Army Style Fat Bob Speedometer

Drive Ratio

1:1 Drive Ratio

fits all transmission-mounted drive units on FL models from 1962–1980, FX models 1971–1972 and FXWG 1980-1983. 1000 full turns of the cable equal 1 mi of way, so 1,000 rpm of the cable corresponds to 60 mph.

2:1 Drive Ratio

fits all transmission-mounted drive units on 1936–61 Big Twins and 1952-72 K/XL, all rear wheel drive units on 45” models from 1937–61 and front wheel drive units on FX/XL models from 1973 to present. 2,000 min^-1 of the cable corresponds to 60 mph.

2240:60 Drive Ratio

fits all FLH 1981–84, FLST and FXST models 1984-95. 2,240 min^-1 of the cable corresponds to 60 mph.

So far for OEM speedos. Aftermarket speedometers may show yet another calibration:

700 rpm = 60 km/h

This is no standard for original Harleys but you will find speedometer heads with such labels on the market — to our grief many designs are only available with this calibration. If 700 min^-1 of the speedo cable correspond to 60 km/h of hand reading and you fit this speedo to an older 1968-1981 FLH that requires a 1:1 speedo, it will show about 15% too low. And the higher you gear your FLH the lower the reading will be.

The calibration 700 rpm = 60 km/h means that for 96 km/h (= 60 mph) the cable has to spin at 1120 rpm. That looks a bit familiar, doesn´t it? Yea, it's just the half of 2240 (see above). Just a common Eastern Asia calibration way. Many old Japanese bikes had such speedos and when H-D started to buy instruments from Nippon they had to use the new calibrations that seem a bit odd — if you convert them to mls.