When did bicycles first have equal-size wheels?
Just over a hundred years ago, in 1886. They were called safety bicycles to distinguish them from their forebears with the unstable combination of one very large wheel and one very small one. Early velocipedes, as they were called in the 19th century, were difficult to mount and very dangerous in case of an accidental dismount. Whereas only about 20,000 bicycles were in use in America in 1882, that number jumped to more than a million as the first improvements began to appear and stability was improved. The appearance of the safety bicycle furthered that trend considerably.