Had an email from a guy yesterday telling of his recent success tuning his rear derailleur, following my recent post on the topic. However, his bike also has a front derailleur...
So, with sincere apologies for neglecting the front end, here is how to whip those doubles and triples into shape.
The procedures and adjustments are very similar to the rear but, we do have one rather important extra step. Unlike the rear, there is not just one single point of simple attachment. We have to set the height and angle using our own judgment.
So, what we are looking for is clearance of the cage of the derailleur as it swings over the chain rings, while still keeping it low. A gap of about 1mm between the top of the big ring and the bottom of the outer cage plate is ideal; manually pivot the cage out to get a look at the gap.
Next we need to set the angle. As you look down onto the chain rings the cage of the derailleur needs to run parallel with the rings.
Now you have your derailleur mounted correctly we can set the limit screws. We start on the low limit screw first.
Change gear at the rear to the high gear, small cog. Here is where it gets a little tricky. You now have to manually swing the front derailleur out while turning the crank to shift into the high gear, big ring. It might take you a couple of tries, the spring on the derailleur is pretty tough. Once you get it pushed out to its stop, adjust the High limit screw to get clearance between the chain and outer cage plate of 1mm, when you are happy, release hold of the derailleur and cycle the chain back to the small ring. Attach the cable making sure that the shifter is set on the low gear or number 1.
Try it out. If you have a slack in the cable, just take it out using quarter turns on the barrel adjuster, until it works perfectly.