That is not what I am saying. My calculator has ATS front/Cobra rear at 72.7% and Cobra R front/Cobra rear at 69.3%. The data I have found says the ATS calipers have a taller pad than the Cobra R calipers so on the same 13" rotors, they have a slightly smaller effective rotor radius. But, the much larger pistons overcome that and result in the ATS calipers having a higher front bias than Cobra R calipers.Below is a picture from the maximum motorsports website showing all the different brake bias percentages. I trust their math.
You're basically telling me the ATS calipers with 13 inch (cobra) rear rotors have a better bias than the 00R Brembos that have smaller pistons.
View attachment 1802201
I definitely trust Maximum Motorsports' numbers too; they're the experts. I was unaware of this chart!
A slight difference in determining the effective radius and piston diameter could result in the slight discrepancies between their numbers and mine. My calculator does effective radius = rotor diameter / 2 - pad height / 2. This assumes the pad is perfectly at the edge of the rotor (it isn't), that I have decent values for pad heights (found online), and that the caliper pistons are in the middle of the pad. Ideally, the effective radius is from the center of the rotor to center of the caliper piston but I have no reasonable way to get that data.
A few comparisons between MM's results and mine:
front | rear | MM | me | delta |
04 Cobra | 04 Cobra | 72.6 | 72.6 | 0.0 |
04 Cobra | 04 GT | 74.9 | 74.9 | 0.0 |
Cobra R | 04 Cobra | 69.6 | 69.3 | -0.3 |
Cobra R | 04 GT | 72.0 | 71.7 | -0.3 |
04 GT | 04 GT | 72.8 | 74.1 | +1.3 |
98 GT | 04 GT | 75.7 | 75.4 | -0.3 |
98 Cobra | 04 Cobra | 70.0 | 70.3 | +0.3 |
98 Cobra | 04 GT | 72.5 | 72.7 | -0.2 |
It looks like my calculator is working right, but some of my source data may be slightly off. Very small changes to the data can account for the differences in calculated front bias %.
If anyone has better effective radius and piston diameter data, or if you see a bug in my code, please let me know!
Note: edited chart after getting improved data in my calculator!
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