XPost: comp.mobile.android, misc.phone.mobile.iphone   
   From: xenolith@optusnet.com.au   
      
   On 11/5/2022 8:00 pm, NY wrote:   
   > "Vic Smith"  wrote in message   
   > news:2b4m7hp2le1tl7anjbnleua0jiu1qsmfep@4ax.com...   
   >> I agree that rotors don't warp "as in a potato chip."   
   >> Rotors do warp "as in a warped rotor."   
   >   
   > Is "warp" the right word to use for a rotor (disc) that remains as a   
   > flat plane but with a surface that is not uniformly smooth over the   
      
   Short answer - no.   
      
   > whole area? I'd always thought that a warped disc had a wavy surface   
   > like a potato chip (aka potato crisp in the UK) or a vinyl LP - ie where   
   > the pads had to move parallel to the rotor axis to remain in contact   
   > with the disc that was not a perfectly flat plane.   
      
   The most common type of warped disc I have seen is more like a buckle.   
   Think of it like a bicycle wheel that doesn't run true in the lateral   
   plane. I have measured it and I have seen it when truing it on the brake   
   lathe. I have not seen a warp at opposite sides of the disc and in the   
   same plane - like a potato chip. Note however, there are a number of   
   causes of this, some not related to heat. The two most common are   
   incorrect/excessive tightening of wheel nuts and/or grit lodged between   
   disc and hub at the mounting surfaces. If the disc has been warped and   
   shows signs of severe overheating but no other cause can be determined,   
   it's the heat.   
   >   
   > Presumably if the surface becomes glazed in some parts and/or roughened   
   > in some parts that causes different amounts of wear in the different   
   > areas, exacerbating the problem.   
      
   That causes *thickness variation* and will appear as (possibly) pedal   
   pulsations or simply a shudder under braking. Most common cause of that   
   is the creation of *hard spots* caused by excessive hard braking over   
   extended periods of time. The driver needs educating on brake use.   
   >   
   > What is the advice for avoiding rotor warping? How should one brake   
   > differently to avoid it? I presume using engine braking (selecting a   
   > lower gear) when going down a long hill reduces the amount and/or time   
   > that the pads have to be in contact with the discs. I've also heard it   
      
   Yes, I do that. It is also the recommended procedure.  What I do not do   
   is use the transmission gears to *slow* *down*, that's what the *service   
   brakes* are for.   
      
   > said that if you hold the car on the footbrake (rather than applying the   
   > handbrake or transmission lock) after braking to a halt, the area of the   
   > disc that's in contact with the hot disc will not be able to cool as   
   > much as the rest of the disc, leading to "rotor warping" - which is   
   > another reason (in addition to dazzling the person behind with your   
   > brake lights) for applying the handbrake whenever you come to a stop. As   
   > my driving instructor drummed in to me: "footbrake to stop the car;   
   > handbrake to *stay* stopped" - I can still "hear" him saying that 40   
   > years later ;-)   
      
   That sounds fair!  ;-)   
      
   --   
   Xeno   
      
      
   Nothing astonishes Noddy so much as common sense and plain dealing.   
          (with apologies to Ralph Waldo Emerson)   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)