Originally Posted by
meanwhile
The answer to fishtailing is to learn to use both brakes effectively, not to give up using them. SB was wrong that the rear brake shouldn't be used at all - he was an excellent bike mechanic but not a great expert in bike handling. If you want to know how to handle a bike, talk to people who ride off road or to messengers who ride 40 hours a week in city traffic, often in rain. People have conclusively proved that both brakes > front brake > rear brake by experiment.
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. I am somewhat skeptical of bringing motorcycle practice over to cycling too. Motorcycles are far heavier, the weight distribution is different, and the handling may not be the same for several reasons. It is certainly not a gimme that a motorcycle behaves like a bicycle and even though driving both the same way has worked fine so far from some posters here remember that I have ridden bicycles for somewhere at 46 years now and have
never seen this before. If you have a good online article by one of these bike messengers describing his/her technique and experience with braking I would be happy to read it. 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.
You have only so much traction per wheel: turning uses traction, so does braking. But braking increases traction at the front and decreases it at the rear. Which is why you never "grab both brakes hard" - the rear should usually get less brake than the front and this is especially the case in turns; as traction is reduced by braking and eaten up by turning this maybe the one time you want to use no rear brake at all. The best thing you could have done in this case would have been to break hard using both brakes both the corner, release, enter the corner, and then do any more stopping on front only, with maybe squirts of rear. Using both brakes together should get bike a bike from 20mph to 0 in only 5 metres on the level - this is a required federal standard (
http://www.eng-tips.com/viewthread.cfm?qid=74375&page=1.) Bicycles have amazing stopping power once you have tuned your ability to control it.
I probably was not clear but I was not breaking in the corner but before the corner. The onset of the fishtailing was sudden and totally unexpected. If the rear wheel had simply slid to one side as has happened many times before (but possibly not on this bike) I would indeed have modulated the rear brake and steered into the skid to regain control, like I say this is second nature to me, been there too many times to count. Sheldon believed that this was a danger of braking hard with the front wheel and skidding the rear. He isn't usually wrong about things like this but it is possible, I disagree with him myself on some things. What he describes is exactly what happened to me though and that makes me tend to believe him. "Grabbing both brakes hard" should not be taken too far, I have many miles on bicycles over the years and colorful language aside I used both brakes as I normally would to make a sharp but not panic reduction in speed. The rear wheel slipped unexpectedly and then all Hell broke loose, even more unexpectedly!
You've been extremely unlucky and shown a good deal of common sense and steady nerves, but you'd be safer learning to use both brakes and modulating them. Robert Hurst's book "Art Of Cycling" is good on this. Once you learn to got from 20 to 0 in 5 metres there is usually room to let the back roll in a straight line in an emergency and this is much better than trying to brake and turn.
Re. the Fuji, a very large part of how a bike handles is determined by the tyres. There might not be a handling problem at all, but just in case- what tyres did you have on the bike for each crash? Did they have a tread pattern? Were they a colour other than black? What model and with were they?
Another (unlikely!) possibility is that you suffered the dreaded "front end shimmy" - a resonance phenomenon:
http://www.spectrum-cycles.com/615.htm
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.
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. I suppose it could be that this bike just happens to have a natural response time that is optimally poor for my 58 year old nervous system and that is why I have never seen this before. I rode my Dahon folder down a railroad embankment covered in turf all last summer. It required braking hard on the front because the rear alone was insufficient even when I moved back as far as I could. On dewy mornings the rear wheel would often skid and I would have to back off on it to straighten out. If anything this was an even more extreme situation that I saw on the Fuji but I could handle that day after day without problems.
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