question on rear brakes c5
01-30-2014, 09:38 AM
#1
Instructor
Thread Starter
question on rear brakes c5
For you guys that run the c5 front calipers on the rear brakes what are you using for a rotor??? do you keep the stock parking brake??
Thanks for any help
Thanks for any help
02-03-2014, 12:52 AM
#3
Burning Brakes
. Can't use parking brake. Just make sure you park on a flat surface or have a friend block the tires for you in the paddock , if not left in gear.
02-03-2014, 07:18 AM
#4
Instructor
Thread Starter
I was thinking about this and woundering if there was a way to keep the e-brake just to make getting a sticker easier....
02-26-2014, 01:01 PM
#5
Le Mans Master
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Does the front caliper bracket bolt up to the rear spindle without any shims or alterations? You just swap the bracket and rotor to the rear?
02-26-2014, 02:22 PM
#6
Drifting
how many rotors and what kinds of pads left over? start a for sale thread !!!
02-26-2014, 03:52 PM
#7
Burning Brakes
A couple thoughts on this:
- The piston area of the C5 stock rear caliper is ~2.43 square inches. The area of the stock front ~ 3.92. So you are adding about 1.5in/per side to the size of the pistons when you put the front calipers on the rear.
- Stock, the front brake bias of a C5 is about 62% (62% of the braking force is distributed to the front axle, 38% rear)
- The AP Racing 8350 caliper has a front area 3.82 square inches (assuming thats the caliper the OP is putting on the front). Note this is slightly smaller than the stock fronts - by AP's design it it intended to slightly increase the stock rear bias.
- So the net effect of this change is the front bias would drop from 62% to just over 50% (all other things remaining equal: pads, rotor size, master cylinder bore, bias proportion, etc).
Link to awesome braking calculator: http://www.tceperformanceproducts.com/bias-calculator/
I've read the posts where guys do this mod and claim no issues, that the braking is awesome. But come on - changing to a near 50/50 front to rear static bias can not be good in threshold braking scenarios where weight dynamically transfers to the front of the car - the whole reason we have front bias in the first place. I suspect what saves thems is the dynamic proportioning of the C5 braking system. But they are essentially relying on the computer to coverup the hack job they have done to the braking system.
Personally I'd be very wary of doing this without changing the master cylinder to one that allows bias adjustment.
- The piston area of the C5 stock rear caliper is ~2.43 square inches. The area of the stock front ~ 3.92. So you are adding about 1.5in/per side to the size of the pistons when you put the front calipers on the rear.
- Stock, the front brake bias of a C5 is about 62% (62% of the braking force is distributed to the front axle, 38% rear)
- The AP Racing 8350 caliper has a front area 3.82 square inches (assuming thats the caliper the OP is putting on the front). Note this is slightly smaller than the stock fronts - by AP's design it it intended to slightly increase the stock rear bias.
- So the net effect of this change is the front bias would drop from 62% to just over 50% (all other things remaining equal: pads, rotor size, master cylinder bore, bias proportion, etc).
Link to awesome braking calculator: http://www.tceperformanceproducts.com/bias-calculator/
I've read the posts where guys do this mod and claim no issues, that the braking is awesome. But come on - changing to a near 50/50 front to rear static bias can not be good in threshold braking scenarios where weight dynamically transfers to the front of the car - the whole reason we have front bias in the first place. I suspect what saves thems is the dynamic proportioning of the C5 braking system. But they are essentially relying on the computer to coverup the hack job they have done to the braking system.
Personally I'd be very wary of doing this without changing the master cylinder to one that allows bias adjustment.
02-26-2014, 04:37 PM
#8
Race Director
A couple thoughts on this:
- The piston area of the C5 stock rear caliper is ~2.43 square inches. The area of the stock front ~ 3.92. So you are adding about 1.5in/per side to the size of the pistons when you put the front calipers on the rear.
- Stock, the front brake bias of a C5 is about 62% (62% of the braking force is distributed to the front axle, 38% rear)
- The AP Racing 8350 caliper has a front area 3.82 square inches (assuming thats the caliper the OP is putting on the front). Note this is slightly smaller than the stock fronts - by AP's design it it intended to slightly increase the stock rear bias.
- So the net effect of this change is the front bias would drop from 62% to just over 50% (all other things remaining equal: pads, rotor size, master cylinder bore, bias proportion, etc).
Link to awesome braking calculator: http://www.tceperformanceproducts.com/bias-calculator/
I've read the posts where guys do this mod and claim no issues, that the braking is awesome. But come on - changing to a near 50/50 front to rear static bias can not be good in threshold braking scenarios where weight dynamically transfers to the front of the car - the whole reason we have front bias in the first place. I suspect what saves thems is the dynamic proportioning of the C5 braking system. But they are essentially relying on the computer to coverup the hack job they have done to the braking system.
Personally I'd be very wary of doing this without changing the master cylinder to one that allows bias adjustment.
- The piston area of the C5 stock rear caliper is ~2.43 square inches. The area of the stock front ~ 3.92. So you are adding about 1.5in/per side to the size of the pistons when you put the front calipers on the rear.
- Stock, the front brake bias of a C5 is about 62% (62% of the braking force is distributed to the front axle, 38% rear)
- The AP Racing 8350 caliper has a front area 3.82 square inches (assuming thats the caliper the OP is putting on the front). Note this is slightly smaller than the stock fronts - by AP's design it it intended to slightly increase the stock rear bias.
- So the net effect of this change is the front bias would drop from 62% to just over 50% (all other things remaining equal: pads, rotor size, master cylinder bore, bias proportion, etc).
Link to awesome braking calculator: http://www.tceperformanceproducts.com/bias-calculator/
I've read the posts where guys do this mod and claim no issues, that the braking is awesome. But come on - changing to a near 50/50 front to rear static bias can not be good in threshold braking scenarios where weight dynamically transfers to the front of the car - the whole reason we have front bias in the first place. I suspect what saves thems is the dynamic proportioning of the C5 braking system. But they are essentially relying on the computer to coverup the hack job they have done to the braking system.
Personally I'd be very wary of doing this without changing the master cylinder to one that allows bias adjustment.
02-26-2014, 04:38 PM
#9
Racer
Front calipers
A couple thoughts on this:
- The piston area of the C5 stock rear caliper is ~2.43 square inches. The area of the stock front ~ 3.92. So you are adding about 1.5in/per side to the size of the pistons when you put the front calipers on the rear.
- Stock, the front brake bias of a C5 is about 62% (62% of the braking force is distributed to the front axle, 38% rear)
- The AP Racing 8350 caliper has a front area 3.82 square inches (assuming thats the caliper the OP is putting on the front). Note this is slightly smaller than the stock fronts - by AP's design it it intended to slightly increase the stock rear bias.
- So the net effect of this change is the front bias would drop from 62% to just over 50% (all other things remaining equal: pads, rotor size, master cylinder bore, bias proportion, etc).
Link to awesome braking calculator: http://www.tceperformanceproducts.com/bias-calculator/
I've read the posts where guys do this mod and claim no issues, that the braking is awesome. But come on - changing to a near 50/50 front to rear static bias can not be good in threshold braking scenarios where weight dynamically transfers to the front of the car - the whole reason we have front bias in the first place. I suspect what saves thems is the dynamic proportioning of the C5 braking system. But they are essentially relying on the computer to coverup the hack job they have done to the braking system.
Personally I'd be very wary of doing this without changing the master cylinder to one that allows bias adjustment.
- The piston area of the C5 stock rear caliper is ~2.43 square inches. The area of the stock front ~ 3.92. So you are adding about 1.5in/per side to the size of the pistons when you put the front calipers on the rear.
- Stock, the front brake bias of a C5 is about 62% (62% of the braking force is distributed to the front axle, 38% rear)
- The AP Racing 8350 caliper has a front area 3.82 square inches (assuming thats the caliper the OP is putting on the front). Note this is slightly smaller than the stock fronts - by AP's design it it intended to slightly increase the stock rear bias.
- So the net effect of this change is the front bias would drop from 62% to just over 50% (all other things remaining equal: pads, rotor size, master cylinder bore, bias proportion, etc).
Link to awesome braking calculator: http://www.tceperformanceproducts.com/bias-calculator/
I've read the posts where guys do this mod and claim no issues, that the braking is awesome. But come on - changing to a near 50/50 front to rear static bias can not be good in threshold braking scenarios where weight dynamically transfers to the front of the car - the whole reason we have front bias in the first place. I suspect what saves thems is the dynamic proportioning of the C5 braking system. But they are essentially relying on the computer to coverup the hack job they have done to the braking system.
Personally I'd be very wary of doing this without changing the master cylinder to one that allows bias adjustment.
I believe this will change your calculations.
I am in the process of doing this change myself & would be interested.
02-26-2014, 04:46 PM
#10
Race Director
Even if you completely ignore the AP dimensions, in switching from stock rear to front caliper on the rear you are drastically changing the volume which as said, changes the bias.
Last edited by RedLS1GTO; 02-26-2014 at 04:49 PM.
02-26-2014, 05:09 PM
#11
In theory, you could have a rear rotor cut off so that only the center drum is left, then run it behind a stock front rotor in order to keep your e-brake functional. I'd guess that shimming the caliper abutment is all that would be needed to account for the added rotor offset.
02-26-2014, 05:10 PM
#12
Racer
Curiousity here... Essex 6 piston endurance kit can use stock rear brakes. Yet they sell a 4 piston rear setup also. I assume rear 4 piston ap kit is larger area than c5 rear area. I would assume its similar to c5 front. So curious if having 6 piston ap up front what's the difference if it's c5 rear or c5 front or the matching ap 4 piston rear kit???
I have ran cp5555 caliper with c5 front on rear, and I just ordered the new Essex 6 piston endurance kit to upgrade my cp5555 but keeping the stock c5 front on the rear. I have Adjusable master and abs is removed.
I have ran cp5555 caliper with c5 front on rear, and I just ordered the new Essex 6 piston endurance kit to upgrade my cp5555 but keeping the stock c5 front on the rear. I have Adjusable master and abs is removed.
02-26-2014, 06:08 PM
#14
Le Mans Master
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When measuring a fixed caliper vs a slider you only use half the pistons of the fixed. A floating caliper will displace the pistons twice what a fixed caliper will.
02-26-2014, 07:16 PM
#15
Melting Slicks
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I think there is a lot of misinformation out there on brake systems in fact there is so much I'm not sure where to start.
Since this thread is about putting a pair of C5 front calipers on the rear I'll start there.
Initially it sounds like a good idea but it may actually just cause more headaches than it will be worth.
I've come up with my own brake calculator and will share some of the info here.
The stock C5 brake system will put out around 18,300 inch lbs of clamping force on the front axle and 10,500 inch lbs of clamping force on the rear axle for a total of 28,800 inch lbs of clamping force.
This is with 80 lbs of force on the brake pedal using front and rear brake pads with the same brake pad coefficient of .64 (basically an aggressive race pad).
That leaves us with a brake bias of 63.5% (pretty close to the calculation done above).
Some big brake kits actually produce less braking force than the stock system because they have a smaller effective piston area than the stock system so that the pedal feels better and so your pedal doesn't go to the floor when the brake pads are worn down.
The brake kit will however not taper pads like the factory system, handle heat better and produce similar stopping throughout a given weekend.
So don't assume that an aftermarket brake system has more clamping force just because it's a 6 piston or 4 piston etc.
A second misconception is that a larger master cylinder will increase stopping power because you're moving more fluid - this is just false because when you increase master cylinder piston diameter you decrease the pressure of the system overall.
I'm going to use some numbers to give you a clearer picture of this. To use the stock system as an example with 28,800 inch lbs, if you switch to a 1 1/16" master cylinder it goes down to 25,570, switching to a 1 1/8" master goes all the way down to 22,775.
So if you go with a larger master (all other things being equal) you are decreasing overall braking performance by 11.2% with a 1/16" increase in master cylinder diameter and 20.9% with an 1/8" increase in master cylinder diameter.
When you put the stock front system in the rear your pedal will sink by almost 25% - so if you make that up by going with a larger master - a 1 1/8" master will give you about the same pedal height.
You are now at 28,900 inch lbs but now you have 50/50 brake bias and the rears lock up too easy. So either you are going to have to go with a much less aggressive rear brake pad or put a bias **** in to limit the amount of rear brake you have, either way you are taking away from the total clamping force and end up with less than you started with. Going with a rear pad with a coefficient of friction of .5 will put you at a total clamping force of 25,750 inch lbs a decrease of 10.9% (but it will put you at 56.1% front bias).
So there is something to be said for a brake system that takes all of these things into account - brake systems should be looked at more like suspension systems. Each car (and sometimes driver) is different and can use more or less clamping force and or bias - depending on tire sizes, weather or not they are running aero, how long will they be running how much cooling can/do you have etc. Unfortunately it's not one size fits all if you really want some good brakes.
Since this thread is about putting a pair of C5 front calipers on the rear I'll start there.
Initially it sounds like a good idea but it may actually just cause more headaches than it will be worth.
I've come up with my own brake calculator and will share some of the info here.
The stock C5 brake system will put out around 18,300 inch lbs of clamping force on the front axle and 10,500 inch lbs of clamping force on the rear axle for a total of 28,800 inch lbs of clamping force.
This is with 80 lbs of force on the brake pedal using front and rear brake pads with the same brake pad coefficient of .64 (basically an aggressive race pad).
That leaves us with a brake bias of 63.5% (pretty close to the calculation done above).
Some big brake kits actually produce less braking force than the stock system because they have a smaller effective piston area than the stock system so that the pedal feels better and so your pedal doesn't go to the floor when the brake pads are worn down.
The brake kit will however not taper pads like the factory system, handle heat better and produce similar stopping throughout a given weekend.
So don't assume that an aftermarket brake system has more clamping force just because it's a 6 piston or 4 piston etc.
A second misconception is that a larger master cylinder will increase stopping power because you're moving more fluid - this is just false because when you increase master cylinder piston diameter you decrease the pressure of the system overall.
I'm going to use some numbers to give you a clearer picture of this. To use the stock system as an example with 28,800 inch lbs, if you switch to a 1 1/16" master cylinder it goes down to 25,570, switching to a 1 1/8" master goes all the way down to 22,775.
So if you go with a larger master (all other things being equal) you are decreasing overall braking performance by 11.2% with a 1/16" increase in master cylinder diameter and 20.9% with an 1/8" increase in master cylinder diameter.
When you put the stock front system in the rear your pedal will sink by almost 25% - so if you make that up by going with a larger master - a 1 1/8" master will give you about the same pedal height.
You are now at 28,900 inch lbs but now you have 50/50 brake bias and the rears lock up too easy. So either you are going to have to go with a much less aggressive rear brake pad or put a bias **** in to limit the amount of rear brake you have, either way you are taking away from the total clamping force and end up with less than you started with. Going with a rear pad with a coefficient of friction of .5 will put you at a total clamping force of 25,750 inch lbs a decrease of 10.9% (but it will put you at 56.1% front bias).
So there is something to be said for a brake system that takes all of these things into account - brake systems should be looked at more like suspension systems. Each car (and sometimes driver) is different and can use more or less clamping force and or bias - depending on tire sizes, weather or not they are running aero, how long will they be running how much cooling can/do you have etc. Unfortunately it's not one size fits all if you really want some good brakes.
02-26-2014, 07:22 PM
#16
Racer
Brake bias
We would be talking about 4- AP 8350 pistons per side on the front,
& 2- stock front Z06 pistons per side on the rear..
The stock pistons are 1 9/16.
I would have to find out about the AP.
I believe the stock master has a 7/8 piston.
Thanks for your help..
Last edited by outsideline; 02-26-2014 at 07:47 PM.
02-26-2014, 08:32 PM
#18
Burning Brakes
I posted a link to an online calculator for braking numbers. If you look there and read the notes at bottom of the page it will tell you that you only use the area of one side of pistons. You don't double the area just because you have 4 pistons instead of 2.
02-26-2014, 08:53 PM
#19
Former Vendor
Yes that would be very helpfull.
We would be talking about 4- AP 8350 pistons per side on the front,
& 2- stock front Z06 pistons per side on the rear..
The stock pistons are 1 9/16.
I would have to find out about the AP.
I believe the stock master has a 7/8 piston.
Thanks for your help..
We would be talking about 4- AP 8350 pistons per side on the front,
& 2- stock front Z06 pistons per side on the rear..
The stock pistons are 1 9/16.
I would have to find out about the AP.
I believe the stock master has a 7/8 piston.
Thanks for your help..
What is brake bias? A representation of the mathematical brake torque values at each end of the car.
Can it be altered? Easily. The three most common ways are higher bite (Cf) pads, larger rotors (leverage) and greater piston AREA- not necessarily qty.
The sum area of the caliper is commonly expressed as "half" the body due to the floating aspect of the slider. Think that doesn't really work compared to the big six piston you may be thinking about? Try taking out your stock outer pad and see how that works out. Sliders are a push/pull arrangement. This is not correct in calculating true torque however but using the same formula on each end of the car is what we are looking to for bias. You can use both sides or one side...the ratios are the same and that's bias.
Pads alone can swing bias by 5% or more. Larger rotors a bit less. More piston area quite a bit more. Pick your poison. I've been doing this (having fallen into it of all things) for 20yrs and have one basic rule to 'try' and apply: INREASE rotor diameter, DECREASE piston area, TUNE with pad. Dress it up any way with any spin from any other (big name) supplier and that's the root formula.
Larger discs are more efficient in that they increase torque, decrease pad wear, lower (or rightly balance) heat and decrease line pressure. Lowering the piston area a bit, keeping it the same, balancing it to th rear...a variety of things keeps the pedal firm.
Larger bore calipers tend to clamp harder for the same pressure but create a long pedal. What's missing in this equation of "front to rear" is not only the bis being all f'd up but the simple fact that the total displacement of the calipers piston area is greatly increased. Result; long, soft hard to modulate pedal feel. The fix? A larger bore mc will bandaide the issue. It will NOT fix bias issues- you still only have one.
I can go on and on...but the reality is that this is a very poorly designed plan with mostly negative effects. Adding a prop valve may help you from passing yourself but again a bandaide to what needs to be corrected. If the car were so out of whack to start with you can be certain GM would have gotten much closer to what this does. And they didn't knowing it's not correct.
Hope that helps some. You're always welcome to the BIAS CALCULATOR to compare cause and effect.
FWIW...all this goes out the window if you move to a true twin mc set up. Here you can do nearly anything with the right combo. I think someone like Joel may be one of the few to enjoy using the DUAL MC CALCULATOR...the rest of us; stick with the basic one!
Last edited by Todd TCE; 02-26-2014 at 09:00 PM.
02-26-2014, 11:41 PM
#20
Racer
Thanks guys for all the input!!! Todd, great calculator. I learned something new today. Thanks!!!
I plugged some numbers in.. The 4 piston ap8350 front with 12.9 inch rotors with c5 front(12.9) on the rear create an approximate 49/51 rear favorite with equal pads. However going with the 6 piston ap kit numbers with 14 inch rotor in front and c5 fronts on the rear (12.9 rotor size) equal pads nets you about a 55/45 favor for the fronts. Not factory ideal, but close enough that the bias adjustable master cylinder should get you driver likable situation... I didn't plug numbers for leaving c5 rear assembly or apracing 4 piston rear setup. Sorry.
I plugged some numbers in.. The 4 piston ap8350 front with 12.9 inch rotors with c5 front(12.9) on the rear create an approximate 49/51 rear favorite with equal pads. However going with the 6 piston ap kit numbers with 14 inch rotor in front and c5 fronts on the rear (12.9 rotor size) equal pads nets you about a 55/45 favor for the fronts. Not factory ideal, but close enough that the bias adjustable master cylinder should get you driver likable situation... I didn't plug numbers for leaving c5 rear assembly or apracing 4 piston rear setup. Sorry.