The oldest self-propelled two-wheel vehicle or "steam-powered bicycle" in the Smithsonian Museum of American History is the Roper Steam Velocipede built in the late 1860s by Sylvester Howard Roper, of Roxbury, Massachusetts, and demonstrated by him at fairs and circuses.
At first glance the machine appears to be a converted velocipede, but examination reveals that its frame was forged expressly for this self-powered vehicle.
The two 34-inch-diameter wooden-spoke wheels have wooden felloes and iron-band tires. The front wheel is supported in a forged wrought-iron fork having a straight handlebar with wooden grips. Footrests are provided at the bottom of the fork. The wheelbase is 49 inches.
A vertical, fire-tube boiler is suspended between the wheels, and a chimney angles back from the top of the boiler housing. The lower half of the housing served as the firebox (the grate of which is missing). Charcoal was fed through a small circular door on the left side of the firebox. The housing is suspended from the center of the frame by means of a spring-loaded hanger (intended to absorb some of the road shock) and is braced at the bottom by two stay rods connected to the rear of the frame.
A hand-operated water pump is mounted vertically on the left forward side of the boiler housing. Three water-level cocks are located nearby, and there is a drain valve at the left rear of the boiler's base.
Oscillating steam cylinders are pivoted on each side of the frame, next to the chimney. From outside measurements, it is estimated that the bore of the cylinders is about two and one-quarter inches. The piston rods worked on 2-inch cranks on the ends of the rear axle. Piston valves for the cylinders were operated by eccentrics adjacent to their cranks, and a feed-water pump was operated by the left-cylinder crank. The exhaust steam, carried by tubing into the base of the chimney, provided forced draft. Apparently, while the machine was at rest a forced draft was provided by a tiny steam pipe that leads from the safety valve at the top rear of the boiler to the base of the chimney. There is a damper valve within the chimney.
The throttle, located at the top front of the boiler housing, was actuated by forward twisting of the handlebar. A friction brake was applied against the rim of the front wheel when the handlebar was twisted toward the driver. Heavy tubing leads from the throttle to the steam chests of the cylinders, and other tubing leads from the boiler to a steam gauge at the front of the frame.
The water supply for the boiler was contained in a tank that also served as the saddle. The filler opening is at the front of the tank. Water was supplied to the hand pump and the feed-water pump by means of tubing that leads from the bottom of the tank.
It is clear that the builder of this early self-propelled vehicle was an ingenious as well as an accomplished machinist.