If you just want to use the calculator, here it is: SN-95 Brake Bias Calculator
Background:
I, like many others, have upgraded my front brakes. I upgraded to 14" (07-12 GT500 front rotors) and Brembo monoblock calipers about 8 years ago. This dramatically improved my car's braking performance!
Problem:
With improved front brakes, the bias is too far to the front (~75/25 in my case). I have read that optimal brake bias on SN-95s is 70/30 and calculated the 93/95 Cobra R to be ~70/30 and 00 Cobra R to be ~69/31 which seems to confirm this. Full Tilt Boogie Racing does make a 13" rear brake conversion kit (changes bias to ~72/28 in my case). My issue with their kit is that I would be locked into using their rotors instead of something off-the-shelf, also maybe I can get closer to that optimal 70/30!
Rotor solution:
2013-2014 GT500 rear rotors check all of the boxes for me!
Bracket solution:
I designed brackets that push the rear calipers out and down to minimize how much further the parking brake cable has to reach. I ran structural analysis on the brackets and determined that 6061 aluminum is plenty strong for this purpose.
brackets:
Putting everything together:
I bought a set of 13-14 GT500 rear rotors and 03-04 Cobra pads. The bracket bolts to the spindle with new bolts and nuts and the caliper bolts to the bracket with the factory bolts. Because the GT500 rotors are 1mm thicker than Cobra rotors, I removed the insulators from the back of the pads to easily fit the rotor. I read that Ford ran in production for a while with no insulators on the pads so this is acceptable! Where the parking brake cable attaches to the lower spring perch no longer reaches, so I attached it using cable ties (mine has been held on with cable ties for 8 years; I broke the bolt off in the lower control arm a long time ago):
11.65" 03-04 Cobra rear rotors:
14" 13-14 GT500 rear rotors:
14" front Brembo monoblocks:
Results:
Results with common big brake setups:
I created a calculator which shows the brake bias for common SN-95 front/rear brake combinations. Select the desired front caliper/rotor combination on the left and it will calculate and highlight the optimal rear caliper/rotor combination on the right.
SN-95 Brake Bias Calculator
note: I am happy to add more caliper/rotor combinations to the calculator! I just need caliper piston diameters, radial pad heights, and rotor diameters.
Some optimal results:
If you are interested in the adapters, send @lowranger96 a DM. I have designed versions for IRS and SRA (SRA brackets fit GT and Cobra axle brackets; require Cobra caliper brackets). All adapters are now machined and sold by S&S Engineering. The only additional parts are 13-14 GT500 rear rotors ($68+ for a pair) and 03-04 Cobra rear pads ($26+ for a set).
IRS installation instructions: https://lawpaul.github.io/SN95-Brake-Bias/doc/instructions/13-14_GT500_IRS.pdf
Wheel fitment: it looks like most/all 18” wheels will fit. Cast 17” wheels will not fit; forged 17” are plausible if someone is willing to take some measurements.
Background:
I, like many others, have upgraded my front brakes. I upgraded to 14" (07-12 GT500 front rotors) and Brembo monoblock calipers about 8 years ago. This dramatically improved my car's braking performance!
Problem:
With improved front brakes, the bias is too far to the front (~75/25 in my case). I have read that optimal brake bias on SN-95s is 70/30 and calculated the 93/95 Cobra R to be ~70/30 and 00 Cobra R to be ~69/31 which seems to confirm this. Full Tilt Boogie Racing does make a 13" rear brake conversion kit (changes bias to ~72/28 in my case). My issue with their kit is that I would be locked into using their rotors instead of something off-the-shelf, also maybe I can get closer to that optimal 70/30!
Rotor solution:
2013-2014 GT500 rear rotors check all of the boxes for me!
- readily available (as cheap as $68 for a pair)
- diameter of 13.77" (vs 11.65") (larger diameter means increased rear bias)
- thickness of 19mm (vs 18mm) (fits factory 03-04 Cobra pads)
Bracket solution:
I designed brackets that push the rear calipers out and down to minimize how much further the parking brake cable has to reach. I ran structural analysis on the brackets and determined that 6061 aluminum is plenty strong for this purpose.
brackets:
Putting everything together:
I bought a set of 13-14 GT500 rear rotors and 03-04 Cobra pads. The bracket bolts to the spindle with new bolts and nuts and the caliper bolts to the bracket with the factory bolts. Because the GT500 rotors are 1mm thicker than Cobra rotors, I removed the insulators from the back of the pads to easily fit the rotor. I read that Ford ran in production for a while with no insulators on the pads so this is acceptable! Where the parking brake cable attaches to the lower spring perch no longer reaches, so I attached it using cable ties (mine has been held on with cable ties for 8 years; I broke the bolt off in the lower control arm a long time ago):
11.65" 03-04 Cobra rear rotors:
14" 13-14 GT500 rear rotors:
14" front Brembo monoblocks:
Results:
- unmodified factory (13-14 GT500) rotors
- factory (03-04 Cobra) pads with insulators removed
- unmodified factory (03-04 Cobra) caliper
- working parking brake
- optimal ~70/30 brake bias
Results with common big brake setups:
I created a calculator which shows the brake bias for common SN-95 front/rear brake combinations. Select the desired front caliper/rotor combination on the left and it will calculate and highlight the optimal rear caliper/rotor combination on the right.
SN-95 Brake Bias Calculator
note: I am happy to add more caliper/rotor combinations to the calculator! I just need caliper piston diameters, radial pad heights, and rotor diameters.
Some optimal results:
| front setup | bias Cobra rear | good bias | optimal rear caliper | optimal rear rotor |
| 00 Cobra R 13" Brembo | 69.3% | 69.3% | 94-04 Mustang | 99-04 Cobra |
| FTBR 14" Brembo F50 | 75.0% | 71.3% | 94-04 Mustang | 13-14 GT500 |
| FTBR 14.5" Brembo F50 | 75.8% | 72.2% | 94-04 Mustang | 13-14 GT500 |
| FTBR 14.5" Brembo F50 | 75.8% | 71.1% | 96-99 Taurus | 99-04 Cobra |
| 13-19 ATS 13" Brembo | 72.7% | 68.8% | 94-04 Mustang | 13-14 GT500 |
| 13-19 XTS 14" Brembo | 74.5% | 70.7% | 94-04 Mustang | 13-14 GT500 |
If you are interested in the adapters, send @lowranger96 a DM. I have designed versions for IRS and SRA (SRA brackets fit GT and Cobra axle brackets; require Cobra caliper brackets). All adapters are now machined and sold by S&S Engineering. The only additional parts are 13-14 GT500 rear rotors ($68+ for a pair) and 03-04 Cobra rear pads ($26+ for a set).
IRS installation instructions: https://lawpaul.github.io/SN95-Brake-Bias/doc/instructions/13-14_GT500_IRS.pdf
Wheel fitment: it looks like most/all 18” wheels will fit. Cast 17” wheels will not fit; forged 17” are plausible if someone is willing to take some measurements.
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