Probably some relationship between wheel flop, descent angle/weight distribution and tire compliance. My commuter shimmies badly if I lean back no hands. I should check the alignment on that frame though.

The standard "common sense" model of bike handling has been conclusively debunked so most of the comments in this thread can be disregarded.

If you have a look at the equations in this paper from Cal polytechnic two things become apparent:

Increasing the height of the BB (and by extension the centre of mass of the bike / rider) decreases the trail for a given desired steering "feel" while increasing the trail tolerable for a given amount of wheel flop.

The other effect which is usually not considered is that a higher CG will therefore more further WRT the steering centre with a change in effective gravitational vector (braking, riding hills) .

That's an interesting assertion, but I'm not sure that I follow your conclusions. And your last sentence doen't make sense.

Thanks for the link.

You're right, it's not the distance to the centre of mass that changes, it's the distance between the steering centre and the line of force through the centre of mass due to the effective gravitational vector.

I poked around on that guy's site, and the reason he made those equations is that he is interested in designing recumbents. He says that diamond frame builders have good rules for designing their frames, but bent designers don't. One thing I've learned is that equations don't always help you with people's perceptions, although they can complete the puzzle.

It's not like there are two views, one right and another wrong. There are a number of "traditional" views, there's the Cal Poly one, there's a very extensively researched one by Andy Ruina, Jim Papadopoulos and their students, and in their body of work, an extensive literature review evaluating their new work against a very broad collection of historical papers on bike handling. This history dates back to the 1890's if not earlier.

So which traditional view are you talking about?

This link http://en.wikipedia.org/wiki/Bicycle...cycle_dynamics is a very good summary of single track dynamics. Reference 1 in that article is the Ruina/Papadopoulos paper. It had a significant hand in debunking a lot of old explanations. Recommended reading, though the math is not the easiest.

Equations are good tools for engineers, if they're simple enough. Combined with an understanding of the human factors, they can improve the engineer's ability to design a well-liked bike that also handles well.

I wonder if he goes on to describe his various handling criteria in more descriptive terms, and if he has tried to use his methodology on an upright bike design. Seems to me he has the ability to fine-tune a design at teh outset, and this could possibly benefit the design of conventional bikes.