1957 "Ironhead" overhead-valve engine introduced.

1958 XLH touring high compression model and XLCH sportier "Competition Hot" model introduced.

1967 Electric starting introduced on XLH 
1972 "Ironhead" 1,000 cc overhead-valve engine replaces 900 cc.
Claimed power was 61 hp (45 kW) @ 6,200 rpm and a top speed of 116 mph (187 km/h)
1975 Switched to left-side gear change (DOT mandate)
1977 & 1979 Dual exhaust "Siamese" pipes used, introduced on Willie G. Davidson's XLCR café racer in 1977 all models 1979, along with the triangular frame and rear hydraulic disk brake also introduced on the XLCR.
In 1977 a  limited edition Confederate Edition Sportster was introduced for one year only.

1979 Last year for the kickstart only XLCH, only 141 made.

1985 Last year for the "Ironhead" overhead-valve engine.

1986 "Evolution" engine introduced in 883 cc and 1,100 cc sizes.

1988 1200 cc engine replaces 1,100 cc engine.

1988 Constant velocity carburetor replaces butterfly carburetor.

1991 Five-speed transmission replaces four-speed.

1991 Belt drive replaces chain drive on 883 Deluxe and all 1200 models.

1993 Belt drive made standard on all Sportsters.

1994 Improved oil tank, battery tray, and clutch made standard.

1994 New electrical system with sealed connectors.

1995 Speedometer is now electronic, not mechanical.

1996 XL1200C Custom model introduced.

1998 XL1200S gets dual spark plug heads and high performance cams
2000 Introduced sealed wheel bearings and updated four-piston brake calipers.

2003 Last year for the frame mounted Evolution engine.

2004 All-new frame including rubber-mounted engine for decreased vibration.
Elimination of the transmission trap door, New shape hamcan, Exhaust balance pipe moved from running under the air filter and disguised and hidden behind the silencers to show more of engine, new smoother style oil tank right side panel with push and turn filler/dipstick, and the previously exposed battery is now enclosed in a matching side panel on the left
2005 Enlarged rear axle to 1 inch (25.4 mm) for increased stability.

2006 New XR1200 is announced at Intermot in Cologne, Germany.
 The XR1200 is the first Harley-Davidson to utilize Down Draft DDFI II fuel injection.
 To be released as a late 2006 model.
Introduction of helical gears in transmission (2nd-5th).

2007 Fuel injection replaces carburetion on all models.

2008 front axle enlarged from 3/4 inch to 25 mm, rear axle decreased from 1 inch (25.4 mm) to 25 mm
2009 "One size fits all" front mudguard approach replaced by improved mudguard contour to match each model's respective wheel diameters.

2010 The ECU is relocated to allow more variation in aftermarket seat selection.
Side-mounted license plate option on some models
2014 new electrical harness, new larger brakes, antilock brakes (ABS) option, keyless entry, new speedometer with gear indicator/tachometer, increased engine compression ratio, catalytic converter
1957 "Ironhead" overhead-valve engine introduced.
1958 XLH touring high compression model and XLCH sportier "Competition Hot" model introduced.
1967 Electric starting introduced on XLH 
1972 "Ironhead" 1,000 cc overhead-valve engine replaces 900 cc. Claimed power was 61 hp (45 kW) @ 6,200 rpm and a top speed of 116 mph (187 km/h)
1975 Switched to left-side gear change (DOT mandate)
1977 & 1979 Dual exhaust "Siamese" pipes used, introduced on Willie G. Davidson's XLCR café racer in 1977 all models 1979, along with the triangular frame and rear hydraulic disk brake also introduced on the XLCR. In 1977 a  limited edition Confederate Edition Sportster was introduced for one year only.
1979 Last year for the kickstart only XLCH, only 141 made.
1985 Last year for the "Ironhead" overhead-valve engine.
1986 "Evolution" engine introduced in 883 cc and 1,100 cc sizes.
1988 1200 cc engine replaces 1,100 cc engine.
1988 Constant velocity carburetor replaces butterfly carburetor.
1991 Five-speed transmission replaces four-speed.
1991 Belt drive replaces chain drive on 883 Deluxe and all 1200 models.
1993 Belt drive made standard on all Sportsters.
1994 Improved oil tank, battery tray, and clutch made standard.
1994 New electrical system with sealed connectors.
1995 Speedometer is now electronic, not mechanical.
1996 XL1200C Custom model introduced.
1998 XL1200S gets dual spark plug heads and high performance cams
2000 Introduced sealed wheel bearings and updated four-piston brake calipers.
2003 Last year for the frame mounted Evolution engine.
2004 All-new frame including rubber-mounted engine for decreased vibration. Elimination of the transmission trap door, New shape hamcan, Exhaust balance pipe moved from running under the air filter and disguised and hidden behind the silencers to show more of engine, new smoother style oil tank right side panel with push and turn filler/dipstick, and the previously exposed battery is now enclosed in a matching side panel on the left
2005 Enlarged rear axle to 1 inch (25.4 mm) for increased stability.
2006 New XR1200 is announced at Intermot in Cologne, Germany.  The XR1200 is the first Harley-Davidson to utilize Down Draft DDFI II fuel injection.  To be released as a late 2006 model. Introduction of helical gears in transmission (2nd-5th).
2007 Fuel injection replaces carburetion on all models.
2008 front axle enlarged from 3/4 inch to 25 mm, rear axle decreased from 1 inch (25.4 mm) to 25 mm
2009 "One size fits all" front mudguard approach replaced by improved mudguard contour to match each model's respective wheel diameters.
2010 The ECU is relocated to allow more variation in aftermarket seat selection. Side-mounted license plate option on some models
2014 new electrical harness, new larger brakes, antilock brakes (ABS) option, keyless entry, new speedometer with gear indicator/tachometer, increased engine compression ratio, catalytic converter
Harley-Davidson Sportster