Disc Brakes - Thermal Expansion Drag

I recently purchased a Giant 2002 NRS1 with Hayes disc brakes. On the
long downhills where the brakes need to be applied regularly to attempt
to keep the speed a little in control ( 3 clavical fx in 12 years) , the
hot pads or rotor expands enough to cause a serious drag like I need to
pedal hard to continue on slight downhill grades. Once the brakes cool
off a bit the expansion goes back down and the brake drag lessens enough
as to not be noticed. Is this just a phenom with the Hayes brakes or is
this thermal expansion problem inherent in all the dics brake systems.
Any knowledge, experiences or remedy with this issue would be greatly
appreciated. I really love riding this full suspension machine but those
brakes suck real bad so far. Previously riding a Specialized Extreme
FSR with LX V-brakes - no problems........... Help,,,,,,,,,,,,,,

Thanks for your time.!

"Vincent J. Souki" wrote in message
...
I recently purchased a Giant 2002 NRS1 with Hayes disc brakes. On the long
downhills where the brakes need to be applied regularly to attempt to keep
the speed a little in control ( 3 clavical fx in 12 years) , the hot pads or
rotor expands enough to cause a serious drag like I need to pedal hard to
continue on slight downhill grades. Once the brakes cool off a bit the
expansion goes back down and the brake drag lessens enough as to not be
noticed. Is this just a phenom with the Hayes brakes or is this thermal
expansion problem inherent in all the dics brake systems. Any knowledge,
experiences or remedy with this issue would be greatly appreciated. I really
love riding this full suspension machine but those brakes suck real bad so
far. Previously riding a Specialized Extreme FSR with LX V-brakes - no
problems........... Help,,,,,,,,,,,,,,

Thanks for your time.!



It's not actually the disc rotors or the pads expanding, its the heat from
friction being channeled through the caliper into the break fluid, causing
the fluid to expand, and apply the piston, as if you were squeesing the
lever a little. Effect is called pump-up, and is well known. I have never
owned Hayes, so i can't comment as to whether the problem is worse with this
brand. I know that Hope use stainless steel cylinder inserts specifically to
reduce the heat transfer. The only solution i know of is to pulse the brakes
on and off on the downhill sections, in order to give them a chance to cool.
Road racers have always had to do this to avoid overheating the small
surface area of their rims and melting the innertubes on long decents.

--
Mark

In ,
Mark (UK) typed:
"Vincent J. Souki" wrote in message
...
I recently purchased a Giant 2002 NRS1 with Hayes disc brakes. On
the long downhills where the brakes need to be applied regularly to
attempt to keep the speed a little in control ( 3 clavical fx in 12
years) , the hot pads or rotor expands enough to cause a serious drag
like I need to pedal hard to continue on slight downhill grades. Once
the brakes cool off a bit the expansion goes back down and the brake
drag lessens enough as to not be noticed. Is this just a phenom with
the Hayes brakes or is this thermal expansion problem inherent in all
the dics brake systems. Any knowledge, experiences or remedy with
this issue would be greatly appreciated. I really love riding this
full suspension machine but those brakes suck real bad so far.
Previously riding a Specialized Extreme FSR with LX V-brakes - no
problems........... Help,,,,,,,,,,,,,,

Thanks for your time.!



It's not actually the disc rotors or the pads expanding, its the heat
from friction being channeled through the caliper into the break
fluid, causing the fluid to expand, and apply the piston, as if you
were squeesing the lever a little. Effect is called pump-up, and is
well known. I have never owned Hayes, so i can't comment as to
whether the problem is worse with this brand. I know that Hope use
stainless steel cylinder inserts specifically to reduce the heat
transfer. The only solution i know of is to pulse the brakes on and
off on the downhill sections, in order to give them a chance to cool.
Road racers have always had to do this to avoid overheating the small
surface area of their rims and melting the innertubes on long
decents.

What Mark said and...

With Hayes if you pull the lever the least little bit it will close off the
hole in the master cylinder and prevent the expansion of fluid into the
bladder. This will instead close the caliper. Lay off the levers every now
and then to allow expansion of the fluid to go into the bladder. Pump up is
generally not a problem with a open system like Hayes but if you nurse the
lever the system will become closed and the fluid will have nowhere to go
except to close the caliper.

Mike