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      12-07-2007, 02:01 AM   #184

Drives: E92 M3 and Elise
Join Date: Oct 2006
Location: Land of the Microchip

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Originally Posted by bruce.augenstein@comcast. View Post
I know that nobody talks about this (rotational inertia), but it's far from a tiny issue. As an example, if you have a car with a three to one first gear and a two to one second gear, you would naturally expect first gear to accelerate 50% harder in first gear than in second. Not so, however. The least loss I've encountered during instrumented testing on many cars over the years is about 12%. The most is near 20%. That particular record was achieved in a German car, and we well know that German cars use flywheels that may as well have been liberated from old Panzer tanks, or U-boats.

OK, I'll shut up now. Too many points

Thanks again Bruce for trying to illistrate this. Trying to explain this has become an exercise in frutration for me.

I keep hoping that the move away from MT gearboxes will reduce their usage of heavy flywheels since drivability won't still be an issue.

I have always been a fan of taller 1st and 2nd gears in high HP cars. It makes little sense to use a 1st gear that always traction lmited. 50mph 1st and 72mph 2nd would be about right in my mind. A while back I was instructing someone driving a superchared Atom. It turned out to be best to launch the car in 2nd and save the time of the shift and focus on the first zig in the course.

If you are putting drag radials on the car, then a lot changes. For street or DOT-R tires a super short first gear isn't really usefull.