240D 1982 Speedometer vs Tachometer

[NLatkovic]

FYI. After checking my speedometer against numerous speeds apps, I find that indicated 70 mph is actually 65 mph. And yes, have correct wheel and tire sizes.

Just trying to figure out RPM w/o a tach. Frustrating. Engine sounds like it is about 4500 rpm at 60 mph but who knows. It runs great, valves adjusted etc. would love to know rams though

[Frank Reiner]

Originally Posted by NLatkovic

FYI. After checking my speedometer against numerous speeds apps, I find that indicated 70 mph is actually 65 mph. And yes, have correct wheel and tire sizes.

Just trying to figure out RPM w/o a tach. Frustrating. Engine sounds like it is about 4500 rpm at 60 mph but who knows. It runs great, valves adjusted etc. would love to know rams though

1) Measure circumference of rear tires.
2) Calculate wheel speed @ 65 MPH.
3) Clean off lower corners on the back of the differential housing, and read gear ratio stamped into housing.
4) Multiply the wheel speed from step 2 by the gear ratio. =RPM @ 65 MPH.