Would be interested why you think think wheel weight matters so much, unless you are constantly reaccelerating (as in a crit, or out of hairpins climbing l'Alpe d'Huez).

As I said above, on a flat TT course, you accelerate exactly twice: at the start, and at the turn. A "heavy" wheel might cost you 1 second, twice. Even on a fairly normal, non-technical course, wheel weight in timetrialing is a pretty minimal consideration.

Aerodynamics are far, far more important. See also my comment above about the Saavedra (and it's an aero profile rim).

As for 35kph+, that really isn't that "fast" -- we're hardly talking about a niche group of riders at that speed. For example, even under awful (wet/windy) conditions, in our June 1 State TT race, over 80% of the 184 finishers (including all masters up to 70+, masters women, juniors, etc.) averaged better that 35kph over 40k at sea level. Under better conditions, probably 90%+ would have.

Thanks again, Kraig. I think your final sentence is the bottom line, eh? Interesting that rotation is a second order effect.

You mention possible widening the fork crown to free this up. The ad copy Oval uses for their new Jetstream fork claims benefits from a different approach -- it was actually the contention made in that copy that I cribbed for raising this sub-topic, as it struck me as interesting (if true). FWIW:

"The top of the wheel and fork area is the primary source of aerodynamic drag on the bike except for the rider. A. The spokes on top of the wheel are moving twice as fast as the bike. Wind hits the fast moving spokes creating turbulence (which means drag). That is a bad thing. B. The paired aero shapes of each jet stream fork leg create a vacuum effect, sucking the turbulent air from around the spokes, compressing it back into a laminar flow and accelerating out the back of the fork. It's optimized 3-to-1 aspect ratio minimizes the fork drag. These are good things. C. The laminar flow exiting the rear of the fork is directed about 15° outward from the spokes behind the fork, reducing the drag effect of these fast moving spokes. This is a good thing..."

I edited the final sentence of this, as it literally reads "This is a goof (sic) thing" on their site. :-)

My e-mail address is in my user profile -- would be interested in just your gut reactions to this approach (either here on this forum, or privately and off-the-record via e-mail).

I was generalizing, referring to the "average" triathlete doing the "average" race. The average triathlete doesn't ride the speeds you're talking about and very few triathlons I've done have flat bike courses. Your perspective, a time trial championship, is a little different. In that case I totally agree with you, aerodynamics is much more important. Again, I'm talking about an average triathlete doing an average triathlon, which means it has hills and speeds aren't that fast.

Fair enough -- I didn't mean that to come across as it perhaps did, BTW.

But even on a hilly Tri course, I think wheel weight (and the time cost of overcoming inertia in each reaccelaration) can easily be overstated. You aren't sprinting to react to moves or close gaps, nor are you constantly braking and then reaccelerating as you are in climbing hairpin turns. It's basically you vs. terrain and wind, over time.

Studies show, for example, that a rear disk in generally an advantage even most uphill course. And disks (even the cool new Zipp) sure ain't the lightest option, wheelwise. (I have about 12 front/rear race wheels of all types and descriotions; only very rarely does their relative weight factor in when making my choice come race day).

For fun: run some test runs on the "wind on rider" link at http://www.analyticcycling.com/DiffEqWindCourse_Page.html, choosing a course that is hilly. You'll see the estimated effects for yourself. You can even test this for various wattage outputs (AKA, ave speeds, all else being equal)...

Kraig, apparently your <sarcasm> quote marks weren't obvious enough to help him understand you weren't serious. Then again, some folks don't have a sense of humor in the first place and tend to take themslves a little too seriously.

I was in a hurry the other day at a rainy race, and put my front H3 on backwards...really easy to do. Still had a very nice bike split, but I imagine I didn't help myself by putting it on backwards! Check that possibility on your wheel. The other possibility to check is a difference in calibration of your computer/wheel circumferences between the two sets.

The weight thing might be a bit more complicated. There are some people that think the heavier systems are actually faster on TTs.

Also, when one speaks of acceleration, there isn't just two instances of acceleration (the start, and the turnaround) because you have to constantly accelerate against the forces that are working to slow you down (friction, and wind resistance-the big one!) or you would not even be maintaining your speed. If you aren't accelerating against these forces, you are slowing down, unless you are going downhill...then gravity is an acceleration force in the equation. I'm just saying that using the term "acceleration" is more complicated than describing the start and the turnaround.

FWIW, I'm always faster on H3's than on traditionally spoked wheels that I've ridden.

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)

I didn't think this thread would last a week, but there you go! Alas I think the answer laid in the most unscientific and least alarming thing- wheel circumference. I will have to check the 2 wheels and then program the computer accordingly.

FWIW- The weight issue is moot- I live on a very flat place- and no traffic lights, so basically never have to stop, turn etc... until it is time to head home. Also lighten up a little- we're talking about tire widths- it isn't the next U.N resolution. Humor on any forum is difficult to notice- give people the benefit of the doubt- cool. Now here are your rattles, go play nicely. :)

Weeman

As far as the humor goes...didn't one person actually say "Call me crazy..."? And that's all KW did, called him what he asked to be called! I thought it was funny. KW is unusual in that although he is very scientifically minded, he has a sense of humor, too.

Also, I ride 23mm's all the time because they're more resistant to snakebite flatting. I can tell you I've hit things during races that have bounced my entire bike up off of the road surface...and I was sure glad I had that extra amount of tire between the object(s) and the rim during those times.

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)

Hi again. Here, I'm speaking of "acceleration" as overcoming inertia (which is where wheel weight enters in -- especially weight away from the axis of rotation, e.g, at the rim).

By the def. you use above, essentially ALL force applied to rotate your cranks is "acceleration", even smoothly spinning a fixed gear while riding indoors on a track velodrome.

Also, remember that inertia has both negative AND positive components, as in "a body at rest tends to remain at rest; a body in motion tends to remain in motion".

There is a cool demonstration of this -- using iron wheels of different weights -- at the Children's Museum in Philadelphia. The lighter wheel is easy to start spinning with your hand, yet brakes very easily as well as it establishes little ongoing inertia. The heavy wheel, of course, has exactly the opposite characteristics.

Again, on most courses and under most conditions, aerodynamics easily trump weight.

(As I said, I have about 12 race wheels -- all of which I paid for myself, so I've no commercial interest in any side of this debate :-) -- and weight virtually never factors into the choice of which to use on a given course/given set of wind conditions).

Your comment about inertia got me thinking...I've never really considered whether or not a heavier wheel would feel more stable at high speeds...the gyroscopic effect would be greater, wouldn't it? So, as long as you weren't knocked off-line by wind or bumps, that heavy disc wheel might be a double advantage when screaming downhill at 40+mph...again, as long as the course were relatively straight. You might feel more at ease tucked into a smaller, narrower profile on aerobars with the gyroscopic effect of the heavier wheel helping you stay straight. Or, is this too little of a difference to actually feel?

Sorry to get off topic about tires...

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)

The "positive side" is really conserved energy (momentum) more than 'inertia' (my bad). But yes. And the gyroscopic effect effect adds stability -- you bet.

Kids: Mr. Science has a task for you. Find an old tire and the steepest hill you can, and (doing what we did as bored juvenile delinquents) take it to the top and kiss it goodbye.

Gyroscopic force makes it stable as all hell on any kind of surface, and momentum coupled with gravity is impressive as well. There's a gas station at the bottom of the longest hill in Plymouth, NH that can testify to this.

Luckily, no lasting harm done -- but trust me: when they say force = mass times velocity squared, they mean it :-).

PS: That's not Yaqui as in Yaqui del Norte, Republica Dominicana, by any chance, is it?

(Wish I were in the hut near Monabao right now, out on the porch under the stars, sipping some Brugal, listening to some live perrico ripiao from the coffee farmers down the hill -- QUE BUENO!)....

The story goes that it is Yaqui as in "Yaqui Pass". The top of a decent climb somewhere in California, and it refers to the Yaqui Indian tribe.

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)

Well it sure is linked historically -- and altitudewise -- anyway. FWIW: in the DR, that river flows down the >11,000 ft tall Pico Duarte. Columbus's crew trekked up it shortly after their first landing on the north coast (1493? 1494?), looking for -- and actually finding -- some gold. The upper reaches of it are as wild and pristine today as they were then -- complete with flocks of wild Caribbean parrots. Heaven on earth.

Little off-topic here I know, but just had to ask -- not a name you often hear...

> Timemachine wrote: I just think a lot of people get the impression from wind tunnel tests, that throwing a relatively heavy set of aero-wheels on their bike is going to make them a lot faster regardless of their speed or terrain they're riding. >

Personally I believe so.. lots of aero wheels are not particularly heavy, anyway. The Zipps will be lighter than practically anything else. I have a Hed CX from the early 90's, aluminum rim and carbon fairing, and even that is lighter than my training rear wheel (420gm Ritchey rim, 32 spoke 105 hub). Testing so far (only 1 ride, but more to come) indicates these wheels are about 2min faster than my training wheels, over a 15 mile TT route I do regularly. There are lots of turns, tunnels, and other excitements on the multi-use-trail section of this route, so many de- and accelerations. I'm a mediocre biker, average 21-22mph in most races.