8" Rotor For Better Braking Power?

I have read almost everywhere that 8" rotor gives you better braking
power than 6.
I do a lot of downhills, although it is just an XC bike. I am thinking
about upgrading
my rotor size. A friend of mine who recently upgraded his told me that
he did not feel
any difference other than just the better look.

But I can not comprehend why bigger rotor gives you better braking
power, unless
you also increase the size of your brake pads.

Without changing the pads, the contact area is still the same. Although
8" rotor
disperses heat better, because of bigger total surface, yet in theory,
it should also generate
more heat because the rotor passes thru the pads at higher speed when
brake is applied.
(sort like the outter area of a spinning disc travels faster than the
inner area)

So shouldn't this be a wash in terms of heat disperse? What else could
make a bigger
rotor better for stopping?

Pardon my ignorance in this, but I like to understand the basic physics
behind this
theory before deciding if I should upgrade. Thanks.

wrote:
I have read almost everywhere that 8" rotor gives you better braking
power than 6.
I do a lot of downhills, although it is just an XC bike. I am thinking
about upgrading
my rotor size. A friend of mine who recently upgraded his told me that
he did not feel
any difference other than just the better look.

But I can not comprehend why bigger rotor gives you better braking
power, unless
you also increase the size of your brake pads.

Without changing the pads, the contact area is still the same. Although
8" rotor
disperses heat better, because of bigger total surface, yet in theory,
it should also generate
more heat because the rotor passes thru the pads at higher speed when
brake is applied.
(sort like the outter area of a spinning disc travels faster than the
inner area)

So shouldn't this be a wash in terms of heat disperse? What else could
make a bigger
rotor better for stopping?

Pardon my ignorance in this, but I like to understand the basic physics
behind this
theory before deciding if I should upgrade. Thanks.


This smells like a troll, but I'll bite:
Braking power (the ability to stop the bike) is entirely dependent on
the dirt/tire interface. Better, bigger, stickier tires will stop you
faster than banana peels. Old school cantilever brakes can lock your
front wheel (the one that matters). Everything else is lever force and
degrees of modulation.

Shawn

wrote:

Without changing the pads, the contact area is still the same. Although
8" rotor
disperses heat better, because of bigger total surface, yet in theory,
it should also generate
more heat because the rotor passes thru the pads at higher speed when
brake is applied.

Conservation of energy, dude.

The amount of heat generated in your brakes depends only on the height
of the hill you're riding down, plus any energy you put in by pedaling.
Not rotor size.

CC

Corvus Corvax wrote:
wrote:
Without changing the pads, the contact area is still the same. Although
8" rotor
disperses heat better, because of bigger total surface, yet in theory,
it should also generate
more heat because the rotor passes thru the pads at higher speed when
brake is applied.

Conservation of energy, dude.

The amount of heat generated in your brakes depends only on the height
of the hill you're riding down, plus any energy you put in by pedaling.
Not rotor size.

CC


I thought it was that a bigger rotor minimized the fade. No?

(Never saw the need for anything more than the 160. I'm not heavy
enough and I don't go fast enough.)

--
o-o-o-o Ride-A-Lot o-o-o-o
www.schnauzers.ws

Ride-A-Lot wrote:

I thought it was that a bigger rotor minimized the fade. No?

Sure. Since the total amount of heat generated is independent of rotor
size, a larger rotor (with better heat dissipation) will fade less, all
else being equal.

That's why I run 26" rotors, also known as V-brakes. ;-)

CC

Be aware that your fork manufacturer may not recommend that size rotor.
--
DTW .../\.../\.../\...

D T W .../\... wrote:
Be aware that your fork manufacturer may not recommend that size rotor.
--
DTW .../\.../\.../\...


Exactly. An 8" rotor on a single crown fork may be a recipe for
tearing that fork into little bitty fork bits under the right rider.
It's all about physics.

JD

Per :
But I can not comprehend why bigger rotor gives you better braking
power, unless
you also increase the size of your brake pads.

I can't either, but I've got an 8" rotor on my front and a 6" on my rear and
there's definitely a diff. Complicated, of course, but different brands; mech
vs hydraulic, and different pad sizes.

The front one is a Hope C2. The rear is an Avid mech.

I usually use steady pressure my front brake for the heavy lifting and just play
the rear for trim. To compare, I'll go down a hill using only one or only the
other.

Funny thing though: the rear definitely has more power at first. Grabbier pad
would be my guess - and with steady pressure, it actually gets stronger as it
heats up before fading.

But on a long hill, I can feel the rear start fading way, way before the front.
In fact, it's got to be a pretty extreme hill for the front to fade. Just
about any old hill will make the rear fade.
--
PeteCresswell

JD wrote:

It's all about physics.

It always is, man.

CC

On Tue, 26 Sep 2006 12:04:53 -0700, wrote:

I have read almost everywhere that 8" rotor gives you better braking
power than 6.
I do a lot of downhills, although it is just an XC bike. I am thinking
about upgrading
my rotor size. A friend of mine who recently upgraded his told me that
he did not feel
any difference other than just the better look.

But I can not comprehend why bigger rotor gives you better braking
power, unless
you also increase the size of your brake pads.

Without changing the pads, the contact area is still the same. Although
8" rotor
disperses heat better, because of bigger total surface, yet in theory,
it should also generate
more heat because the rotor passes thru the pads at higher speed when
brake is applied.
(sort like the outter area of a spinning disc travels faster than the
inner area)

So shouldn't this be a wash in terms of heat disperse? What else could
make a bigger
rotor better for stopping?

Pardon my ignorance in this, but I like to understand the basic physics
behind this
theory before deciding if I should upgrade. Thanks.



It's all about torque. Try loosening a BB with a wrench that has 12"
handle, then try it with a 24" handle
much easier because you have greater (longer) torque arm.

8" vs 6" rotor is similar exercise, only difference is now you have a
spinning mass. Heat build up and fading are largely due to rotor design
and brake pad material, but the type and quality of brake fluid are also
very important. If your friend didn't notice a diff., then he's either a
corpse, setup the brakes wrong or is using really-really crappy brakes.

http://www.hayesdiscbrake.com/hayesu_product1.shtml
--
Slack