Definition of "treader"

Why, he weren’t no more’n knocked offen his treader. An’ now he’ve rid off home on it!

1958, Dominic Reeve, Smoke in the Lanes, London: Constable & Co.; republished London: The Country Book Club, 1959, page 82

The Royal Academy has just two orange hoops on to which four early-bird visitors can chain their treaders. It is left to the railings outside for the rest.

1996 June 6, Ben Summers, “Saddle-weary commuters left with a sore deal”, in The Independent‎, London, page 6

He set off from Oxford on a standard old "treader" bike, often at night – navigating by the stars and napping under a hedge if got[sic] tired on his way to Holt.

2015 July 25, Richard Batson, “Family set for 156-mile charity ride in memory of Holt doctor”, in Eastern Daily Press‎, Norwich