pHEnomIC

iTrader: (14)

I was wondering about brakes... Any car Ive ever had up in the air has some brake drag when you try to spin the tires even when the brakes arent on. I am wondering if this wastes horsepower or do calipers work in a way that whenever there is any significant rotation, they dont make any friction?

wssix99

iTrader: (5)

The brake pads ride very close to the rotor so they can work quickly when you press the brake. As you get the car going, the pads will move further away from the rotor and eliminate the drag you are feeling.

Since you applied the brakes just before you lifted the car, the pads and rotors are still in physical contact. All your pedal does is increace the pressure between the pads and rotor - there is no mechanism to reduce that pressure other than moving the car at some speed.

So, if you drove your car and were able to bring it to a stop without pressing the brakes before hand, you'd get a different experience - but I wouldn't recommend that.

roninsonic

iTrader: (3)

Well, some Nascar teams use to press the pads into the calipers before qualifying, if that tells you anything

pHEnomIC

iTrader: (14)

Ahhh... very interesting, thanks!

therealcreeper

iTrader: (37)

I read an article somewhere that claimed that replacing the clips picked up a few hp on back to back dyno runs, it was only a few. The author was mentioning how often times he neglected to replace the clips or just threw them out, when actually they hold a slight tension that holds the pad away from the rotor.

In my googling I did come across patents for "active brake retraction" systems, which may be related so maybe there is something to it

wssix99

iTrader: (5)

I'm pretty sure you heard that they pull the pads away from the rotors. The rotors pull air between them and the brake pads. I'm not a mechanical engineer, but understand that this is the same mechanism that causes the pads (on a floating caliper) to pull away from the rotor. I understand that teams pull the pads away to reduce the drag created by this air going in between the rotors and pads. (This in turn creates a situation where the driver needs to pump the brakes a little bit before they can get any grab and stop the car after qualifying.)


I recall that trains and other industrial brakes use these. Having a car pull through the pads resting on the rotors so they pull off is one thing. Having a locomotive do this for a train with thousands of wheels/brakes is another larger problem.