Originally Posted By: stephen9666
Originally Posted By: SLCraig
I have never seen a warped rotor and I have turned some on the lathe personally myself. Change in thickness yes, 100%. Warping, 100% no.
This is one of the major problems in discussing brake pulsation issues. When people say "warped" rotors, what they sometimes are experiencing is thickness variation caused by runout, which then leads to a pedal pulsation.
I think the article posted by the OP almost does more harm then good when people read it. While pad deposits clearly can be an issue in some cases, in many other cases it's either runout in the hub or rotor or another issue. That causes the rotor to wear unevenly and the pulsation starts.
More info on pedal pulsation and runout in this document from Raybestos:
http://www.raybestos.com/wps/wcm/connect...pdf?MOD=AJPERES
This. Runout and warping are real concerns. Warping becomes really prevalent in the real world when one or two wheel lugs are torqued (uncontrollably ie with impact wrench) more than the others. Then you go out on the road and heat those discs up, the high torque on one side of the rotor will encourage warping; mostly with steel wheels. Another big issue is rust forming on the friction surface of the rotor. This causes uneven contact, uneven heat distribution (including very hot tracks of raised/pitted rotor), this will tear off and melt the organic component of pad friction material onto the rotor. It's very difficult for a regular road car, with perfectly scrubbed rotors under normal conditions to ever become so hot as to deposit pad material onto the rotor where it can't be scrubbed off. This would need something like heavy braking for a mile downhill and coming to a complete stop and holding the smouldering brake pad against the rotor at that exact spot that the rotor stopped. This could easily result in both pad deposition and warping.
Originally Posted By: Chris142
The only way to get pad deposits on your rotors is to come down a mountain with smoking hot brakes and stop or driving erratically enough to get the brakes and rotors extreemly hot.
Normal people don't drive like that. I can set s brake lathe up to just scuff the surface and it will remove magnetic metal and not pad material.
Exactly. A fella with track experience trying to transpose his experience onto regular motorists who barely change their oil. His points are good, but that first one-- to come out and say that most people's pulsating problems are mostly because of phenomena observed on the track with race-compound brake pads, and not warping from cheap casts of iron and improperly torqued lugs. He does raise some excellent points that many of us have not considered before, I'll learn from it.
Originally Posted By: 901Memphis
I still think I'm going to shop for the cheapest coated rotors I can find, maybe centric premium m they are affordable but appear quality.
This is probably a sound plan. If a rotor is going to be coated, it is probably of above average quality.
Anyway, thanks for posting the link!
Originally Posted By: SLCraig
I have never seen a warped rotor and I have turned some on the lathe personally myself. Change in thickness yes, 100%. Warping, 100% no.
This is one of the major problems in discussing brake pulsation issues. When people say "warped" rotors, what they sometimes are experiencing is thickness variation caused by runout, which then leads to a pedal pulsation.
I think the article posted by the OP almost does more harm then good when people read it. While pad deposits clearly can be an issue in some cases, in many other cases it's either runout in the hub or rotor or another issue. That causes the rotor to wear unevenly and the pulsation starts.
More info on pedal pulsation and runout in this document from Raybestos:
http://www.raybestos.com/wps/wcm/connect...pdf?MOD=AJPERES
This. Runout and warping are real concerns. Warping becomes really prevalent in the real world when one or two wheel lugs are torqued (uncontrollably ie with impact wrench) more than the others. Then you go out on the road and heat those discs up, the high torque on one side of the rotor will encourage warping; mostly with steel wheels. Another big issue is rust forming on the friction surface of the rotor. This causes uneven contact, uneven heat distribution (including very hot tracks of raised/pitted rotor), this will tear off and melt the organic component of pad friction material onto the rotor. It's very difficult for a regular road car, with perfectly scrubbed rotors under normal conditions to ever become so hot as to deposit pad material onto the rotor where it can't be scrubbed off. This would need something like heavy braking for a mile downhill and coming to a complete stop and holding the smouldering brake pad against the rotor at that exact spot that the rotor stopped. This could easily result in both pad deposition and warping.
Originally Posted By: Chris142
The only way to get pad deposits on your rotors is to come down a mountain with smoking hot brakes and stop or driving erratically enough to get the brakes and rotors extreemly hot.
Normal people don't drive like that. I can set s brake lathe up to just scuff the surface and it will remove magnetic metal and not pad material.
Exactly. A fella with track experience trying to transpose his experience onto regular motorists who barely change their oil. His points are good, but that first one-- to come out and say that most people's pulsating problems are mostly because of phenomena observed on the track with race-compound brake pads, and not warping from cheap casts of iron and improperly torqued lugs. He does raise some excellent points that many of us have not considered before, I'll learn from it.
Originally Posted By: 901Memphis
I still think I'm going to shop for the cheapest coated rotors I can find, maybe centric premium m they are affordable but appear quality.
This is probably a sound plan. If a rotor is going to be coated, it is probably of above average quality.
Anyway, thanks for posting the link!
