I knew that the '34 Ford had 17" wheels, that is why I limited my measurement to a 16" cover @26.5", I do not have a '34 or a 15" cover to measure.
Actually the wheel size is somewhat of a mute subject if you have a tire size that is compatible with the average OD of a 600x16, approx 27.5". The average 22575R15 has the same general OD as a 600x16, the big difference is in the tire width.
In response to Roberts question about the tire cover on his '34 Ford... Mike stated in the above that '34 covers have 1/2 " wide S/S trim where-as '35's have 3/8" S/S", this info could give Robert a clue as to what his cover is..