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SubscribeFront Derailleur Setup with Mark Purdy
Wed, 10/07/2009 - 7:28pm by Andy
Photographer:
Andy Shen I recently got a new BH G4, and I had a really hard time setting up the front derailleur. I've never had trouble setting one up, but for reasons unknown I couldn't get things to work right. Some chain rub when in the cross-over gears is acceptable (the big-big and small-small sets that 'they' always tell you never to go into), but it was happening in the 4-5 smallest cogs/small ring combination. Part of the problem was that the frame has very short chainstays, which makes the chain run at slightly sharper angles. But even so, I knew there was something I was missing, so I contacted Mark Purdy of NYCVelo to give me a remedial lesson on front derailleur setup.
Step #1 for Purdy is to insure that the BB and crankset are both installed properly onto the frame. Next, mount the FD before installing the chain. Most carbon frames use a braze-on style mount, while most round tubed aluminum and steel frames use clamp-on style mounts. Some carbon frames have mounts attached to the frame with bolts and slotted holes instead of rivets (my BH has this), which is nice as you can tweak its angle so the FD tracks the chainring as closely as possible. If the mount can't pivot and the angle doesn't match well (this can be the case if you're running compact cranks), SRAM makes a wedged insert that lets you adjust the angle. Next set the height so that the closest point between the FD and Chainring is 1-3 mm. Remember that most chainrings have teeth that are profiled differently, so set up on a tall tooth.
Before you tighten the mounting bolt, set the middle part of the outer cage parallel to the chainrings. Later, if the chain is rubbing in crossover gears in the small ring you can angle the tail of the cage outboard. In drastic cases, Purdy will bend the outer cage to make appropriate clearance.
Next, roughly set the limit stops by eye. Now you can install the chain and set up the rear derailleur. RD’s are a whole class on their own, but that’s a story for another day. For now, let’s just assume that the RD is aligned and adjusted properly. Shift the chain onto the biggest cog on the rear, and double check the inner limit stop. Get the inner cage as close to the chain as you can without rubbing. Now it’s time to connect the cable to the FD. This may sound remedial, but make sure the cable is routed correctly through the BB cable guide. Incorrect routing can cause excess friction and sluggish shifting. Purdy suggests cleaning and lubing this spot frequently to keep it smooth.
Now, pull the cable as taut as you can with your fingers and tighten the pinch bolt. Purdy prefers to install without using a cable pulling tool, which he thinks can pull the cable too tight. The cable should have no slop, but shouldn't be as tight as a guitar string – the FD should move as soon as you move the shift lever. If the FD won't rest on the inner limit stop then the cable's too tight. Another indication that the cable's too tight is if the FD doesn't move slightly inward from the big ring when you trim it. That's a sign that the cable's under excessive tension as the FD is pushed against the outer limit stop. Unfortunately modern bikes have done away with barrel adjusters on the cable stops, so you may have to attach and reattach the cable a few times to get this just right.
Next set the outer limit screw. With the chain on the smallest cog on the rear and the big ring in front, set the outer limit to 1 mm of clearance between the chain and the inside edge of the derailleur cage. Some people think the FD should be able to travel a little past its outboard position to complete the shift, and then settle back a touch, but that isn't Purdy's preference. If your chain and rings are in good shape you shouldn't need to do this, as it can cause the chain to derail to the outside. 8000 miles later, if your chain won’t shift up to the big ring then you know it’s time to replace that chainring.
From this point there can be a lot of small adjustments to each of these settings to insure proper function. Once you get the shifting just right on the stand, go outside and ride it to make sure it actually works that way on the road, then tweak as necessary.
So what was my problem? I hadn't matched the angle of the derailleur to the chainring closely enough, so the tail of the derailleur had too much clearance, making it more prone to rubbing. I also hadn't tightened the FD mount enough, so the whole setup slipped a few times. It took a few tries for me to finally get things locked down. The last thing I wanted to do was strip the threads and render the whole frame useless.
“I really wish there were better rules for front derailleur setup”, Purdy says. “But the truth is, each bike has its own personality.” Some suggestions for maintaining your front derailleur function: Clean and lube the pivot points as well as the cable guide, keep your chain clean and lubricated, put a new chain on every 2000 miles and replace your large chainring at about 8-10,000 miles.
This bolt-on mount has slotted holes so you can tweak the angle of the FD.
Almost there. The tail needs to rotate a bit more towards the chainring. Lots of trial and error here.
Purdy checks for clearance.
Different makes have different cage shapes. As a rule Purdy makes the middle part parallel to the big ring.
Setting the inner limit stop with the chain all the way inboard.
And vice versa
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Add a comment"See how he uses that spanner!"
Always respected Mark as a mechanic and good guy but exposing himself to this site takes balls of steel...here's some footage from is pre-stash days. http://bit.ly/1RkBpV
so all I have to do is read 'dummy's guide to bike racing?!!'
yes so does every part numbnuts, just like the FD, then why is there an article written about it? because those little pamphlets are written by technical writers that tell you the bare minimum, and don't explain the finer points and nuances of installation and adjustment. The RD is one of the most mystifying components to deal with, an article covering it would solve a lot of people's problems.
When you buy a derailleur it comes with a pamphlet that will tell you how to set it up. Take a few minutes to read it.
Nice Article. It provided the impetus for me to fix my on fd and the tips worked nicely.
Team Village People presented by Park Tool Co.
"The best thing you can do to prevent Premature cassette wear is to keep your chain Lubed and shift a lot."
Mark gave me the same advice with the ladies. Is there anything this guy doesn't know?
Kev-- A good rule of Thumb for cassette Longevity is 2 chains to one cassette. Not a Hard and Fast rule mind you. The best thing you can do to prevent Premature cassette wear is to keep your chain Lubed and shift a lot. If you ride in one or two gears all the time they will wear out Faster and you will waste your money.
And Yes, Campy chains do work with Shimano drivetrains. Neither of those two companys will admit it, but they do work.
Dude, Mark ain't no black belt. He's the fucking master. That belt is invisible.
I avoid this by buying a new bike every now and then.
Mark - your black belt mechanic status is now confirmed as that is exaclty what the Campy chian guy says happens with Campy Chains - they don't elongate so they are hard to judge wear but I guess I'll just keep track of exactly when I replace them from now on. Last question: If I throw new chain on every 3500 do I need to do new cassette each time ?or can I rotate two chains for 6-7K and keep same cassette - assume campy chain and steel Campy cassette?
Thanks!
Great article. Please have this guy teach us how to tune the rear derailleur, or is that a mechanic's bread and butter?
"So what was my problem? I hadn't matched the angle of the derailleur to the chainring closely enough, so the tail of the derailleur had too much clearance, making it more prone to rubbing"
Mark, do Campy chains work on Shimano drivetrains?
Kevlar Kid--5000 miles is excessive, even for Campy chain. Don't get me wrong, i'm a huge fan of Campy chains. I use and recommend them for all drivetrains. But even a record chain should be replaced between 3-4 thousand miles. they don't elongate the same way Shimano/Sram/Wipperman, etc. do, but they do wear laterally which affects shifting. The problem is that, since they don't elongate, if you test it with a chain checker tool it will show almost no wear. You may not have noticed you shifting getting sloppy since it happens gradually, but a new chain at 3500 miles will make your drivetrain work like new again. For a while...
I needed some of those tips on my new bike I'm setting up. Well a review but still good.
purdy's stache smells like lithium grease
Actually, Purdy picked up a 2nd job as a bike mechanic. He's been working in porn under the pseudonym Phil Stabbins for 15 years. I'm a big fan.
Did Purdy pick up a 2nd job in porn?
Mark is one of the best mechanics in the city, and thanks for sharing some of his insight and experience with the rest of us.
Great guide thanks Mark... one question though - 2K miles for a new chain? It has been pretty well established by wrenches posting on Road Bike Review that Campy chains can go 4000-5000 with proper care and regular cleaning? 2,000 means almost 4 new chains a years? Can you get more if you rotate a few chains?
http://www.acecosportgroup.com/content/
Chain catcher. All the gold ballast in dental work.
Another thing to watch for is that the derailleur you are using will work with your seat tube angle. Check the back of the derailleur, some will tell you what seat tube angle range they will work with.
What's that gold thing attached to the derailleur mounting bolt? Is it some sort of chain catcher? Or is your bike so light weight you need to add gold as a ballast to bring the weight back up to UCI limits?
so calming, so zen
is it possible to get a high resolution version of the purdy picture for my desktop wallpaper, thanks
What if I just bring the bike to you, Mark, and you can figure this out, and I just pay you some money?
i don't understand any of this.
SRAM red front derailleurs suck
More cereal, too
EIEEE KID, EIEEE KID. MARK IS THE BEST.
Mark's awesome. There's more bike mechanical knowledge in that stache than in your whole body.
you guys wonder why you don't get more people contributing content...
Actually, Mark is the love-child of Thurman Munson. He was born with that 'stache.
Is that the guy from Mythbusters?
Oh, THAT's Mark Purdy. I see him in the park after hours wearing his usual trench coat. It's nice to see the front of him for a change.
Love me some Purdy.
Did he demand you eat Quaker Oats and try to sell you insurance?
Man... that mechanic sure is Purdy, I'd like to fly him like an aeroplane.
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