[hpv] Steering head bearing loads in front-drive bike

[Mark Stonich]

Why not bushings? "Stiction" (STarting frICTION) 

The tiny, subconscious corrections you are always making to balance a bike require little or no friction at the start. With a bushing the force needed to initiate the movement would initially be high then suddenly drop off.  

My Raleigh Twenty folder has a bushing replacing the top bearing, with a conventional lower headset bearing.  With a steep head angle and a steerer almost as long as the blades, this is as favorable an application for a bushing as you are likely to find.  I find it "tolerable" but many who use their Twenties more than I do have converted with an Aheadset type upper bearing. 

OTOH the Greenspeed trikes get by with bushings as they don't have to be balanced.

Mark Stonich Bikesmith Design
612-824-2372
5349 Elliot Ave S.
Minneapolis MN 55417
www.bikesmithdesign.com

On Aug 13, 2013, at 10:37 AM, Garrie Hill <garrie at recumbents.com> wrote:

> One of the things I've pondered over the years is, "Why do we use ball or roller bearings in head sets?"  Nothing is rotating more than a couple degrees ( more than 90% of the time) plus or minus, and a good shock through the wheel into the fork can cause indentation of the balls into the races.  Use a bushing and you spread forces over infinitely larger bearing surfaces than the contact area of balls/races.  In the case of MBB FWD, bushings have the added advantage of extra drag dampening some pedal induced oscillation.
> 
> 
> Garrie "carbon based lifeform" Hill
> HPRA Co-Dictator of the East
> for pics of some of my time and money sucking projects
> http://garriehill.winkflash.com/ 
> and 
> http://s58.photobucket.com/albums/g277/cfbb/
> and videos
> http://vimeo.com/5513519
> 
> [IMG]http://i58.photobucket.com/albums/g277/cfbb/newKanjGarrie.jpg[/IMG]
> 
> 
> 
> 
> 
> On Aug 12, 2013, at 10:55 AM, Ben Brown <hbb at cs.cmu.edu> wrote:
> 
> I'm working on a front-drive bike, similar to Tom Traylor's design (http://traylor_fwd.home.mindspring.com/) or Cruzbike (http://cruzbike.com/). I was considering the loads on the headset bearings, since the pedaling loads will be transmitted to the front fork assembly through these, along with the usual load from the weight on the fork. With strong pedaling thrust (I assumed 200# to be possible), I estimate the side load on the lower headset bearing to be around 400#-500#, depending on the headset bearing separation. This seems like a lot for typical steering bearings, certainly more than would be encountered in a conventional diamond-frame bike. Has anyone else considered or had experience with this?
> 
> I'm attaching a copy of my analysis, in case anyone is interested in the details.
> 
>    Thanks, Ben
> 
> _____________________________________________
> 
> H. Ben Brown
> Carnegie Mellon University
> Pittsburgh, PA
> hbb at cs.cmu.edu
> 
> --
> This message comes to you via the hpv at hupi.org mailing list.
> Visit http://bikelist.org/mailman/listinfo/hpv to manage your subscription.
> 
> --
> This message comes to you via the hpv at hupi.org mailing list.
> Visit http://bikelist.org/mailman/listinfo/hpv to manage your subscription.
> 
> 
> _______________________________________________________
> Unlimited Disk, Data Transfer, PHP/MySQL Domain Hosting
>              http://www.doteasy.com