[rzm3]

Update 2:

Question: why does BMW limit its cars to 155 mph intead of unlimited?

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Update 1:

Recalculated using frictional losses derived from a 320i coupe. Total frictional loss, which includes transmission loss, tire resistance, etc., adds to about 30%.

The updated top speed is 183.62 mph.

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Assumptions:
front wheel rolling losses not included (since power at wheels are found from a dyno, where the front wheels are stationary
Air density at standard sea level used
factors from gear ratio neglected

Result:
with a transmission loss of 13.29%, the M3 is capable of reaching a top speed of 196.95 mph.

Method:
when power generated by the engine equals the power induced by drag force, the car cannot accelerate anymore and thus reaches top speed.

Let me know if there is anything I can modify to make the calculation more sound.