Touring bike build: chainline
I am building up a touring bike from a Velo Sport Alpin frame (very much like the one is this thread).
I have a 7 speed freewheel and a Sugino XD triple crank. The rear spacing is 126mm and the chainline (middle sprocket) is 42.5mm. Sugino recommends a 113mm (or larger) spindle length; this give me a front chainline (middle chainring) of 47.5mm. Does anyone think the chainline being off by 5mm is going to be a problem?
I don't have much choice in the back, but I could try to see if the crank will mount on a smaller spindle as there is plenty of frame clearance. Right now I have a Shimano UN54 113mm that I could exchange for a 110mm or 108mm, but there may not be enough room as the Shimano bottom brackets seem to have a spacer or stop installed (see attached image). I assume the crank is not supposed to be touching this?
If anyone has any thoughts, advice, or comments I would like to hear them.
5mm is quite a lot to be off. It won't make the bike unrideable by any means but you won't get the proper usage of the cassette range in either the middle or large chainrings and you may be severely limited in the large ring. Good news is you'd probably be able to use every rear cog when in the small ring
Originally Posted by sfclearwater
Sugino's recommendations are likely based on a 135mm spaced rear triangle common on touring frames. With your rear spacing, you will need a more narrow BB to get the correct (for your application) chainline.
The Shimano square taper BBs don't always lose the same amount of spindle from both sides as the width shrinks. I believe Sheldon Brown's site goes through all of this. The UN54 107mm BB would be a good starting point. It should get you close enough to what you are looking for.
Originally Posted by sfclearwater
The arrow in your picture is not pointing at a stop on the BB. Square taper BB's don't utilize a stop for the crankset. The spindle is designed so that the crank stops sliding down the spindle prior to contacting anything. Your crank will fit just fine on a 107mm BB. The only limiting factor with BB width is frame/chainring clearance and it sounds like you have plenty of room there.
I have a Sugino XD2 crankset on an old road bike with 126mm spacing. I forced in a 130mm wheel and have a 110mm bb in there - chain line is great. The 113mm bb works for a mountain bike or something but 110 or 107 is probably going to be better on a road bike.
Also, I think the Shimano 107 bb is asymetrical - the non-drive side is shorter than the 110 to give a narrower q-factor but the drive side is the same so they both give the same chainline.
Thanks for the info guys; I will take the 113mm back and try a 110mm or 107mm. I just went with the smallest recommended one, but I should have read Sheldon's crank page first as he confirms that a 107mm BB may work with some road bikes.
Yeah I hear you. I wonder why Shimano puts those circular rings on the drive side of some of their BB's and not others.
Originally Posted by joejack951
I read a few other threads that say the same thing about the 110mm/107mm BBs, hopefully the drive side length of the 110mm/107mm will get me close enough. I don't fancy replacing the wheels and respacing the frame (not yet anyway), although it would be nice to have a freehub to avoid bent axles. Good to know somebody has done it and it works though.
Originally Posted by Al Criner
Last edited by sfclearwater; 06-09-09 at 11:59 AM.
In case anybody finds this thread in a search...
The shimano UN53/54 107mm and 110mm do indeed have the same length drive side. I ended up using a 107mm with the older touring frame, this resulted in a chainline of about 46mm (1mm off the standard road triple 45mm). As you can see from the picture it is pretty much as far inboard as it will go.