Technology as a Topic

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Ace Rimmer
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Postby Ace Rimmer » Wed Sep 17, 2008 7:39 pm

It's been a while since I've ridden a bike, but I have been on both kinds and unless those pads have spikes or something, they don't have near the power two feet connected to two legs.
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jelco
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Postby jelco » Wed Sep 17, 2008 7:59 pm

I learned to ride those bikes long before I learnt to ride 'proper' brakes as you call them. However, here these non-freewheel bikes are considered the standard, or at least as common as hand brakes (which is the name they go by over here). Note that I went to school by bike since I was six years old or so, so when I learned to ride a freewheel bike with hand brakes after 5 years I can justifiably say that I tried non-freewheel bikes a lot. ;) It took me quite a while to get used to hand brakes, but when I had to switch my bike for a non-freewheel version again for a week some years ago (because my own was being repaired after being left alone at night in the wrong place) there were two things I found terribly difficult to get used to. First, I usually spin the pads backwards when I'm just rolling away, which results in stopping unexpectedly on a freewheel bike :P and second, I almost got hit by a car when I was searching for the non-existing handbrakes when reaching a road/bike lane crossing and found out almost too late that I had to brake using the pedals.

Note that the old bikes I rode as a kid had both 'reverse-pedalling brakes' and hand brakes, but I usually stuck to the former because they worked better. This is not in the last place because the hand brakes I had back then were disc brakes as opposed to the drum brakes I have now.

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moth
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Postby moth » Wed Feb 18, 2009 2:12 pm

Ace Rimmer wrote:It's been a while since I've ridden a bike, but I have been on both kinds and unless those pads have spikes or something, they don't have near the power two feet connected to two legs.


Wrong and irrelevant.

On a surface with good grip, front wheel braking beats back wheel braking. As deceleration is increased, the weight of the bike and rider acts further forwards. Maximum deceleration is achieved when all of the weight is acting through the front wheel and the bike is on the point of flipping over. This can be achieved with a good front hand brake. At this point there is no weight acting on the back wheel, the only thing keeping it turning is inertia, and if it is braked too it will lock up without helping to slow the bike. Maximum rear wheel braking is achieved when the brake force equals the frictional force that the wheel can sustain without slipping, that force is itself proportional to the weight acting on the back wheel, so decreases with increasing brake force as weight transfers forwards.

The braking 'power' (force) applied to the wheels by any system depends on the mechanical advantage and coefficient of friction as well as the input force, so it is quite possible for a hand-actuated rim brake with good compound pads to achieve more force than a leg-powered grease-packed coaster brake without resorting to spikes. The mechanical advantage and pad compounds of rim brakes have improved a lot over the last decade or so.

The only way 'two feet and two legs' could decelerate a bike quickest is if the feet were placed on the ground forwards of the front wheel, and sufficient friction achieved to transfer all of the weight onto the feet.
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xander
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Postby xander » Wed Feb 18, 2009 3:14 pm

That is a really nice bump you have there. Was there a particular reason you felt it necessary to post now?

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world idiot
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Postby world idiot » Wed Feb 18, 2009 3:30 pm

it isnt really a bump given it is stickied
moth
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Postby moth » Wed Feb 18, 2009 6:34 pm

i blame its stickiedness, and that i didn't notice how old the thread was, and i'm sorry for the somewhat harsh tone - i was in an odd mood.

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