# Yup, you're getting it...

Posted by mentat (93se 5spd) on September 09, 2002 at 10:56:21:

In Reply to: Thank-you posted by MIKE on September 08, 2002 at 20:26:34:

What you said about stopping distance is close... Here's another way to picture the lever-handle idea... draw a circle, that is your rotor. a point at the top of that circle is your caliper. draw a line from the center of the circle to that point. that's your "lever", for the sake of this example. bigger the caliper, the longer that line. the longer that line, the more leverage you have in stopping that rotor from turning, regardless of caliper size, pad size, clamping force, etc.

I also realized that with this larger caliper, there is still an increase in surface area for a given rotation of the wheel. Imagine our wheel circle again, but this time the big outter circle is your wheel/tire, and a smaller circle inside is the rotor. Imagine a cross type X/Y graph with the cross at the center of the rotor. say you wanted to stop the wheel within 90 degrees of rotation, ie from your top Y axis to your bottom X axis... a larger rotor circle means that even for the same rotation (90 degrees) there is still more surface area travelling thru that caliper ( I wish I could draw this, but I think you can get me) So the force of the "stop" is distributed throughout more surface area, which as you already know contributes to better stopping. I'm kind of picturing a stripe along the outter edge of the rotor, as wide as the caliper is... so even tho the WIDTH of that stripe is unchanged with bigger rotor, the LENGTH of that stripe IS increased too, see? Now I dont know if this is yet another part of the Total Stopping Power equation, or if it like a subset of the torque/leverage aspect.

Of course, with the stock calipers, Matt isn't taking full advantage of that big rotor, ie he is not making use of all the surface area by using the old caliper, but it is still an improvement over the smaller one. I wish I knew the actual math for all this, but this is the best I can do. In any case I've been thinking way too hard about all this, and my brain hurts =)

m@

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: What you said about stopping distance is close... Here's another way to picture the lever-handle idea... draw a circle, that is your rotor. a point at the top of that circle is your caliper. draw a line from the center of the circle to that point. that's your "lever", for the sake of this example. bigger the caliper, the longer that line. the longer that line, the more leverage you have in stopping that rotor from turning, regardless of caliper size, pad size, clamping force, etc. : I also realized that with this larger caliper, there is still an increase in surface area for a given rotation of the wheel. Imagine our wheel circle again, but this time the big outter circle is your wheel/tire, and a smaller circle inside is the rotor. Imagine a cross type X/Y graph with the cross at the center of the rotor. say you wanted to stop the wheel within 90 degrees of rotation, ie from your top Y axis to your bottom X axis... a larger rotor circle means that even for the same rotation (90 degrees) there is still more surface area travelling thru that caliper ( I wish I could draw this, but I think you can get me) So the force of the "stop" is distributed throughout more surface area, which as you already know contributes to better stopping. I'm kind of picturing a stripe along the outter edge of the rotor, as wide as the caliper is... so even tho the WIDTH of that stripe is unchanged with bigger rotor, the LENGTH of that stripe IS increased too, see? Now I dont know if this is yet another part of the Total Stopping Power equation, or if it like a subset of the torque/leverage aspect. : Of course, with the stock calipers, Matt isn't taking full advantage of that big rotor, ie he is not making use of all the surface area by using the old caliper, but it is still an improvement over the smaller one. I wish I knew the actual math for all this, but this is the best I can do. In any case I've been thinking way too hard about all this, and my brain hurts =) : m@