Rotor material?

On 10/8/2017 8:05 PM, James wrote:
On 07/10/17 00:51, wrote:
On Thursday, October 5, 2017 at 6:37:10 PM UTC-7, James wrote:
On 06/10/17 09:41, jbeattie wrote:


All one piece rotors I know of are SS, although you can buy CF
rotors.Â* Magura (and I think Avid) makes thick rotors (2mm) that
are supposed to be good at shedding heat, but I don't know of
anyone who makes them thicker than that. You'll have to do some
detective work.



I wouldn't have guessed that slightly thicker rotors would be
appreciably better at "shedding heat".

On MTB's on difficult descents the rotors are almost red-hot. Since
I've never seen rims that hot I can only assume that the disks allow
you to hang it out a lot further.


Since bicycle rims have enormous cooling surface area compared to a disc
rotor, it is obvious why they don't get so hot yet can still provide
adequate braking performance.

And let's face it, aluminium tends to phase change from solid to liquid
without appearing "red hot".

.... which adds some challenge when trying to weld it.

I've not yet succeed in welding aluminum by oxy-acetylene, although my
weak defense is that I haven't tried it more than a couple times.

Still, I admire anyone who can do that well.

--
- Frank Krygowski

On Sunday, October 8, 2017 at 5:05:32 PM UTC-7, James wrote:
On 07/10/17 00:51, wrote:
On Thursday, October 5, 2017 at 6:37:10 PM UTC-7, James wrote:
On 06/10/17 09:41, jbeattie wrote:


All one piece rotors I know of are SS, although you can buy CF
rotors. Magura (and I think Avid) makes thick rotors (2mm) that
are supposed to be good at shedding heat, but I don't know of
anyone who makes them thicker than that. You'll have to do some
detective work.



I wouldn't have guessed that slightly thicker rotors would be
appreciably better at "shedding heat".

On MTB's on difficult descents the rotors are almost red-hot. Since
I've never seen rims that hot I can only assume that the disks allow
you to hang it out a lot further.


Since bicycle rims have enormous cooling surface area compared to a disc
rotor, it is obvious why they don't get so hot yet can still provide
adequate braking performance.

And let's face it, aluminium tends to phase change from solid to liquid
without appearing "red hot".

--
JS

And the modern bicycle rim is very likely to be 30 mm deep or deeper for aero purposes. Lots of material and with a very low coefficient of conduction.

On Sun, 8 Oct 2017 23:30:22 -0400, Frank Krygowski
wrote:

On 10/8/2017 8:05 PM, James wrote:
On 07/10/17 00:51, wrote:
On Thursday, October 5, 2017 at 6:37:10 PM UTC-7, James wrote:
On 06/10/17 09:41, jbeattie wrote:


All one piece rotors I know of are SS, although you can buy CF
rotors.* Magura (and I think Avid) makes thick rotors (2mm) that
are supposed to be good at shedding heat, but I don't know of
anyone who makes them thicker than that. You'll have to do some
detective work.



I wouldn't have guessed that slightly thicker rotors would be
appreciably better at "shedding heat".

On MTB's on difficult descents the rotors are almost red-hot. Since
I've never seen rims that hot I can only assume that the disks allow
you to hang it out a lot further.


Since bicycle rims have enormous cooling surface area compared to a disc
rotor, it is obvious why they don't get so hot yet can still provide
adequate braking performance.

And let's face it, aluminium tends to phase change from solid to liquid
without appearing "red hot".

... which adds some challenge when trying to weld it.

I've not yet succeed in welding aluminum by oxy-acetylene, although my
weak defense is that I haven't tried it more than a couple times.

Still, I admire anyone who can do that well.

It is easier then it first appears. We used to use a flux but cleaning
and preheating was still important, But other then that the technique
is very similar to TIG welding it. In fact a properly gas welded joint
will look very much like a TIG welded joint - the so called stack of
dimes appearance.
--
Cheers,

John B.