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

Go Back   > >

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.

User Tag List

Thread Tools Search this Thread
Old 06-11-11, 08:57 PM   #1
Senior Member
Thread Starter
Join Date: Jun 2008
Posts: 47
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Headset bearing loads

I was thinking about building a variation on the Bilenky Viewpoint hybrid tandem. This would be a tandem touring bike. Since the stoker rides up front over the 20" front wheel I want to make sure headset bearings can handle the loads and that I have sufficient distance between the bearings. Anybody have guidelines for shock loads on a small diameter bicycle wheel? Are there industry practices for estimating the design maximum bending moment generated by the front wheel/fork assembly when under shock loads?

Thanks in advance.
tmoritz is offline   Reply With Quote
Old 06-15-11, 04:13 AM   #2
Senior Member
ftwelder's Avatar
Join Date: Apr 2010
Location: vermont
Bikes: Many
Posts: 3,092
Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Most people use a vast existing knowledge base for frame engineering. I have looked at some testing standards and they fall way short of what I would consider reasonable strength.
ftwelder is offline   Reply With Quote
Old 06-15-11, 05:15 AM   #3
Mark Kelly 
Senior Member
Mark Kelly's Avatar
Join Date: Oct 2009
Location: Willy, VIC
Posts: 644
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Yves Champoux has some interesting measurements of vertical acceleration from bumps in his 2007 Paper "Bicycle Structural Dynamic" He measured vertical shock forces of ~800 and ~1100 N for front and rear wheels traversing a bump. I can't find any reference to the size of the bump but it appeared to be a piece of 12mm dowel. These loads would be of the order of twice the static load in the tests and since the accelerometers show the static load as a zero baseline you'd need to add them for total load eg 1200 N and 1600 N respectively.

This would probably make a reasonable base for estimation of repetitive load for the bearing. The maximal load could be calculated by considering the usual 15% rule for tyre compression: turning that on its head, the largest load before rim damage will be around 7 times the static load.

The maximal bending moment could be calculated by considering the shock load as vertical and mutliplying be the moment arm which will be the horizontal disatance between the hub centre and the headset centre and thus equal to axle to crown distance x cos (headtube angle) + rake x sin (headtube angle).

Last edited by Mark Kelly; 06-15-11 at 05:57 AM.
Mark Kelly is offline   Reply With Quote
Old 06-15-11, 07:00 AM   #4
Join Date: Aug 2008
Location: Happy Valley, Pennsylvania
Posts: 15,774
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
All else being equal, the moment on the headset bearings is smaller with a smaller wheel. It doesn't seem like a good idea to have a very slack head angle, because the wheel flop would be a pain. Of course, all things aren't equal because the front wheel being under the front rider will increase the load a little over a standard tandem. You'd have to come up with a design to calculate how much.
unterhausen is offline   Reply With Quote

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 01:21 PM.

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to and affiliated sites.
  • Ask a Question
    get answers from real people!
Click to start entering your question.