Pad to Disc Clearances

[Will]

Also possibly minute runout from the end float in wheel bearings (even that '00th of a mm!) causes fractional side-to-side movement on the disc (plus any minute runout on the disc itself) which pushes the pads away slightly from the disc's surface. If you drive a car with slightly loose wheel bearings or slightly 'warped' discs you'll notice that the initial pedal travel is greater than it should be.

What about any heat/gases from the pads themselves?

Nice idea though - aside from fractionally increased pad wear/minute fuel economy issues I can't see any real drawbacks

 

[iscaboy]

the mechanism for the pistons to draw back after braking is the piston seal.

they are deformed slightly when the piston moves to brake, but as the seal is fixed in the grove, the action of the seal to regain it's composure again pulls back the piston to its position.

the fluid pressure is off at this moment.

these are very small movements.

give that man a cigar.

it's a slow movement, not a small one, a new / clean caliper / piston etc will pull all the way back in, a rusty one with a knackered seal won't move a thou

 

[renault12ts]

I am not saying the pistons don't move back, they do. But the pads are not retracted at the same time. They merely lose the force of the piston behind them. So with a perfect disc and no bearing end float the pads will touch the discs after the brake pedal has been released, albeit lightly.