[dradernh]

Originally Posted by CP911

One thing to note on the topic of gas mileage is that the 6-speed M240i will not get 30+ mpg like the automatic will due to the short 6th gear. I'm not sure why BMW did this as I can't see 6th gear being used on any tracks and it only sacrifices good gas mileage on the highway. I'm having trouble remembering what cruising rpms were before my LSD upgrade, but I'm almost certain the LSD made things worse as I'm seeing 2500rpms or higher when cruising at 70mph. Luckily, I don't commute with this car and don't take it on the highways much, so not a huge deal for me, but it is still worth mentioning.

My 6-speed gets 30+ on the highway.

70 MPH @ 2500 RPM is stock for the 6-speed. That's with a 3.08 diff; if you change the diff ratio, then you'll affect the RPMs at a given speed in any gear.

Below are links to a couple of gearing calculators that can be downloaded.

DiffsOnline's calculator allows for six speeds, but has limited editing. Bob Tunnell's sheet allows editing. It's set up for five speeds, and when I use it I start with 2nd gear. Tunnell's sheet also allows you to enter your tire diameter (instead of having it calculated as the DiffsOnline calculator does).

DiffsOnline Gearing Calculator http://diffsonline.com/images/GearingCalculator.xls

Tunnell Racing Gearing Calculator http://www.tunnellracing.com/gearcalc.xls

This is Tunnell's sheet with my data in it. Note that the stock rear tire diameter on a staggered MPSS setup is 24.8". That makes a slight difference. The tire size (255/35-18 in this example) is not used in any calculations - it's just in the sheet for reference.



This is the same data graphed: