The fact that you refer to them as 700CC and 650CC only serves to prove your ignorance.

It's 700c and 650c. That "c" is not for centimeters either. It's designation used to indicate the width of the rim opening as I recall.

"The fact that you refer to them as 700CC and 650CC only serves to prove your ignorance."

C'mon, lighten up on the guy. That's getting really picky and personal. Most likely that's just a typo error.

No typo there. It's in his original post and every other post of his that I looked at, even after those who referred to them correctly.

If you are going to argue points over wheel sizes, you better have enough knowledge to call them the right thing. If he doesn't even know what the name of thing is, how can I put any validity behind his arguments?

What I know of the guy comes only from his posts. That is an unfortunate part of this medium. As a result, being able to express yourself and your ideas properly in writing is critical to the way you are perceived. My perception of him, based on his use of the "CC" instead of the proper terminology, is negative. This combined with his obvious lack of facts, is what makes me say what I did.

Craig

If you are interested, Sheldon Brown, keeper of all extraneous information bicycle, has a section on the size of wheels and where all those numbers come from.

Interestingly enough the diameter of a 650c rim compared to a 700c rim is 51mm. Can we have someone who is good with numbers determine the rotational inertia of a wheel of diameter 622 and 571?

http://www.sheldonbrown.com/tire_sizing.html

Craig

Actually, I never referred to them as 650CC or 700CC. I used a quote from another post that was written that way.

If you really want to get picky, I believe it is a capitol C not a lower case c.

jaretj

Mea culpa.

Shall we continue the pissing contest or cease and desist?

craigwsullivan,
The Cannondale 700c bike is not the only 700c bike I've tried to make work. It happened to be the last one. If you understood frame geometry you would know that it is much more than just the seat tube angle. 650c wheels on a 650c frame will enable the bike to have a shorter head tube, shorter top tube and shorter fork. This makes the difference between the seat and the arm pads greater. Thus, a lower position. It can't be done on a 700c tri-bike with my short inseam. Tried it. Ain't gonna happen. Just can't get low enough. It's the wheel size that make the difference for shorter folks. So don't tell me it's just because of ROAD geometry. Look, I usually have the top 1st, 2nd, or 3rd bike split in the very competitive 35-39 AG in every race I compete in. I speak from experience and success. It's the overall fit that makes the difference. And the 650c size fits me best. Nuff said.

Thanks, I was flattered.

I have been planning to do some testing on this subject when work slows down. Christmas time is generally slow. I will keep you posted, even if it turns out that I'm totally wrong.

These were the ideas I was going to test.
1. How much power does it take to turn each wheel unloaded and without a headwind.
2. Same test but with a couple of different headwinds and at different angles.

Problems to overcome. I need a 650C and 700C wheel of the same brand or construction. It would be difficult to claim one is better than the other if I'm testing 700C ksyriums to my 23mm 650C's

Any other suggestions are welcome.

I don't expect to find much of a difference between them since I can only measure accuractly down to about .5 inlb.

One thing that 700C wheels do have going for them is that they have more contact with the road and would probably have better traction on the turns which would be very important to a lot of people.

jaretj

If one neglects the fact that a wheel has a hub and spokes, then one will be happy to learn that the moment of inertia of a ring goes with r^2 (I=mr^2). So going from a radius of 285.5 to 311 increases the radial component of I by 15211 mm^2. The increase corresponds to 18.6% ... of course, one has to consider differences in mass (rim and tire), but these are linear.

In a previous post, I suggested using a 300g tire on 650c wheels and a 250g tire on 700c wheel. The difference is 20%, pretty close to 18.66% ...

Dre'

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It seems we are in violent agreement. You are lower and faster on your bike because the 650c wheels make all the stuff you said possible. Not because 650c wheels are inherently faster than 700c wheels.

Congratulations on your palmares.

NO ... both wheel size offer *the same* contact with the road. The contact patch has to do with tire inflation, not radius. The 650c wheel has a greater proportion of its circumference being "flattened" which would lead me to believe that it also offers greater rolling resistance.

Dre'

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OK, well I had to know for sure about the contact patch thing.

650C bike, 78 deg seat tube, 135lb kid sitting with hands on cowhorns, Alex 300 tri wheels, michelin pro race 650X23, 120 psig in both tires
front 2 3/4 inches of tire touching ground
rear 3 1/4 inches of tire touching ground

700C bike, 76 deg seat tube, 135lb kid sitting with hands on hoods, Mavic Ksyriums, michelin axial pro 700X23, 120 psig in both tires
front 2 3/4 inches of tire touching ground
rear 3 7/8 inches of tire touching ground

I wish I had the same wheels and tires on both bikes to make a better comparison.
Please someone else do this to check over my results.

jaretj

If you're telling me both tires are the same width and pressure, the total area of flattened tire *must* be the same on both bikes. There should be a total of 1 1/8 sq. inch of contact with the ground (135 lbs on 120 psi, I'm neglecting sidewall flex acting as a force against flattening). I can tell you right away that you'll measure the 650c to be faster if you don't fix this little problem ...

Dre'

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I don't understand what your saying.
How did you come up with 1 1/8 sq. inch of contact?
Is that from the 135lb load?
What do you mean by I'll measure the 650C to be faster if I don't fix this little problem?
Intuition would tell me that there is less rubber front to back touching the ground on the 650C because the radius is smaller which makes the curve tighter. But if the pressures and widths are the same for both tires, they should push on the ground equally for both bikes provided the bikes are similar in mass. Which means that the 650C would be deflected more. Maybe the sidewalls of the 650C's are stiffer and they are holding some of the load. OK, I got that, answered my first question. Help me with the meaning of the second

jaretj

indeed the mavic cars DO NOT carry 650 wheels...
I do not have two years of experience with this in conjunction with mavic usa...but many more years racing in France with Mavic France...
they do not get 650 wheels period.
if you want one, it will be on your team director's team....

OK, since I understand close to nothing of this last post of yours, I'll randomly answer questions as I read them ... ;)

135 pounds of rider ... you have air at a pressure of 120 pounds per square inch, so you'll flatten the tires to an area of (135/120=1.125) square inch ... just make the units work ... dimensional analysis ...

With your current data, I can tell that there is *way* more tire flex on your 700c setup: the 650c wheeled bike will measure faster. No need to run an experiment with these data. the "problem" is the issue of different "areas" measured for both bikes, with the same load and same tire pressure. I'm assuming that both bikes are the same mass, within experimental error.

The radius has nothing to do with how much rubber is touching: tire *pressure* tells you how much rubber lays flat on the ground.

The tighter curvature of the 650c wheels tells you that, given equal load and pressure, a larger fraction of the circumference will be flattened when compared to a larger wheel. Nothing else.

Yes, if the sidewalls are very stiff, they "hold" some of the load: this is the principle behind "run flat" car tires (not quite, but the idea is the same). This is why you need to compare *same* tires, mounted on the *same* rim (rim width affects the tire profile, thus the contact patch).

Oh oh ... dinner's ready.

Dre'

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now that I remember...

Jeannie Longo does many TT in Tx, NM every year (usually before the worlds...even though we didn't see her this year).
she rides with 650 wheels. I guess with 4 gizillion
world titles she qualifies as a pro cyclist...

Are you sure about that Francois? I thought Longo rides an old white 700c Hooker with the logos peeled off?

she also has a white bike (maybe a hooker, not sure, no logo) and the wheels were definitely 650c.
unless mine were 750c and I didn't realize :-)

This is another debate over an old subject. Science has already examined this.

Facts:

1- 700 wheels have higher inertia than 650 wheels. So in theory they will be harder to accelerate. (see bottom note for discussion)

2- All other things beign equal, 650 wheels will have a higher rolling resistance (due to larger curvature - as discussed bu others)

3- 650 wheels will have less aerodynamic drag (because of a smaller frontal area - please do note that although 650 wheels will rotate faster than a 700 wheel for the same speed, the tangential velocity (the one that counts for drag) is the same for both wheel size, that is twice the bike velocity at 12 o-clock)

4- 650 wheels will have higher mechanical resistance because of higher rotational speed

However:

1-difference in inertia is something that translates in fractions of seconds over one hour, and only if you spend a significant amount of time accelerating and decelerating over your one hour ride.

2-this is also a very small difference, much smaller than the difference between two different tires. Again we are talking fractions of seconds over hour. Much much more important is riding high-pressure tires or matching tire and rim width

3-the advantage of 650 wheel in terms of drag is offset by having a longer headtube to achieve identical position (obviously, in you are small or ride in an extremely agressive manner that is impossible to achieve with 700 wheels, you will be faster with 650 wheels, but this has nothing to do with the wheels but with position).

4-insignificant for well maintained hubs

It's my educated opinion that it would be impossible to set-up an experiment to show which wheel size is faster or slower. Differences would be much much smaller than experimental imprecisions.

Francois in Montreal

Mr. Plummer, scientific references do exist on the claims made above. I would be very happy to provide them to you if you are willing to financially compensate my time for the two hours it would take me to gather everything. Starting debates with unsupported claims is not helpful to anyone.

"But until someone out there can provide me with the data supporting that 700c wheels ARE NOT faster than 650c, don't just through out argumentive questions and statements."

http://www.cbss.ca/tip11.htm