Things You'll Need:
- Bicycle tire air pressure gauge Air pump Tape measure
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Step 1
Use a bicycle tire air pressure gauge to make sure the tires are completely inflated.
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Step 2
Give the tires a bit more air with an air pump or let some air out, if necessary. Overinflated or under-inflated tires will give an inaccurate reading.
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Step 3
Prop the bike up against a wall or other supportive surface so that it is standing up straight on both wheels.
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Step 4
Measure the diameter of the bike tire with a tape measure. Starting at the center of the base of the tire, measure the tire from the ground up in a vertical line. Measure the tire from the spot where the rubber touches the ground to the tread on top of the tire. The resulting number is the tire size.










