Pad knockback

kannibul · 09-26-2009, 07:37 PM

Quote:

Originally Posted by semtex

Well, when I posted this question originally (over 3 months ago), what I was referring to is that sometimes it feels like there's a little more travel in the brake pedal before the brake pads bite. So I guess you could call that delayed braking time, sorta. If I release the brakes then step down again, then it bites with barely any pedal travel at all. See what happens is that when there's a lot of lateral load (as during hard cornering), the wheel hubs can flex a bit, which makes the rotors push or knock the pads back into the calipers (hence the phrase 'pad knockback'). The result is a small gap between the pads and the rotors, which in turn accounts for why you have to push the brake pedal down deeper before the pads bite into the rotors. If you go up to my original post and click on the link, it'll take you to StopTech's page explaining it all, complete with a little graphic to illustrate. I've gotten into the habit of double-tapping my brakes now, which means then when I want the brakes to really bite hard, I don't just step down on the pedal, but do a quick step-release-step on the pedal.

I always thought that was a combination of two things.

1) Pumping the brakes will always build up pressure in the lines. In a sense, that's what you're describing (first hit of the brakes is "long" then if you release, it's quick) - every hydralic brake system I've had has done this, even my motorcycle which doesn't have power brakes.

2) Air pressure builds up between the rotors and the pads, creating a small gap, much like the heads on a hard drive float above the platter. I imagine this would be amplified by BBK's (more surface area) and slotted rotors (larger pockets of air to pump with)

I can't imagine the braking system "flexing" under any type of cornering - it doesn't make sense. There's not enough mass there to cause a centrifugal force to pull or push a rotor. There's not enough mass in the pads to push or pull them from the caliper to where they'd be any more or less engaged in either the rotor or the piston(s).

Anyone that has done their own brake job would know the amount of force needed to squish the piston(s) back into the caliper, would see what I'm referring to. There are too small of a force at play for cornering causing anything like what you (or StopTech) is claiming. StopTech is in the market of selling brakes. Of course they'll come up with some kind of phenominon to explain something as a marketing tool...