# answers....

Posted by Matt (93SE) on September 08, 2002 at 00:41:35:

In Reply to: I got a question or two posted by MIKE on September 07, 2002 at 21:24:29:

As you know about torque and longer handles on ratchets, the same goes for brakes.

time for a physics lesson...
the real braking force comes from the pads rubbing against the rotors with a certain amount of friction. the more pressure you exert on the pads, the more stopping force you exert on the brake rotors.

now for torque.. force applied at a distance from a point is torque.. so the stock rotors are around 10" diameter (5" radius). if you have 1000lb of stopping force on the caliper applied at 5" from the center point, you have 5000in-lb of torque.

NOW you use a larger rotor- one that's 11" in diameter, (so you have 5.5" of radius). you stick the same caliper and pad on that distance, and you have 5500in-lb of torque.
so by increasing the rotor diameter 10%, you also increase the torque applied by 10%.

This is why larger rotors work better to stop the car than smaller rotors.
There are many other factors, such as rotating inertia, mass of iron actually absorbing/dissipating heat, pad compounds and etc etc etc...
but if you keep the caliper and pads and rotor material the same with the only variable changing being the rotor diameter, you will have more brake torque applied to the wheels.

That all make sense?

: Can you explain exactly how your rear breaking force has increased with the larger diameter rotor and you're still using the OEM size caliper/pads (pads could be after-market) Granted with a larger diameter rotor it will resist and dissapate heat easier when compared to a smaller piece, but if the actual square inch of the clamping force hasn't increase it would seem to me you're still going to have that large brake bias as before during your everyday daily driving. Now if you take your new brake set-up to the tracks, this is where they will perform well and hold up better with the heat. I haven't really had a chance to look at any of these big brake kit for which ever car, but it seems to me that these kits include larger calipers and rotors. Before I leave, two thumbs up for your rear brake set-up because all those with SE's and 17" plus wheels know how dinky the stock calipers look within those wheels. Thanks again, copy/paste/filed.

Replys:

- I understand and know advantage of using a longer handles MIKE (93VE) 10:44:51 9/08/2002 (11)
  - As Mentat said, it doesn't change the pressure exerted on the rotor... The same pressure is applied farther from the center point to provide more torque to stop the car. nm Matt (93SE) 13:26:53 9/08/2002 (0)
  - I'm well out of my knowledge here but I think the key is putting the point of application of the force (the caliper) further from the actual center of rotation would increase leverage? I'm picturing a line drawn from the hub to the caliper here... and the longer that line, the more leverage? am I on the right track here? mentat (93se 5spd) 12:24:24 9/08/2002 (9)
    - Yes, another example would be.. Maximamike (92 SE) 12:37:12 9/08/2002 (8)
      - Dont get we wrong I totally understand the longer handle for more leverage, but MIKE (93VE) 14:00:07 9/08/2002 (5)
        - Uhhhh, the axle? Since that's where it's turning around, and attached to the moving part of the car. hmmmm. nm Matt (93SE) 14:58:42 9/08/2002 (4)
          - Interesting MIKE (93VE) 17:10:56 9/08/2002 (3)
            - I would say you're correct as far "clamping force", but thats only part of the "Stopping Force" equation.... mentat (93se 5spd) 18:20:37 9/08/2002 (2)
              - Thank-you MIKE (93VE) 20:26:34 9/08/2002 (1)
                - Yup, you're getting it... mentat (93se 5spd) 10:56:21 9/09/2002 (0)
      - OT mike any update on your friend's rims... email me n/m mentat (93se 5spd) 12:44:27 9/08/2002 (1)
        - Oh shit, sorry bout that. I'll send ya an email when I get back to school tomorrow.. Maximamike (92 SE) 13:10:18 9/08/2002 (0)

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: As you know about torque and longer handles on ratchets, the same goes for brakes. : time for a physics lesson... : the real braking force comes from the pads rubbing against the rotors with a certain amount of friction. the more pressure you exert on the pads, the more stopping force you exert on the brake rotors. : now for torque.. force applied at a distance from a point is torque.. so the stock rotors are around 10" diameter (5" radius). if you have 1000lb of stopping force on the caliper applied at 5" from the center point, you have 5000in-lb of torque. : NOW you use a larger rotor- one that's 11" in diameter, (so you have 5.5" of radius). you stick the same caliper and pad on that distance, and you have 5500in-lb of torque. : so by increasing the rotor diameter 10%, you also increase the torque applied by 10%. : This is why larger rotors work better to stop the car than smaller rotors. : There are many other factors, such as rotating inertia, mass of iron actually absorbing/dissipating heat, pad compounds and etc etc etc... : but if you keep the caliper and pads and rotor material the same with the only variable changing being the rotor diameter, you will have more brake torque applied to the wheels. : That all make sense? : : : : Can you explain exactly how your rear breaking force has increased with the larger diameter rotor and you're still using the OEM size caliper/pads (pads could be after-market) Granted with a larger diameter rotor it will resist and dissapate heat easier when compared to a smaller piece, but if the actual square inch of the clamping force hasn't increase it would seem to me you're still going to have that large brake bias as before during your everyday daily driving. Now if you take your new brake set-up to the tracks, this is where they will perform well and hold up better with the heat. I haven't really had a chance to look at any of these big brake kit for which ever car, but it seems to me that these kits include larger calipers and rotors. Before I leave, two thumbs up for your rear brake set-up because all those with SE's and 17" plus wheels know how dinky the stock calipers look within those wheels. Thanks again, copy/paste/filed.