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<blockquote data-quote="Avispa" data-source="post: 16075726" data-attributes="member: 78552"><p>Thanks! That's exactly what I needed to know. The answer seemed intuative, but you can't substitute actual experience. No point in spending the $ if there isn't going to be a noticeable benefit.</p><p></p><p>Just to clear up a couple of things in the thread, if by "braking efficiency" you mean braking force with respect to pressure on the brake pedal, yeah <em>if everything else is equal</em>, 4 piston calipers will brake harder for the same pedal pressure (and resulting brake fluid pressure) as 2 piston, depending on the total piston area for each kind of caliper. It looks like the Cobra R calipers have four pistons that are about the same size as the 2 pistons in the PBR calipers, so the clamping force would be about twice that for the same fluid pressure in the Corbra R caliper as the PBRs. Is that gonna mean the proportioning valve needs to be changed? The factory set it up proportioning for the relative braking force front/rear for the calipers and rotors actually used. Seems like the car is going to dive under hard braking unless the rear brakes get increased fluid pressure for the same amount of pedal force - unless the required increase in brake fluid volume to the front balances things out. Any comment on that?</p><p></p><p>If you mean the Cobra R brakes give total higher braking torque that can by applied to the rotor, no. Total braking torque depends on surface area of the brake pads, where relative to the center of rotation on the rotor the pad area is and the coefficient of friction between the pad and the rotor surface. So yeah, for the same pad area and caliper force, putting the pad area on the outside of a 14 inch rotor will give more torque than a similar setup on a 13 inch rotor. A Cobra R caliper won't have twice the maximum braking torque of a stock 2 piston PBR caliper. If by "clamshell" you mean the caliper tends to spread apart when clamped, that by itself isn't related to whether the caliper has pistons on one side or both. On one-sided calipers, the clamping force generates the same reactive force on the other side of the caliper. It's the total force that spreads the caliper, not where it comes from. If you mean the Cobra R calipers have a thicker bridge between sides, that's another matter altogether.</p><p></p><p>Thanks again!</p></blockquote><p></p>
[QUOTE="Avispa, post: 16075726, member: 78552"] Thanks! That's exactly what I needed to know. The answer seemed intuative, but you can't substitute actual experience. No point in spending the $ if there isn't going to be a noticeable benefit. Just to clear up a couple of things in the thread, if by "braking efficiency" you mean braking force with respect to pressure on the brake pedal, yeah [i]if everything else is equal[/i], 4 piston calipers will brake harder for the same pedal pressure (and resulting brake fluid pressure) as 2 piston, depending on the total piston area for each kind of caliper. It looks like the Cobra R calipers have four pistons that are about the same size as the 2 pistons in the PBR calipers, so the clamping force would be about twice that for the same fluid pressure in the Corbra R caliper as the PBRs. Is that gonna mean the proportioning valve needs to be changed? The factory set it up proportioning for the relative braking force front/rear for the calipers and rotors actually used. Seems like the car is going to dive under hard braking unless the rear brakes get increased fluid pressure for the same amount of pedal force - unless the required increase in brake fluid volume to the front balances things out. Any comment on that? If you mean the Cobra R brakes give total higher braking torque that can by applied to the rotor, no. Total braking torque depends on surface area of the brake pads, where relative to the center of rotation on the rotor the pad area is and the coefficient of friction between the pad and the rotor surface. So yeah, for the same pad area and caliper force, putting the pad area on the outside of a 14 inch rotor will give more torque than a similar setup on a 13 inch rotor. A Cobra R caliper won't have twice the maximum braking torque of a stock 2 piston PBR caliper. If by "clamshell" you mean the caliper tends to spread apart when clamped, that by itself isn't related to whether the caliper has pistons on one side or both. On one-sided calipers, the clamping force generates the same reactive force on the other side of the caliper. It's the total force that spreads the caliper, not where it comes from. If you mean the Cobra R calipers have a thicker bridge between sides, that's another matter altogether. Thanks again! [/QUOTE]
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