[flyga3]

Originally Posted by italia

Exactly. I'm sure. Wait ... what were we talking about? Havin' a wee dram of an 18 year old single malt. So, yeah ... your math looks good.

I'm with ya!

[Lucky13]

I'm torn between getting a 228 M Sport convertible or an M235 coupe. The only complaint I have with my E93 335 manual is the car is almost 4,000 lbs and handling suffers. I figure a 228 M Sport convertible will be about 3,600 lbs. Performance shouldn't be far off with a 400 lb savings on the E93. I've owned 3 E46's M3's but 5 BMW convertibles and its a toss up right now on which way to go.

[DrFranknFurter]

Originally Posted by flyga3

On that point agreed, the circumference changes and the section height delta between them is 10mm for those 2 tires sixes. You get more forward distance traveled on a larger circumference tire given the same input force. I stand corrected.

OK, so maybe this is all a moot point, if a 228 with the M-Package which has a somewhat similar front/rear wheels/tires (i.e. circumferences) as the 328 manual.
Given the gearing is ALMOST the same and holding that constant, here are my calcs:

328 6MT
Front: 225x50R17
225 * 0.5 + 431.8 (wheel) = 544.3 * pi = 1709.1mm circumference

Rear: 225x50R17
225 * 0.5 + 431.8 (wheel) = 544.3 * pi = 1709.1mm circumference

228 6MT w/M-Line
Front: 225x40R18
225 * 0.4 + 457.2 (wheel) = 547.2 * pi = 1718.2mm circumference

Rear: 245x35R18
245 * 0.35 + 457.2 (wheel) = 542.95 * pi = 1704.8mm circumference

So MAYBE better acceleration number then? Course then we have not included surface area friction, weight, etc, etc.
Jeeeez, the engineer in me has come out! I'm not sure where I'm going anymore…..
I just need to bite it, get the 6MT and enjoy the slower ride but the joy of shifting!

Nice workings! the problem is there are so many variables and sources of information (some invarably incorrect) that it's difficult to be sure. In any case I think a few fractions of a second have less impact to the overal driving pleasure than other factors such as engine, supension and gearbox will have.