Front derailleurs are simple to fit and adjust. We show you how to get them working right.
If replacing a front derailleur on its own it is essential to buy the correct replacement, and this can be complicated. Front derailleurs come in different versions to suit different chainring combinations, frames, shifters, chain types and cable runs.
With road bikes, front derailleurs are available for compact (typically 50/36T or 50/34T) chainrings and standard double chainring combinations, and also for triple chainrings set-ups. Braze-on or clamp-on fittings are available for several sizes of seat-tube: steel frames take 28.6mm, while 31.8mm and 34.9mm are available for use on aluminium and titanium framed bikes. Almost all road bikes use cable run from below, but it’s common practice on cyclocross bikes to use a cable from above. An MTB front derailleur will probably be needed here.
Shimano road STI shifters can only be used in combination with a front derailleur designed to work with them; Shimano MTB front mechs will not index properly with the left-hand STI lever but can be used with down-tube or bar-end shifters. 10-speed front derailleurs may not always work with 11-speed chains. You need to check with the manufacturer’s websites: http://cycle.shimano-eu.com and http://www.campagnolo.com/home.php
- Front derailleur fitting
Before doing anything, make certain that you have the correct front derailleur for the rest of your drivetrain and your frame. Loosen the cable clamp bolt and remove the derailleur’s cage bolt and spacer. Slide the derailleur cage over the chain. If fitting to a braze-on, bolt the derailleur into place, tightening the fixing bolt to hold it firmly in place. With a front derailleur fitted with a clip to the tube, open the clip, fit the derailleur into place and tighten the clamp. Do not use any tape between the derailleur clamp and tube.
- Front derailleur position
Push down on the cable operating arm so that the cage moves outwards over the outer chainring. Loosen the derailleur’s fixing bolt and position it so that the outer cage clears the big chainring by 1-3mm. Turn the derailleur so that a center line along the cage runs parallel to the chainrings. Tighten the derailleur mounting bolt and check that the derailleur cage does not touch the outer chainring. Finally tighten the derailleur’s seat-tube clamp bolt firmly but not too tightly; some tubes are very thin and can easily be crimped by an overtightened front derailleur clamp.
- Small ring limit, cable fitting
With the rear derailleur shift the chain onto the largest rear sprocket; move the chain by hand to the inner chainring. The outer limit screw is normally the high gear stop and the inner limit screw the low gear stop. Check on your own derailleur. Adjust the low limit screw so that the inner plate of the cage is about 1mm from the chain. Back off all the adjustment on the down-tube adjuster. Attach the cable to its clamping and pull through until there’s no slack and then firmly tighten the bolt, checking that the cable is routed correctly through the clamp.
- Big chainring limit and final checks
Shift the rear derailleur on to the smallest sprocket and with the front derailleur shift the chain onto the large chainring. Adjust the high limit screw so that the outer plate of the cage is about 1mm outboard of the chain. Now check the shifting at the extremes on the rear derailleur with the chain on both the smallest and largest sprockets. Check that there is no chain rub at these extremes on the front derailleur cage and that the chain does not overshift the small or large chainrings.
- Cable adjustment on Shimano triples
Move the chain onto the middle chainring and largest rear sprocket. Adjust the cable tension with the down-tube adjuster so that the clearance between the derailleur’s cage inner plate and the chain is between 0.5 and 1mm. Click the front STI lever one click so the chain moves outboard a little. With the rear derailleur select the smallest rear sprocket. Check that there is about 1mm of clearance between the chain and inner plate of the derailleur cage. If not readjust the cable tension (1/8 or 1/4 turn) of the down-tube adjuster and then recheck the clearance when the front derailleur is in the inner trim position and with the chain on the largest rear sprocket.
- Front derailleur maintenance
Clean the derailleur with a degreaser and apply a little lube to the parallelogram pivots. Wipe off any excess. Check the height of the derailleur as in step 2 and its alignment with the chainrings. Check the derailleur’s stops are set correctly (steps 3 and 4). Check the inner cable for fraying at the clamp and replace if necessary as in step 7. Check the shifting of the front derailleur with the chain on both the smallest and largest sprockets on the cassette as in step 8. There should not be chain rub on the front derailleur cage at the extremes.
Cable condition is critical to your gears working correctly. Check the outer cable from the STI or Ergopower lever to where it is fitted to the stop on the frame. Renew both the inner and outer gear cables if they have not been recently replaced. They only have a finite life which can be between a year and two year’s use. If they are reasonably new check the inner cables for fraying, particularly at the cable clamp bolt. Ensure that the inner cable always has a cable end cap fitted – frayed cable ends sticking into your calf can be especially painful!
- Front derailleur final checks
Shift onto the largest rear sprocket. Check that under repeated shifting from the largest to the smallest chainring the chain shifts without hesitation, but does not overshoot the small chainring inwards. If necessary adjust the low gear limit screw half a turn at a time either to make the shifting cleaner (anti-clockwise) or to prevent overshifting (clockwise). Shift into the smallest rear cog. Repeatedly shift onto the biggest chainring, adjusting the high limit screw half a turn at a time until it does so without hesitation but does not overshoot the largest ring.