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if you wanted maximum braking, where would you sit?
if you could position your center of gravity anywhere, to ensure
maximum braking power, where would it be? obviously over the front wheel is no good, you would flip. there is a point, leaning either ahead of the front wheel, or behind the back wheel, that the opposite wheel is off the ground. clearly those are 2 limits, the answer must lie between them. if there were very little friction, it would hardly matter. assume a level road, brakes that can cause a skid no matter what. ok, so where do you sit? state assumptions, like coefficient of friction between tire and road, weight of bike and rider. show your work. :) now for extra credit, make it a function of road slope. wle. |
if you wanted maximum braking, where would you sit?
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if you wanted maximum braking, where would you sit?
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if you wanted maximum braking, where would you sit?
wle wrote:
if you could position your center of gravity anywhere, to ensure maximum braking power, where would it be? obviously over the front wheel is no good, you would flip. there is a point, leaning either ahead of the front wheel, or behind the back wheel, that the opposite wheel is off the ground. clearly those are 2 limits, the answer must lie between them. if there were very little friction, it would hardly matter. assume a level road, brakes that can cause a skid no matter what. ok, so where do you sit? state assumptions, like coefficient of friction between tire and road, weight of bike and rider. I would sit near or below the level of the front axle to reduce or elminate the tendency for the rear wheel to lift off of the ground, and I would also be near the rear wheel for more favorable weight distribution for braking. This describes a recumbent lowracer. Braking can be improved by adding a second wheel in front (tadpole trike) as weight transfers forward to two contact patches during braking, and locking one or both front wheels under braking will not lead to a loss of balance. Tom Sherman - Quad Cities |
if you wanted maximum braking, where would you sit?
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if you wanted maximum braking, where would you sit?
I find the idea position changes depending on speed and deaccelleration
while breaking. So, that means it's constantly changing... It's hard to put into words actually, so I'm trying to think about it.. First of all, I wouldn't "sit" anywhere. I"d definately get out of the saddle, but I'd stay very low. I'd apply the breaks lightly and fairly evenly with more front than rear. Then, I'd increase pressure and the faster I de accellerate the farther I'd slide my ass (which is still off the seat) rearwards. Under the heaviest breaking, Ideally my weight would probably want to be above the rear axle althought I doubt I could get it that far back on even ground. While breaking, I think it's impossible to lean far enough back where you would not put enough weight on the front wheel (which should do the majority of the breaking). So, when you're leaning as far back as you can under the hardest breaking you're putting your physical weight onto the rear wheel so you can break with that better than normally, plus because of the deaccelleration a LOT of weight is still on the front wheel so you can get as much out of it as well. Mike http://mikebeauchamp.com "wle" wrote in message om... if you could position your center of gravity anywhere, to ensure maximum braking power, where would it be? obviously over the front wheel is no good, you would flip. there is a point, leaning either ahead of the front wheel, or behind the back wheel, that the opposite wheel is off the ground. clearly those are 2 limits, the answer must lie between them. if there were very little friction, it would hardly matter. assume a level road, brakes that can cause a skid no matter what. ok, so where do you sit? state assumptions, like coefficient of friction between tire and road, weight of bike and rider. show your work. :) now for extra credit, make it a function of road slope. wle. |
if you wanted maximum braking, where would you sit?
Well, for maximum braking power you'd want to have max power for both
wheels. Because the rear tends to lose braking power as weight shifts forward, moving back just far enough to balance the effect ought to produce the max. I suppose you could tell where that is by trial and error, determining how far back you need to move so that both wheels skid at the same time. No, wait a minute - on reflection it seems moving back would reduce front braking power. Maybe it doesn't make any difference at all, so long as both wheels stay on the ground or, theoretically, maybe not even then, until braking itself causes the rear wheel to lift. -- Steve Juniper "Donald Rumsfeld took that job as Secretary of Defense because he couldn't get a job with a death squad." -- Barbara Bush -- "wle" wrote in message om... if you could position your center of gravity anywhere, to ensure maximum braking power, where would it be? obviously over the front wheel is no good, you would flip. there is a point, leaning either ahead of the front wheel, or behind the back wheel, that the opposite wheel is off the ground. clearly those are 2 limits, the answer must lie between them. if there were very little friction, it would hardly matter. assume a level road, brakes that can cause a skid no matter what. ok, so where do you sit? state assumptions, like coefficient of friction between tire and road, weight of bike and rider. show your work. :) now for extra credit, make it a function of road slope. wle. |
if you wanted maximum braking, where would you sit?
Tim McNamara wrote:
(R15757) writes: (wle) if you could position your center of gravity anywhere, to ensure maximum braking power, where would it be? snip Under "maximum braking" the front wheel stops dead, the bicycle flips, and the rider is ejected. If you are talking about keeping both wheels on the ground that is far less braking force than maximum. That can be circumvented. Build a bike that positions your center of gravity below the front axle. You could lock the wheel up tight and still not do an endo. No. The important dimension is where the center of mass is in relation to the front wheel's contact patch. An endo is possible with the weight below the axle, although not likely because of insufficient traction. -- Ted Bennett Portland OR |
if you wanted maximum braking, where would you sit?
Tim McNamara wrote:
Under "maximum braking" the front wheel stops dead, the bicycle flips, and the rider is ejected. If you are talking about keeping both wheels on the ground that is far less braking force than maximum. That can be circumvented. Build a bike that positions your center of gravity below the front axle. You could lock the wheel up tight and still not do an endo. It actually has nothing to do with the axle, since a locked-up wheel doesn't rotate, so it effectively stops being a wheel. The critical thing is the angle of a line drawn from the tire contact patch to the center of mass of the bike-and-rider. If this angle is steeper than a critical value, locking up the front wheel will cause an endo. This is the case for typical upright bikes. If the angle is shallower than the critical angle, locking up the front wheel will cause it to skid. This is the case for tandems and many recumbents. The value of the critical angle depends on the coefficient of friction between the tire and the road surface. For vehicles where the angle is steep, the rear brake is useless at maximal braking. For vehicles where the angle is shallow, both brakes are needed to achieve maximal braking. Note that the _length_ of the line doesn't matter, only the angle. See also http://sheldonbrown.com/brakturn.html Sheldon "Geometry And Physics" Brown +------------------------------------------+ | So we'll go no more a roving | | So late into the night, | | Though the heart be still as loving, | | And the moon be still as bright. | | | | For the sword outwears its sheath, | | And the soul wears out the breast, | | And the heart must pause to breathe, | | And Love itself have rest. | | | | Though the night was made for loving, | | And the day returns too soon, | | Yet we'll go no more a roving | | By the light of the moon. | | --Lord Byron | +------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide http://captainbike.com http://sheldonbrown.com |
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