Chainline database

Uh oh...

Does +- 2 or 3 mm really make any difference? I've never measured any of my chainlines and they all seemed to run fine. Is it really worth the pain to get it right?

In simple terms anything more than +/- 1mm will increase drive train noise and more significantly increase wear on components (the noise being caused by bits rubbing together more of course). If you are running a beater and are mechanically insensitive then as long as your chain isn't slack enough to climb off the sprocket it's fine. If you've spent a load of hard-earned on a top notch drive train then it would be a waste not to get it dialled in, because you are just throwing cash away on rapid wear of components and also not getting the benefits of the extra quality. At the very least you will be going through chains faster. Finally, if you are using it competitively you will be wasting valuable watts wearing out your expensive drive train.

The other thing to bear in mind with the database figures is that they are not absolutes - if all the data was measured using brand new components then you could reasonably assume that if you bought the same items brand new you should get pretty much the same result. However, things like crank tapers do wear and can also be compromised by fitting to the wrong type of BB, overtightened, undertightened etc. The alignment of an old frame might be out +/- 2-3mm without being immediately obvious. The surest way round these issues is to get a BB with adjustable chainline in the right ballpark length and then run a long straight edge across the chainring and see if it lines up with the sprocket - if yes job done. If not disassemble drive train and adjust BB centreline, reassemble, recheck. Laborious it can be, but gives surest results.

Not really sure best way to approach this - I have a Dolan Track Champion with a Stronglight Track 2000 crankset and chainring on it, which tbh I've never been happy with (had to send the first one back for being ridiculously oval).

Noticed when a mechanic changed my rear sprocket recently that my chainline is a little out - chainring is perhaps (guesstimate) a couple of mm too close to the frame to keep the chain line totally straight.

It's not a huge deal, but if I can straighten this out by buying a new crankset I will.

Any info on how exactly I work this out? Do crank manufactuers provide info that will make it easy for me to compare?

This was started a fair while ago but might be a good starting point.

Sigh. Was actually hoping for some help. Been searching around all morning - can't even get Dolan to tell me the frame dimensions I need. Now I've just had my thread moved somewhere where no one will ever see it :(

What's your BB length? The important measurements are to do with crankset/BB and hub. If you want to keep the cranks then get a slightly longer BB, if not then measure the chainline of your hub and get a crankset/BB to match.

Try this for more info

As to the stronglight site - have a look at this.

http://www.stronglight.com/stronglight/index.php/welcome/afficher_Produit?id=222

What's your BB length? The important measurements are to do with crankset/BB and hub. If you want to keep the cranks then get a slightly longer BB, if not then measure the chainline of your hub and get a crankset/BB to match.

Sorry, to clarify I'll likely be getting new BB as well as crankset as the BB i have is very specific to the current cranks.

Measure up your hub chainline and check in here if you want to be certain of the same chainline for your new cranks then.

^this

As to the stronglight site - have a look at this.

http://www.stronglight.com/stronglight/index.php/welcome/afficher_Produit?id=222

That doesn't tell me much - however it made me look up my original crankset + BB order and I have a 107mm BB. Stronglight do them in quite a few variations, so perhaps if I can get one of the 110mm BB that will sort it? Or will my BB then be too big for the frame?

Measure up your hub chainline and check in here if you want to be certain of the same chainline for your new cranks then.

Will need to get some more accurate measuring tools! Then shall look up exactly what to measure.

Thanks.

Check the sheldon link above for how to measure, the whole point of the BB axle length is to match your cranks to the correct chainline, as long as you get the right thread and shell width then the BB can't be too big for the frame, although the cranks could end up far too close or far away from it. The frame you've got is pretty unimportant unless there is an issue with chainstay clearances or something.

Going from a 107 to 110 should move the chainline out by 1.5mm, so check your current chainline and see if that's what you need.

The cheapest way to fix the problem is to get a longer BB (sounds like you need normal square taper), as outlined above.
If you're getting a new square taper crankset because you want to, fit it on your existing BB, measure the chainline, and then get a new square taper BB to fix the chainline. I don't think that a BB to fit Stronglight 2000's will be specific.
If you are going GXP or Octalink, then you need to know what your hub chainline is from the centre.

That doesn't tell me much - however it made me look up my original crankset + BB order and I have a 107mm BB. Stronglight do them in quite a few variations, so perhaps if I can get one of the 110mm BB that will sort it? Or will my BB then be too big for the frame?

That is the manufacturers information on which BB goes with which Crankset. That was part of your original request and that will give you half of the equation.

I have the ST200 paired with a 111mm BB to work with my Goldtec hubs (notorious for their 45mm chainline). It's not perfect but it works. If you can get within +/- 1mm of where you need to be that is going to be close enough for average hack riding.