Front Derailleur How-To popular
Written by: Greg Kopecky
Added: Sat Jul 20 2013
I hesitate to call this any sort of all-inclusive guide on front derailleurs. It’s not. There are too many types, brands, and potential ‘What Ifs’. We will focus on mechanical cable-actuated devices, and those which I consider to follow ‘standard’ setup procedures. Because I’m also testing some Rotor products at the moment (and non-round rings seem to be getting more popular by the day), I’m going to discuss some unique setup tips for their chainrings.
Basic front derailleur setup is easy in theory. It just is. If the frame is in-spec and all of the components jive, it’s almost impossible to screw something up. The problem is that things don’t always jive so well or fall within the proper specifications. More and more, frames are becoming ‘modules’. Rather than a clean slate to which you can attach any parts you want, the frames are starting to dictate what you can use. The more integration you seek, the more assumptions must be made by the frame maker.
Assumptions… like what?
1. The smallest and largest sizes of inner and outer chainring you are going to use
1a. Whether or not you’ll ever use a non-round chainring
1b. The number of chainrings you’ll use (i.e. double, triple)
1c. The brands of ring you might use, and the stiffness of each
2. The brands of crank you may want to use
2a. All of the baggage that comes along with that
3. That the parts you’re installing are properly made
4. That a major components manufacturer doesn’t decide to change their specifications in the middle of your frame’s life. Chainline, q-factor, bearing specification, crank spindle length – the list could go on.
That’s just a few examples. This is stuff that you never want to have to think about as a consumer, but ultimately it can affect your shift performance. You may have a preference for a component or combination of components that simply do not work with your frame. I’ve seen stranger things happen.
That being said, we’ll cover the ‘textbook’ installation for front derailleurs, and list as many possible exceptions, caveats, and special situations. If your FD setup looks, tastes, and smells perfect, but somehow doesn’t function like it should, you could very well be victim to one of these mysterious incompatibilities.
There are four key components of proper front derailleur setup:
1. Derailleur height
2. Derailleur angle
3. Cable tension
4. Limit screws
NOTE: This can vary by brand. For example, WickWerks recommends a slightly higher derailleur height for use with their chainrings (2-4mm).
ALSO NOTE: Depending on your brand of derailleur, this height can change throughout the derailleur’s swing path. It might look like you have 1mm of clearance when the derailleur is resting in the full-inboard position – but when the derailleur swings away from the bike, your clearance could suddenly be at zero (meaning that your derailleur is hitting the chainring teeth). The easy way to check for this is to move the derailleur with your hand as you’re setting it up. See how the clearance is when the derailleur is in various positions. You want to clear the teeth, but not be so high that your chain retention suffers.
ALSO ALSO NOTE: If you’re adjusting the height of a front derailleur that already has the cable attached, your life will be more difficult. Because the cable pulls from the bottom on a road or triathlon bike, that means that your cable is going to want to pull the derailleur down. Just be aware of this; you can still made the adjustment, but it will be more difficult. If you’re a beginner, just loosen the cable anchor bolt all the way before attempting to adjust the height.
Next, let’s talk about derailleur angle. Angle, you say? Really, there should be no angle. With most derailleurs, you want the outside of the cage to be parallel with the chainrings:
The most important thing to think about when setting up derailleur height and angle is the fact that you’re adjusting both at the same time. That’s the tricky part. If you’re not careful, you might let the derailleur slip down a couple millimeters as you’re fine-tuning the angle, and then have interference with your chainring teeth. A steady hand is key – so don’t drink ten cups of coffee before setting up that derailleur.
This is also where your frame becomes a dictator of shift performance. If the front derailleur mount isn’t straight, it can be impossible to set up the derailleur properly. Most modern triathlon frames use a ‘braze-on’ mount, such as this Cervelo P2C:
Clamp-style front derailleurs and adapters make life easy. With an adapter, I’ll usually tighten down the main derailleur bolt first and let the derailleur ‘find’ where it wants to rest. It will find the straightest, most secure position on the clamp. Then, I use the clamp bolt to adjust derailleur height and angle. NOTE: tightening the clamp bolt usually pulls the whole clamp one way or the other, affecting cage angle. You have to figure out which direction and how much this is going to happen, and compensate for it before tightening the clamp bolt.
Cable Tension and Limit Screws
These two topics get lumped together because they affect each other. Especially when building up a bike from scratch, there is a method that you can use that will make your life MUCH easier.
First, we want to adjust the lower limit screw. ‘Low’ and ‘High’ limits are just what they sound. The low limit adjusts the stopping point for the small chainring (your low gear), and the high limit adjusts the stopping point for the big chainring (your high gear).
Before adjusting the low limit, we need to put the rear derailleur into its lowest gear (biggest cog). My bike doesn’t have a rear shift cable yet, so what am I going to do? I can’t shift!
Or can I?
There’s a nifty trick – pedal the cranks forward, and push on the derailleur parallelogram with your left thumb to manually shift through all of the gears:
Before we go any further, I should note that you want your front shifter to be in the position of the small chainring (ALL the way), regardless of whether you’re using bar-end shifters or road shifters.
To do so, I need to turn the low limit screw counter clockwise.
You only want to move the cage enough that it just clears the chain, like this:
This is also something that is hugely affected by the mysteries of component choice, quality, and wear. A worn out chainring or chain – or one that is designed poorly – can cause shift hesitation when going to the small ring. The ‘solution’ is to let the low limit out further, but that also increases your risk for a chain drop. Sometimes a matter of 0.25 or 0.5mm of derailleur adjustment can be the difference between a system that ‘works’ and one that drops chains at every opportunity.
Now that the low limit is set, we can set the cable tension via the cable anchor bolt.
How tight should the cable be? Exactly seventy-niner Newtons of Pound Feet. If you’re off by even a little bit, nothing will work and your bike may burst into flames.
Actually, this adjustment is fairly subjective. If it’s a new cable and housing, I just tighten the heck out of the cable, because I know it’s going to get substantially looser after a couple shifts to the big ring. The best way I’ve found to do it is this – with a friction-style shifter, I want the derailleur to start moving right when I move the shifter. If I move the shifter a few millimeters and the derailleur doesn’t move, that means that those first millimeters of lever throw are taking up cable slack (meaning that the cable is loose). On a tri bike, that’s not the end of the world, but it’s still something to avoid. Some road shifters, such as lower-end SRAM right shifters have a measure of ‘slop’ designed into them, so it’s always best to read your instructions or call the manufacturer when in doubt.
If your cable tension is too high, this can limit the derailleur’s inward travel (towards the bike frame). In this case, you might think that the low limit screw is threaded in too far – you’re trying to move the cage further to the left. If the cable tension is high enough, you can unthread that lower limit screw all day long, and the cage isn’t going to move any further left; you’ve created an effective ‘stop’ with the tension. This is why we set the derailleur’s position and inner limit before setting cable tension. If you’re adjusting a low limit on a bike that already had the cable cinched down, just understand this: turning the limit screw clockwise will reduce cable tension, and turning the limit screw counterclockwise will increase cable tension.
Now that our cable tension is set, we need to set the high (or ‘outer’) limit screw. This is done in the same fashion as the low (or ‘inner’) limit.
High limit adjustment can, however, be an indicator of cable tension. If your high limit is dialed way out, but you still can’t get the chain to go into the big ring, that means your cable tension is insufficient. The cable tension drives how far the derailleur can move, and the limit is simply a means to stop (or ‘limit’) the farthest distance it can travel.
Guess what. That’s it! That’s all there is to setting up a run-of-the-mill cable actuated front derailleur.
But… BUT – I’m still having trouble with my front shifting! I’ve done everything you said, and it still doesn’t work right! As I previously alluded to, there is often more going on than meets the eye. That’s what makes a good mechanic with his or her salt – being able to diagnose what’s going on under the surface.
I’m going to attempt to list some of the most common things that can cause poor shifting even if it looks like everything is set up properly. As always, proceed with caution and always wear protective eyewear when reading my advice.
1. Chainrings are worn out.
2. Chainrings were installed improperly – backwards or timed incorrectly.
3. Chainrings are mismatched (i.e. using an inner and outer ring that aren’t supposed to be paired together). A fairly common one with triathletes is to use the fastest-looking solid time trial ring matched to any small ring, regardless of shift performance between the two.
4. Chainring bolts are loose.
5. Chain is worn out.
6. Chain was installed incorrectly. It could have been installed backwards if it’s directional (or a directional master link was installed backwards). Also: Shimano installation pin installed wrong, causing a stiff link.
7. Poor chain choice for the rest of the drivetrain.
8. Chainrings aren’t designed for the application you’re using them for – i.e. a non-ramped and non-pinned ring on a multi-speed bike.
9. Chainrings and/or crank spider aren’t stiff enough.
10. Derailleur cage isn’t stiff enough.
11. Derailleur, chain, and chainring are incompatible. Perhaps the derailleur and chain are intended for a 10-speed system, but the chainring is intended for an 11-speed system. Or – one is an off-brand or lightweight part that just doesn’t perform like a stock system would even when setup properly.
12. Frame braze-on mount is weak or inaccurately placed.
13. Derailleur is old or cheap. Long story short, the newer and more expensive ones usually work better. My first ‘real’ road bike had 9-speed Campagnolo Veloce. I could not figure out what was causing my poor front shifting – everything checked out. I spent days mulling it over. Eventually, I bought a newer-style Chorus 10-speed front derailleur, and the shift performance was night-and-day better with an otherwise identical setup.
14. Incorrect crankset or front derailleur was installed on the frame, resulting in an effective chainline incompatibility between the two.
15. Bike never gets washed, so all of the derailleur pivots are gummed up, the cables drag, and the chain has more Gatorade than lube on it.
16. Out-of-spec parts - also known as a warranty item. Bad parts happen.
17. Rider error or poor technique.
Rotor Q-Ring installation notes
Now that we’re through the basics, I’d like to show you a few tips for setting up Rotor chainrings. If you’re not familiar with Rotor, they make those curious-looking oval chainrings. I’m not here to discuss the effectiveness of the chainring shape in terms of your pedaling efficiency; I’m only going to talk shifting performance.
With Rotor rings, all of the basics are identical to normal rings – limits, cable tension, height, and angle. You want to set the cage up parallel with the rings, and so that there is 1-3mm of clearance between the top of the tallest tooth on the big chainring and the bottom of the derailleur cage.
The odd part is that, because of the oval ring shape, your clearance between the derailleur and big chainring will vary wildly. The derailleur in the following photo is set up with the proper amount of clearance at the closest point; here is the farthest point:
Does that mean you need to time your shifts to only happen when the ring is close to the derailleur? In my experience, no. The latest crop of Rotor rings shift very well. I’d heard mixed reviews on the older rings, but never tried them for myself. When set up properly, I put the new rings on-par with competitors such as Shimano Ultegra and SRAM Red, and above many lower-end rings. I think they’ve really done their homework.
The trick with Rotor is that you’re likely going to need a shim to set the position of the derailleur properly. That means that you want to use a braze-on style front derailleur (with a clamp adapter if needed). A clamp-ONLY style derailleur will not allow the use of shims to manipulate angle and placement.
When I first set up the bike in the following photos, I did not have any shims. The frame has a 78-degree seat tube angle. When in the small chainring and the smallest four cogs, the chain would actually drag on the bottom of the derailleur cage during parts of the crank cycle:
Unfortunately, this rotated the derailleur too much, so the tail of the cage was far too low relative to the front:
Luckily, Rotor USA makes their own shims. They make two versions – one is a solid 6mm, which pushes the derailleur towards the rear of the bike. The other is 6mm at the top and 4mm at the bottom, which pushes the derailleur back and angles it down. Because of my steep seat tube, I went with the angled 6mm/4mm:
Rotor also makes a couple more shims, seen here:
I don’t know exactly why Rotor rings work better when the derailleur is pushed towards the rear of the bike, but they do. I also found that they seem to work best with the newest crop of derailleurs. For example, I tried an Ultegra 6600 front derailleur, and the shifting was not acceptable. With a 6700 or Dura Ace 9000 derailleur, however, they work really well. I also tried a 2012 model SRAM Force derailleur, and it worked just fine. I’ve only used Rotor (by KMC) and Shimano 6700 chains, so I cannot speak for the Q-Rings’ shift performance with anything else.
After speaking with the folks at Rotor USA and spending hours fiddling with different rings and bikes, this is my go-to shim guide for their products (NOTE – this is only a rough guide; the best way to know for sure is to try it yourself):
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