| Better acceleration vs. Lower theoretical top-end and bad fuel economy explained.
What is the theoretical top speed?
It is the max. RPM divided by peak gear ratio of your tranny, divided by your final drive ratio (differential). All this will= your wheel rotations per a time unit.
Can it be reached in our BMWs?
I am not so sure for two reasons: A. As I mentioned earlier we are blessed with these electronic gadgets to limit our speed and B. Don’t forget the laws of nature and the whole subject in 101 college classes in aerodynamics but shorter ratios do enhance BMWs shifting points; this partly explains how BMW get away with using similar 6 speed manuals coupled with individual ratios.
When Dinan suggests a ratio of 3.15 from 2.89 and Jonathan prefers to go with 3.64 ratios. What we talking about here is taking the 2.89 in Jonathan’s example above and subtract it from 2.89 the difference is 0.26; now divide 0.26 by 2.89 = 0.089 X 100 = 8.9. This is the percentage change in Dinan and /or Jonathan’s example. Fair? In fact BMW did just that back in 1999 with its 540 6 speeders when they changed their ratio from 2.82 or 2.83 (don’t quote me) to 3.15 and yes they continued using the same ratio in their mighty 3700 plus pounder M5. It was a brilliant engineering move to correct gears but such a move took the Bimmer away from its natural habitat of autobahns. Welcome to the new world of speed limits! | 
