Tire Size and Air Volume

 

Wheel Tire Volume Increase over 700x23C Example Tires
700C 23mm 3.5 L 0% The old standard
700C 19mm 2.4 L -33% Oh, dear!
700C 21mm 2.9 L -17% Eek!
700C 26mm 4.5 L 29% Grand Bois Cerf Blue (222g, 184g), Compass Cayuse Pass (248g)
700C 27mm 4.9 L 39% Challenge Parigi-Roubaix (285g)
700C 28mm 5.3 L 50% Compass Chinook Pass (229g)
700C 30mm 6.1 L 74% Challenge Strada Bianca (355g)
700C 32mm 6.9 L 99% Compass Stampede Pass (291g, 254g)
700C 33.333mm 7.6 L 117% Jack Brown (435g, 295g)
700C 35mm 8.4 L 140% Compass Bon Jon Pass (355g, 303g)
700C 38mm 10 L 185% Compass Barlow Pass (390g, 359g), Soma C Line (400g)
700C 42mm 12.3 L 252% Soma Supple Vitesse (380g, 340g)
700C 44mm 13.6 L 289% Compass Snoqualmie Pass (378g, 329g)
700C 50mm 17.8 L 411% Schwalbe Marathon (1.0T)
700C 55mm 21.9 L 527% Schwalbe Marathon (1.125T)
650B 32mm 6.6 L 88% Hutchinson Confriere (320g), Grand Bois Cypress (285g, 261g)
650B 38mm 9.4 L 170% Compass Loup Loup Pass (354g, 333g), Panaracer Pari Moto (340g, 300g)
650B 42mm 11.6 L 233% Compass Baby Shoe Pass (390g, 362g), Grand Bois Hetre (412g)
650B 48mm 15.5 L 343% Compass Switchback Pass (478g, 413g)
26″ 32mm 6.3 L 81% Compass Elk Pass (178g)
26″ 38mm 9.1 L 159% Compass McClure Pass (366g)
26″ 44mm 12.4 L 254% Compass Naches Pass (350g, 300g), Compass Slumgullion Pass (447g)
26″ 50mm 16.3 L 366% Schwalbe Big Ben (1.5T)
26″ 54mm 19.2 L 450% Compass Rat Trap Pass (454g, 418g)
26″ 55mm 20.0 L 473% Schwalbe Big Ben (2.0T)

Air volume was calculated in MS Excel with the following formula (this example is for 650B/584ISO with 38mm tires):

=2*PI()^2*(584/2+38)*38^2
This will give results in cubic millimeters. Volumes above have been convert to liters (dividing by 1 million), rounded to the nearest tenth.

Some variances may be introduced from rounding, unit conversions, and other factors.

This is all white coat, clean room, armchair nerdery stuff only. Real life measurements of tires can vary based on many factors including miles, rims, tubes, production batch, etc.

Tire weights are manufacturer published weights, except for Schwalbe which were 100% fabricated for my own amusement.

Sources:

https://en.wikipedia.org/wiki/Torus

http://www.metric-conversions.org/volume/cubic-millimeters-to-liters.htm

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3 thoughts on “Tire Size and Air Volume

  1. I could be wrong, but as I understand in your example 38 is the “small” diameter not the radius. I think your formula should be: 2*PI()^2*(584/2+38/2)*(38/2)^2. Maybe I’m missing something…

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  2. Ernesto, good question.
    First, I should point out that this calculation uses tire width as a proxy for tire height. In the real world, this isn’t a perfect assumption.
    The calculation is based on the radius (of the rim + tire; which is 1/2 * bead seat diameter + 1 * the tire width) and the tire width.
    Another way to think about is that the (584/2+38/2) is fundamentally incorrect because the tire is on the outside of the rim, so if you were to calculate the diameter, you would add the tire width twice (since the a bike at rest will have tire at the top of the rim; e.g. under a fender…and tire between the rim and terra firma). This can also applied to the disprove the *(38/2)^2 portion of the formulae because the tire height is the full height of the tire; not half of it.
    I hope this helps!

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