please see attached
this illustrate a problem when using the same caliper but bigger rotors
rotor thickness is the same but diameter is about 2" difference. Pad/rotor contact went from 100% to maybe 85% after the rotor upgrade.... so it looks like a roughly 15% of pad can not be used.
Faster pad wear aside, my question is that will braking power decrease due to lesser surface contact? I mean that's what I thought at first but someone said the following:Quote »There is no performance decrease due to the smaller pad area, this is because friction is only a function of piston pressure and coefficient of friction. [/quote]so what do you guys think? will bigger rotor alone actually decrease braking power?
brake physics question pertaining bigger rotor kits
Re: brake physics question pertaining bigger rotor kits (Loveless)
noLoveless wrote:will bigger rotor alone actually decrease braking power?
Re: brake physics question pertaining bigger rotor kits (chmercer)
man... read what I'm saying with the bigger rotor comes with smaller contact surface with pads
that's is what I am asking
that's is what I am asking
Re: brake physics question pertaining bigger rotor kits (Loveless)
From a physics standpoint, it depends.
Braking depends on the torque acting against the rotor, which comes from the frictional force between the pad and rotor times it's distance from the center of the rotor (torque=force*radius).
So in a simple answer, it depends. But my gut tells me that your braking will improve due to the bigger rotor. The rear brake pads on the 300zx have less swept area than the stock 240sx rear brakes, however, the rotor has a much greater diameter, so it improves braking.
Braking depends on the torque acting against the rotor, which comes from the frictional force between the pad and rotor times it's distance from the center of the rotor (torque=force*radius).
So in a simple answer, it depends. But my gut tells me that your braking will improve due to the bigger rotor. The rear brake pads on the 300zx have less swept area than the stock 240sx rear brakes, however, the rotor has a much greater diameter, so it improves braking.
Re: brake physics question pertaining bigger rotor kits (crzycav86)
when you use a bigger rotor you have to move the caliper further away from the hub. this increases leverage which gives you more brake torque. better braking.
here's the equation for friction. F= mu N
mu is the coefficient of friction
i had to look this up to be sure but the some of the laws of friction are... the total friction force (F) is independant of the magnitude of the area of contact and... proportional to the normal force (N).
so actual friction levels have nothing to do with contact area. (thoretically of course, and with only a 15% change, that's a reasonable assumption.) so what you quoted is right.
the only downside to the lower contact area is the heat is more concentrated, leading to earlier fade. but again, with only a 15% change; all of the pad being there; and a larger rotor to even out the heat anyway; there shouldn't be much difference there either (on the pad side, the rotor can certainly absorb more heat on it's own.)
the extra torque from the longer lever arm from the axle of the wheel to the center of the pad can either be a blessing or a curse, depending on tire choice, master cylinder, etc, etc. setup is key. you'll get better performance from a larger rotor, but only if you do it right.
mu is the coefficient of friction
i had to look this up to be sure but the some of the laws of friction are... the total friction force (F) is independant of the magnitude of the area of contact and... proportional to the normal force (N).
so actual friction levels have nothing to do with contact area. (thoretically of course, and with only a 15% change, that's a reasonable assumption.) so what you quoted is right.
the only downside to the lower contact area is the heat is more concentrated, leading to earlier fade. but again, with only a 15% change; all of the pad being there; and a larger rotor to even out the heat anyway; there shouldn't be much difference there either (on the pad side, the rotor can certainly absorb more heat on it's own.)
the extra torque from the longer lever arm from the axle of the wheel to the center of the pad can either be a blessing or a curse, depending on tire choice, master cylinder, etc, etc. setup is key. you'll get better performance from a larger rotor, but only if you do it right.
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Re: (cdlong)
Measure [calculate] the swept area of the pad on the rotors.
13 x pi= 40.811 x pi= 34.55 measure the 2 different pad sections and use Calculus to find both swept areas.
To simplify things most just measure the torque from the midpoint of pad, so a quick and dirty would just subtract half the lost pad area and create a new smaller imaginary diameter.
11 vs [13 minus 7.5%or a 12" rotor equivalent] so 12/11= 1.0909 more torque.
Obviously what pad does make contact with rotor will get hotter by the amount of non contact area..........heat force into smaller area.
13 x pi= 40.811 x pi= 34.55 measure the 2 different pad sections and use Calculus to find both swept areas.
To simplify things most just measure the torque from the midpoint of pad, so a quick and dirty would just subtract half the lost pad area and create a new smaller imaginary diameter.
11 vs [13 minus 7.5%or a 12" rotor equivalent] so 12/11= 1.0909 more torque.
Obviously what pad does make contact with rotor will get hotter by the amount of non contact area..........heat force into smaller area.