Road Disc Brakes on HC descents - interesting findings

road brake dude
road brake dude Posts: 2
edited May 2015 in Road buying advice
It took me 5 weeks and 22,000 feet of descending to get my road disc brakes better than rim brakes. You can read about it in a short blog I put together at roaddisc.wordpress.com

Comments

  • meanredspider
    meanredspider Posts: 12,337
    I found mine fantastic on my first HC descent. 6 descents of Alpe D'Huez and they were just brilliant - 85kg of me so plenty of energy to dissipate.
    ROAD < Scott Foil HMX Di2, Volagi Liscio Di2, Jamis Renegade Elite Di2, Cube Reaction Race > ROUGH
  • ugo.santalucia
    ugo.santalucia Posts: 28,310
    I don't understand why your calipers are hotter than your rotors, something is not quite right there!

    At the bottom of a descent, I can put my hand on the caliper no problem, but if I touch the rotor I lose the skin
    left the forum March 2023
  • rafletcher
    rafletcher Posts: 1,235
    ugo.santalucia wrote:
    I don't understand why your calipers are hotter than your rotors, something is not quite right there!

    Maybe because the rotor loses heat a lot quicker than the (more massive) calliper? So by the time he's hopped off to take the pic they've cooled down at different rates,
  • ugo.santalucia
    ugo.santalucia Posts: 28,310
    rafletcher wrote:
    ugo.santalucia wrote:
    I don't understand why your calipers are hotter than your rotors, something is not quite right there!

    Maybe because the rotor loses heat a lot quicker than the (more massive) calliper? So by the time he's hopped off to take the pic they've cooled down at different rates,

    Point is the caliper is normally not that hot... if hot at all...
    left the forum March 2023
  • sungod
    sungod Posts: 17,155
    with hydraulics i thought i'd read of them getting squishy if the calipers got too hot, think this was in mtb context though
    my bike - faster than god's and twice as shiny
  • apreading
    apreading Posts: 4,535
    Its not just sintered vs organic, either can get glazed and sometimes you just get a rogue pair. I fitted new pads of the same variety I use all the time (Superstar Kevlar) when I went to Italy last year and took them on a couple of rides in the UK before flying out, to bed them in. On the first day, they started to overheat really quickly on the front on long decents and I had to cool them before I could use them again as once they started overheating/squealing, they lost all power! I had brought a spare pare and fitted them after two days of this and the new pair were perfect for the rest of the trip. Bad prep, contamination or just a bad set of pads? Who knows but its not just about the compound/design...
  • jezzpalmer
    jezzpalmer Posts: 389
    In real money (Celsius) that's only 55degrees, that's not hot; and as ugo says I'd expect putting your hand on it wouldn't be too much of an issue.
    The caliper will retain heat longer than the disc though, so perhaps why it looks hotter in the photo?
    Decent brake fluid (Motul 600, Castrol SRF) boils at around 300 degC.
  • bob6397
    bob6397 Posts: 218
    That I would expect to be normal - on my mtb the discs will cool down to not-hot-to-touch levels in about 3 mins after a long descent (where I wouldn't touch them with gloves on when I first stopped) whereas the caliper stays hot much longer than the disc - heat is generated in the caliper, more of it stays in the caliper due to the way that you have a metal conductor on the back of the pad (the piston) and that it has much less surface area to dissipate the heat from.

    The fluid won't boil anyway - not on the road at any rate - but comparing Shimano Mineral Oil to car brake fluid is not valid as they are different chemicals and therefore respond differently to the heat.

    bob6397
    Boardman HT Team - Hardtail
    Rose Pro-SL 2000 - Roadie
  • jezzpalmer
    jezzpalmer Posts: 389
    bob6397 wrote:
    The fluid won't boil anyway - not on the road at any rate - but comparing Shimano Mineral Oil to car brake fluid is not valid as they are different chemicals and therefore respond differently to the heat.

    bob6397

    Sorry I'd wrongly presumed all bike brakes used DOT fluid, seems Shimano and a couple of others don't. That said the claimed boiling point of Shimano fluid is high @ 280 DegC

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