Quote:
Originally Posted by Drifty//
...There are two answers to this question. The first answer is how to shift when cruising. This is a matter of personal style, wife in the car, interest in fuel economy, longevity, etc.
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Pretty much agreed, but if fuel mileage is at issue, BMW says to shift at minumum rpm and max throttle, and they've been saying this for at least thirty years that I know of.
In this car, that means a low 2000s shift point (or even a bit lower as the gears progress), using a bunch of throttle. One could shift even lower than this, but you're likely to get into some engine lugging after the shift, which will absolutely not harm the engine, but is hard on the driver's teeth.
Quote:
Originally Posted by Drifty//
The second answer is how to shift when you need to go fast in a hurry. I can absolutely guarantee you that the best quarter mile times are not set by shifting all gears at 8.4k RPMs. To find the optimal shift points, you need to find at what RPMs you can get more wheel torque by upshifting, and it's progressively lower as you get to higher and higher gears.
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Drive wheel torque is obviously important, but you don't need to bother with calculating it, because horsepower is the great shorthand in this context. More power means more drive wheel torque and quicker acceleration at any given car speed, and torque and gearing simply don't matter - at all - in that context.
The only - ONLY - modifier to this is that rotational inertia is reduced every time you upshift, which has the effect of lowering optimal shift points to some degree, more on the one-two shift, and less and less as the gears progress.
A general rule of thumb is to shift at around 10% above the power peak (if you can) for best acceleration. In point of fact, using one of the many currently available software packages available that model vehicle acceleration, you'll find that a completely stock current M3 would be quicker than it currently is if you shift it at somewhere in the vicinity of 9000 rpm - providing it didn't blow up, of course.
Now, about that guarantee. How about you provide some data to prove your point.
Bruce