Go Back  Bike Forums > Bike Forums > Framebuilders
Reload this Page >

Adjusting a frameset to 650B Geometry Question

Framebuilders Thinking about a custom frame? Lugged vs Fillet Brazed. Different Frame materials? Newvex or Pacenti Lugs? why get a custom Road, Mountain, or Track Frame? Got a question about framebuilding? Lets discuss framebuilding at it's finest.

Adjusting a frameset to 650B Geometry Question

Old 03-01-19, 06:54 PM
  #1  
Gyro_T
Senior Member
Thread Starter
 
Gyro_T's Avatar
 
Join Date: Apr 2011
Location: Oregon
Posts: 225

Bikes: 1974 Jack Davis, Zeus Competition, Bridgestone MB2, Kona Rove Ti 1 X 11, Salsa Fargo Ti

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Adjusting a frameset to 650B Geometry Question

I have an old 531 tubing kit and the main triangle is already together. I hope to fit 42mm tires on 650B rims and wanted to know if I should trim the length of the fork blades (pre-raked) to keep the geometry correct, i.e. didn't want the head tube lifted up too much, or the chain stays to be too long. This is going to be an all around touring bike. With 42mm tires the total diameter may be not far from 700C wheels with narrow tires, so possibly no trimming would be necessary?
Gyro_T is offline  
Old 03-01-19, 10:03 PM
  #2  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 11,376

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1653 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Can we make assumptions?

Like what tire diameter tires (rim diameter and tire width) the frame (and hence the main triangle) was designed for? How about steering geometry or stay lengths? Can you indent stays, have you done this before? Have you drawn out any aspects of the original or modded designs?

By shifting BB drop fork height issues can be dealt with to a degree without seat or head angles shifting too much. But the devil is in the planning. I'd design a new frame and see how the old main triangle overlaps with the new. I don'[t think we can offer specific suggestions without a lot more info. Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 03-01-19, 10:35 PM
  #3  
calstar 
Senior Member
 
calstar's Avatar
 
Join Date: Mar 2012
Location: santa barbara CA
Posts: 973
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 48 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Using the chain stays that are with the kit? You might have to modify/indent them to fit 42s. Same with the fork, check the crown to see what the max tire size may be, maybe not 42s.

regards, Brian
__________________
"The older I get the better I was" Brian
calstar is offline  
Old 03-02-19, 06:56 AM
  #4  
dsaul
Senior Member
 
Join Date: Jan 2013
Posts: 937
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 203 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Theoretically, the outer diameter of a 700 x 23 tire is exactly the same as a 650b x 42 tire at 668mm.

In any event, if you are using the same size tires front and rear, none of the angles will change. If the tire diameter is different from the original, bottom bracket drop and trail will be the only things that change. Tire clearance is a different matter and 42's may not be possible with a road frame and fork.
dsaul is offline  
Old 03-02-19, 09:00 AM
  #5  
Gyro_T
Senior Member
Thread Starter
 
Gyro_T's Avatar
 
Join Date: Apr 2011
Location: Oregon
Posts: 225

Bikes: 1974 Jack Davis, Zeus Competition, Bridgestone MB2, Kona Rove Ti 1 X 11, Salsa Fargo Ti

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by dsaul View Post
Theoretically, the outer diameter of a 700 x 23 tire is exactly the same as a 650b x 42 tire at 668mm.

In any event, if you are using the same size tires front and rear, none of the angles will change. If the tire diameter is different from the original, bottom bracket drop and trail will be the only things that change. Tire clearance is a different matter and 42's may not be possible with a road frame and fork.
Thanks dsaul! I thought it might be pretty close, just wanted to hear it from someone else. And to answer the others, yes, I have flattened the profile of the inside of the chain stays, and I have ordered a wider fork crown to fit the wider tires. This is my first complete frame, but I have been practicing with brass and silver on racks and scrap tubing for a while. I had to get a new pair of chain stays (from Henry James) since I lost one from the kit somehow. I bought this kit from the shop I worked in from 1973-1978. We got ten sets on a closeout deal from the distributer. We paid $20 each for the double butted tube sets. I am prepared to down size the tires a bit. I have a gauge and the 42mm would fit based on the gauge but it would be a tight squeeze. I am able to flatten the inside of the chair stays a bit more and plan to do that today. I used a sculpted out block of wood and a vice for that purpose.
Gyro_T is offline  
Old 03-02-19, 09:18 PM
  #6  
unterhausen
Randomhead
 
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 17,883
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 1 Time in 1 Post
you can fit wider tires if you make the stays longer than you might otherwise make them. Many people say that longer stays is imperceptible to them, and they certainly are for me.

Also, you can braze the rear dropouts on the stays and then check the fit before you braze anything else on the rear triangle. It's a lot better if you have a fork for that, but you don't need a fork for rear stay clearance checks
unterhausen is offline  
Old 03-04-19, 10:35 AM
  #7  
Gyro_T
Senior Member
Thread Starter
 
Gyro_T's Avatar
 
Join Date: Apr 2011
Location: Oregon
Posts: 225

Bikes: 1974 Jack Davis, Zeus Competition, Bridgestone MB2, Kona Rove Ti 1 X 11, Salsa Fargo Ti

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by unterhausen View Post
you can fit wider tires if you make the stays longer than you might otherwise make them. Many people say that longer stays is imperceptible to them, and they certainly are for me.

Also, you can braze the rear dropouts on the stays and then check the fit before you braze anything else on the rear triangle. It's a lot better if you have a fork for that, but you don't need a fork for rear stay clearance checks

Thanks Unterhausen,
I left the stays a bit longer and now I am pretty confident there will be no problem with 38mm tires, not positive about 42mm but I can be happy with 38s. The method I used for shaping the chain stays did not work as well as I would have liked. I was shooting for maintaining a convex surface on both the inside and outside and getting a nice regular "D" shaped cross section. I shaped a block of oak and placed the stay in that "U" shaped groove and used a piece of softer wood on the inside and squeezed it in a vice. An arbor press might have been better. Basically it wound up squeezing in on both sides despite my groove on the outside face. Consquently, it looks a little flattened on the outside face, and I can chalk that one up to a "first frame" lesson. I thought I could get the clearance without creating a concave crease on the inside of the stays, but maybe that is just not feasible.
Gyro_T is offline  
Old 03-04-19, 10:46 AM
  #8  
unterhausen
Randomhead
 
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 17,883
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Liked 1 Time in 1 Post
I have used a hammer. Don't go crazy with it.
unterhausen 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


Thread Tools
Search this Thread

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

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.