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Daily Archives: April 2, 2018

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Bicycle Maintenance with Professor Jim: Shifting, from How it should Work to Making it Work (The Front Derailleur).

I’ve done a couple of posts already on simple adjustments for the front derailleur and how to change the front derailleur cable, so I’ll lean a little bit on those. However, I didn’t give the front derailleur much thought, in terms of its own “Professor Jim” post because I thought it was too easy to bother, that I’d insult the intelligence of the people who read my blog if I went into great detail about something so simple… This is when I was maintaining the shifting on three bikes.

Today, I’m responsible for the shifting of a small fleet of bikes in our family. Since dealing with all sorts of issues I’ve come to appreciate and understand the true complexity of getting the front derailleur right. There’s a lot more to it than I once thought as a noob – and getting the shifting up front right is anything but simple. My ignorance can only be chalked up to inexperience.

With that, here’s the link to my companion post for the rear derailleur. Then I’ve got one on how to adjust the front derailleur on the fly (whilst riding). This takes some dexterity, balance and some amazing concentration. Be sure you have the skill to attempt such a thing or save that for a spin on the trainer – the best thing there is to play around with shifting until you get it right.

The front derailleur, for someone in the know, is fairly simple and straight forward. For the uninitiated, it seems simple enough but getting the thing to work just right is anything but simple. For someone like me, I know just enough to be dangerous. Let’s get rid of the danger.

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Trim

A mechanic will tell you it shouldn’t be necessary to use the trim feature in your front shift lever, but that isn’t necessarily the entire truth. I’ve come to find that the trim feature can be used to get that last gear, so they’re all accessible without the chain rubbing.

Most won’t even know there’s a trim feature built into their shifters. Mechanics are usually willing to accept a certain amount of derailleur cage rub (the metal piece the chain runs through is the cage), especially in the very top (small cog in back) gear for the small chain ring up front, and the very bottom gear (big cog in back) for the big ring. The trim adjustment will allow you access to those gears without rubbing in either ring. For instance, I have my Venge adjusted so that I can hit any gear in the big ring without trimming the derailleur. In the small ring up front, I can’t get to the higher gears (smaller sprockets on the back) without some rub. One half-click on the front shifter and I can get everything down to the smallest cog on the back. Those half-clicks are there by design…

Cross-chain

Cross-chaining is when you use the smallest gear up front in combination with the smallest on the cassette, or the biggest up front with the biggest in the back. Your chain isn’t meant to stretch like that, especially with 8, 9, 10 and 11 speed bikes. You end up doing a lot of damage to the chain, making it work in that manner. On the other hand, when you’re on a steep hill and you’ve mistakenly failed to shift into the small ring, you aren’t going to give a $#!+ about cross-chaining. You’re going to use the gear you’ve got to get your butt up the hill, before you have to shift into the small ring. Most of us do it, just don’t make a practice of it.

Set Screws

These are the set screws on your front derailleur – unless your bike is new or you just installed a new crankset, you do not need to touch them – and if you do need to touch them, you know enough about how to do it that you wouldn’t be reading this post. In other words, don’t. The set screws only limit how far in or out the cage can go when shifting the front derailleur. They’re not used to fine-tune cable tension and travel of the derailleur – this is very important, folks. These set screws almost never have to move once they’re properly set the first time:

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So let’s get down to the nuts and bolts of this. First up, for the purpose of this post, let’s assume that the derailleur was set properly. 2 or 3mm of clearance above the big ring, meaning the bottom of the cage is 2-3mm above the teeth of the big chain ring (see the photo above. To adjust this, release the cable tension bolt and loosen the bolt in front of the two set screws (photo above). Raise or lower the derailleur until the cage is 2-3mm above the big chain ring teeth. Tighten the bolt, maintaining proper alignment of the derailleur cage to the chain rings (the cage has to run exactly parallel with the chain rings – when you loosen that bolt, there will be a little play with which to fine tune the angle of the cage in relation to the chain rings). The likelihood of you having to do this, unless the bike is new to you or you’re installing smaller chain rings, is slim to none.

Next up is what really dials in the derailleur – the adjustment barrels. There are now two types of barrel adjusters for the front and rear derailleurs. The old-school external cable barrel adjusters and the newer, in-line cable adjusters:

Both work the same way.  Twist left (lefty, loosey) and it makes the cable longer.  Twist right (righty, tighty) and the cable shortens… which changes where the derailleur cage sits in relation to the big chain ring.

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So, the idea is pretty simple, shift the chain between the rings up front so let’s get right into it.  First, triples are a little more persnickety than doubles to get right (I have four triples – two mountain bikes, my Trek road bike and the tandem and two doubles – my Venge and the gravel bike).  Before you start, snap a picture of how your cable attaches to the derailleur (see my next photo, below).  It may come in handy later.

The easiest way to do a full adjustment is to shift to the smallest chain ring up front (I like to do this on the trainer, by the way, with no resistance on the rear wheel – in a pinch, I’ll flip the bike upside down).  Next, loosen the retaining bolt that holds the cable (just enough to free up the cable).  Then you want to crank down your barrel adjuster so the cable is at it’s shortest – once it’s all the way cranked down, give it one full twist the other way to give you some play once you tighten the cable.  Next up, grab a pair of needle nosed pliers (or Park Tool does make a special cable tensioning tool) and pull the cable as tight as you can get it.  Then tighten the cable retaining bolt, making sure to keep the cable hooked around the nub like so:

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With your cable pulled tight and properly pulled over the bolt, tighten the bolt down.  From there, all we have to do is use the barrel adjuster to fine tune the shifting.  Any adjusting you’re going to do, you’ll want to do in the small ring where you’ve got more slack in the cable.  If you’re in the big ring, the cable is tightest…  First, before you start cranking on the barrel adjuster, try to shift from the little to the big (or middle for a triple ring).  If it shifts cleanly, try the next shift to the big ring.  If it shifts cleanly, shift the rear derailleur to the smallest gear in the back.  Does the chain rub the derailleur cage?  If so, try one more click on the shifter to make sure you’re already using the trim click on your shifter.  Either the rubbing will stop or it won’t…  If it does stop, Bob’s your Uncle.  If it doesn’t (and it likely won’t), then shift to the small ring up front and give a half a twist to the left (making the cable longer) and try again going to the big ring.  Keep adjusting in this fashion until you’re shifting easily between all of the chain rings and making sure that the chain isn’t dropping when you shift (usually down to the small ring).

This can take some time to get right, especially with a triple.  If you struggle and become frustrated, step away for a bit and try again later, starting at the beginning.  Make sure your cable is attached properly to the rear derailleur – on my Trek, if I don’t have the cable looped over that little nub, the front derailleur can’t be adjusted to shift properly (this is where that photo comes in handy).  Avoid going for the set screws – a rookie mistake, usually made in frustration.  If it worked before, it’ll work again – you just have to get the tension right.

If you absolutely can’t get it right, take it to the shop – just call ahead and tell them you’ll simply be bringing the bike in for a front derailleur adjustment and see if they can slide you in rather than having to leave the bike.  It shouldn’t take a mechanic more than a few minutes to get you on your way.

And if it comes to that, to taking your bike to the shop, pay extra to watch the mechanic work.  Then do what they do next time.  Why pay extra?  You pay one price to leave the bike.  You probably will pay a little more to watch the mechanic.  If you want to help the mechanic, expect to pay triple.  Chuckle.  That’s a joke.

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