Originally Posted by
khutch
Well, Sheldon also did a lot of bike riding and I presume he read a lot of other people's opinions on everything to do with biking. I would not be too quick to dismiss his opinions.
When someone is proved wrong by experiment, then they are wrong. Brown was wrong. These, for example, are the results of tests by a US company that provides forensic evidence for cycling cases:
Very different to SB's opinion!
The paper gives reasonably complete details of how they tested and you can repeat the results yourself. (Ok - modified to do without the doppler radar gun.) But remember that when you are turning that grip is used by turning force too, and this grip has to be subtracted from the braking power of each wheel. Eg a in turn that uses up the equivalent of 50% of the braking power of the front wheel then front will have 100-50%=> 50% braking left, but the rear only 76-50%=> 16% braking power left. Go beyond this and the back wheel will slide.
Sheldon does make a lot of sense from the physics standpoint. When you are braking hard with either or both brakes you do transfer weight from the rear to the front, making the rear brake less effective and eventually causing it to skid if you break hard enough. With only rear wheel braking this is not a problem, for me anyway, I have years of experience with rear wheel slides in automobiles and the coaster brake bike I had as a kid. I know how to recover from that, it is second nature.
The physics is true, but he got the numbers wrong. I think he was influenced by the MIT Press "Bicycling Science" book which states, based on theory, that rear max brake is 10% of front. BiSci is an impressive work but when it disagrees with experiment then I take experiment.
I probably was not clear but I was not breaking in the corner but before the corner.
Got it.
I will look for that book. The bike had the same Hutchinson Acrobat 32 mm tires in both the accident and the fishtailing incident. The Acrobats come in any color you want as long as you want black and they have little in the way of tread but they do have knobs on the side that might come into play if you are leaned far enough over. They could not have been a factor in the fishtailing and as far as the accident goes there is no way to know but I think it unlikely that I would ever lean the bike far enough. They are intended for deep mud or other soft surfaces, I believe.
Yes, if you weren't turning then the knobs weren't to blame.
If shimmying takes place at 5-10 Hz then this could not have been shimmying. This was more a case of the bike responding to inputs at a frequency that corresponds to the reaction time of the human driver. Reaction time is effectively a transport delay and transport delays can be deadly to the stability of a feedback control system. I don't think a bike can fishtail on its own, the fishtailing comes from the human overcontrolling the bike and possibly getting out of phase with what input is required at what time.
That sounds like good logic to me. Perhaps the problem was just that you held the bars too rigidly and denied the bike the ability to make the constant self-generated auto-steering motions that keep a bike under control.
I don't know, but thanks for your comments. It has given me some more to think about. For now I continue to brake with the front alone unless I am on slippery surfaces and then I use the rear alone. Sheldon did write what he wrote later in life (and very late in his life as it sadly turned out). It could be that he gives a late 50 something rider more appropriate advice than 20 something bike messengers do.
Ken
That sounds reasonable. Especially if you have practised front brake only emergency stops. The difference between front-only and front-plus-rear isn't huge, and modulating one brake is much easier than two.