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New review of AP Racing BBK from Urge Designs

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New review of AP Racing BBK from Urge Designs

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Old 03-11-2015, 12:59 PM
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I would caution against making statements like this in general, since the answer usually is "it depends". We don't know the exact moment of inertia of this rotor vs. other kits. While the diameter is less, they are thicker and have more vanes than competing products. So without doing actual measurements or inside knowledge of the CAD files we are just guessing at moment of inertia. Having said that, for two disks of identical moment of inertia, and thus the same angular momentum, then applying torque further from the center (as in the case of a larger diameter, but thinner/lighter rotor) would result in quicker deceleration, or less "work" to decelerate the same amount as a torque applied closer to center. That example is for braking applications. When accelerating, the torque is always applied at the center of rotation through the hub and so the disk with the lower moment of inertia will always accelerate faster.
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Old 03-11-2015, 01:11 PM
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Originally Posted by Sylvan View Post
I would caution against making statements like this in general, since the answer usually is "it depends". We don't know the exact moment of inertia of this rotor vs. other kits. While the diameter is less, they are thicker and have more vanes than competing products. So without doing actual measurements or inside knowledge of the CAD files we are just guessing at moment of inertia. Having said that, for two disks of identical moment of inertia, and thus the same angular momentum, then applying torque further from the center (as in the case of a larger diameter, but thinner/lighter rotor) would result in quicker deceleration, or less "work" to decelerate the same amount as a torque applied closer to center. That example is for braking applications. When accelerating, the torque is always applied at the center of rotation through the hub and so the disk with the lower moment of inertia will always accelerate faster.
True, thanks Sylvan. Good points about the differences in torque application between acceleration from the hub and deceleration caused by brake pads.

I was definitely over-generalizing in my earlier post in terms of knowing the relative moment of inertia between two rotors just based on diameter. While a smaller diameter rotor would have lower inertia if all else was equal, if it was enough thicker or had enough extra internal vanes, it might actually carry more inertia than a larger but less "dense" design.
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Old 03-11-2015, 03:15 PM
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Brakes are complex systems, and it's necessary to generalize when talking about them. I In fact did so myself just talking about the disk brake in isolation, when really the entire wheel/tire/hub/disk must be taken into account as the entire rotating assembly in order to be thorough. I read a good book about disk brake systems in college, I wish I still had it to refer to.
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Old 04-22-2015, 10:51 AM
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We appreciate your business..
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Old 04-22-2015, 05:26 PM
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Originally Posted by rhouck View Post
Originally Posted by will010100' timestamp='1425969548' post='23533903
Drawbacks: A minor drawback is that the pistons are harder to compress when you need to change pads. There is no fancy tool to push them in like with the OEM, but this is probably the case with any opposing-piston system.
Remove one old pad. Flip it 90 degrees and stick back in center. The width of the backing plate will hit both pistons. Then just apply pressure to the end sticking out and it will retract both pistons.

99SH (user on here) bought an actual tool to do it which is pretty slick, but iirc it was $$$.
For those interested in the tool:

http://www.girodisc.com/Caliper-pist...er_p_5970.html
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Old 04-22-2015, 06:20 PM
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I found this pad separator to be very useful for aftermarket brake systems. quite a bit cheaper than the above...

http://www.amazon.com/gp/product/B00...r_notf_fhv_prd

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Old 08-02-2015, 09:28 AM
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Bumping a good BBK Review..

Great reviews for the common novice racer.
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Old 08-03-2015, 05:28 PM
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Originally Posted by thomsbrain View Post
Originally Posted by Sylvan' timestamp='1426107553' post='23536345
I would caution against making statements like this in general, since the answer usually is "it depends". We don't know the exact moment of inertia of this rotor vs. other kits. While the diameter is less, they are thicker and have more vanes than competing products. So without doing actual measurements or inside knowledge of the CAD files we are just guessing at moment of inertia. Having said that, for two disks of identical moment of inertia, and thus the same angular momentum, then applying torque further from the center (as in the case of a larger diameter, but thinner/lighter rotor) would result in quicker deceleration, or less "work" to decelerate the same amount as a torque applied closer to center. That example is for braking applications. When accelerating, the torque is always applied at the center of rotation through the hub and so the disk with the lower moment of inertia will always accelerate faster.
True, thanks Sylvan. Good points about the differences in torque application between acceleration from the hub and deceleration caused by brake pads.

I was definitely over-generalizing in my earlier post in terms of knowing the relative moment of inertia between two rotors just based on diameter. While a smaller diameter rotor would have lower inertia if all else was equal, if it was enough thicker or had enough extra internal vanes, it might actually carry more inertia than a larger but less "dense" design.

Do the rules let you run a brake proportioning valve?



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