Chainline
11-07-18, 08:17 PM
#1
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Chainline
Building my first fixed gear by myself, and the chainline is off by 3mm. Does it need to be closer, or is it ready for a chain?
Dave
Dave
11-08-18, 04:30 AM
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The chainline on my daily rider is off by 0.3mm
11-08-18, 05:46 PM
#5
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I might have to get it re-dished. The freewheel side is even more off than the fixed side. Probably can't use the freewheel otherwise.
Dave
Dave
11-08-18, 07:28 PM
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Dave
11-12-18, 08:23 AM
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Straighter is theoretically better for 4 reasons:
1) The chain has to bend less as it leaves/joins the sprocket and chainring. That's 4 points where it bends. However, modern chains are very flexible and the amount of energy required to bend it is tiny.
2) The vector: if you pull something at an angle to the desired direction, only part of the force is moving it in the required direction. This can be worked out with sines and cosines if you're so disposed, but in reality, a few mm sideways over the full length of your chain stays is negligible as a percentage.
3) Additional friction and noise if it's so far out of line that it starts to "tinkle" on the teeth of the sprocket, like a badly adjusted derailleur. This is an annoyance.
4) Worst case: it's so far out of line that it rides off the sprocket and you have an accident: in effect, the bike spontaneously changing to the next gear when there isn't one!
Each to his own, but:
I wouldn't worry about 1 or 2 (above) too much, given that on my other (geared) bike, the chain is out of line on 9 of the 10 sprockets, whichever chainring I use. (OK, 8 out of 10, as I would never "cross chain" — honest!)
If 3 is noticeable, you certainly need to do something about it before 4 happens.
Of course, if everything else on your bike is absolutely perfectly set up in terms of lubrication of the chain, tyre pressure, seat height, reach and all those other variables, and adjusting the chain line by 3mm is the only remaining marginal gain, you may see things differently. There will always be someone who tells you it needs to be perfect, and someone else who says, "near enough is good enough".
1) The chain has to bend less as it leaves/joins the sprocket and chainring. That's 4 points where it bends. However, modern chains are very flexible and the amount of energy required to bend it is tiny.
2) The vector: if you pull something at an angle to the desired direction, only part of the force is moving it in the required direction. This can be worked out with sines and cosines if you're so disposed, but in reality, a few mm sideways over the full length of your chain stays is negligible as a percentage.
3) Additional friction and noise if it's so far out of line that it starts to "tinkle" on the teeth of the sprocket, like a badly adjusted derailleur. This is an annoyance.
4) Worst case: it's so far out of line that it rides off the sprocket and you have an accident: in effect, the bike spontaneously changing to the next gear when there isn't one!
Each to his own, but:
I wouldn't worry about 1 or 2 (above) too much, given that on my other (geared) bike, the chain is out of line on 9 of the 10 sprockets, whichever chainring I use. (OK, 8 out of 10, as I would never "cross chain" — honest!)
If 3 is noticeable, you certainly need to do something about it before 4 happens.
Of course, if everything else on your bike is absolutely perfectly set up in terms of lubrication of the chain, tyre pressure, seat height, reach and all those other variables, and adjusting the chain line by 3mm is the only remaining marginal gain, you may see things differently. There will always be someone who tells you it needs to be perfect, and someone else who says, "near enough is good enough".
11-12-18, 05:04 PM
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11-12-18, 08:07 PM
#10
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Is this rim off center when you flip the wheel around? Dishing will fix that but not the chainline. Spacers on the axle can be used to adjust chainline and then you have to redish to center the rim.
11-12-18, 08:30 PM
#11
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Dave
11-12-18, 08:57 PM
#12
Fresh Garbage
Assuming your wheel has the appropriately sized spokes and all, I wouldn't worry about it. Technically that's correct but road and mtb wheels have lots of dish and can take a good amount of abuse when built well. Adding spacers will put more strain on the axle but, again, it's not much to worry about considering you're only moving things around a few millimeters.
11-13-18, 05:30 AM
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in fairness though, as long as the chainline doesn’t look obviously skewed, with the naked eye, it’s good enough.
11-13-18, 08:18 AM
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Most people would simply eye-ball it and call it good enough. Even the Campagnolo "G" tool straightedge for assessing chainline is little more than an assist for eyeballing chainline.
Last edited by JohnDThompson; 11-13-18 at 08:21 AM.
11-13-18, 08:33 AM
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A
no doubt about it, that getting a remotely accurate chainline measurement is really difficult. And I actually measured my hubs with freewheel mounted BEFORE the wheels were built. But at the end of the day, it’s actually more about how your specific chosen parts mate together. Nothing is ever to proper spec or stated sizes. Also, I’m running single speed, so it’s easier to get a good chainline than with fixed, especially since this is a road conversion, not a track frame. Again, in the bigger picture, it all just ‘worked out’. I will admit to being a bit OCD about this, because I’m really OCD about having the smoothest possible drivetrain and I’m very consciously aware to when anyithing feels ‘off’, while riding. OCD enough that I’ve considered having a 1.3mm spacer machined.
as far as eyeballing it, I think, anything more than 1 or 1.5mm off, can probably be seen with a good eye. So I personally wouldn’t want a chainline that was off by any more than that, especially if I were running 1/8. But I also think anything within the range of about 2mm, is perfectly fine. In large part because that 2mm range can be rectified easily with spacers. But you don’t need perfect measurements to get into that range. What you need are the right parts, and that leaves a lot of room for basic luck of the draw, as far as perfection goes. Most people with bad chainlines, have them because they build something on the cheap and just throw a bunch of low quality parts together hoping for the best. No amount of meticulous measuring will help you there.
No sarcasm; if you've actually made the effort to measure that precisely — and it appears you have — more power to you.
Most people would simply eye-ball it and call it good enough. Even the Campagnolo "G" tool straightedge for assessing chainline is little more than an assist for eyeballing chainline.
Most people would simply eye-ball it and call it good enough. Even the Campagnolo "G" tool straightedge for assessing chainline is little more than an assist for eyeballing chainline.
as far as eyeballing it, I think, anything more than 1 or 1.5mm off, can probably be seen with a good eye. So I personally wouldn’t want a chainline that was off by any more than that, especially if I were running 1/8. But I also think anything within the range of about 2mm, is perfectly fine. In large part because that 2mm range can be rectified easily with spacers. But you don’t need perfect measurements to get into that range. What you need are the right parts, and that leaves a lot of room for basic luck of the draw, as far as perfection goes. Most people with bad chainlines, have them because they build something on the cheap and just throw a bunch of low quality parts together hoping for the best. No amount of meticulous measuring will help you there.
Last edited by seamuis; 11-13-18 at 08:44 AM.
