Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

User Tag List

Reply
 
Thread Tools Search this Thread
Old 12-11-05, 05:56 PM   #1
squeakywheel
domestique
Thread Starter
 
squeakywheel's Avatar
 
Join Date: Nov 2005
Location: off the back
Bikes:
Posts: 2,004
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
impossible chainline

I'm converting my old steel Specialized MTB to singlespeed. I have a Surly singlespeed MTB rear wheel. I have Primo BMX cranks. I figured I would measure the chainline error and then buy a BB that would align them.

I figure I need a 148mm square taper BB to make the chainline perfect. I don't think such a thing exists. The longest Shimano BB I found was 127mm That would leave me over 1 cm offset between the chainring and freewheel.

Looks like I bought a crank and wheel which are not compatible in terms of chainline. Ooops.

Options:

1. Mount the chainwheel on the outside of the crank arm spider. Anyone do this? It fits better on the inside. There is a machined ledge there for it. The outside of the spider has countersunk holes that help allign the bolts. This option alone doesn't solve the problem, but it gets me closer.

2. Use a rear wheel with a narrower hub. This probably means a custom built wheel. Save the Surly wheel for another project.

3. Buy a set of MTB cranks. Save the Primo's for another project.

4. Get the longest BB I can find and don't worry about the allignment error.

What whould you do?
squeakywheel is offline   Reply With Quote
Old 12-11-05, 06:32 PM   #2
trons
yo yo yo yo yo
 
Join Date: Nov 2005
Location: delaware
Bikes:
Posts: 2,518
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
my conversion is 1cm more or less off. i ran it, i threw the chain once, and then made the chain really ****ing tight and it hasn't given me problems since. of course "just ****ing doing it" probably isnt the best solution, but if you must. you can probably also find chainring bolts that are a bit spaced out to make up a few mms difference.
trons is offline   Reply With Quote
Old 12-11-05, 07:25 PM   #3
r-dub
likes avocadoes
 
Join Date: Nov 2004
Location: oakland, ca
Bikes: heh, like that info would fit here...
Posts: 1,125
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
...um, I think your math is off...
r-dub is offline   Reply With Quote
Old 12-11-05, 09:46 PM   #4
squeakywheel
domestique
Thread Starter
 
squeakywheel's Avatar
 
Join Date: Nov 2005
Location: off the back
Bikes:
Posts: 2,004
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I measured from the center of the bottom tube to the end of the BB on the right side. That is 61mm. So, if the BB were symetrical it would be 122 wide. It isn't symetrical because the original crankset was a POS with chainrings rivetted to the right crank. I'm shooting for a 52mm chainline to match my Surly singlespeed MTB rear hub.

I put the right crank and chainring on the existing BB. It measured 39mm from center of bottom tube to center of chainring. I want to move the chainline from 39mm to 52mm. That is a 13mm increase. The right half of the BB would grow from 61 to 74. To make the left and right the same I need 74 x 2 = 148mm BB width.
squeakywheel is offline   Reply With Quote
Old 12-12-05, 03:50 AM   #5
pyze-guy
Yup
 
pyze-guy's Avatar
 
Join Date: Jan 2004
Location: where the sunbeams end and the starlight begins
Bikes: Kona Unit, planet X cx bike, khs fixed gear
Posts: 3,054
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I re-dished the rear wheel to get a better chainline on my MTB.
__________________
When sadness fills my days
It's time to turn away
And then tomorrow's dreams
Become reality to me
pyze-guy is offline   Reply With Quote
Old 12-12-05, 04:50 AM   #6
Batavus
Senior Member
 
Join Date: Nov 2004
Location: Netherlands
Bikes: Wabi Lightning, fixed 13.6 pounds. Cera steel road bike Campy veloce 9s
Posts: 521
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
redishing doesn't change your chainline. you can try to respace the hub by adding or removing washers on the drive side to get correct chainline and then you would have to redish to get the rim centered.
Batavus is offline   Reply With Quote
Old 12-12-05, 04:56 AM   #7
LóFarkas
LF for the accentdeprived
 
Join Date: May 2005
Location: Budapest, Hungary
Bikes:
Posts: 3,549
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Get cheap MTB cranks. The Surly has 52 cm chainline designed to line up with the big ring on MTB cranks, so it will, with a 118ish BB Just get shorter bolts and losre two chainrings.
LóFarkas is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 08:35 AM.