Achieving perfect chainline
 

Hi there,

I'm in the process of converting a 1980s Holdsworth Avanti road bike to a fixie. It's taken me a while to get here, but I'm on the home straight, all I need to do is get the right bottom bracket/chainset combo for perfect chainline.

My girlfriend kindly gave me her flip flop rear wheel, which I've put in my frame (spacing is approx. 127mm - I imagine it was originally 126mm but the guy I bought it off had forced in a freewheel with too many sprockets and probably stretched it out over time). The hub on the rear wheel is 120mm, so I bought two 3mm spacers to go either side of the hub and it seems to sit fine.

I've measured my rear chainline, which is approx. 41.5mm, by measuring the distance from sprocket to inside of dropout (21.94mm), and subtracting this from half of 127 (63.5).

The bottom bracket currently on my bike is the one the previous owner installed. It's an SKF Thun with strange plastic lock rings, which I plan to replace. Its spindle is 119mm. I've borrowed a friend's Miche Xpress chain set just to get an idea of what the chainline looks like (this is my first conversion) and installed that. Currently, front chainline is 46mm.

So, I'm out by 4mm, which is obviously too much. By my calculations, I need a bottom bracket with a 111mm spindle (or something close to that) in order to shave 4mm off the drive side (obviously this assumes the spindle is symmetrical, which it may not be) and get the front and rear chainline the same.

Having said that, I've ridden it a little bit and despite the chainline being off it seemed OK. Chain didn't slip or threaten to fall off or anything. Didn't really push it though.

I'm thinking of also getting a Miche Xpress chain set, just to eliminate one of the variables, and get a suitable bottom bracket. If anyone could point out where I've gone wrong or something I've overlooked before I go ahead and get a bottom bracket, I would really appreciate it.

Reading these forums and others has got me this far and it would be great if your advice could give me that final push! Thanks. :)

As people often do, you're overthinking it. A chainline being off by 4mm is hardly a big deal.

All the info I've seen says the Miche Express crankset uses a 107mm JIS BB spindle for a 42mm chainline.

Thanks. Yes, that's right. I was just a little confused because, by my calculations, I'd need a 111mm-ish bottom bracket for a 42mm chainline, so sought some advice. I would have thought I'd get a 40mm chainline with a 107 bottom bracket.

Anyway, as you say, I'm probably overthinking it. I might just get the Xpress cranks and shove 'em on my current bottom bracket. May as well keep it until it's knackered. From what I've read it's JIS so it should be fine. If chainline turns out to be a problem in practice, I'll upgrade then!

Thanks again.

If it bothers you, there's always the option of getting some 1mm axle spacers and shuffling yours around so that there's, say, 4 or 5mm on the left and 2mm on the right, as well.

Are you running a 1/8 or 3/32 chain?

I am totally a newbie at this but I had to set up a Langster that did not have a rear wheel. I used a Campy HF road hub temporarily and had all kinds of chain line issues with a new freewheel and 1/8 chain. I used BB spacers to get the freewheel aligned just right to keep the chain from making noises associated with chain line being off.

All this disappeared with a used SS/Fx hub.

BTW: I have a Sugino Messenger crank and ring with a IRD BB of 103. It is an English BB, IIRC.

i had thought about that but didn't do it as the wheel would no longer be centred in the frame?



a 1/8 chain

*

i went and ordered the Miche Xpress chainset and a KMC B1 1/8 chain. everything seems fine apart from a clicking noise that seems to be caused by the chain's discs coming into contact with the rear cog's teeth. having done some digging this can be caused by a number of things, such as mixing and matching old and new drivetrain parts. however, this can't be it as they're all brand new. another cause could be the chainline, which is admittedly off, but the problem is, when i installed my friend's old chain it was practically silent!

so i'm not sure what to do. why would a brand new chain be more noisy than an old (and presumably worn out) one? his chain is also a 1/8 KMC. the only difference between his and mine is that his seems slightly thinner. i discovered this when using a chain tool: his chain fit in but mine didn't, despite them both being 1/8 KMC chains...

will the noise quieten down when the components have had time to 'bed in' together? one of things that drew me to fixed gear was the lack of noise, so would really appreciate any help anyone can offer

New drivetrain parts are often noisy and you didn't exactly buy a good chain. Also, your chain may be too tight.

If the whole chainline "dilemma" is still keeping you awake at night just use a Miche Primato 107mm BB, which is adjustable by 5mm from side to side.

i experimented with different tensions but nothing changed. as you indicate, it's probably the fact it's cheap. i guess my friend's is of higher quality. are there any, in particular, you'd recommend?

personally, the chainline doesn't bother me now i know it hasn't that big of a deal. if i can quieten it down without having to change the bottom bracket i'd prefer that

How slack was the loosest you tried?

Sometimes you can correct chain line by either flipping the cog around or moving the chain ring to the other side of the crank spider. Also, I've had several chains that made noise even when chain line was dead on and components were new. It was a vibration that I felt more than heard. Look up "chordal action." If that's what you're experiencing, the official word is to ignore it - it's not hurting anything and may go away as parts bed in.