Right now for school I’m drawling a bike on AutoCad for a project. I’m attempting to do a Cervelo P3 w/ Zipp 909 set and Hed bars. But right now, does anyone know either the circumference or radius of 700cc wheels in metric units?
The bead diameter of a 700c wheel is 622 mm. Add approximately 25 mm in height for the tire, all the way around, so total diameter will be 672 mm.
If you want 650c, the bead diameter is 571 mm.
Cheers
J
It will depend on the tire, but the approximate diameter of a 700c tire is, appropraietly enough, 700 millimeters. For an 18 mm tire it will be less, for a 35 mm tire it will be more.
You are incorrect. the diameter of a 700c wheel and tire combo used to be 700mm, back in the days of Fausto Coppi. Tires have gotten smaller since then, now 700c is nothing more than a designation.
A full history of tire nomenclature is available on Sheldon Brown’s website.
I don’t see where Sheldon’s articles contradict anything I said. I said the 700 mm tire diameter is approximate. Without knowing the tire that the original poster wants to “draw” one cannot get very specific.
A 700 x 35c tire (if it is a true 35mm tire, many are not) will have a total diameter just shy of 700mm, depending on the profile of the tire etc.
A drawing of a P3 should not have a 35mm tire on it, do you agree? For the sake of accuracy, best to use the actual bead diameter, assume a 20-23 mm tire, plus add a bit for the rim depth, hence total diameter of 622+2(25) = 672mm, ie 28mm less than 700mm. You wouldn’t set your cyclocomputer by a circumference that is 88mm off, would you? If this guy wants to be an engineer later in life, I hope accuracy takes precedence over approximation. If not, let me know what bridges he designs.
I am an engineer and I know I wouldn’t be carrying my recommendations out to 3 signifcant figures without knowing what tire he is using.
Maybe I’m missing something, but I don’t believe setting cyclocomputers has anything to do with this. If you have a cyclocomputer presumably you have a specific tire you are going to run on the bike that you can use for measurement.
Check out the site below. When you are finished with your AutoCAD drawing, you can compare it to what the BikeCAD drawing shows and see if there are any major differences.
672 mm diameter with the tire on sounds very close, but slightly large. I get accurate mileage with the wheel circumference set to 2094. 672 would yield a reading of 2111 by my calculation.
On the other hand, the tire compresses as you ride, so that effect probably lowers the effective circumference a bit for odometer purposes. For the purposes of a drawing, your 672 number is probably right on.
The difference you are talking about works out to about 2.5 mm difference in effective diameter, which can be explained by tire compression.
Hmmm…Wouldn’t a tape measure answer this question just as well?
Yeah, I wasn’t sure either if 700cc was an exact 700mm diameter. I know enough about bikes to take one apart and put one back together but once I started this project, I found out how little I really knew about them.
Thank you for the site John except I am drawling the bike in 3-D, not 2-D, so it is a lot more complicated than their drawlings. But I will definitely be referencing that quite often. For anyone who doesn’t know AutoCads 3-D mode, I’m pretty much generating a model of the bike on the computer that I can spin, rotate and look at from any angle I choose. I’ll post pictures when I finish the project but right now, the Fizik Airone saddle has become a challenge. Also, I do hope to be an Engineer later on in life… but I’m in 11th grade: plently of time to decide. =)
Good luck, 3D is tough. That extra dimension takes a heck of a lot of extra time.