8" Rotor For Better Braking Power?

[[email protected]]

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.

 

[Shawn]

[email protected] 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

 

[Corvus Corvax]

[email protected] 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

 

[Ride-A-Lot]

Corvus Corvax wrote:
> [email protected] 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

 

[Corvus Corvax]

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

 

[D T W .../\\...]

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

 

[JD]

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

 

[(PeteCresswell)]

Per [email protected]:
>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

 

[Corvus Corvax]

JD wrote:
>
> It's all about physics.

It always is, man.

CC

 

[Slack]

On Tue, 26 Sep 2006 12:04:53 -0700, <[email protected]> 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

 

[tom]

What he (Slack) said. Tom
Slack wrote:


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

 

[Roberto Baggio]

A single crown fork will be fine, unless it's made out of noodles.

What you need to consider is the dropout. A standard 9mm dropout can have
excessive force applied to the axle, whereas a 20mm axle will be fine. Most
bike/fork manufacturers will state that 8" rotors are not a good idea on a
fork with standard dropouts. Marzocchi made a triple clamp fork with
standard dropouts, and with a month I saw 3 that broke the axle when an 8"
rotor was used. On the other hand, I see numerous single crown forks with
8" rotors (I've run the setup myself), and there are no issues.

The advantages of an 8" rotor over a 6" rotor is increased braking power
because of the additional torque, and increased heat dissipation, because of
the larger surface area. The disadvantage is the weight the additional
weight, as well as a rotor that is easier to damage in crash because there's
more rotor to hit something.

"JD" <[email protected]> wrote in message
news:[email protected]...
> 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.

 

[[email protected]]

Corvus Corvax wrote:
> 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

The rim may be a 26" rotor, but the V-brakes you have are "dual piston
calipers." ;-)

R

 

[JD]

Roberto Baggio top posted:
> A single crown fork will be fine, unless it's made out of noodles.


Tell us all bags, which manufacturers recommend that you use an 8"
rotor on their single crown forks?

You freerider neophytes crack me up.

JD

 

[Michael Halliwell]

JD wrote:

Roberto Baggio top posted:



A single crown fork will be fine, unless it's made out of noodles.



Tell us all bags, which manufacturers recommend that you use an 8" rotor on their single crown forks? You freerider neophytes crack me up. JD


No freerider here, but to be honest, I don't think manufacturers actually recommend a rider run a specific size of rotor....OTOH they often do state a maximum rotor size. Fox states the maximum rotor I can put on my single crown Float 130 is an 8".

Mike

 

[Ed Pirrero]

Michael Halliwell wrote:
> JD wrote:
> Roberto Baggio top posted:
>
>
> A single crown fork will be fine, unless it's made out of noodles.
>
>
>
>
> Tell us all bags, which manufacturers recommend that you use an 8"
> rotor on their single crown forks?
>
> You freerider neophytes crack me up.
>
> JD
>
>
> No freerider here, but to be honest, I don't think manufacturers actually recommend a rider run a specific size of rotor....OTOH they often do state a maximum rotor size. Fox states the maximum rotor I can put on my single crown Float 130 is an 8".

The 8"/single-crown combo being no good is a lot of myth. The forces
on the crown from braking are small to begin with, and don't increase
much from a larger rotor.

Someone metnioned physics - I don't see anyone presenting even *one*
set of calculations, or a drawing, or anything, to substantiate the
claim.

But then again, there's a whole newsgroup fully of hot air over bicycle
tech. Probably shouldn't drag it over here...

E.P.

 

[Ride-A-Lot]

Ed Pirrero wrote:
> Michael Halliwell wrote:
>> JD wrote:
>> Roberto Baggio top posted:
>>
>>
>> A single crown fork will be fine, unless it's made out of noodles.
>>
>>
>>
>>
>> Tell us all bags, which manufacturers recommend that you use an 8"
>> rotor on their single crown forks?
>>
>> You freerider neophytes crack me up.
>>
>> JD
>>
>>
>> No freerider here, but to be honest, I don't think manufacturers actually recommend a rider run a specific size of rotor....OTOH they often do state a maximum rotor size. Fox states the maximum rotor I can put on my single crown Float 130 is an 8".
>
> The 8"/single-crown combo being no good is a lot of myth. The forces
> on the crown from braking are small to begin with, and don't increase
> much from a larger rotor.
>
> Someone metnioned physics - I don't see anyone presenting even *one*
> set of calculations, or a drawing, or anything, to substantiate the
> claim.
>
> But then again, there's a whole newsgroup fully of hot air over bicycle
> tech. Probably shouldn't drag it over here...
>
> E.P.
>

Where's Phil (squid)? Isn't he a materials engineer?

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

 

[Dre]

"Ed Pirrero" <[email protected]> wrote in message
news:[email protected]...
>
> Michael Halliwell wrote:
>> JD wrote:
>> Roberto Baggio top posted:
>>
>>
>> A single crown fork will be fine, unless it's made out of noodles.
>>
>>
>>
>>
>> Tell us all bags, which manufacturers recommend that you use an 8"
>> rotor on their single crown forks?
>>
>> You freerider neophytes crack me up.
>>
>> JD
>>
>>
>> No freerider here, but to be honest, I don't think manufacturers
>> actually recommend a rider run a specific size of rotor....OTOH they
>> often do state a maximum rotor size. Fox states the maximum rotor I can
>> put on my single crown Float 130 is an 8".
>
> The 8"/single-crown combo being no good is a lot of myth. The forces
> on the crown from braking are small to begin with, and don't increase
> much from a larger rotor.
>
> Someone metnioned physics - I don't see anyone presenting even *one*
> set of calculations, or a drawing, or anything, to substantiate the
> claim.
>
> But then again, there's a whole newsgroup fully of hot air over bicycle
> tech. Probably shouldn't drag it over here...
>
> E.P.
>
Same here, my Marzocchi 66RCX2's dont say anything about not recommending an
8". They do state max 8" though...

How do these brake forces compare to doing endo's then?? I would have
thought endos would put more stress on the crown than the brakes...

Cheers Dre

 

[Slack]

On Thu, 28 Sep 2006 21:08:45 -0700, Dre <[email protected]> wrote:

> "Ed Pirrero" <[email protected]> wrote in message
> news:[email protected]...
>>
>> Michael Halliwell wrote:
>>> JD wrote:
>>> Roberto Baggio top posted:
>>>
>>>
>>> A single crown fork will be fine, unless it's made out of noodles.
>>>
>>>
>>>
>>>
>>> Tell us all bags, which manufacturers recommend that you use an 8"
>>> rotor on their single crown forks?
>>>
>>> You freerider neophytes crack me up.
>>>
>>> JD
>>>
>>>
>>> No freerider here, but to be honest, I don't think manufacturers
>>> actually recommend a rider run a specific size of rotor....OTOH they
>>> often do state a maximum rotor size. Fox states the maximum rotor I
>>> can
>>> put on my single crown Float 130 is an 8".
>>
>> The 8"/single-crown combo being no good is a lot of myth. The forces
>> on the crown from braking are small to begin with, and don't increase
>> much from a larger rotor.
>>
>> Someone metnioned physics - I don't see anyone presenting even *one*
>> set of calculations, or a drawing, or anything, to substantiate the
>> claim.
>>
>> But then again, there's a whole newsgroup fully of hot air over bicycle
>> tech. Probably shouldn't drag it over here...
>>
>> E.P.
>>
> Same here, my Marzocchi 66RCX2's dont say anything about not
> recommending an
> 8". They do state max 8" though...
>
> How do these brake forces compare to doing endo's then?? I would have
> thought endos would put more stress on the crown than the brakes...
>
> Cheers Dre
>
>

Biker Fox, is that you?

Is someone recommending endos?
--
Slack

 

[Dre]

"Slack" <[email protected]> wrote in message
newsp.tgmjx3pmntnj34@slacker...
> On Thu, 28 Sep 2006 21:08:45 -0700, Dre <[email protected]> wrote:
>
>> "Ed Pirrero" <[email protected]> wrote in message
>> news:[email protected]...
>>>
>>> Michael Halliwell wrote:
>>>> JD wrote:
>>>> Roberto Baggio top posted:
>>>>
>>>>
>>>> A single crown fork will be fine, unless it's made out of noodles.
>>>>
>>>>
>>>>
>>>>
>>>> Tell us all bags, which manufacturers recommend that you use an 8"
>>>> rotor on their single crown forks?
>>>>
>>>> You freerider neophytes crack me up.
>>>>
>>>> JD
>>>>
>>>>
>>>> No freerider here, but to be honest, I don't think manufacturers
>>>> actually recommend a rider run a specific size of rotor....OTOH they
>>>> often do state a maximum rotor size. Fox states the maximum rotor I
>>>> can
>>>> put on my single crown Float 130 is an 8".
>>>
>>> The 8"/single-crown combo being no good is a lot of myth. The forces
>>> on the crown from braking are small to begin with, and don't increase
>>> much from a larger rotor.
>>>
>>> Someone metnioned physics - I don't see anyone presenting even *one*
>>> set of calculations, or a drawing, or anything, to substantiate the
>>> claim.
>>>
>>> But then again, there's a whole newsgroup fully of hot air over bicycle
>>> tech. Probably shouldn't drag it over here...
>>>
>>> E.P.
>>>
>> Same here, my Marzocchi 66RCX2's dont say anything about not
>> recommending an
>> 8". They do state max 8" though...
>>
>> How do these brake forces compare to doing endo's then?? I would have
>> thought endos would put more stress on the crown than the brakes...
>>
>> Cheers Dre
>>
>>
>
> Biker Fox, is that you?
>
> Is someone recommending endos?
> --
> Slack

Nope, just me

I'm not recommending anything, personally I prefer wheelies to endos...

So do they put more stress on the crown or what??

Cheers Dre