# Bicycle Mechanics - What is 700cc a measurement of in a wheel set?

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teachme
10-30-12, 01:50 PM
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

LarDasse74
10-30-12, 02:09 PM
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 :D

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)

TampaRaleigh
10-30-12, 02:10 PM
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.

Andrew R Stewart
10-30-12, 02:11 PM
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.

Doohickie
10-30-12, 02:30 PM
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.)

Doohickie
10-30-12, 02:32 PM
700A, B, and D are obsolete.

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.

LarDasse74
10-30-12, 02:41 PM
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????

teachme
10-30-12, 02:48 PM
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. ??

teachme
10-30-12, 02:52 PM
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 :D

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)

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?

LarDasse74
10-30-12, 02:53 PM
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).

LarDasse74
10-30-12, 02:54 PM
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.

teachme
10-30-12, 02:59 PM
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?

Rootman
10-30-12, 03:17 PM
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

jim hughes
10-30-12, 03:19 PM
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.

Flying Merkel
10-30-12, 03:20 PM
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

Doohickie
10-30-12, 03:20 PM
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.

LarDasse74
10-30-12, 03:22 PM
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.

fietsbob
10-30-12, 03:41 PM
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..

JohnDThompson
10-30-12, 04:10 PM
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 (http://www.etrto.org/page.asp?id=1594) designation

wheelreason
10-30-12, 04:48 PM
I see... The 700 is just a label representing one unit of approx. pi. ??

Step away from the students,....SECURITY!....I'm ordering a Mandarin Rosetta Stone immediately...

ThermionicScott
10-30-12, 05:18 PM
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. :thumb:

FastJake
10-30-12, 05:45 PM
I see... The 700 is just a label representing one unit of approx. pi. ??

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...

10-30-12, 07:15 PM
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.

10-30-12, 08:37 PM
I'm still wondering what "one unit of (approximately) pi" is...

I think it is one slice (approximately).
mmmmm, pi.

teachme
10-30-12, 08:58 PM
I'm still wondering what "one unit of (approximately) pi" is...

When a circle's diameter (http://www.bikeforums.net/wiki/Diameter) is 1 unit, its circumference is pi units.

10-30-12, 09:14 PM
The 700 represents the diameter of the wheel and tire. I think it needs a 32 to 35 mm tire to get the size. Now the designation for the rim and the tire is 622mm (the bead seat diameter) and the width of the tire, usually in milimeters. It is confusing because the manufacturers don't educate the public about their products.

Lexi01
10-30-12, 09:29 PM
Divide 2135 by 700. What do you get?

3.05

teachme
10-30-12, 09:40 PM
3.05

3.05 is appoximate pi...

Jeff Wills
10-30-12, 10:33 PM
The 700 represents the diameter of the wheel and tire. I think it needs a 32 to 35 mm tire to get the size. Now the designation for the rim and the tire is 622mm (the bead seat diameter) and the width of the tire, usually in milimeters. It is confusing because the manufacturers don't educate the public about their products.

For that, we had the late guru, Sheldon Brown: http://sheldonbrown.com/tire-sizing.html
This page not only explains the "700C" designation, but also why there are 6 incompatible "twenty-six inch" bicycle tires.

Bert from Texas: it would be far easier if different tire sizes had different names, like "Shelley" or "Melvin". Then we wouldn't waste time in explaining that tire "sizes" really are meaningless. The conversation at the bike shop would go something like this:

"I need a tire for my bike."
"What size is it?"
"I don't know. All it says is 'Melvin' on the side."
"Here you go..."

RubberLegs
10-31-12, 07:59 AM
I thought in Nederland tires came in three sizes, BIG, BigA\$\$, and BIG-BadA\$\$! You will have to excuse me, I went to High School in Bridge City (for those unversed in TX Geography, it's right across the river...RIVALS!!!) :-)
Tire sizing has confused me for AGES!!! Too many standards, and BEWARE Schwinn Sizing!!!

Ex Pres
10-31-12, 08:06 AM
3.05 is appoximate pi...

No, cobbler is approximate......mmm, cobbler - with ice cream

teachme
10-31-12, 01:05 PM
I thought in Nederland tires came in three sizes, BIG, BigA\$\$, and BIG-BadA\$\$! You will have to excuse me, I went to High School in Bridge City (for those unversed in TX Geography, it's right across the river...RIVALS!!!) :-)
Tire sizing has confused me for AGES!!! Too many standards, and BEWARE Schwinn Sizing!!!
:thumb:

RubberLegs
10-31-12, 01:17 PM
Got my first OK road bike there in Bridge City, a Takara (bottom end, chrome rims, Suntour running gear, cottered cranks) back in 78. The little shop I got it from closed not long after as Walmart moved into town! :-(

Batavus
10-31-12, 03:36 PM
Being from Nederland as well (the country), I can tell you that 700B is still widely used around here. All the 'omafietsen' use the ETRTO size 40-635, also known as 28 x 1 1/2.