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      06-07-2013, 06:10 PM   #103
swamp2
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Quote:
Originally Posted by drob23 View Post
Seems like the biggest source of uncertainty in a 0-60 or 1/4 mile sprint would be the tire model. But maybe you can correlate your model and known benchmarks for the M5?

Also, I'd guess suspension modeling plays a big part with the weight transfer, how is the suspension modeled? I know there are 2 types in the industry, one such as Carsim which uses parametric models and 2nd order approximations (look up tables), while others actually model the linkages and multi-body stuff (is it called ATOM model?). I'm no expert on this as you can probably tell...
Good questions/comments.

The tires are not modeled in any explicit fashion in this level of simulation. The key ingredients are simply the static and dynamics friction coefficients, i.e. whether the tire is spinning or "hooked up". There is probably room for some improvement here but again, above all power and weight are by far the most dominant factors.

Suspension is also not modeled explicitly, in fact there is really no suspension modeling. The only effect is weight transfer which affects the maximum wheel torque possible before wheelspin. A fully rigid chassis is assumed here as suspension movement is not a prerequisite to properly cover basic weight transfer. Of course one can still model RWD or AWD and friction/traction along with weight transfer on both axles.

From my extensive use of this program and the one I wrote myself, the largest uncertainties are parasitic drivetrain losses, drivetrain inertia and tire modeling (again just the two friction coefficients). Getting shift times correct is also a key factor in results, however, this is fairly straight forward (despite some debate here on the forum as to how fast a "fast shifting" human can shift). DCT obviously shifts significantly faster than even the fastest human.

One does need to engage in some ongoing simulation vs. test activities to always keep the simulations correlated to the real world. However, care must be taken as to what is a "real" number from testing. Test result vary quite widely.

The goal here is overall vehicle performance. The tool is both simple enough and complex enough to provide a suitable balance of accuracy, flexibility and speed. Simulations take mere seconds...
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