Quote:
Originally Posted by bruce.augenstein@comcast.
There is some other function within CarTest which handles rotational inertia. Either that or it's a piece of crap, which I don't believe.
If you remember previous conversations, the smallest amount of acceleration "loss" I found in first gear compared to second gear was 12%, on a car with a three to two ratio between first and second gears, showing .50 G max acceleration in second gear, and .66 G in first. This was on an '85 Vette with an undersized trans (Borg-Warner Super T10) and an 18 pound flywheel. Every other car I tested (and there were at least a couple of dozen) showed a larger loss than that.
Rotational inertia is real, and significant. I know you and lucid never bothered to check Gillespie's book, but you should have.
|
I'm pretty sure the author of CarTest confirmed with me that he included drivetrain inertial effects. I never said it is not important. It clearly is, it translates along with the car and it also takes extra energy on top of that to spin up all rotating components. I just doubted certain details of the math relationships with you.
Other than knowing gear ratios there is obviously no way of knowing how large or what materials (i.e. densities) or sized all of the relevant drivetrain components are. I checked Gillespie, he simply substitutes the so called "mass factor" for not knowing the details about each cars drivetrain. The mass factor is an approximation and certainly does not take into account actual details of the driveline. The mass factor in 1st gear between the 335i and M3 does vary by about 18%. I'll try to check CarTest to see if this "mass factor" is used as part of its acceleration calculation by specifically comparing the M3 and 335i.