I just purchased a 2007 R56 and I pick it up next Saturday. I am considering different tire diameters and I'd like to know what RPM the motor sits at 55, 60, 65, 70, 75, 80.

Is this data out there anywhere?

Many thanks!

 

There are calculators out there for this. Bokchoys has one for bmw's, you can simply sub in the ratios for the r56 differential and 6th gear to calculator engine rpm at any given speed.

 

I found the gear ratios and final drive ratio listed here:
http://motoringfile.com/files/2007_M...ical_Specs.pdf

But can you define for me what the "transmission ratio" they are looking for here is?
http://www.crawlpedia.com/rpm_gear_calculator.htm

 

Using your calculator:
http://www.bokchoys.com/differential...calculator.htm

I find:
55MPH - 2267
60MPH - 2474
65MPH - 2680
70MPH - 2886
75MPH - 3092
80MPH - 3298

Sound about right for owners out there?

 

If I went to a 205/50/R15 tire on a 15x7 rim I'd see:
55MPH - 2385
60MPH - 2602
65MPH - 2818
70MPH - 3035
75MPH - 3252
80MPH - 3469

 

Basically it's like 5% across the gears... I wonder if folks get annoyed by that on the highway for hours...

 

Try this: Gear ratio X 168 x MPH/Tire radius = RPM. You have to know your diff ratio and 6th gear ratio, which you multiply to arrive at your final drive ratio to use in the equation. For instance my 2013 R56 JCW has a 3.71 diff ratio and a .816 6th gear ratio for a final of 3.02. That with a 12" tire radius gives me 2748 RPM @ 65 MPH, which is about what I see on my tach at that speed.

 

On my 2008 I run right at 3,000 rpm with the cruise set on 75 (speed = 72 per GPS). This is on 205/55/16 tires. Sorry, haven't really paid any attention to the other speeds you asked about.

 

Thanks for the data point, sounds like my calculations are looking good then. Much appreciated!