What RPM = MPH?

[Jerry]

Changed the speedo on my XJ. Pulled the needle to remove faceplate from old unit to put on replacement, old faceplate was in beter shape. Think the speedo is reading to fast, parhaps I got the needle in the wrong place on its shaft. Anyway, it indicates 55 MPH at 3,500 RPM in 5th gear...been so long since I had a speedomoter I can't remember if this is accurate. 65 MPH is indicated at 3,900 - 4,000 RPM. Can someone tell me if these RPM - MPH numbers are pretty close?

If anyone is going to try swapping speedos on the XJ, get one of those ratcheting, 90 degree Phillips screwdrivers. Will save a lot of frustration and time!

[nashville_bill]

On my '81 special 3000 = 45 mph.

[Mike Hart]

Pretty close, Jerry - my XJ has always shown 55mph=3600rpm

[Dragonrider]

Get on the highway. Go exactly 60mph. Pass mile marker, time youself till next mile marker. 60mph=60 seconds for 1 mile.

More seconds, you are going too slow, less seconds you are going too fast . . .

[crunchbird]

The speedo reads off the front wheel, regardless of gear. On the Specials, 3rd gear = speed i.e. 4000 rpm = 40 mph, 5500 rpm = 55 mph. Also, 5krpm is about 65 mph in 4th, 75 mph in 5th. I have significant hearing loss, yes.