I believe your movie is "Vicious Cycles."
A wild, freewheeling spoof on motorcycle gangs in which tough-looking
cyclists, who roam the highways on invisible bikes leaving visible
tire tracks, lose the girl to members of a children's scooter-riding
club. A classic parody.
See also: Blaze Glory and Sergeant Swell.
Length: 7 minutes"
Pyramid Durect: Vicious Cycles
"Using the same live-action/animation technique, Chuck Menville and
his cohort in comedy, Len Jansen, produced two more effects-filled
shorts of equal originality and humor: 'Sergeant Swell,' starring
another Blaze-like hero of the Canadian Mounties; and 'Vicious
Cycles,' featuring modern bikers who somehow manage to rumble down the
road sans motorcycles (same as the horse-less riders in Blaze Glory)."
New York Times: Chuck Menville: Extraordinary Talent
Video Cassette - 6 minutes - Color - 1967
In this free-wheeling spoof of the Hell?s Angels type of
motorcyclists, tough guys race across the countryside on invisible
machines - which leave visible tire marks. An ingenious mix of live
action and stop motion animation by David Brain, Chuck Menville and
San Francisco State University: Video Cassette - Vicious Cycles
My Google search strategy:
Google Web Search: "invisible motorcycles OR bikes" movie OR film
Google Web Search: "blaze glory" "invisible motorcycles OR bikes"
Google Web Search: "chuck menville" invisible
I hope this is the correct film. If it is not, or if anything is
unclear or incomplete, please request clarification; I'll be glad to
offer further assistance before you rate my answer.