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Old 01-15-06, 09:10 PM   #1
xenochimera
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20 inch brakes wtf?? *pic*

so i was arguing with my friend about how only 12 inch rotors are currently avaliable and he shows me this pic...i think its quite pointless as no body needs that kind of stopping power.

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Old 01-15-06, 09:14 PM   #2
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And not to mention it's on the rear wheel.
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Old 01-15-06, 09:16 PM   #3
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Hahah I was actually going to start a thread on this. I dont get it.
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Old 01-15-06, 09:18 PM   #4
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that looks rediculas.
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Old 01-15-06, 09:32 PM   #5
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uhm, on a trials bike like that, don't you want massive rear holding power? same idea as Magura hydro rim brakes, right?
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Old 01-15-06, 09:34 PM   #6
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That looks like the ultimate trials brake.
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Old 01-15-06, 09:46 PM   #7
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Bend a wheel, bend a rotor......
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Old 01-15-06, 10:00 PM   #8
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butt ugly
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Old 01-15-06, 10:05 PM   #9
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i don't really understand what the difference between that and just a regular magura rim brake would be. for trials riding, i don't see an advantage to having disc brakes.
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Old 01-15-06, 10:53 PM   #10
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I wonder if it does have great stopping power? But it looks stupid IMO.
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Old 01-16-06, 01:06 AM   #11
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Quote:
Originally Posted by xenochimera
so i was arguing with my friend about how only 12 inch rotors are currently avaliable
Okay, correct me if I'm wrong, but where do you see a 12 inch rotor readily avalible? Isn't 203mm the biggest made? Am I the only one who thinks this is weird? What is love? Where is the bathroom? When will they pass the bong?!?!?!


caboose
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Old 01-16-06, 01:06 AM   #12
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Originally Posted by OneTinSloth
i don't really understand what the difference between that and just a regular magura rim brake would be. for trials riding, i don't see an advantage to having disc brakes.
In a hydraulic brake, the leverage creates a large amount of pressure at the caliper. Take the amount of pressure it takes to stop you with a caliper and a 6 inch rotor, and put the same caliper on a rotor that is probably 20 inches in diameter, thats alot of power. The pressure on rim-brake pads is not nearly as much, even with the HS-33's. With this brake, its probably either free or locked.
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Old 01-16-06, 02:01 AM   #13
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That is bloody stupid. For a trials bike you wat either on or off, ok big brake yay. The only advantage a trials bike could gain from a disc brake is that the braking surface is not effected by the shape of the rim. The rim actually flexes quite alot no matter how strong the wheel. Now this has lost the advantage.

Also this set up is going to be heavy compared to hydraulic V brakes (arguably the best thing for trials, lots of power and lighter than discs) another problem with discs in trials is the forces sent through the caliper has been known to rip the brake mounts off a frame.

Finally, the main reason 8 inch rotors have better stopping capability over 6 inch is not the distance from the axel (that helps a bit but is not the main reason). The main reason is a larger surface to dissipate heat! The rotor can cool down better, the brakes don't over heat and voila..... better braking performance. Now on a trials bike there is no draggin of the brakes, therefore little there is little heat created so no need for large surface.
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Old 01-16-06, 02:34 AM   #14
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The larger diamater creates better leverage, thus better braking?
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Old 01-16-06, 03:28 AM   #15
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Ancient picture of an old show bike.
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Old 01-16-06, 10:14 AM   #16
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Originally Posted by Flak
The larger diamater creates better leverage, thus better braking?
Exactly, let me put it into a different perspective. The friction between the pad and the rotor is always parallel with the rotor. You could say that the friction between the pad and the rotor was like a hand pushing on the end of a wrench trying to turn it. Now imagine you had a really stubborn bolt (covered deeply enough in another thread) would you want a long wrench or a short wrench. Of course you would want a long wrench. The same thing applies for brakes. The longer the lever arm, the greater the stopping power from the same amount of frictional force.
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Old 01-16-06, 10:23 AM   #17
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The longer the lever arm, the greater the stopping power from the same amount of frictional force.
...the greater the stopping power due to an increased amount of frictional force.
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Old 01-16-06, 10:33 AM   #18
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Originally Posted by mx_599
...the greater the stopping power due to an increased amount of frictional force.

The frictional force would not change, kinetic friction is defined as the coefficient of kinetic friction x the normal force. The coefficient of friction is derived from the properties of the materials (not changing, regardless of the size and shape of the brakes and pads) The normal force is simply the squeezing power of the brakes,, also doesn't change when the rotors size changes. The only difference is the lever warm, which is why the braking power increases. Also the increased mass would prevent overheating the brakes, but the main difference would be the increased lever arm.
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Old 01-16-06, 10:36 AM   #19
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Quote:
Originally Posted by MattBeaty
Exactly, let me put it into a different perspective. The friction between the pad and the rotor is always parallel with the rotor. You could say that the friction between the pad and the rotor was like a hand pushing on the end of a wrench trying to turn it. Now imagine you had a really stubborn bolt (covered deeply enough in another thread) would you want a long wrench or a short wrench. Of course you would want a long wrench. The same thing applies for brakes. The longer the lever arm, the greater the stopping power from the same amount of frictional force.
Yes its called torque.
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Old 01-16-06, 10:40 AM   #20
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Quote:
Originally Posted by MattBeaty
Exactly, let me put it into a different perspective. The friction between the pad and the rotor is always parallel with the rotor. You could say that the friction between the pad and the rotor was like a hand pushing on the end of a wrench trying to turn it. Now imagine you had a really stubborn bolt (covered deeply enough in another thread) would you want a long wrench or a short wrench. Of course you would want a long wrench. The same thing applies for brakes. The longer the lever arm, the greater the stopping power from the same amount of frictional force.

yes, its called torque. For a given force (the friction of the brake) the stopping power increases as the length of the moment arm (radius of rotor) increases. If there is also more friction due to surface area, that is just another added bonus.
pretty soon they might even put the brakes on the rim... crazy!
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Old 01-16-06, 10:41 AM   #21
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Originally Posted by MattBeaty
The only difference is the lever warm, which is why the braking power increases. Also the increased mass would prevent overheating the brakes, but the main difference would be the increased lever arm.
The above should say lever arm, not warm. For some reason I can not edit the pst it is saying that the thread does not even exist.
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Old 01-16-06, 11:06 AM   #22
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Quote:
Originally Posted by MattBeaty
The frictional force would not change, kinetic friction is defined as the coefficient of kinetic friction x the normal force. The coefficient of friction is derived from the properties of the materials (not changing, regardless of the size and shape of the brakes and pads) The normal force is simply the squeezing power of the brakes,, also doesn't change when the rotors size changes. The only difference is the lever warm, which is why the braking power increases. Also the increased mass would prevent overheating the brakes, but the main difference would be the increased lever arm.
holy crap
dude, are you like an engineer or something?
wow you must be REALLY smart
as for the brakes... i wouldnt have 20" disc(s)
i hardly use my 6" rotors to the max
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Old 01-16-06, 01:01 PM   #23
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A similar setup has been used on the front wheel of Buell motorcycles for the past few years.
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Old 01-16-06, 01:20 PM   #24
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pretty soon they might even put the brakes on the rim... crazy!
That right there just made this thread worth reading
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Old 01-16-06, 02:41 PM   #25
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holy crap
dude, are you like an engineer or something?
wow you must be REALLY smart
as for the brakes... i wouldnt have 20" disc(s)
i hardly use my 6" rotors to the max
I am an engineering student. That is the only rason that the Physics and Statics are fresh in my mind.

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