Then if we compare this value with the one from Fat Cat Motorsports the mistake is obvious.įCM value: 1625.8 lb-ft/deg ->1625.8 lb-ft/deg /2 = 812.9 lb-ft/degįinally, those spreadsheets can still be used, but would require a bit more work. Or the equivalent equation from OptimumG technical papers ( )

Using the equations Milliken book (p.589 and 596) (The spreadsheet can be found there: FCM_MSDS_1_6NA.xls) So let’s start with FCM’s result when only considering the front springs for the roll stiffness (roll bars diameter at 0): Since I don’t expect anybody to simply believe my words, I will demonstrate the error with references:

I did email FCM to inform them that the spring’s contribution in roll stiffness is twice the actual value, but I did not receive any answer and the spreadsheets are still the same. I have been using those spreadsheets myself to calculate FRC% until I discovered the error in the roll stiffness calculation. First of all, I don’t usually contribute to forums, but today I’m making an exception because I believe everyone should be aware of the obvious mistake present in FCM’s spreadsheets.