Originally Posted by
khutch
I have always used both brakes together but now I try to use the front alone unless I am on a slippery/rough surface, per
Sheldon Brown's advice. The reason is something else in that article: fishtailing.
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.
I was riding on a asphalt bike trail with a slight downgrade and a tailwind. So I was cruising along at about 22 mph (not a pace I can sustain normally) and coming to a place where the trail jogs to the right by a bit more than its width to avoid some part of the gravel pit operation it runs alongside of. I realized rather late that I needed to slow down sharply to make the jog so I grabbed both brakes hard, as I normally would. I felt the rear tire slip and the bike immediately went into a rapid, violent fishtailing unlike anything I have ever experienced on a bike before. I thought I was going down, hard and when I regained control I really, really needed to still make that jog on the path to avoid running right into the chainlink fence that runs along the path and follows the jog. I don't know how I did that but I did. I've driven rear wheel drive cars and pickups a lot so I was familiar with how to deal with a rear wheel slide (get off the throttle/brake and steer into it) and I have dealt with similar situations on my other bike (a Dahon Mu P8) without any trouble like this. It put the fear of God in me though and now I follow Sheldon's advice.
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.
Now earlier this year I had a crash on the same bike. It was a nasty one and one of the results of the crash was a concussion that left me with no memory of that afternoon so I don't know how it happened. I was turning off a well used street into my neighborhood and for some reason I apparently went wide and over the curb where I fell and hit my head on the curb or the sidewalk beyond it. One possibility is that I had to brake hard because I was going too fast (again!) or maybe I had to brake hard to avoid a car pulling out in front of me and the bike went into that same oscillating fishtail mode. I won't ever know for sure. I wish I could think of a safe way to intentionally excite this behavior and learn how to deal with it better without crashing but so far I haven't come up with anything for that either. I don't really know why this bike (a Fuji Absolute 1.0) would be susceptible to this when no other bike I have ridden did it. Maybe all bikes do it under the right conditions and I had been lucky enough to avoid this until now. The fishtailing may have had nothing to do with my crash. For the time being I concentrate on using the front brake or the rear but not both.
Ken
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