Around 1910, Arthur William Wall developed a direct drive motor wheel to power a bicycle – it was the first to be powered by gasoline. 4 years later, manufacturing rights for the motor wheel were acquired by the A.O. Smith Corporation of Milwaukee, Wisconsin, and it led to what you see here, the Smith Motor Wheel.
The wheel was powered by a 1-1.5 horsepower motor and it drove a 20 inch wheel. Mounting the motor wheel to the rear tire of a bicycle enabled a top speed of about 20 miles per hour with a fuel range of ~100 miles on a 1 gallon tank. Approximately 25,000 of the Smith Motor Wheels were produced.
Eventually, the Smith Motor Wheel was sold to Briggs & Stratton, who improved power to 2 whopping horses. They then focused on the motor inside the motor wheel, and that evolved into the ubiquitous Briggs & Stratton motors seen in lawnmowers and all kinds of small equipment.
from http://www.oldbike.eu/museum/engines/1910s/cycle-attachment-engines-1915-1919-smith-motorwheel/
For a lot more information on the Smith Motor Wheel (including great vintage ads like the one above), check out this profile on the Online Bicycle Museum.
Find this Smith Motor Wheel for sale in St. Louis here at Michael’s Motorcycles for $6,500.