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#11
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Braking while turning
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#12
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Braking while turning
Joe Riel writes:
... Do you corner anywhere near that lean angle? Few do. Ok, so you first establish that on flat pavement with no surface gunk friction is very high. And you argue that few folks ride anywhere near this limit on corners. So for most people fc is not that high. Second, because the total force on the contact patch is the vector sum of the cornering force and the braking force, which are applied perpendicular to each other, it is possible to apply considerable braking force while barely changing the total force. For example, let the braking force (fb) be 20% of the cornering force (fc). The total force is then You then argue that 20% of fc (which we established is not that high) is a "significant braking force". For some reason, I disagree. :-) ftot = sqrt(fc^2 + fb^2) = fc*sqrt(1+(fb/fc)^2) ~ fc*(1+(fb/fc^2)/2) for fb fc = fc*(1+(2/10)^2/2) = 1.01*fc Here is a much easier way of solving (and understanding) this, with the bonus of getting a more accurate answer: ftot = sqrt(fc^2 + fb^2) Assume that fc = 1unit. Assume that fb = .2*fc = .2units ftot = sqrt(1^2 + .2^2) = 1.02 Now, if you assume that the rider is cornering somewhat conservatively, because they fear that there might be a patch of sand or tar on the corner somewhere, then you can assume that fc is not too high. What happens if they are also going down a steep hill, and want to brake to maintain their speed? If fc=fb, then this changes to: ftot = sqrt(1^2 + 1^2) = 1.41 You have just lost 40% of the margin of safety you planned to have in the corner. I do agree that the best way to learn this is not through math, but through practice. I found that a great way to learn how to deal with low traction conditions in corners is to go out and ride just after a fresh snowfall (before the plows come by). Very low traction, loads of fun, and if you happen to fall then the snow offers some padding... Chris -- Chris Colohan Email: PGP: finger Web: www.colohan.com Phone: (412)268-4751 |
#13
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Braking while turning
"Mike S." mikeshaw2@coxDOTnet writes:
" It may be the safest thing to do, but if you want to descend fast, it's poor technique. Actually, its better to brake and accelerate in straight lines. Don't ask me to explain, its physics... I have a nice scar on my left bicep from braking in a corner and running wide into a barbed wire fence. Grab brakes in the middle of a turn and the bicycle will have a tendency to stand up and widen the arc of the corner you're taking. If you don't know its going to happen, you too can end up with a nifty scar like mine. I doubt that you would have been better off without braking. The point being, unless you are willing to go slow all the time, you are better off learning how to brake in turns. The time to learn is not when you need it...rather practice under known conditions. If you have to brake, do it just like in cars and motorcycles: brake before the corner, corner, then accelerate as you're exiting. You think cars and motorcycles don't brake in turns? That's nonsensical. Furthermore, the amount of acceleration available to a cyclist is trivial compared to the deceleration. Learn to use. If you can help it, don't brake. That's the fastest way down the mountain... Not one with real turns. Joe Riel |
#14
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Braking while turning
"Phil, Squid-in-Training" wrote:
Chalo wrote: Furthermore, slipping the rear can cause a highside, flinging you into the land of broken clavicles. Really now? In my experience, highsides have been limited to the domain of motorcycles, where the speeds of the bikes and massive grips of the tires have the potential to cause a highside. Uh... wait. I recall highsiding on my MTB commuter once. I landed on my forearms, so nothing broken. I now have a dolphin-shaped scar on my arm. Nevermind what I said. Though I've not actually seen video of it, the crash that took Beloki out of the Tour this year (which commands its own thread right now) has been described as a highside. I've highsided both pushbikes and motorbikes, and motorbikes are worse. ;^) Chalo Colina |
#15
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Braking while turning
Christopher Brian Colohan writes:
Joe Riel writes: ... Do you corner anywhere near that lean angle? Few do. Ok, so you first establish that on flat pavement with no surface gunk friction is very high. And you argue that few folks ride anywhere near this limit on corners. So for most people fc is not that high. Second, because the total force on the contact patch is the vector sum of the cornering force and the braking force, which are applied perpendicular to each other, it is possible to apply considerable braking force while barely changing the total force. For example, let the braking force (fb) be 20% of the cornering force (fc). The total force is then You then argue that 20% of fc (which we established is not that high) is a "significant braking force". For some reason, I disagree. :-) ftot = sqrt(fc^2 + fb^2) = fc*sqrt(1+(fb/fc)^2) ~ fc*(1+(fb/fc^2)/2) for fb fc = fc*(1+(2/10)^2/2) = 1.01*fc Here is a much easier way of solving (and understanding) this, with the bonus of getting a more accurate answer: The reason I expanded the term was so that the math would be easier (i.e. I wouldn't have to do the square root in my head). Alas, I apparently can't do squares in my head. My formula gives 1.02 when done properly. ftot = sqrt(1^2 + .2^2) = 1.02 Now, if you assume that the rider is cornering somewhat conservatively, because they fear that there might be a patch of sand or tar on the corner somewhere, then you can assume that fc is not too high. What happens if they are also going down a steep hill, and want to brake to maintain their speed? If fc=fb, then this changes to: ftot = sqrt(1^2 + 1^2) = 1.41 You have just lost 40% of the margin of safety you planned to have in the corner. That's why it's called margin 8-). Consider this. The maximum braking force on dry asphalt is limited to approximately 0.7g, to prevent flipping over. Assume that the maximum contact force (where sliding initiates) is about 1g. It is then possible to be simulateously braking at the maximum (0.7g), while cornering at 0.7g! Cornering at 0.7g corresponds to a lean angle, from upright, of approximately 35 degrees. I have crudely measured my lean angles and know that 35 degrees feels quite aggressive; I consider myself a reasonably fast descender---certainly one of the faster in my club. The point being, the typical margins riders deal with are wide indeed. Naturally, stuff in road can reduce the margins in a hurry, but one of the points of practicing is to learn to maneuver at speed. I do agree that the best way to learn this is not through math, but through practice. Agreed, but I like doing the math anyway... I found that a great way to learn how to deal with low traction conditions in corners is to go out and ride just after a fresh snowfall (before the plows come by). Very low traction, loads of fun, and if you happen to fall then the snow offers some padding... I guess that's one of the downsides to living in San Diego; we don't get much snowfall here 8-). To improve my cornering I have used stiff wire attached to the rear dropout and set to touch the ground at a preset lean angle. Start with a lean angle of about 30 degrees, ride and corner progressively harder until you just hear the wire scraping on the ground. Then gradually increase the lean angle. Joe Riel |
#16
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Braking while turning
On Tue, 22 Jul 2003 03:28:19 GMT, Joe Riel wrote:
Christopher Brian Colohan writes: [...] I found that a great way to learn how to deal with low traction conditions in corners is to go out and ride just after a fresh snowfall (before the plows come by). Very low traction, loads of fun, and if you happen to fall then the snow offers some padding... I guess that's one of the downsides to living in San Diego; we don't get much snowfall here 8-). To improve my cornering I have used stiff wire attached to the rear dropout and set to touch the ground at a preset lean angle. Start with a lean angle of about 30 degrees, ride and corner progressively harder until you just hear the wire scraping on the ground. Then gradually increase the lean angle. Joe Riel I have to try this... -- Chris Bird |
#17
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Braking while turning
MY suggestion is to brake like others said before a corner, but if
your in the corner, i use a small combination of both brakes. Recently I got to learn this, i was going down a dirt road pushing 25mph and went into a dirt corner, my bike has slicks in the middle of the tire and small knobs on the outsides. Well I pushed the tires too far and started to lose traction, so I tried to feather both brakes in a no turning back attemp to slow down. The rear end broke lose which I thought i could handle because me and friends do it all the time for fun, it was all working out but with the bike sideways like I wanted it, I hit the raised portion of the road, and all hell broke loose. No damage to the bike or me! |
#18
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Braking while turning
TJ Poseno wrote:
MY suggestion is to brake like others said before a corner, but if your in the corner, i use a small combination of both brakes. far and started to lose traction, so I tried to feather both brakes in a no turning back attemp to slow down. The rear end broke lose which I thought i could handle because me and friends do it all the time for fun, it was all working out but with the bike sideways like I wanted it, I hit the raised portion of the road, and all hell broke loose. "I had an accident using both brakes, so I suggest you use both brakes in the corners, too." -- David Damerell Distortion Field! |
#19
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Braking while turning
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#20
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Braking while turning
Actually, its better to brake and accelerate in straight lines. Don't ask
me to explain, its physics... The physics have been explained. It doesn't support your claim. Actually, the physics do, if 'better' is defined as 'safer'. One has less chance of losing traction if one stays off the brakes. As others have said, though, it's not the fastest. Doug |
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