Same Size Rotors Front and Rear?

[75slant6]

Hi everyone, I’m installing an HDK suspension in my Duster and am using 13” 99-04 Cobra brakes on the front. So my question is, would it hurt anything to use the 13” ‘15-17 Mustang GT rear brakes on the back? The 2 piston front calipers would obviously be bigger/stronger calipers than the single piston rear calipers, so would that be enough to keep the proper front/rear brake bias or would the added leverage of the larger rear rotors have enough of an impact to mess with the bias?
From my interweb searchings, I’ve found that apparently some new 06-11 police Chargers run same size 12.6” rotors front and rear with the fronts only being thicker. So I’m thinking the 13” front and rear should be fine, I just wanted to hear the opinions of people who probably know more than myself.
Thanks in advance!

 

[jbc426]

Hi everyone, I’m installing an HDK suspension in my Duster and am using 13” 99-04 Cobra brakes on the front. So my question is, would it hurt anything to use the 13” ‘15-17 Mustang GT rear brakes on the back? The 2 piston front calipers would obviously be bigger/stronger calipers than the single piston rear calipers, so would that be enough to keep the proper front/rear brake bias or would the added leverage of the larger rear rotors have enough of an impact to mess with the bias?
From my interweb searchings, I’ve found that apparently some new 06-11 police Chargers run same size 12.6” rotors front and rear with the fronts only being thicker. So I’m thinking the 13” front and rear should be fine, I just wanted to hear the opinions of people who probably know more than myself.
Thanks in advance!

The only two guys I am aware of that could more than likely give you the correct answer to the bias rate the two brake packages you are talking about are Dr Diff -aka Cass-, and AndyF.

It sounds like you are already aware that using an adjustable proportioning valve is generally only a band-aid for mis-matched front and rear brake components.

 

[pishta]

single piston and dual or even 4 piston brakes are not equal. The single piston caliper was cheaper to make than the 4 piston caliper, but the 4 piston caliper was superior in the fact that it gave better modulation of the braking power. Motorcycles use 6 piston calipers now. If you added up all the area of a 4 piston caliper to a single piston, you may be suprised on the difference in total area. if your running 13 brakes front and real and are applying 900 psi to both with the same piston surface area and pad area, they are going to brake equally, then the rear is gonna lock up as the car is gonna dive onto the fronts and unload the rear weight. It can be done but there will be alot of biasing done in the valve to get the rears not to lock up before the fronts. Todays pizza sized rotors are all controlled by ABS computers. Ask an exotic or huge rear brake owner how often the rear brake pads are serviced. I think huge rear rotors are just to balance the look of the exposed rotors, they probably run small piston calipers on them that look the same size outside.

 

[75slant6]

single piston and dual or even 4 piston brakes are not equal. The single piston caliper was cheaper to make than the 4 piston caliper, but the 4 piston caliper was superior in the fact that it gave better modulation of the braking power. Motorcycles use 6 piston calipers now. If you added up all the area of a 4 piston caliper to a single piston, you may be suprised on the difference in total area. if your running 13 brakes front and real and are applying 900 psi to both with the same piston surface area and pad area, they are going to brake equally, then the rear is gonna lock up as the car is gonna dive onto the fronts and unload the rear weight. It can be done but there will be alot of biasing done in the valve to get the rears not to lock up before the fronts. Todays pizza sized rotors are all controlled by ABS computers. Ask an exotic or huge rear brake owner how often the rear brake pads are serviced. I think huge rear rotors are just to balance the look of the exposed rotors, they probably run small piston calipers on them that look the same size outside.

Yeah I definitely wouldn’t run the same calipers front/rear. The fronts would be 99-04 2 piston Cobra calipers and the rear would be 15-17 single piston GT rear calipers. And as you said, I’d like to run the 13’s in the back for a better balanced look. I’ll be running 18” wheels up front and 19s in the back so I’d like to run the 13s in the back to not have as much of an “empty wheel” look.

 

[pishta]

check this pic out, its an AMG with the same size rotors (upgrade to another model spec) and look at the calipers. 4 piston up front and dual (if not single) piston out back and the pads for that caliper are postage stamp sized compared to the playing card sized pads for the fronts. Goes to show what percentage of the braking is up front (~80%) and whats going on out back.

 

[famous bob]

single piston and dual or even 4 piston brakes are not equal. The single piston caliper was cheaper to make than the 4 piston caliper, but the 4 piston caliper was superior in the fact that it gave better modulation of the braking power. Motorcycles use 6 piston calipers now. If you added up all the area of a 4 piston caliper to a single piston, you may be suprised on the difference in total area. if your running 13 brakes front and real and are applying 900 psi to both with the same piston surface area and pad area, they are going to brake equally, then the rear is gonna lock up as the car is gonna dive onto the fronts and unload the rear weight. It can be done but there will be alot of biasing done in the valve to get the rears not to lock up before the fronts. Todays pizza sized rotors are all controlled by ABS computers. Ask an exotic or huge rear brake owner how often the rear brake pads are serviced. I think huge rear rotors are just to balance the look of the exposed rotors, they probably run small piston calipers on them that look the same size outside.

Unless the rear tires are a lot taller = more leverage against lock up .

 

[75slant6]

Unless the rear tires are a lot taller = more leverage against lock up .

Rear tires would be 1.75” taller and 1.25” wider

 

[AndyF]

Hi everyone, I’m installing an HDK suspension in my Duster and am using 13” 99-04 Cobra brakes on the front. So my question is, would it hurt anything to use the 13” ‘15-17 Mustang GT rear brakes on the back? The 2 piston front calipers would obviously be bigger/stronger calipers than the single piston rear calipers, so would that be enough to keep the proper front/rear brake bias or would the added leverage of the larger rear rotors have enough of an impact to mess with the bias?
From my interweb searchings, I’ve found that apparently some new 06-11 police Chargers run same size 12.6” rotors front and rear with the fronts only being thicker. So I’m thinking the 13” front and rear should be fine, I just wanted to hear the opinions of people who probably know more than myself.
Thanks in advance!

Rotor size can be the same front to rear, that isn't where the bias comes from. What you want on a typical RWD car with the engine up front is 2x brake force on the front than on the rear. If you have the same size rotors front and rear then your front calipers need to have twice the piston area as the rears. If you follow that formula then the bias should be close enough that you can dial it in perfectly with an adjustable prop valve. You most likely will want to use the same pad material front and rear and have tires that are roughly the same size front and rear. If you stray from the formula then beware of any panic stops until you get some seat time and figure out what it is going to do when you stomp on it. You don't want to find out the hard way in an emergency.