Go Back  Bike Forums > Bike Forums > Classic & Vintage
Reload this Page >

How to choose a bottom bracket spindle length for new cranks on a new frame?

Notices
Classic & Vintage This forum is to discuss the many aspects of classic and vintage bicycles, including musclebikes, lightweights, middleweights, hi-wheelers, bone-shakers, safety bikes and much more.

How to choose a bottom bracket spindle length for new cranks on a new frame?

Old 06-30-20, 01:54 AM
  #1  
Senior Member
Thread Starter
 
Join Date: May 2020
Posts: 138
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 43 Post(s)
Liked 12 Times in 7 Posts
How to choose a bottom bracket spindle length for new cranks on a new frame?

I'm putting some Stronglight 200lx cranks on a Vitus 787 frame. Both are new to me, so there's no precedent to compare to. I know a need a threaded 68mm square taperered bottom bracket, but I just can't figure out the spindle length I need.

Googling around seems to suggest it's a case of just trying a bottom bracket and seeing how the chain line is. Is that really the case? And if so, what's the best guess I can go with?

Thanks
​​​​
Funktopus is offline  
Old 06-30-20, 04:43 AM
  #2  
Senior Member
 
plonz's Avatar
 
Join Date: Mar 2015
Location: Western MI
Posts: 2,878
Mentioned: 45 Post(s)
Tagged: 0 Thread(s)
Quoted: 648 Post(s)
Liked 451 Times in 293 Posts
Originally Posted by Funktopus
Googling around seems to suggest it's a case of just trying a bottom bracket and seeing how the chain line is. Is that really the case? And if so, what's the best guess I can go with?

Thanks
​​​​
There might be someone here using the same crankset who can tell you the spindle length they’re using. If not, you’ll need to use the method described above. Really only need one BB to get an initial reading, then you can source the correct one. Be mindful of different tapers which can impact arm seating and measurements.
plonz is offline  
Old 06-30-20, 04:52 AM
  #3  
2-Wheeled Fool
 
J.Higgins's Avatar
 
Join Date: Sep 2016
Location: New Hampshire
Posts: 2,486

Bikes: Surly Ogre, Brompton

Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 1385 Post(s)
Liked 677 Times in 457 Posts
My method is simply to use the same spindle length as the original and wing it. It works for me on most builds 99% of the time. I also have several junk sealed BBS, and spindles to fuss about before I order anything new. I also think most manufactures will have a recommended spindle length, but there are other ways HERE.
J.Higgins is offline  
Old 06-30-20, 05:32 AM
  #4  
Senior Member
 
SJX426's Avatar
 
Join Date: May 2008
Location: Fredericksburg, Va
Posts: 9,580

Bikes: '65 Frejus TDF, '73 Bottecchia Giro d'Italia, '83 Colnago Superissimo, '84 Trek 610, '84 Trek 760, '88 Pinarello Veneto, '88 De Rosa Pro, '89 Pinarello Montello, '94 Burley Duet, 97 Specialized RockHopper, 2010 Langster, Tern Link D8

Mentioned: 73 Post(s)
Tagged: 0 Thread(s)
Quoted: 1601 Post(s)
Liked 2,187 Times in 1,092 Posts
Funktopus Having gone through this challenge lately, I learned that you can take a shortcut by finding out what the spindle length needs to be for your specific crank.
Without that knowledge I would start taking measurements. Specifically the distance between the center of the rings and the surface of the boss around the inside of the spindle opening. Next number is the distance between the center of the bike and the center of the sprocket cluster. This last number plus the crank number will give you a close target for half the length of the spindle. Oh of course you need to know how far the spindle is likely to enter the crank.

This last measurement could be taken from an existing bike with a square taper BB. Measure the distance between the washer surface and the end of the spindle and subtract from the overall length of your crank taper and add that number to the last number above. Somewhere between 108 and 118.

It is harder than determining the crank BCD (122)
__________________
Bikes don't stand alone. They are two tired.

Last edited by SJX426; 06-30-20 at 05:42 AM.
SJX426 is offline  
Old 06-30-20, 03:55 PM
  #5  
Senior Member
Thread Starter
 
Join Date: May 2020
Posts: 138
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 43 Post(s)
Liked 12 Times in 7 Posts
Originally Posted by SJX426
Funktopus Having gone through this challenge lately, I learned that you can take a shortcut by finding out what the spindle length needs to be for your specific crank.
Without that knowledge I would start taking measurements. Specifically the distance between the center of the rings and the surface of the boss around the inside of the spindle opening. Next number is the distance between the center of the bike and the center of the sprocket cluster. This last number plus the crank number will give you a close target for half the length of the spindle. Oh of course you need to know how far the spindle is likely to enter the crank.

This last measurement could be taken from an existing bike with a square taper BB. Measure the distance between the washer surface and the end of the spindle and subtract from the overall length of your crank taper and add that number to the last number above. Somewhere between 108 and 118.

It is harder than determining the crank BCD (122)
Wow interesting. I won't have a chance to do this until the weekend, but I'll give it a try. Some phrases I don't understand - what's the "boss around the inside of the spindle opening". A raised lip around the square hole on the bracket-side of the cranks? And when you say center of the bike, is that the center of the bracket opening?

Thanks!
Funktopus is offline  
Old 06-30-20, 05:33 PM
  #6  
Senior Member
 
SJX426's Avatar
 
Join Date: May 2008
Location: Fredericksburg, Va
Posts: 9,580

Bikes: '65 Frejus TDF, '73 Bottecchia Giro d'Italia, '83 Colnago Superissimo, '84 Trek 610, '84 Trek 760, '88 Pinarello Veneto, '88 De Rosa Pro, '89 Pinarello Montello, '94 Burley Duet, 97 Specialized RockHopper, 2010 Langster, Tern Link D8

Mentioned: 73 Post(s)
Tagged: 0 Thread(s)
Quoted: 1601 Post(s)
Liked 2,187 Times in 1,092 Posts
Funktopus Kinda yes. Here is a picture but you really want to measure to the edge of the tapered hole. We are trying to get close, not exact.
P1030067, on Flickr
And yes. One would hope the center of the BB shell is the center of the bike. Better location is the center of the down tube or seat tube.
https://www.sheldonbrown.com/chainline.html
__________________
Bikes don't stand alone. They are two tired.
SJX426 is offline  
Old 06-30-20, 06:06 PM
  #7  
Senior Member
 
Dfrost's Avatar
 
Join Date: May 2013
Location: Pacific Northwest
Posts: 1,988

Bikes: ‘87 Marinoni SLX Sports Tourer, ‘79 Miyata 912 by Gugificazione

Mentioned: 166 Post(s)
Tagged: 0 Thread(s)
Quoted: 500 Post(s)
Liked 464 Times in 255 Posts
You might try Velobase, looking at the Stronglights to find your crank. Their database often lists the correct BB length if your crankset is there.

VeloBase.com - View Brand

Does that model Stronglight crank require special threads on a crankpuller?

Last edited by Dfrost; 07-01-20 at 01:23 PM. Reason: Added crank puller question.
Dfrost is offline  

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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.