Mountain Biking - 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.

http://photo.pinkbike.com/photo/709/pbpic709253.jpg

And not to mention it's on the rear wheel.

Hahah I was actually going to start a thread on this. I dont get it.

that looks rediculas.

uhm, on a trials bike like that, don't you want massive rear holding power? same idea as Magura hydro rim brakes, right?

That looks like the ultimate trials brake.

Bend a wheel, bend a rotor...... :rolleyes:

butt ugly

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.

I wonder if it does have great stopping power? But it looks stupid IMO.

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.

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

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.

The larger diamater creates better leverage, thus better braking?

Ancient picture of an old show bike.

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.

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.

...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.

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.

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!

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.

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

A similar setup has been used on the front wheel of Buell motorcycles for the past few years.

pretty soon they might even put the brakes on the rim... crazy!

That right there just made this thread worth reading :)

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.

That looks like it is attached to the rim directly. That would keep the spokes from getting worked.

Ummmmm ya wouldnt that break the bike instead of stopping it?

no one needs that much braking power lol and wheel wieght matters more than frame weight. this is the most redick thing ive seen companies waste money on in a long time.

wouldnt that brake the bike instead of stop it?

I agree in that the further the the perpendicular distance is the more force, but this is not the main reason you use a larger rotor. You get the larger rotor for more control...... Look at it this way, a 6inch rotor locks up the rear wheel easily, then why add an extra inch to the radius? Theoretically you will gain 33%more power, but this power is not needed, 6inch rotors have the power required however they overheat. By haveing a larger surface on the rotor (8 inch rotorv 6 inch rotor) the heat is able to dissipate.

All the energy from slowing down the wheel needs to go somewhere, and all most all of this energy is converted into heat. If the rotor is already hot, it is harder to convert the energy. You need to look at braking as just energy transfer.

other than the massive brake on the back the frame looks quite good i think..i like the cranks.

sorry matt---

i must have been tired when i tried to school you on physics. i didn't even have to look at your reply. i reviewed my post and was like wtf??? :D

i should stop acting like i know physics because i just made myself look ********.

take care! :)

Ancient picture of an old show bike.

This.

I saw this over a year ago.

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.

Matt-

sorry...i must have been tired when i tried to school you in physics :D i didn't even have to read your post. i took one look at mine and was like wtf...

please accept my apology

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.

matt-

sorry, i was tired when i tried to school you in physics. i didn't even have to read your rebuttal. i looked at my post and was like wtf???

please accept my apology

alrighty!!! obviously a problem with the server...i didn't mean to apologize three freaking times!!!

i wasn't that sorry :D

alrighty!!! obviously a problem with the server...i didn't mean to apologize three freaking times!!!

i wasn't that sorry :D


Thats alright, the server has been acting up with me recently as well. At one point it was saying that this thread did not even exist.

Thats alright, the server has been acting up with me recently as well. At one point it was saying that this thread did not even exist.

where in missouri are you??

My real home is in Fulton (Callaway County), but I am currently in Columbia, where I attend MU. What part of the state are you from?

My real home is in Fulton (Callaway County), but I am currently in Columbia, where I attend MU. What part of the state are you from?
i am in kirksville