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  1. #1
    Senior Member teachme's Avatar
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    What is 700cc a measurement of in a wheel set?

    I teach 5th grade math and we did an activity on the circumference of a circle using the front wheel off my Specialized Sectuer as a manipulative. We measured the circumferance of the tire on the wheel and it measured out to be approximately 84 inches which converts to approximately 213.5cm. So, what does the 700cc stand for?

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    THe wheel size is '700C' not cc... cc is a unit of volume: cubic centimeter. (edit 1) Hopefully you already know that, being a math teacher

    700C today refers to a rim with a bead seat diameter (BSD) of 622mm. Many years ago there were 700A, 700B, 700C and 700D wheels. Each had a different size rim and tire set that resulted in a nominal diameter of 700mm. Modern 700C wheels are used with tires from 18mm (super narrow racing tires) to ~75mm wide (wide '29er' mtb tires which also use 700C rims) so there is great variation in the diameter. But the rim size remains the same.

    (edit 2) 700A, B, and D are obsolete. GT made a few hybrid/cruiser bikes a while back with 700D wheels, and if you have one of those today and the tires wear out you basically need to buy a new bike. Other wheel sizes that used a similar system are 650B (medium width tires used on old dirt path and 'camping bikes, I think, as well as many modern mtbs) and 650C (small racing wheels used for an aerodynamic advantage in time trials and triathlons)

    (edit 3) Read this: http://sheldonbrown.com/tire-sizing.html
    Last edited by LarDasse74; 10-30-12 at 01:15 PM.

  3. #3
    Senior Member TampaRaleigh's Avatar
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    700 mm is the (approximate) outer diameter of the rim WITH a tire mounted. The "c" was an old designation for a tire/rim type. There WERE "700a", "700b", etc... but those are long gone.

    (It's 700c, not 700cc)

    LarDasse beat me to it, and his explanation is much better.

  4. #4
    Andrew R Stewart Andrew R Stewart's Avatar
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    Think of tire "sizes" as labels. It's kind of like clothing sizes. The labeled size is kind of but not really the measured size. Andy.

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    You gonna eat that? Doohickie's Avatar
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    Quote Originally Posted by teachme View Post
    I teach 5th grade math and we did an activity on the circumference of a circle using the front wheel off my Specialized Sectuer as a manipulative. We measured the circumferance of the tire on the wheel and it measured out to be approximately 84 inches which converts to approximately 213.5cm. So, what does the 700cc stand for?

    Thanks,
    Bert
    Divide 2135 by 700. What do you get? (It's off a bit, but it should be pi; 700 refers to the nominal tire diameter at the tread. Kind of. Tire sizes are very weird.)
    I stop for people / whose right of way I honor / but not for no one.



    Originally Posted by bragi "However, it's never a good idea to overgeneralize."

  6. #6
    You gonna eat that? Doohickie's Avatar
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    Quote Originally Posted by LarDasse74 View Post
    700A, B, and D are obsolete.
    Quote Originally Posted by TampaRaleigh View Post
    There WERE "700a", "700b", etc... but those are long gone.
    Not quite. 700B is still used on rod-brake roadsters such as Flying Pigeons. They certainly are not common anymore.
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    Originally Posted by bragi "However, it's never a good idea to overgeneralize."

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    Quote Originally Posted by Doohickie View Post
    Divide 2135 by 700. What do you get? (It's off a bit, but it should be pi; 700 refers to the nominal tire diameter at the tread. Kind of. Tire sizes are very weird.)
    Good thought! By doing this we can see the actual diameter of the OPs wheel is ~680 mm, which, if we assume the tires have a round cross-section with the bottom approxiately at the bead seat, we know the OP has tires that are (680-622)/2 = ~29 mm... Do you, by chance have 700 X 28C tires on your bike, sir????

  8. #8
    Senior Member teachme's Avatar
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    Quote Originally Posted by Doohickie View Post
    Divide 2135 by 700. What do you get? (It's off a bit, but it should be pi; 700 refers to the nominal tire diameter at the tread. Kind of. Tire sizes are very weird.)
    I see... The 700 is just a label representing one unit of approx. pi. ??
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  9. #9
    Senior Member teachme's Avatar
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    Quote Originally Posted by LarDasse74 View Post
    THe wheel size is '700C' not cc... cc is a unit of volume: cubic centimeter. (edit 1) Hopefully you already know that, being a math teacher
    Quote Originally Posted by LarDasse74 View Post
    700C today refers to a rim with a bead seat diameter (BSD) of 622mm. Many years ago there were 700A, 700B, 700C and 700D wheels. Each had a different size rim and tire set that resulted in a nominal diameter of 700mm. Modern 700C wheels are used with tires from 18mm (super narrow racing tires) to ~75mm wide (wide '29er' mtb tires which also use 700C rims) so there is great variation in the diameter. But the rim size remains the same.

    (edit 2) 700A, B, and D are obsolete. GT made a few hybrid/cruiser bikes a while back with 700D wheels, and if you have one of those today and the tires wear out you basically need to buy a new bike. Other wheel sizes that used a similar system are 650B (medium width tires used on old dirt path and 'camping bikes, I think, as well as many modern mtbs) and 650C (small racing wheels used for an aerodynamic advantage in time trials and triathlons)

    (edit 3) Read this: http://sheldonbrown.com/tire-sizing.html
    Yeah, I didn't mean to typ cc, but was confused if the "c" meant centimeter. So the "c" is a label not a unit of measure?
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  10. #10
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    Quote Originally Posted by teachme View Post
    I see... The 700 is just a label representing one unit of approx. pi. ??
    Not sure what you mean.

    700mm is the nominal diameter of the wheel with a medium width tire (~35 mm).

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    Yeah, I didn't mean to typ cc, but was confused if the "c" meant centimeter. So the "c" is a label not a unit of measure?
    Correct. 'C' is just the name. 700 cm is ~23 feet.

  12. #12
    Senior Member teachme's Avatar
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    Quote Originally Posted by LarDasse74 View Post
    Not sure what you mean.

    700mm is the nominal diameter of the wheel with a medium width tire (~35 mm).
    Is that where the 700 comes from? The measure of diameter in millimeters?
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    Quote Originally Posted by teachme View Post
    Is that where the 700 comes from? The measure of diameter in millimeters?
    Yes, millimeters, the C is just a designator of the rim width, as already pointed out there used to other widths named A, B, and D with A being narrowest and D the widest, C was the most commonly used so they just went with C's as the standard 700 mm rim, discontinuing the others for the most part. They are also called 29 inch rims : https://en.wikipedia.org/wiki/29er_%28bicycle%29

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    I might be wrong from a historical perspective, but I don't think the number 700 has any specific meaning today -700c just identifies a standard.

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    Senior Member Flying Merkel's Avatar
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    Quote Originally Posted by Andrew R Stewart View Post
    Think of tire "sizes" as labels. It's kind of like clothing sizes. The labeled size is kind of but not really the measured size. Andy.

    I have had 4 bikes with 26" inch rims that were all different diameters. Like to drive me shugbit
    Pronounced "Murkle"

  16. #16
    You gonna eat that? Doohickie's Avatar
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    Using bicycle tires to try to show how things are measured is kind of like wading into the deep end. There is a lot to bicycle tire sizing that is not really obvious.
    I stop for people / whose right of way I honor / but not for no one.



    Originally Posted by bragi "However, it's never a good idea to overgeneralize."

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    Quote Originally Posted by Rootman View Post
    Yes, millimeters, the C is just a designator of the rim width, as already pointed out there used to other widths named A, B, and D with A being narrowest and D the widest, C was the most commonly used so they just went with C's as the standard 700 mm rim, discontinuing the others for the most part. They are also called 29 inch rims : https://en.wikipedia.org/wiki/29er_%28bicycle%29
    Actually, it is the diameters of A, B, C, and D rims are all different, not necessarily the widths. The different sizes were meant for use with tires that were different widths (and also heights) so that each size would result in a wheel diameter of approximately 700 mm.

  18. #18
    coprolite fietsbob's Avatar
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    cc is a measure of Volume not length. Cubic Centimeters.

    [Don't they consider the metric system, subversive, in Texas?]

    The numbers that count are a agreement between Tire/tyre and Rim Manufacturers.
    They use a tire-bead seat diameter.. for 700C it's 622mm.
    so look at tire sidewalls 622-32 is size & width.. Metric .

    nearest fractional size 27 x 1.25" is (approximate), a 630-32.. not same..
    The ETRO numbers are on the sidewall ..

    circumference changes with tire width. of course..
    Last edited by fietsbob; 10-30-12 at 02:49 PM.

  19. #19
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by Andrew R Stewart View Post
    Think of tire "sizes" as labels. It's kind of like clothing sizes. The labeled size is kind of but not really the measured size. Andy.
    ^^^^^
    This.

    If you want the "real" size, look for the ETRTO designation

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    Quote Originally Posted by teachme View Post
    I see... The 700 is just a label representing one unit of approx. pi. ??
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    7-speed doomsday prepper ThermionicScott's Avatar
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    Quote Originally Posted by jim hughes View Post
    I might be wrong from a historical perspective, but I don't think the number 700 has any specific meaning today -700c just identifies a standard.
    Well, if you mount up some 39mm tires it will mean something.
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    Constant tinkerer FastJake's Avatar
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    Quote Originally Posted by teachme View Post
    I see... The 700 is just a label representing one unit of approx. pi. ??
    Quote Originally Posted by wheelreason View Post
    Step away from the students,....SECURITY!....I'm ordering a Mandarin Rosetta Stone immediately...
    I'm still wondering what "one unit of (approximately) pi" is...
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  23. #23
    I let the dogs out AlphaDogg's Avatar
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    Quote Originally Posted by FastJake View Post
    I'm still wondering what "one unit of (approximately) pi" is...
    I think he meant like in a unit circle... But in the case of a 700c wheel, instead of the unit being 1, the unit is 700.
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    Quote Originally Posted by FastJake View Post
    I'm still wondering what "one unit of (approximately) pi" is...
    I think it is one slice (approximately).
    mmmmm, pi.

  25. #25
    Senior Member teachme's Avatar
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    Quote Originally Posted by FastJake View Post
    I'm still wondering what "one unit of (approximately) pi" is...
    When a circle's diameter is 1 unit, its circumference is pi units.
    Last edited by teachme; 10-30-12 at 08:04 PM.
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