XPost: comp.mobile.android, misc.phone.mobile.iphone   
   From: me@privacy.invalid   
      
   "Andy Burnelli"  wrote in message   
   news:t5g3bk$1qs$1@gioia.aioe.org...   
      
   > They go on by citing reliable references at the brake companies, where   
   > prior to that they explain the basic physics which makes it impossible.   
   > "Even if you're traveling straight down the side of a mountain with your   
   > brakes applied the entire way. Your brake pads will fade and start to   
   > disintegrate long before you come close to heating your rotors enough to   
   > soften them to the point where they could possibly warp"   
      
   I saw a demonstration in a TV program(me) about physics in the early 1980s,   
   in which a car was repeatedly braked from high speed (and then accelerated   
   back up to speed) over a very short time. A camera mounted so it could see   
   one of the front discs showed the disc was glowing cherry red after n   
   iterations (for unknown n!). They were demonstrating the conversion of   
   kinetic energy into heat.   
      
   I wonder what effect that high temperature had on the pads once they were   
   red hot. Would you want to ride in that car afterwards - would the pads have   
   been made less effective? How hot do discs get if you descend a long hill   
   (let's say a mile long, average 1:4 aka 25%) using brakes only. My wife   
   remembers a friend descending such a hill (Porlock Hill in Devon, England)   
   in a motor caravan which may have had a mixture of discs and drums. By the   
   end of the hill, there was smoke coming from the wheels (brake pads,   
   presumably) - the driver learned an important lesson: to engage a low gear   
   on a long steep hill so there is a bit of transmission braking to supplement   
   the normal friction braking.   
      
      
   Incidentally, I can vouch for the fact that if the pads wear through to the   
   mounting studs and these start to score the discs, the braking effect is a   
   lot less. (Yikes!) My car had passed its MOT test (annual safety test in the   
   UK for all vehicles once they reach 3 years old) a few months earlier, and   
   braking was acceptable at that time. And nothing had been picked up when the   
   car was serviced. And yet the pads wore through to the studs. The first I   
   knew was a loud scraping metal-on-metal noise and the car didn't brake as   
   effectively as it should. I drove very cautiously to the nearest garage that   
   fitted brakes and got them to replace the relevant pads and discs. I *think*   
   it may have been only the front brakes that were affected, so I had working   
   rear brakes. I don't like to think what would have happened if all four   
   brakes had worn through at the same time. It turned out that the pads   
   *should* have triggered a warning light (wires embedded in the pads making   
   contact with the disc) before the pads wore down to the studs, but the   
   sensor wire had corroded. The warning bulb itself was working - it still   
   came on briefly as part of the self-test whenever the ignition is first   
   turned on.   
      
   I was rather horrified than the brakes had got to that state without   
   anything being picked up. Nowadays I always explicitly ask a garage to check   
   the discs and pads when my car is being serviced - because pad thickness is   
   not an easy thing to check yourself unless you know what to look for - and   
   unless you have a ramp, it means taking each wheel off in turn.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)