1970 Harley Davidson Sportster Gear Ratios

The chart below shows the various gear ratios for the 1970 Harley Davidson Sportsters. The engine, clutch and rear wheel sprockets were not changed. The transmission sprocket is the only change. The engine RPM at 60 MPH is assuming high gear and a standard rear tire (4.25x18) measuring 26.5 inches in diameter. If you run a larger or smaller rear tire, your engine rpm's will be different. I have included the gear ratios from a 2000 Sportster just for comparison purposes.

19, 20, and 21 tooth sprockets are available from Harley Davidson. 22, 23 and 24 are available from other vendors.

Transmission Specifications - Number of sprocket teeth and gear ratios
Sprocket & Gear Ratios XLCH XLH Optional Optional Optional Optional 2000 883
Engine 34 34 34 34 34 34 ?
Clutch 59 59 59 59 59 59 ?
Transmission 19 20 21 22 23 24 ?
Rear Wheel 51 51 51 51 51 51 ?
First (low) 11.75 11.16 10.63 10.15 9.71 9.30 9.717
Second 8.51 8.08 7.70 7.35 7.03 6.74 6.69
Third 6.43 6.11 5.82 5.56 5.31 5.09 5.18
Fourth (High) 4.66 4.43 4.21 4.02 3.85 3.69 4.267
Fifth (Over Drive) N/A N/A N/A N/A N/A N/A 3.615
Engine RPM @ 60 MPH 3545 3368 3207 3062 2929 2806 ?
MPH @ 6,800 RPM 115 121 127 133 139 145 ?
1970 Sportsters are geared very high from the factory. With the standard gearing, you have lots of power but a terrible highway cruising machine. Any Sportster can go up to a 22 tooth transmission sprocket without modifications, but going to a 23 or 24 will require some cutting of the sprocket cover. A 22 is a good compromise and does not require any modifications to the sprocket cover.

Be careful, the size of your rear wheel will effect your engine speed at any given m.p.h. This next table shows how the diameter of your rear wheel effects your engine rpm at 60 m.p.h. The 19/51 means 19 tooth front sprocket, 51 tooth rear sprocket. The number in the table is engine rpm at 60 m.p.h.

Diameter 19/51 20/51 21/51 22/51 23/51 24/51
26.50 3545 3368 3207 3062 2928 2806
26.00 3613 3432 3269 3120 2985 2860
25.50 3684 3500 3333 3182 3043 2916
25.00 3758 3570 3400 3245 3104 2975
One other thing to note. Changing the overall gear ratio will affect the accuracy of your speedometer. 1970 Sportster speedometers are driven off the transmission. If that is a concern, see my BC800 page.

P.S. I am still running a 19 tooth sprocket but am going to try a 22 tooth very shortly.

Have fun... Ride safe...

Sportster Page