First conceived in the early 1900s, the front derailleur and its purpose – to move the chain between chainrings – hasn’t changed a whole lot. Where road bike front derailleur options remain simple and minimal, mountain bike suspension designs have forced multiple mounting types onto the market. In the first of a series of articles delving into the mysteries of componentry, we take a look at, and explain the various types, of front derailleurs on the market today.
Mountain bike front derailleurs
With Shimano’s latest XT M8000 groupset offering a ‘simplified’ 12 different models of front derailleur, and SRAM’s X0 range made up of 40 models, it’s absolutely normal to be confused and overwhelmed when picking out a front derailleur. If you’re not set on ditching the front derailleur entirely and running a ‘single ring’ setup, then below we detail mountain bike front derailleurs in three basic categories – cable pull direction, gearing and mounting type.
Cable pull refers to the direction at which the cable enters and pulls the derailleur. It’s decided by your frame design and where the cable routing leads the cable.
Top pull derailleurs refer to the cable being pulled from the top. If your cable routing follows the top tube and then drops down to the front derailleur, it’s a top pull.
Bottom pull derailleurs – wait for it – refer to cable being pulled from the bottom. If your cable routing follows the down tube and then takes the cable past the bottom bracket, it’s a bottom pull.
Dual pull is something that came out as a solution to make front derailleur options more universal. Simply, a dual pull derailleur allows the cable to be routed from either the top or bottom.
Shimano Side Swing
Shimano's Side-Swing derailleurs have the cable enter at the front
This is a new standard introduced in Shimano 11-speed mountain bike (currently on M9000 XTR and M8000 XT). The Side Swing derailleur (which, as the name suggests, swings sideways) was designed out of a need for increased clearance due to wheel and tyre sizes forever growing. The derailleur standard hopes to remove compromises frame manufacturers must make to chainstay length, chainring chainline and tyre clearance in order to fit a front derailleur.
Side Swing features it’s own new cable routing, where the gear housing comes in from the front of the derailleur – right at the bike’s seat tube. It’s possible to achieve this on an existing bike by using zip ties to route a cable, but it’s not a recommended (or pretty) thing to do.
Looking at Shimano’s range, Side Swing front derailleurs are currently coded by the last two digits as ‘20’ – ie: Shimano XTR FD-9020 and XT FD-8020.
Currently just available in XTR, electronic gears use an electric wire instead of a mechanical cable. Cable pull direction is not a part of the electronic derailleur decision.
Looking back a decade, nearly all mountain bike front derailleurs attached to the frame via a band clamp. Where band clamps remain popular, they are now far from standard. New suspension designs, frame tube shapes and material thicknesses have forced brands to re-think the front derailleur attachment point.
How the derailleur attaches (or doesn’t) to the frame is no doubt the most confusing part of purchasing a front derailleur; below we detail the various mount types.
Low clamp (aka top swing)
This is the most traditionally common of the mountain bike front derailleurs. It mounts low down to a round seat tube with a band clamp. As the clamp sits low on the frame (near the bottom bracket junction) and the derailleur itself pivots above it, these are commonly also known as a ‘top swing’ front derailleur.
You need to be aware of your seat tube diameter. Most commonly, these derailleurs now come in a 34.9mm diameter with shims included to fit smaller 31.8 and 28.6mm diameter seat tubes.
High clamp (aka bottom swing)
Wrapping around the seat tube at a much higher point than the low clamp, the high clamp derailleur has become popular on many full suspension frames or where bottom bracket clearance is limited.
With the clamp siting above the derailleur pivots, this is also commonly referred to as a ‘bottom swing’ derailleur.
It’s mounting method is quite similar to that of the low clamp, with 34.9mm diameter mounts the most common and smaller diameters often catered for by the use of shims.
On some frames with a consistent seat tube diameter, the use of a high clamp or low clamp front derailleur is completely interchangeable. Generally speaking, the low clamp type offers greater water bottle cage clearance, a cleaner look, and is a lighter option if it fits your bike.
Direct mount (aka DM, high direct mount or H0)
Fast becoming a popular choice on the modern mountain bike, the direct mount derailleur features a single attaching bolt and a grove on its back to keep it aligned with the frame mount.
In order to fit one of these, the frame must feature an appropriate mount. See our gallery above for an example of what this mount looks like.
E-type (aka low direct mount, E2-type, S3)
Shimano’s E-type front derailleur traditionally included a backplate that was held behind a threaded bottom bracket. This pre-dates current direct-mount designs and was filler for when brands started to move away from traditional band clamp derailleurs.
Nowadays, ‘E-type’ is more commonly sold without this backing plate and is sometimes referred to as a ‘low direct mount’ or ‘E2-type’ front derailleur.
Following the direct mount above, this is the next most common form of direct-mount derailleur and features two bolts 22.1mm apart, with right-side hole of the derailleur 5mm forward offset to the left one.
SRAM also offers compatible derailleurs with this mount type – they’re called ‘S3’ or ‘Spec 3’.
This mount style is becoming increasingly popular, because it's near-hidden if you decide to exchange front shifting for a simpler 1x11 setup.
Direct mount S2
Beyond the common E-type/S3 low direct mount derailleur, SRAM offers a further two options that look extremely similar, but are not cross compatible.
The SRAM S2 (or Spec 2) is perhaps the one most easily confused with the S3 (or E-type). It shares the same 22.1mm hole spacing, but instead sits far further outward and doesn’t offer the 5mm hole offset. S2 derailleurs are not commonly used.
Direct mount S1
Finally, SRAM offers the low direct mount ‘S1’ (Spec 1) derailleur. This is characterized by a 42.7mm distance between the two bolt holes. This far wider bolt placement makes it rather specific, and something – to our knowledge – only Specialized has used in the past.
Number of gears
Because of variance in leverage and pull ratios, Shimano double ring front derailleurs are slightly different to their triple ring derailleurs. With this, even the latest 11-speed groupsets offer a different model of derailleur for triple chairing users – these feature the designation of the last three digits as ‘000’, ie: Shimano FD-9000 (XTR) and FD-8000 (XT).
You never needed to worry about chainring size with band clamp derailleurs as you could just match it by sliding the derailleur up and down the seat tube. However, the limited range of adjustment afforded by direct mount designs has meant more limited chainring sizes. With this, pay close attention to the recommended chainring sizes with each direct mount front derailleur, nowadays; Shimano’s latest aren’t designed to go above a 40t chainring.
Mix and match compatibility
Naturally, neither Shimano nor SRAM would ever dream of recommending it, but you can generally mix and match front derailleur and shifter brands with reasonable success. The key here is to ensure that all other factors (cable pull, mount type and gearing are correct).
Road bike front derailleurs
As it was previously mentioned, road bike front derailleurs remain a relatively simple device with far fewer options than those in mountain biking. Road front derailleurs are bottom pull, with the cable pulling from beneath the bottom bracket.
With Shimano and Campagnolo offering electronic groupsets, this has added a few additional options and one must pair an electronic front derailleur of the same brand to the matching electronic shifters.
Breathe a sigh of relief here, as currently road bike derailleurs don’t have many mount options. There are really just two types.
Band clamp (aka band-on)
Clamping to a round seat tube, the derailleur band clamp needs to be matched in diameter. Common sizes include 34.9mm, 31.8mm and 28.6mm. It’s becoming more common for drivetrain brands to just offer braze-on models – see below.
Braze on mounts are commonly riveted or bolted to road frames
This is the more common form of road front derailleur mounting and can be made compatible with frames needing a band clamp too. Braze-on derailleurs just feature a small nub with an internal thread to accept a mounting bolt. Many road frames will feature a ‘braze-on’ mount, which the derailleur simply is bolted onto.
If a braze-on mount is not given, then either a band clamp or alternative frame-provided mount is required to attach a braze-on derailleur.
Much like mountain bike derailleurs, the derailleurs are slightly different depending on whether you’re using a double or triple chainring. Double chainrings make up the vast majority of road bikes nowadays, but triple front derailleurs can still be sourced easily.
Mixing and matching generations of groupsets introduces another issue – older eight- and nine-speed front derailleurs are typically more 'open' than newer 10- and 11-speed models. With this, you may experience greater chain rub if using a newer front derailleur on an older ‘fewer-speed’ drivetrain.
Mix and match compatibility
Generally we’d suggest keeping the front derailleur in the same brand and series as your shifter. However, if for some reason you’re not fond of this, then you can generally mix and match older front derailleurs and shifters with reasonable success.
With the advent of 11-speed gearing, newer derailleurs and shifters have played with various cable pull ratios (the amount of cable pulled by the shifter) to increase shift speed and lower the shift effort. Therefore on newer drivetrain models, we’d certainly recommend keeping the components matching.