What is the proper way to measure the diameter of a bicycle tire?

Question

I bought a speedometer for bike tire and I have to program the size. It wants an exact number. I dont know if its 26 inches or 26.5 inches because I dont know where to measure from. Is it just the rim? Is the rubber included?

Answer 1

Tag1 ^^^ IS AN IDIOT lol, no need for new tires, take out a meter stick or something that you can accurately measure with and measure frm end to end. round to the nearest tenth and thats the size you should place.

it actually depends on where the speedometer is placed, if its placed by the rubber tire, then get the whole size of the wheel with the tire,

if its placed by the rim, insert the rim size

Answer 2

i have never heard of a spedometer that uses the tire. it should say on the tire the size rim it fits in but i dont know about the diameter. if worst comes to worst you can measure it your self. the only spedometers ive ever seen attach to the forks and react to a thing you clip on the spoke to tell you your speed

Answer 3

Stand the bicycle upright on a hard, flat surface, mark any point on the wall of the tyre with a fine chalk mark, turn the wheel so that the mark is exactly at the bottom of the wheel and mark the path or road surface precisely in line with the mark on the tyre, wheel the bicycle in a straight line until the chalk mark on the tyre has completed one revolution and is once more adjacent to the road surface, again, mark the road or path surface with the chalk, measure between the two chalk marks on the ground and this will give you the exact diameter of the wheel plus tyre, if you can get some help, sit on the bicycle with the tyres at the pressure you will normally use, and get a supported push in a straight line, marking as above, this gives the most precise measurement because it measures the circumference of the tyre under load.

Answer 4

Just look on the side of the tire. If it's so worn that you can't read the measurements, then it's time for new tires anyway. Visit the bike shop in that case...

Answer 5

Most bike speedometers will need the distance a tire will travel for one revolution. You can find this value several ways,

1) measure the circumference.(wheel height in mm x 3.14)

2) take the bike or wheel place a make on the ground, roll the tire one revolution and measure the distance.

3) most instruction manual have a reference chart going by tire size.

Method two is the most accurate to use, a note to remember most speedometers want the value in mm.

Answer 6

The speedometer needs to know the dimensions of the wheel plus tire combination. What matters is the actual circumference of the tire as mounted and properly inflated. I find it odd your computer is asking for diameter, but if it is, measure directly across the hub to the two outermost (diametrically opposed) points on the rubber tire - not just the rim.

Answer 7

The computer needs the proper tire info; it can't accurately measure speed based on rim diameter alone.  Tires that vary in width, even though they will fit on the same rim, will also vary in actual diameter.

I would think that your computer would have come with a chart describing the different codes that you enter for various tire sizes.  Have you read through the instructions?  If you don't have such a chart, perhaps you can supply the dimensions given on your tire as well as the brand/model of your computer.  Someone should then be able to assist.