New thread.. Brakes what has Pat tried, and what is his summary, Ryan and others may chime in
06-02-2005, 02:39 PM
#44
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Depends on which pad you have in there...
OEM pads are made by a variety of manufacturers, so they are not all the same. I've had one set that was very grabby (what you might define as great initial bite), and another set where the braking feel was more progressive (what you might define as soft).
To parrot what Ryan has previously stated, what aftermarket brakes mostly buy you is better heat capacity, more consistent braking as temps rise, and better pedal modulation at the limit. Your observations on the stock brakes are mostly limited to the pad being used, and not the other characteristics that define better braking.
To parrot what Ryan has previously stated, what aftermarket brakes mostly buy you is better heat capacity, more consistent braking as temps rise, and better pedal modulation at the limit. Your observations on the stock brakes are mostly limited to the pad being used, and not the other characteristics that define better braking.
06-02-2005, 02:41 PM
#45
well, you have to assume the same pad. At that point, pedal feel is going to be based on pistons...
...bigger pistons means more displacement, means more pedal travel
...smaller pistons means less displacement, means less pedal travel
This is just one application of braking. Once you start going in/out of the brakes, and in/out of ABS and really pushing the car around on the braking limits, the different kits will behave differently (reaction time, etc.).
Of course, this assumes all else is equal, which it rarely is. Pads will skew this beyond all recognition once you start messing around with different compounds, and different stuff front vs rear.
...smaller pistons means less displacement, means less pedal travel
This is just one application of braking. Once you start going in/out of the brakes, and in/out of ABS and really pushing the car around on the braking limits, the different kits will behave differently (reaction time, etc.).
Of course, this assumes all else is equal, which it rarely is. Pads will skew this beyond all recognition once you start messing around with different compounds, and different stuff front vs rear.
06-02-2005, 08:59 PM
#48
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Got another question for you if you don't mind...
"Because the trailing edge of the pad is hotter then the leading edge, and this fact is what makes a 2 piston (or single piston floating) caliper cause the pads to taper. By adding another set of pistons, you can make the first set smaller then the second, thus offsetting the taper from the heat buildup."
Wouldn't you want the smaller piston to be at the trailing edge of the pad to decrease the pressure there and even out the wear?
P.S. Thanks for the write-up. Definitely some good info in there.
Wouldn't you want the smaller piston to be at the trailing edge of the pad to decrease the pressure there and even out the wear?
P.S. Thanks for the write-up. Definitely some good info in there.
06-02-2005, 09:05 PM
#49
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That's a good point. I have always wondered about the ability of stock master cylinders to be able
to supply proper pressure or volume for larger displacement brake systems.
Of course all this is just theory to me. I wouldn't know a good set of brakes if they bit me in the ***.
Of course all this is just theory to me. I wouldn't know a good set of brakes if they bit me in the ***.
06-02-2005, 09:09 PM
#50
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Jumping to eight pistons often means less pad area.
That's the main problem with RS6 brakes, considered totally inadequate by many. The pad area of their 8-pot Brembo is much less than even the S8's 4-pot Brembo, and obviously much less than this 6-pot Movit caliper.
All of which leads to another disadvantage of less pad area ... the pads run hotter. On the RS6, it's difficult to find pads that don't fade on track. Hotter pads also means hotter pistons, more heat transferred into the brake fluid, and an increased likelyhood of brake fade from boiling brake fluid.
<img src="http://www.movit.de/images/audrs611.jpg">
But back to your original question ... Without knowing any better, I'd assume that in this respect, brake pads behave like tires. The total friction of a pad (or grip from a tire) is almost but not quite proportional to piston area (or the vertical load on the tire).
The black line is grip versus vertical load available from a tire. As a result, a larger tire footprint gives more grip, even though vertical load is the same. I believe brake pads behave similarly.
<img src="http://pictureposter.audiworld.com/17157/tiregrip.jpg">
All of which leads to another disadvantage of less pad area ... the pads run hotter. On the RS6, it's difficult to find pads that don't fade on track. Hotter pads also means hotter pistons, more heat transferred into the brake fluid, and an increased likelyhood of brake fade from boiling brake fluid.
<img src="http://www.movit.de/images/audrs611.jpg">
But back to your original question ... Without knowing any better, I'd assume that in this respect, brake pads behave like tires. The total friction of a pad (or grip from a tire) is almost but not quite proportional to piston area (or the vertical load on the tire).
The black line is grip versus vertical load available from a tire. As a result, a larger tire footprint gives more grip, even though vertical load is the same. I believe brake pads behave similarly.
<img src="http://pictureposter.audiworld.com/17157/tiregrip.jpg">