3x front shifters pull the same amount of cable, but I could be wrong on that.

Total capacity: maximum accepted difference between big chainring and small chainring teeth count.

Top-mid tooth difference: for triples, how much smaller is the middle ring than the big ring? 3x FDs tend to have some shaping that’s specific to where the chainring is expected to be.

Chainline: distance from the center of the bike to the center of middle chainring, or the average of the chainrings on a double.

Chainstay angle: angle between the line through the center of the rear axle and the bottom bracket, and the seat tube to which the FD is mounted. Only a concern generally for clamp band derailleurs, and generally only for MTB type front derailleurs. Can be measured directly, found in the geometry tables for a bike, or by referencing the old FD’s specified range of chainstay angles.

Mount type: how it attaches to the frame. Could be a: -Band clamp: usually includes shims for use with smaller seat tubes -Braze-on: road bikes, sort of a curved plate on the side of the seat tube, with a vertical slot for the fixing bolt -Direct mount: mountain bikes, either High Direct/DM, consisting of one threaded hole next to a vertical slot/groove; or E-type/Low Direct, with two bolts a little under an inch apart horizontally -E-type with bottom bracket plate adapter: older style mtb front derailleur mounted to a plate held by the bottom bracket cup)

Swing/action: -top swing/low clamp: the derailleur parallelogram swings above the main pivot, generally corresponding to a lower clamp position for a band-type derailleur -down swing: more traditional style where the cage swings below the main pivot, generally placing the clamp band further up the seat tube -side swing: instead of a vertical parallelogram, the parallelogram is horizontal; can be had in low, mid, or high clamp band configurations as well as direct mount.

Pull: Top pull: cable must approach from the top of the derailleur Down or bottom pull: the cable must approach from below the derailleur Dual pull: the cable can approach from either above or below the derailleur Side swing: side swing front derailleurs require the cable to enter from the front, usually with full-length housing along the downtube