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It seems like I have a worn drive-train (sad trombone previous question) and should think about improving it.

I'm a little leery about throwing good money after bad into a used bike. Must I buy a new drive-train as a whole or can I buy the components separately and see an improvement? If the latter, in what order should I buy components?

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Note that chain and rear cluster aren't necessarily that expensive. You might be able to get the pair for under $50, though of course installation will be extra. –  Daniel R Hicks Jan 27 '12 at 23:03
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5 Answers 5

It really depends on how worn out the drivetrain is. The best way to check this is by checking your chain with a chain gauge. If the gauge reads under 1.0 you might be alright with just changing the chain out. If it reads 1.0 or higher (ie the guage at its max reading easily fits onto your chain or even has some play) you probably have a toasted drivetrain. That is not always the case - sometimes I'm surprised by how worn out a drivetrain can appear yet still be improved with a new chain. On the flipside, which is the more common side, if you have a chain that reads completely worn out chances are the rest of your drivetrain has worn with it and replacing the chain will only make things worse. You'll know pretty quickly if this is the case and if it is you'll to start replacing other components:

  • Replace your chainrings if you chain jumps or chainsucks in the front. Sometimes you can get away with just replacing middle and/or small chainrings as the largest chainring tends nto to wear out as quickly.
  • Replace your cassette if your chain jumps in the rear or shifts very poorly or both. With newer cassettes there is no option of chainging individual cogs. It's all or nothing.

If you don't own a chain gauge or you're unsure as to what components need to be replaced, find a good mechanic to inspect it for you. They should be able to diagnose your issues and suggest replacement parts as needed.

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Others may disagree with me on this, but I feel that, if the sprockets are usable at all, it never hurts to try simply installing a new chain. Yes, the chain will likely wear faster, but chains aren't that expensive, and usually you'll get at least marginally better behavior than with the old chain.

And it's usually safe to replace a worn rear cluster without replacing the front chainrings. The rear cluster usually wears about twice as fast as the chainrings, so the front may still have some life in it. (And the chainrings can be replaced one at a time -- no point in replacing your small ring, eg, if you never use it and it's not worn.)

But never replace cluster or chainrings without replacing the chain (unless it's relatively new and tests OK with a chain gauge).

You can lengthen the life of your sprockets by replacing the chain at relatively frequent intervals.

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There is a lot of truth in all other answers so far. This being a somewhat complex matter, but considering it's perhaps the biggest operational cost of a bicycle (the other would be new tubes), I want to offer my cents.

First of all: The chain has ALL responsibility for the wearing of the drivetrain. If you take new cogs and rings with an old chain, the drivetrain will be destroyed VERY quickly. But taking worn-out cogs and rings, and using them with a "theoretical perfect chain" which wouldn't wear out, would actually make the cogs and rings wear BACK to good: the teeth would be progressively thinner, but their profile ramp would be fine.

This happens because a worn chain, having a greater distance between pins, touches "higher" on the teeth and creates a ramp (sharktooth) profile, causing a new chain to skip. A new chain, in the other hand, always touches the bottom of the teeth, then wearing them out by "thinning", instead of "ramping"

An excellent text about chain wear and wear measurement can be found here: http://pardo.net/bike/pic/fail-004/000.html

The problem is: usually you can ride sligtlhy worn cog with slightly worn chain, but sometimes you cannot ride wlightly worn cog with NEW chain, because the chain skips. It depends how much the cog is worn. The same might happen with chainrings, but it is much more rare and usually happens only when the bike is seriously neglected (and seriously ridden!)

So, answering your question, I propose this "plan" to extract every kilometer a drivetrain can give, with the least money spent. Some tips might require boring manual labor, so you should measure this cost, too. In the other hand, I feel "wrong" throwing away a part which I know is still usable. The planet thanks.

  1. Replace the chain for a new one. Always replace chain first. Never replace anything else before putting a new chain. Chain must be new. There's no need to remove the "glue" it comes with, neither add another lube (this is objectionable, but I think a bit of initial wear and settling - if any - of the new components is more good than harm).
  2. If the chain skips in the rear, you can take the following approaches, in that order:
    1. Ride slowly at first, and wait for the said settling down of components. This means the old cog should wear a bit and regain its proper shape. This requires a lot of patience, sometimes.
    2. If you have a not-so-worn-out chain (read below), you can install it and ride with it for a while. Then you can install the new one.
    3. If not number 1 or 2, replace the cogs and rest your mind.
  3. Disregarding the rear cogs, if the front chainrings skip, first and foremost REGRET A LOT, then do one of the following approaches, in that order:
    1. Flip the ring inside out if possible, or if you don't want to perform the (preferrable) next step.
    2. Disassemble the ring, take a round file, and remove a bit of the base of each tooth, yelding the proper round base and vertical tooth end (and not the ugly sawtooth shape it has now it's worn-to-the-core). This sounds odd, but works like a charm, is easy to do. The same approach might help for the rear cogs, but requires Heavy Wizardry on Metal Handcrafting (I saved a lot of expensive clusters this way, but my last attempts were not successful. I gave up buying expensive clusters anyway, but my old failed clusters are hidden here, waiting for advances in technology to appear).
    3. Spend the bucks and sigh in relief.

Not to say everything on the subject hasn't been said, let's suppose you finally reached the dynamic equilibrium of replacing a chain each time it stretches by X per cent (it's not good measuring on KM ridden. It is always adviseable to measure distance between pins. The distance between 24 pins should be 12 inches.)

This would give you an absurdly long-lasting cogset and crankset. If you only ride dry on-road, 30 thousand kilometers are expected from them. BUT you end up with A LOT of chains which would look pretty much as new. And here comes the trick:

If you really want to suck every possible cheapest kilometer from a drivetrain, at some moment you just stop buying new chains and START TO USE THE SAME (NOT SO) OLD CHAINS AGAIN.

For example: if you replaced chains five times when they were, say, 1% stretched, you (still should) have five chains 1% stretched, and a "1% stretch compatible" drivetrain. Then you use the first chain until it is a bit more stretched, say, 2%, and replace for another 1% chain, until all the five chains AND the drivetrain are together at 2%. Get the idea?

This way, after many, many, MANY kilometers you'll end up with a crappy drivetrain with teeth so thin you could make ninja weapons with them. But that would be after destroying 5 chains, not one, and having made FIVE TIMES more distance for the buck.

Of course, if the process is made with more chains, you get each time more kilometers per buck, with not so much work or patience required. Only an unusual dose of discipline.

Hope it helps

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+1 for the "reconstructive" approach. I just happen to do something similar. I have successfully restored teeth in my sprockets using a rotary tool (a.k.a. dremel) and a small cylindrical grinding stone, such as its circumference is a little bit smaller than the curvature that forms the teeth. Is a fast-per-tooth method, but still needs to be done carefully and with patience. –  Jahaziel Jan 31 '12 at 15:28
    
@Jahaziel I have never had good success with dremel, it happens to spin the wrong direction, climbing the teeth and spoiling the work. The cilindrical file (chainsaw sharpening type) has given the best results. Glad to see more people have thought about this problem and its solution! –  heltonbiker Jan 31 '12 at 15:50
    
first time I tried it, i had a similar problem, I resolved by using a more fine grit stone, increasing the tool's speed and using light touches of the stone rather than pressing it hard against sprocket. Somebody may even have a reversible tool ;) –  Jahaziel Jan 31 '12 at 17:26
    
Will turning the chain ring around the other way not work? –  mattnz Apr 26 '12 at 6:30
    
best answer of the lot..... Even if you suggestions aren't taken, they give a precise picture of whats happening to a drive train as it wears –  mattnz Apr 26 '12 at 6:31
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If you need to change your chain due to wear then expect to get a new freewheel cassette too as the wear on the teeth in the back are going to cause issues in the smaller cogs. However you could try it with just a new chain at first.

If you want to keep things cheap, you might be able to get the bike shop to change out the smaller cogs but I think many cassettes are one piece so you might not have a choice about that.

Front chain rings can sometimes just be reversed so the shark toothing isn't an issue for now but new rings are going to be needed. Some rings won't allow you to do the flip so be aware of that. Lots of rings have chain climbing stuff built in to help with the ring changes. If yours does then get new.

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Looking at this and your previous question, and to answer whether you should be throwing good money after bad, the big question is how much riding you expect you're going to do.
You may not know that yet, but what is obvious is that the more regular riding you do, the more you'll spend on maintenance.
If the bike is old, you may find the bottom bracket bearings worn, the headset bearings worn, the hub bearings worn, the rims worn (if you have rim brakes), brake pads worn, cables in need of replacement, derailleur adjustment / replacement required, the wheels in need of truing, and so on.
These things can be tolerable if you do only a little riding, but if you become a regular rider, you'll probably want to replace or fix a lot of that stuff.
It may benefit you to go to a shop to have it looked at and they can assess the things that need replacing, before they go ahead and do anything. Try and find a shop that focusses on the type of riding you're doing. I'm mostly a commuter so I go to an urban commuting type shop. The road racing focussed shop near me will do it, but they don't have quite as much patience for me.

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These are all things that can be addressed one at a time. Taking care of the first few problems (chain and maybe a rear cluster) is relatively inexpensive in most cases, and provides valuable experience on how to do maintenance, even if the actual work is done by a shop. –  Daniel R Hicks Jan 29 '12 at 23:34
    
The chicken-and-egg problem with gear and exercise is "will gear frustrations dissuade me from exercising or will I invest all this money only to not use it frequently?" But assuming that my conviction doesn't waver, my weekly commute would be about 30 miles. So not a great distance by any stretch of the imagination. –  Larry OBrien Jan 30 '12 at 22:16
    
@LarryOBrien Yep, if you're not sure if you'll stick to it then maybe spend a little to get going, and 30 miles (50km), is around about where you can get away with a few worn parts. Unless you're really keen on tinkering though, even if you stick to 30 miles, you'll probably find yourself weighing up options of new vs repairing old. Although that depends highly on how serviceable the old one is. Only someone who has seen your bike can have an idea of that. –  Jason S Jan 31 '12 at 3:22
    
@DanielRHicks You are right, but I was mostly just answering "I'm a little bit leery about throwing good money after bad into a used bike" (which other answers hadn't), by pointing out there could be many more maintenance costs down the track with the old bike. Hence the recommendation for someone to look at it and assess future costs. –  Jason S Jan 31 '12 at 3:31
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