# I would say you're correct as far "clamping force", but thats only part of the "Stopping Force" equation....

Posted by mentat (93se 5spd) on September 08, 2002 at 18:20:37:

In Reply to: Interesting posted by MIKE on September 08, 2002 at 17:10:56:

The LOCATION of that clamping force is also a factor. Matt mentioned the torque effect, it may help to think of it almost as a negative force here... here's a new analogy since we are all sick of the ratchet-handle one... say you wanted to turn a wheel; picture a pipe valve, or a bulkhead hatch on a ship. The smaller the diameter of that wheel, the harder it is to turn, agreed? The further from the center of that circle you apply a force to, the greater the force becomes when measured at the center. Thats a really lame way of stating that but I think you know what I mean. The principle is the same for the larger brake rotor, just sort of in reverse. You are still applying a force, just a negative one if you will; instead of turning the wheel, you are stopping it.

Another way to look at it, and this may be a bit of a stretch, is having different size drive wheels on your car... we know that smaller wheels (I mean overall diameter, ie a constant tire sidewall for either size wheel) spin up faster than a larger wheel would. say a 15" wheel vs a 20" wheel, given a same sidewall size. The same thing that makes the larger wheel slower to spin makes it easier to stop - the radius from the point of rotation (center of the wheel) to the poing of force (the ground) I may be wrong on that, I know it's a crappy example, but I believe the physics are pretty much the same.

So you are correct, Matt has't altered the "clamping force" in any way. The surface area of the calipers is indeed still the same, but moving that clamping force away from the center of rotation increases the net "stopping force". It's not the surface area of the larger rotors helping in this case, it is the larger diameter, (actually I think the radius is the operative measurement here, if one were to actually write out some equations here) and the way that larger radius moves the location of your clamping force from the center of rotation.

I know these are kind of vague examples, but since I do not know the actual math involved, it is the best way I can describe it. I think the key is to realize that your well-described "Clamping Force" is only one factor in your "Overall Stopping Force".

has the jury reached a verdict? ;)
m@

Replys:

- 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)

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: The LOCATION of that clamping force is also a factor. Matt mentioned the torque effect, it may help to think of it almost as a negative force here... here's a new analogy since we are all sick of the ratchet-handle one... say you wanted to turn a wheel; picture a pipe valve, or a bulkhead hatch on a ship. The smaller the diameter of that wheel, the harder it is to turn, agreed? The further from the center of that circle you apply a force to, the greater the force becomes when measured at the center. Thats a really lame way of stating that but I think you know what I mean. The principle is the same for the larger brake rotor, just sort of in reverse. You are still applying a force, just a negative one if you will; instead of turning the wheel, you are stopping it. : : Another way to look at it, and this may be a bit of a stretch, is having different size drive wheels on your car... we know that smaller wheels (I mean overall diameter, ie a constant tire sidewall for either size wheel) spin up faster than a larger wheel would. say a 15" wheel vs a 20" wheel, given a same sidewall size. The same thing that makes the larger wheel slower to spin makes it easier to stop - the radius from the point of rotation (center of the wheel) to the poing of force (the ground) I may be wrong on that, I know it's a crappy example, but I believe the physics are pretty much the same. : : So you are correct, Matt has't altered the "clamping force" in any way. The surface area of the calipers is indeed still the same, but moving that clamping force away from the center of rotation increases the net "stopping force". It's not the surface area of the larger rotors helping in this case, it is the larger diameter, (actually I think the radius is the operative measurement here, if one were to actually write out some equations here) and the way that larger radius moves the location of your clamping force from the center of rotation. : I know these are kind of vague examples, but since I do not know the actual math involved, it is the best way I can describe it. I think the key is to realize that your well-described "Clamping Force" is only one factor in your "Overall Stopping Force". : has the jury reached a verdict? ;) : m@