Road Bike Front Derailleurs
The front derailleur, or front mech as it is more commonly known, is the device just above the front cogs, chainset, which moves the chain on to the large or small cog at the front, i.e. changes your front gears. It is operated by a cable, or electronically on some modern systems, which pulls the mech a certain distance away from or towards the frame moving the chain at the same time. Most mechs tend to be indexed in that they move the chain a certain distance without sending the chain over the big cog or sending it too far in and off the smaller cog. There is a certain amount of leeway built into the changing process which allows riders to move the mech slightly to avoid chain rub on the mech itself without changing gear, a process called ‘trimming’, depending on which gear you are in on the back and the angle of the chain from front to back cogs.
There are several types of front mech which are named after the way the mech is mounted on the frame, the way the cable enters the mech and the number of cogs the mech has to move across.
Front mechs can be attached to the frame via a clamp attached to the mech, clamp on, which goes around the seat tube of the seat tube of the frame. The diameter of the seat tube determines the size of the clamp you need but most modern frames are either 31.8 or 34.9 sizes. If there is already a mounting tab on your frame for a mech to bolt to without a clamp then this is known as a braze on front mech.
- Since nearly all road bikes have the cable running down the down tube of the frame and entering the mech from the bottom bracket area underneath the mech then they are called bottom pull as this is the direction the cable coming up pulls them.
- The number of front cogs the mech has to move between determines whether you need a double, two cogs, or triple, three cogs, as the more cogs then generally you need a larger back plate on your mech to cope with the greater jump in cog sizes.
There are three main companies which produce road front mechs; Shimano, Campagnolo and SRAM, which may look and operate very similar, are unfortunately incompatible with each other’s systems. This is because each system has a certain amount of movement from the gear lever and differs slightly with each manufacturer. As an aside, they do work with each other to a certain degree but it is not as slick and not recommended for long term use.
Each manufacturer also recommends only using the correct rear mech for each groupset as some mechs may not work with differing numbers of gears, i.e. Dura Ace 11 speed must use an 11 speed front mech as it is different in size to a 10 speed front mech. You can mix front mechs from the same manufacturer as long as they are designed for the same number of gears, i.e. you can use a 10 speed Shimano 105 mech with an Tiagra 10 speed groupset as they are both 10 speed compatible. Some front mechs will work across different numbers of gears but it can be tricky to set up so it’s always easier to run a matching mech with the specified amount of gears.
Shimano are the world’s biggest cycle groupset manufacturer making front mechs for all types of bikes and riders. From professional riders to shopping bikes, Shimano make a front mech for it and all are commercially available to buy so if you fancy using the same rear mech as a Tour de France winner you can easily buy that part although it is very expensive.
The hierarchy of Shimano road front mechs from professional to entry level is as follows:
- Dura Ace
Campagnolo are the world’s oldest manufacturer of cycle gears and the company which actually invented the rear derailleur. They produce professional level components for some of the world’s top cycling teams down to weekend warrior suitable gears with prices to suit
The hierarchy of Campagnolo road front mechs from professional to entry level is as follows:
- Super Record
SRAM are the newest groupset manufacturer and have come up with a series of ingenious inventions which have quickly gained a wide fan base from professional to recreational with their alternative view on operating systems.
The hierarchy of SRAM road front mechs from professional to entry level is as follows: