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30-10-2012, 22:05   #1
 
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Wheel Diameter

Hey all

Just wonder if anyone could tell me the best way to calculate the diameter of my bike wheel...

Its a standard road wheel, with 700x23c tires...

Cheers in advance
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30-10-2012, 22:06   #2
Raam
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It's twice the radius, BOOM!
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30-10-2012, 22:09   #3
 
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It's twice the radius, BOOM!
Cheers but how can I work it out accurately
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30-10-2012, 22:33   #4
Needalift
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stand your bike up with the valve directly over the ground. mark the ground with some chalk. walk the bike forward until the wheel has completed one revolution and the valve is directly over the ground again. mark with chalk. measure distance between chalk marks for the diameter of your wheel. repeat a couple more times and take the average. ta dah
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30-10-2012, 22:35   #5
Raam
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stand your bike up with the valve directly over the ground. mark the ground with some chalk. walk the bike forward until the wheel has completed one revolution and the valve is directly over the ground again. mark with chalk. measure distance between chalk marks for the diameter of your wheel. repeat a couple more times and take the average. ta dah
That's the circumference.

What you need it for? A bike computer?
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30-10-2012, 22:37   #6
Eamonnator
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Originally Posted by A_Sober_Paddy View Post
Hey all

Just wonder if anyone could tell me the best way to calculate the diameter of my bike wheel...

Its a standard road wheel, with 700x23c tires...

Cheers in advance
Not trying to second guess you, but is it not the circumference of the wheel that you want?. If so the circumference of a wheel with a 700 X 23 tyre is about 2096mm. If it is the diameter you want divide by 3.14159.
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30-10-2012, 22:37   #7
Raam
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Maybe this will help...
http://sheldonbrown.com/rim-sizing.html
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30-10-2012, 22:40   #8
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So take the circumference, divide by pi (3.14159 .... ) to get the diameter

... alternatively take a tape measure and measure from the floor to the top of the inflated tyre

... or if you want the diameter excluding the tyre, do the same measure from one side of the rim to the opposite side
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31-10-2012, 00:54   #9
boege
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Am I missing something here!

Diameter of 700x23 wheel......

Anyway help at hand
http://sheldonbrown.com/rim-sizing.html
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31-10-2012, 10:11   #10
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If it is the circumference that you want to measure, then marking the ground, rolling the bike, and marking the ground again, as described above, is probably the simplest option. But if you want *real* accuracy then remember that when sitting on the bike your weight will compress the tyres a little so sit on the bike when rolling forward. Then bear in mind that your weight can fluctuate from one day to the next so repeat that measuring exercise every day, at around the same time each day, for a week or two, and average the results. Then, recall that you forgot to put a consistent pressure in the tyres before each test, so repeat the whole process but this time use a track pump with an accurate gauge to inflate the tyres to a consistent pressure before each measurement.

Eventually, consider the fact that your weight on the bike will also be affected by how much food and drink that you carry on any particular ride, the weather (heat = more sweating and evaporation of water = reducing weight; cold = more layers = added weight; wet = absorbing water = weight increasing during ride), elevation will affect air pressure in the tyres, etc.

Then have a good cry, or consider a nervous breakdown if you are truly devoted to the scientific method, and just select the default measurement that your bike speedometer suggests as being accurate enough.
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31-10-2012, 12:52   #11
 
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Originally Posted by doozerie View Post
If it is the circumference that you want to measure, then marking the ground, rolling the bike, and marking the ground again, as described above, is probably the simplest option. But if you want *real* accuracy then remember that when sitting on the bike your weight will compress the tyres a little so sit on the bike when rolling forward. Then bear in mind that your weight can fluctuate from one day to the next so repeat that measuring exercise every day, at around the same time each day, for a week or two, and average the results. Then, recall that you forgot to put a consistent pressure in the tyres before each test, so repeat the whole process but this time use a track pump with an accurate gauge to inflate the tyres to a consistent pressure before each measurement.

Eventually, consider the fact that your weight on the bike will also be affected by how much food and drink that you carry on any particular ride, the weather (heat = more sweating and evaporation of water = reducing weight; cold = more layers = added weight; wet = absorbing water = weight increasing during ride), elevation will affect air pressure in the tyres, etc.

Then have a good cry, or consider a nervous breakdown if you are truly devoted to the scientific method, and just select the default measurement that your bike speedometer suggests as being accurate enough.
I'm in need of the measurement as I'll soon be setting up my bike on a trainer...so body weight will have no effect, as the wheel will be locked in place and the only pressure on the tire will be from the motor/trainer/resistance band...

Think I got it sorted now, the measurement didn't need to be all that accurate as i first though
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31-10-2012, 13:34   #12
 
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Originally Posted by Eamonnator View Post
Not trying to second guess you, but is it not the circumference of the wheel that you want?. If so the circumference of a wheel with a 700 X 23 tyre is about 2096mm. If it is the diameter you want divide by 3.14159.
Actually you need to divide by 3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067982148086513282306647

or thereabouts
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31-10-2012, 13:55   #13
Flandria
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Actually you need to divide by 3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067982148086513282306647

or thereabouts
Or just multiply by 22 and divide by 7
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