Originally Posted by
Wilfred Laurier
Again, you have provided your interpretation of the text (or a figure in the text), and you obviously misunderstand the text.
I provided you with a
quote. There is no "interpretation" on my part. That is what Wilson wrote. It's pretty hard to take a statement like "...before he risks going over the handlebars..." and interpret it any other way.
Originally Posted by
Wilfred Laurier
When the rear wheel is lifted, the rider has begun going over the handlebars. If nothing changes (rider keeps the brakes on with the same force) then he will continue rotating around the front wheel. The diagram you created does not show the centre of mass over the front wheel, just the point about whicht he rider and bike are rotating, and that point is the same regardless of how far the rear wheel is lifted.
I doubt that you would find anyone else who agrees with your interpretation that lifting the rear wheel is equivalent to "going over the handlebars". Lifting the rear wheel on just about any bike is fairly easy...every time you slide the rear wheel you have lifted the rear wheel off the ground. I don't think anyone who has actually experienced "going over the handlebars" would equate sliding the rear wheel with doing an endo. Having done lots of both, I can tell you that they aren't the same.
Actually braking hard enough to get the bike into a situation where the rider is "risk[ing] going over the handlebars" is an altogether different situation. To put the rider over the bars (and carry the rear wheel with the rider) requires lifting the bike and rider into the air. It's almost something you have to
want do on level ground or you have to stop the wheel immediately.
Granted, you are correct that "if nothing changes" the center of mass of the system will continue rotating around point 3. But most people aren't that ham handed and will back off on the brakes as the rear wheel lifts off the ground. But lifting the rider and bicycle's mass to the point where the whole system rotates around point 3 isn't that easy. If it were, we could all do nose wheelies all the time. Getting a bike to the point where you are doing a nose wheelie is very difficult.
Originally Posted by
Wilfred Laurier
THe problem with your understanding is that deceleration when the centre of mass is over the front wheel is impossible. The maximum theoretical deceleration when balanced n a nose wheelie is zero. In order to stop from rolling forward in a nose wheelie the rider must shift his weight and rotate slightly back.
If you are
balanced in a nose wheelie, the bicycle has stopped, then you have reached the point of maximum possible deceleration. If you go past that point, you transition from stopping to falling.
But that is not what Wilson is saying. He isn't talking about "balance" but pitch over (aka face plant aka endo aka header aka dental appointment aka head trauma). That isn't implying that the rider stops just before pitch over. His calculations show a theoretical maximum deceleration but not a real practical one. He sets the load on the rear wheel to zero which will happen when the wheel lifts off the ground but you are missing the moments of torque (i.e. rotation) about point 3
Originally Posted by
Wilfred Laurier
Your failure to understand this indicates a major and disturbing misunderstanding of physical systems in motion.
You have your own failings. The first, and foremost, is not understanding what "going over the handlebars" means. Your interpretation of going over the handlebars is hardly "risky".