Braking power: Rotor size, front vs. back

[porqui]

26'ers are so last season .............

 

 

.......   .. and it is officially the start of Friday.!!

[Captain Fastbastard Mayhem]

....... .. and it is officially the start of Friday.!!

He can only say that cos he's just sold his 6er.

[Tony datoy]

Why do motorcycles have two large discs on the front?

So that you can maintain a straight line under hard braking.

With one disc upfront a superbike would pull to one side which could result in man overboard.

T

[boemelaar_bob]

Dankie oaks!

 

Thanks for all the constructive answers 

[Halfdoesyn]

So that you can maintain a straight line under hard braking.

With one disc upfront a superbike would pull to one side which could result in man overboard.

T

   

[Neverfit]

So that you can maintain a straight line under hard braking.

With one disc upfront a superbike would pull to one side which could result in man overboard.

T

So the braking force is bigger than the acceleration seeing that they have a single sided drive chain... next upgrade...2 chains... woohoo 

[GrahamS2]

I don't understand why nobody has invented something where you let the breakpads cling directly to the rims - just imagine the stopping power... 

Magura used to make hydraulic wheel brakes. They crushed rim sidewalls in a spectacular manner.

[eddy]

This is true - they stop fast enough the first time - BUT - do they stop well enough after a 1500m of fast decent with lots of hard braking corners....  THAT is the question you need to ask yourself.

 

Bigger brakes work better for longer - but are unneccesary if you don't need the added capacity of the bigger brakes - so despite haveing monsters on one of my bikes, my XC bike runs 160/160 - and that has been enough for me on everything I am willing to take that bike on so far.

I have have a 180/160 combination on my bike.

 

I weigh 94kg.

 

Should I fit a 203/180 ?

 

Ps.

 

I only ride the spruit.

[droenn]

Heres an idea from my friday afternoon fried brain:

 

the angular velocity increases as you move out from the centre of the wheel, so applying brake pads at the edge of a 203 mm rotor allows you to modulate braking more than on a smaller 160 mm rotor. this is because you have more surface area to play with at the same speed.

[bertusras]

So the braking force is bigger than the acceleration

 

Yes

 

http://i.imgur.com/5EGjdIT.png

[Halfdoesyn]

Heres an idea from my friday afternoon fried brain:

 

the angular velocity increases as you move out from the centre of the wheel, so applying brake pads at the edge of a 203 mm rotor allows you to modulate braking more than on a smaller 160 mm rotor. this is because you have more surface area to play with at the same speed.

Angular velocity (rotational speed) does not change with change in diameter. It is constant. Your discs rotate at the same speed as the wheel - hopefully. The tangential speed does. The bigger the circle, the faster the tangential speed. I suspect this is what you are referring to.

[Capricorn]

Heres an idea from my friday afternoon fried brain:

 

the angular velocity increases as you move out from the centre of the wheel, so applying brake pads at the edge of a 203 mm rotor allows you to modulate braking more than on a smaller 160 mm rotor. this is because you have more surface area to play with at the same speed.

surface area stays the same. It's the lever arm from the center of rotor to the center of the brake pad that increases. Same force + longer lever = more torque with which to counter the rotation of the wheel.

 

Braking is basically friction, and friction does not rely on surface area. Simply the normal force exerted by the pads on the brake rotor is all that matters.

[Halfdoesyn]

Yes

 

http://i.imgur.com/5EGjdIT.png

Might be, but a single disc on a wheel does not cause it to pull to one side. The purpose of 2 brake discs might be:

• to increase the braking power
• to introduce redundancy - provided you have separate circuits
• for bling

If a single disc would cause such an effect, I'm sure we would have noticed SOME evidence on single disc implementations.

[TIB]

Might be, but a single disc on a wheel does not cause it to pull to one side. The purpose of 2 brake discs might be:

• to increase the braking power
• to introduce redundancy - provided you have separate circuits
• for bling

If a single disc would cause such an effect, I'm sure we would have noticed SOME evidence on single disc implementations.

 

I love this graph.

[bertusras]

Might be, but a single disc on a wheel does not cause it to pull to one side. The purpose of 2 brake discs might be:

• to increase the braking power
• to introduce redundancy - provided you have separate circuits
• for bling

If a single disc would cause such an effect, I'm sure we would have noticed SOME evidence on single disc implementations.

 

http://i.imgur.com/Xzj0GBj.jpg

So why does the right hand fork have a stiffer spring than the left hand fork? Buells are notoriously bad when trail braking into corners, and the feel is different trailling to the left and trailling to the right. And as all motorcycle racers know, feel is extremely important.

 

That's also why the lightweight GP bikes run two tiny disks, as opposed to one large disk. Sure, overall weight might be higher, but the mass is located closer to the centre of the rotation, improving resistance to rotation and providing much better feel and modulation.

 

http://i.imgur.com/NYrQnJP.jpg

[NotSoBigBen]

I have have a 180/160 combination on my bike.

 

I weigh 94kg.

 

Should I fit a 203/180 ?

 

Ps.

 

I only ride the spruit.

 

For the Spruit I would take no less than a 203mm Carbon Fiber rotor with 4 pot calipers