I've found which variables go wrong. A couple of very small floating point variables are 100x bigger than they should be. Also interesting: when I run the logger, the decimal separator in the files is a comma, while in the files from the bugged version it's a point. How this is possible, I don't know. But I've added an option that will divide those variables by 100. This might do the trick for now. (Probably only your own car, not the AI.)
This is the first formula with the bad number:
maxSlipWeighted = massaR * 9.8f / maxWheelForceR - 1f;
maxSlipWeighted, massaR and maxWheelForceR are floats. Does someone understands why maxSlipWeighted is suddenly 100x bigger? MassaR and maxWheelForceR are the same as on my system, except for the decimal seperator now being a point instead of a comma.
EDIT:
It has nothing to do with my code, but with the regional settings of Windows. I changed the country from Belgium to USA and yes, the car went uncontrollably fast. The option to multiply the values didn't solve the issue, but perhaps I can now find a solution.
That means if you change your setting to Belgium, the game might work. (The downloadable version at least.)
EDIT 2:
Never mind, I believe I've found the culprit: a text file that represented the tire slip curve had commas as the decimal separator. English systems wouldn't recognize this and simply removed that comma, multiplying the values by 100. I removed the comma altogether and divided the value in the code itself. Problem solved!