Originally Posted by Comrade Alfonzo
from what I hear the mechanical speedos were designed for 27in wheels with 27/1.25in tires, aka old schwinns like my '73 'Burban because they were so common
I would be supprised if they are accurate for any wheel size over the full scale. However it can be calibrated for reasonable +- 3mph over 25 to 30% of the scale. It probably is diffrent with each unit. What do you get for accuracy with the 27" tire?