Cycling UK Forum

Hello Chris,
So does that mean that the gyroscopic moment of precession of a bicycle's back wheel about the steering head counteracts the gyroscopic moment of precession of its front wheel, for stable directional input?
Obviously, the rider would be leaning into & out of a turn along the balancing/counterbalancing continuum. A straight line counts as a curve of infinite radius on either side of the bike.

Normally I wouldn't bother for the speeds I ride at. However, I hear that track riders reach 50mph around the corners.

Sorry if I'm a little slow on the reading list, only I'm still developing the next prototype. If I can complete & test it, I'll have more idea of how it goes around corners.

Kind regards, Peter

It's the same gyroscopic effect for both wheels: lean left and they both want to turn to the left.

The influence of the rear wheel in this regard is in any event very small compared to the front. And as David Jones proved with his URB (unrideable bicycle) model 1, which he equipped with a counter-rotating dummy front wheel so as to negate the effect, but was nevetheless able to ride perfectly well: gyroscopic precession contributes very little to the human control of a bicycle.

That precession plays some small part was shown by the riderless behaviour of this bicycle. Take a bicycle, any bicycle (that you don't care about too much!), give it a running shove in a large paved area, and it will not immediately fall over. It'll actually continue to balance by itself for some way, then gradually capsize in a slowly tightening curve. This is how URB1 behaved before it was modified. With the contra-rotating dummy wheel however, it immediately fell over. This loss of stability was not simply caused by the off-balance weight of that wheel, for when Jones made it spin in the same direction as the bicycle wheels, URB1 went even further before capsizing than it did originally.

URB1 was also very difficult, but not impossible, to ride no hands.

David Jones made a whole series of URBs, to test the varoius theories as to how bicycle steering works, all of which nevertheless turned out to be rideable, proving that the most important component of bicycle steering is the nut that holds the handlebars! But some were more difficult than others, with the no-hands and in particular the riderless behaviour of these bikes providing some useful pointers with regard to the relative importance of varoius parameters.

Of course nowadays the complex mathematics involved in all this has been number crunched and analysed pretty well with the aid of computers. However the sheer quantity of variables and their interactions affecting attendant behaviours such as steering shimmy, are so complex as to so far defy complete analysis.

Hello Chris,
I've had a chance to borrow the 3rd edition of Bicycling Science from the library now and read it through. It's about as much science as I'd ever need for a bicycle. It provides some useful cross-references.

Chapter 8 covers steering and balance and in there, figure 8.3 shows 2 connected sub-assemblies rather than 2 assemblies because of the steering head bearings. If it were 2 assemblies, they would be front and rear unicycles.

Also, figure 8.3 is incosistent with figure 7.5 of chapter 7 on braking. Figure 8.3 would be more consistent with figure 7.5 if some of the rider's mass were applied to the handlebars. In order to follow the principle of connected sub-assemblies (see note above on figure 8.3), the handlebar mass component could be connected to the remaining mass by a spring and/ or damper.

P.S. Figure 8.15 does not seem to relate to figure 8.3 because the saddle mass from the rear assembly in figure 8.3 is on the same assembly as the front wheel in figure 8.15

View (c) is missing from figure 8.16

A conversion table between the various units used would be useful.

Kind regards, Peter

CJ's recommended book on Bicycle Science (3rd edition) mentions "body English". This seems to be more of an art than science, as some of it is intuitive movement of the body as learned by the brain.

As the front wheel is controlled by a rider's hands, it can turn & lean. The rear wheel also turns and leans although it has to cope with counterbalancing and inverse working. Is there a case for labelling the interim conditions of the rearwheel-to-saddle as "float", please Moderator?

Peter

Cyclenut wrote:Dr Jones' work is mentioned in this excellent Velonews article that reduces the complexities of steering geometry into reasonably simple terms.

This is an interesting but very old thread – so old, in fact, that I can’t find any trace of the above VeloNews PDF on the web. The chances must be small, but does anyone happen to have a saved copy of it on their computer?

I found the very thing on the 'wayback machine'

http://web.archive.org/web/20070221112500/http://www.velonews.com/media/Block40.pdf



I also found this more recent article which puts a different mathematical spin on the subject of shimmy;

http://velonews.competitor.com/2013/11/bikes-and-tech/technical-faq/technical-faq-bifurcation-and-high-speed-shimmy_309601

cheers

Some previous discussion on the subject, including details of how gyroscopic precession isn't necessary to help to keep a bike upright.

viewtopic.php?f=1&t=82637&start=0

I searched the Wayback Machine by entering the PDF URL here, but to no avail. It returned no results for 2007, the year your PDF was saved, and only dead links in later years. You must have better search-fu than I do!

Thanks, though.

Thanks guys. If anyone is interested in taking the design (as opposed to the discussion) forwards, please let me know.

Happy cycling, Punk_shore