Here's one for you science bods...
10 November 2000, 11:57 AM
#31
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DavidRB,
Your contradiction lies in the following two statements...
"force=number x another force" (which proves that *number* is dimensionless.)
and then
"I was just trying to point out that bigger brake pads provide more friction than small pads."
If the second statement were true, *number* would be of the units, m^-2, and the equation would read:
F = uAR.
KF.
Edited, cos I forgot that greater-than and less-than are non printing...
[This message has been edited by KF (edited 10 November 2000).]
Your contradiction lies in the following two statements...
"force=number x another force" (which proves that *number* is dimensionless.)
and then
"I was just trying to point out that bigger brake pads provide more friction than small pads."
If the second statement were true, *number* would be of the units, m^-2, and the equation would read:
F = uAR.
KF.
Edited, cos I forgot that greater-than and less-than are non printing...
[This message has been edited by KF (edited 10 November 2000).]
10 November 2000, 04:14 PM
#34
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LMAO RichS
I know what you mean.
I was anticipating some slightly technical answers but that was a little beyond my A-Level physics knowledge.
And yes the Friday afternoon comment was certainly welcomed
thanks very much for the info and debating guys. feel free to continue if you like
I know what you mean.
I was anticipating some slightly technical answers but that was a little beyond my A-Level physics knowledge.
And yes the Friday afternoon comment was certainly welcomed
thanks very much for the info and debating guys. feel free to continue if you like
10 November 2000, 08:33 PM
#36
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So as stated friction is not related to area.
The frictional resistance is independent of the area of the surface in contact.
So how come wider tyres(up to a point) improve your cars handling.
I once asked my A level phycis teacher this,but he didn't have an answer.
The frictional resistance is independent of the area of the surface in contact.
So how come wider tyres(up to a point) improve your cars handling.
I once asked my A level phycis teacher this,but he didn't have an answer.
10 November 2000, 09:30 PM
#38
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Bit of info for you
The pistons in the Subaru 4 pots are 39.5mm in diameter.The pistons in the Alcon Prodrive setup are 2 at 34.9mm and 2 at 41.3mm.(so I read somewhere)
This means the piston area for
-the Subaru 4 pots is 24.5cm2
-the Prodrive 4 pots is 22.96cm2
So if my info and figures are correct for the same fluid pressure the Subaru 4 pots will press on the pads the hardest,therefore most of the reduction in pedal pressure associated with the Prodrive setup must be due to the extra leverage of the bigger discs and not due to piston area.
Also how come the 2 pots have both pots on the same side yet the 4 pots have an extra 2 pistons of the same diameter on the other side.
This means the 4 pots have twice the piston area of the 2 pots yet they don't make the pedal twice as light (when I changed from 2 pots to 4 pots the pedal was not any lighter than before,but it was firmer)
I bet my mate that the 4 pots don't press the pads any harder than the 2 pots(with both pistons on same side) He could not understand why this was so,and in the end I gave up.Anybody got a good way of explaining it ?
Andy
The pistons in the Subaru 4 pots are 39.5mm in diameter.The pistons in the Alcon Prodrive setup are 2 at 34.9mm and 2 at 41.3mm.(so I read somewhere)
This means the piston area for
-the Subaru 4 pots is 24.5cm2
-the Prodrive 4 pots is 22.96cm2
So if my info and figures are correct for the same fluid pressure the Subaru 4 pots will press on the pads the hardest,therefore most of the reduction in pedal pressure associated with the Prodrive setup must be due to the extra leverage of the bigger discs and not due to piston area.
Also how come the 2 pots have both pots on the same side yet the 4 pots have an extra 2 pistons of the same diameter on the other side.
This means the 4 pots have twice the piston area of the 2 pots yet they don't make the pedal twice as light (when I changed from 2 pots to 4 pots the pedal was not any lighter than before,but it was firmer)
I bet my mate that the 4 pots don't press the pads any harder than the 2 pots(with both pistons on same side) He could not understand why this was so,and in the end I gave up.Anybody got a good way of explaining it ?
Andy
11 November 2000, 08:24 AM
#39
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Guys there's a couple of points which haven't been considered here...
1) Why differential pistons are better (much better!!)
2) Why opposing pistons (4 pot/6pot) are better.
Differential pistons exert different amounts of pressure along the length of the pad. As the pad gets hotter, it is more prone to fade, so more force is required. By matching the pressure with the heat build up along the pad, more friction and more even pad wear can be achieved. The larger pistons will always press against the trailing edge of the pad.
If you have experienced pad knock off, on a country lane blast, you will know exactly how much fun this can be... NOT!!!
Opposing pistons have a unique advantage over sliding callipers, in their resistance to pad knock off. Pad knock off is where the pedal unexpected falls to the floor, but can be pumped back up to pressure. This is caused by excess heat getting into the wheel bearings and boiling the hub grease. The lack of grease increases the play between bearing and housing, which is greatly amplified by the time it is measured at the edge of the disc. The disc presses against the pads, forcing them back into the calliper. In a sliding calliper set up, any disc movement, in or out, will de-flood the pistons, forcing the fluid back up to the master cylinder reservoir. In a 4 or 6 pot set up, deflooding on one side will result in that fluid over filling the pistons on the opposing side, to maintain disc/pad contact across the calliper. So pedal feel is always constant.
Stopping distances... at 30mph, nothing really in it. From 100+ speeds, or after repeated heavy use, the difference is just amazing. Not only is there no fade, but you are able to fully, and more accurately, load up the front wheels, allowing more grip from the tyres (due to the increased vertical loading) which in turn allows even more brake friction to be applied.
Pad size... Length is important, but depth is directly related to the friction that can be achieved. The greater the width of swept disc area, the greater the braking torque.
The rest is quite rightly all about leverage.
One other point though... most aftermarket kits use fatter (phatter ) discs. This results in a massive increase in the volume air going between the friction plates... much quicker disc recovery times. AP discs actually pump air using a fan type construction for the central webs.
1) Why differential pistons are better (much better!!)
2) Why opposing pistons (4 pot/6pot) are better.
Differential pistons exert different amounts of pressure along the length of the pad. As the pad gets hotter, it is more prone to fade, so more force is required. By matching the pressure with the heat build up along the pad, more friction and more even pad wear can be achieved. The larger pistons will always press against the trailing edge of the pad.
If you have experienced pad knock off, on a country lane blast, you will know exactly how much fun this can be... NOT!!!
Opposing pistons have a unique advantage over sliding callipers, in their resistance to pad knock off. Pad knock off is where the pedal unexpected falls to the floor, but can be pumped back up to pressure. This is caused by excess heat getting into the wheel bearings and boiling the hub grease. The lack of grease increases the play between bearing and housing, which is greatly amplified by the time it is measured at the edge of the disc. The disc presses against the pads, forcing them back into the calliper. In a sliding calliper set up, any disc movement, in or out, will de-flood the pistons, forcing the fluid back up to the master cylinder reservoir. In a 4 or 6 pot set up, deflooding on one side will result in that fluid over filling the pistons on the opposing side, to maintain disc/pad contact across the calliper. So pedal feel is always constant.
Stopping distances... at 30mph, nothing really in it. From 100+ speeds, or after repeated heavy use, the difference is just amazing. Not only is there no fade, but you are able to fully, and more accurately, load up the front wheels, allowing more grip from the tyres (due to the increased vertical loading) which in turn allows even more brake friction to be applied.
Pad size... Length is important, but depth is directly related to the friction that can be achieved. The greater the width of swept disc area, the greater the braking torque.
The rest is quite rightly all about leverage.
One other point though... most aftermarket kits use fatter (phatter
) discs. This results in a massive increase in the volume air going between the friction plates... much quicker disc recovery times. AP discs actually pump air using a fan type construction for the central webs.
11 November 2000, 06:23 PM
#41
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Yeah I know Kurt.
My football has been cancelled due to our lovely weather (?) so I will be there at about 11:30
Looking forward to seeing Lauren again
I'll have a couple of friends with me - one interesting in changing his M3 to a scooby. The other interested in scoobies but i beat him to it and he just got a celica GT4 (quite nice)
See you in the morning
My football has been cancelled due to our lovely weather (?) so I will be there at about 11:30
Looking forward to seeing Lauren again
I'll have a couple of friends with me - one interesting in changing his M3 to a scooby. The other interested in scoobies but i beat him to it
and he just got a celica GT4 (quite nice)See you in the morning
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