Speedometer Calibration help

[Spartan8029]

Hey everyone, so I just installed a new speedometer into the bike but I feel like an idiot because I can't figure out the circumference of the front wheel to calibrate the thing. Right now it is set to 1995mm but that is not right because the speedo barely goes over 10mph when I know I'm doing at least 25 to 30, any help would be much appreciated.

 

[Wolfe_11B]

What tire? Manufacturer will list true circumference, but it will differ between rims, air pressure, etc. So best to use a wire around the tire and measure, or make a mark on the tire, mark the ground, roll the bike til the mark hits the ground again, and measure. There is the circumference.

 

[Spartan8029]

Ok cool, thanks, that makes perfect sense.

 

[XSLeo]

Another way is to stand the bike upright and measure from the center of the axle straight down to where the tire sets on the ground. The measurement is the radius, multiply by two to get diameter, multiply by 3.14 to get circumference. Or go to the tire manufacturer's website and see if they have a chart that gives tire specs.
Leo

 

[nuke]

What speedometer did you get?
I'm searching to change the original one and still in doubt.