30-10-2012, 22:05 #1 Join Date: Apr 2012 Posts: 4,200 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
 30-10-2012, 22:06 #2 Raam Registered User     Join Date: Sep 2003 Posts: 14,107 It's twice the radius, BOOM!
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30-10-2012, 22:09   #3

Join Date: Apr 2012
Posts: 4,200
Quote:
 Originally Posted by Raam It's twice the radius, BOOM!
Cheers but how can I work it out accurately

 30-10-2012, 22:33 #4 Needalift Registered User   Join Date: Mar 2009 Posts: 6 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
30-10-2012, 22:35   #5
Raam
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Join Date: Sep 2003
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Quote:
 Originally Posted by Needalift 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?

30-10-2012, 22:37   #6
Eamonnator
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Quote:
 Originally Posted by A_Sober_Paddy 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.

 30-10-2012, 22:37 #7 Raam Registered User     Join Date: Sep 2003 Posts: 14,107 Maybe this will help... http://sheldonbrown.com/rim-sizing.html
 30-10-2012, 22:40 #8 Beasty Put that light out!     Join Date: May 2009 Posts: 43,662 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
 31-10-2012, 00:54 #9 boege Registered User     Join Date: Jan 2010 Posts: 462 Am I missing something here! Diameter of 700x23 wheel...... Anyway help at hand http://sheldonbrown.com/rim-sizing.html
 31-10-2012, 10:11 #10 doozerie Registered User   Join Date: Apr 2005 Posts: 4,798 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

Join Date: Apr 2012
Posts: 4,200
Quote:
 Originally Posted by doozerie 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

31-10-2012, 13:34   #12

Join Date: Dec 2008
Posts: 19,999
Quote:
 Originally Posted by Eamonnator 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

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31-10-2012, 13:55   #13
Flandria
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Quote:
 Originally Posted by Jawgap Actually you need to divide by 3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067982148086513282306647 or thereabouts
Or just multiply by 22 and divide by 7