The owners manual for my 88 740 includes a list of all the gear ratios, rear axles etc, and MPH per 1000 RPM in each gear for the various combinations. I suspect the 240 manual has this too (in the "specifications" section, toward the back) If you have stock size tires you should find it very useful.

Use the mile markers on the hwy, drive 60 mph which is a mile a minute. This will give you a rough idea of how close it is. Dan

That's a lot of math! :-)

Once for each gear, then you've got to account for tire diameter and wear. You've got measuremnt error there, and error in the tachometer (it's close, but not perfect).

Just find a place where the highway has measured miles, drive a couple miles and look at the odometer. Better still, find a friend with a GPS.

-Ryan
--
--------------------------
Athens, Ohio
1990 245 DL 130k M47, E-codes
1991 745 GL 280k (Girlfriend-mobile)
Buckeye Volvo Club

Gears 1 thru 3 reduce the RPM in favor of torque. 4th is about even, and 5th gear is an overdrive gear. I believe the multiplier for 5th gear (before 1990) is 1.22. So let's say that you're doing 2500 rpm and your clutch isn't slipping.

2500rpm x 1.22 5th gear = 3050 rmp before the rear end

I know some rear ends (automatics, though) were 3.91, so we'll use that as our example.

3050rpm / 3.91 = 780 rpm at the wheels

The diameter of your tire is dictated by your tire size.
http://www.sstire.com/tireheights.html

Mine happen to be a diameter of 24.98"; circum is Pi x diameter
3.14159 x 24.98 = 78.48 inches per revolution

78.48 ipr x 780 rpm = 61214 inches/minute

There are 63360 inches in a mile
61214 inches per minute / 63360 = .9661 miles per minute => 57.98 mph

That sounds about right. You'll need to find your rear-end ratio and tire size for your car. If only it were so easy for automatics.