You guys forgot the most important factor. The more spokes you have, the more time you have to spend wiping down each spoke when you clean your bike. So, less spokes is definetly better. Duh! :D

Commenting w/o thinking here, but I think that this is not true. When you're going up a hill, gravity is going to be applying an similar ******ing force, irrespective of where the mass of your wheels is concentrated. So, a rider will not suffer any more to maintain speed--on a bike of the same weight--by having rim-heavy wheels. Wheel weighting should have an effect on the speed curve though, and if a rider with rim-heavy wheels decided to just coast up the hill, you'd see his speed drop off very slowly at first, then quite rapidly (the opposite of accelerating up to speed). More uniformly weighted wheels would decellerate more...well, uniformtly :) Both bikes should both coast to a stop a the same point...uh, I think :D

That's just conservation of angular momentum. Imagine that instead of a figure skater, you had rotaing wheel whose radius you could change at will. If you made the radius smaller it would spin faster but it would still be rolling along the ground at the same speed.

Weight doesn't ever matter. Only wind resistance and thermal build up from friction.

I was assuming the bike was the same...we were talking about wheels. The bike with the heavier wheels (and therefor a heavier bike), is going to require more energy to get it up the hill. You're also under a greater constant accelleration/decelleration when you are climbing, thanks to gravity working at your momentum.

56-11 Fixed! Wow, you da man!

I'm beyond that.

You mean you're beyond being a man? :eek:

Yup, you're right on that. But I still stand my observation that weight at the hubs is better than weight at the rims ...

I have a set if "touring" wheels with 36 spokes in the front and 40 in the back. These wheels are twenty years old and have all 76 of the original spokes. On a regular basis, in these forums, I see posts from guys whose newest set of ultra-light wonder wheels has come apart after just a few weeks of use.

Last year, a UK magazine had an article about the wheels used in the one day Paris to Roubaix race. They look like my touring wheels, not like "wonder" wheels. The article said "wonder" wheels can not survive one day of severe use.

Your "Ferrari and Porches" example may be correct. My friends with that sort of car are always begging for a ride from someone with a car that actually runs - their Porsche is back in the shop - again.

Paris Roubaix is essentially Cyclocross. The set up they run on most bikes there is different from what they run in the majority of other races. It's brutal and they spend as much time in the dirt next to the Pave as on it.

Most of the folks you see standing by the road next to their bike either aren't doing the required maintanence, or they are silly enough to put race parts on bikes they use for touring, or they are too heavy for what they bought. I own a set of Zipp 303's, one of the lightest wheels out there, and they go on the bike when I'm racing or for the occasionally big climbing session. I don't use them for screwing around.

But my everyday set of wheels still come in at under 1300 grams, and I put a lot of good mileage on them, without any problems. I think a properly laced 32 spoke wheel cross three is more than reliable enough for everyday use on training rides, provided you buy quality, and you're not a Clydesdale (again see proper application).

I look at Road Bike Review from time to time and have to laugh at the folks who buy the lightest racing tire and ***** that they only got 1000 miles on them, or flatted after a few hundred miles. And did you think an 18 spoke, 400 gram wheel was a good idea for your touring bike?

But there are also a lot of high mileage carbon frames out there that are still plugging along, because they are inherently well built and designed, and the people who own them take care of them.

There's a lot of "ultralight" products coming on the market, and some of them are c**p. There's also a lot of inexpensive, heavy c**p out there too. It's important to make distinctions between the good and bad and not make blanket assertions about the quality of something based on weight or price.

You can even find light and inexpensive with some products. I've been roundly ridiculed for putting a Weyless carbon/aluminum stem on my race bike. I should have spent a lot more money and gotten something heavier I suppose, but I've been using these stems for years with no problems...at 130grams and $25 on sale, I'll listen to the derision.

If your friends can't afford a second car for everyday use, they shouldn't have bought a Ferrari or Porsche in the first place. I hope they make better decisions in their personal lives :)

Perhaps I misread you initial post since I thought I was talking about wheels too :) Anyway, I agree, that a heavier bike/wheel combo will take more energy to get up a hill.

However, after having had my morning coffee, I am more certain than ever that neither the weight nor the distribution of weight in a wheel set (provided that the overall weight of the bike stays the same) will by itself affect the total energy expended by a rider (ie, an avg speed over a set distance). Wheel weight and wheel weight distribution will only affect the rate of acceleration/decelleration--the work being preformed by the rider will stay the same.

This may or may not be true--I have a nagging suspicion that a bike wheel (in terms of physics) is more than a simple disk. There may be some harmonics involved in the spokes or the way the wheel flexes may make hub-centering the mass more deisreable--I just don't know. Gyroscopically speaking, a wheel weighted more toward the rim will be harder to rotate perpendicular to the plane ot its rotation--so, if one's pedaling style involves a lot of tiny movements in the front wheel, or a swinging of the bike, I can see how a rim-weighted wheel might be more exhausting/inefficient. Nevertheless, I'm taking a very simplistic approach and I admit it :D

One thing I DO know for a fact is that low-spoke-count wheels mean that you're SOL if you break a spoke in the middle of nowhere :(

Thats what i'm talk'n about. After acceleration/decelleration,rotating weight doesnt matter,except going up those hills,then you want less weight.

or going down hills when you want more weight ;)

Since weight only affects power required linearly with speed, that's where you want to compromise if you want to go fast on flat ground or downhill.
My guess is that aero wheels with three really wide "spokes" (more like wings) will have the least amount of drag, without much of the sidewind problem solid discs have. Given the relative unimportance of weight for top speed, they could very well be made strong enough to match a spoked wheel in terms of strength and durability, and still be much faster.
Like this:
http://www.msgbikes.com/acatalog/Wind%20Cheeter%20.jpg

Yes, weight will affect the rate of accelleration, but also the peak rate of velocity and energy use. Assuming you want to maintain a constant speed.

For practical physics I like to use extreme examples:

Think rolling a tennis ball and a 100 lb lead ball up a 15% grade. You want to keep them both rolling at 1 MPH. Which will require more energy? Obviously the lead ball. Now which takes more energy to keep moving on a flat surface? Again, the tennis ball, but the difference in energy required to keep both objects in motion narrows considerably.

Next, think about rolling two wheels, both six feet in diameter. Both weight 100 pounds. One has
a 99 pound lead weight as the axle.

The other has 99 pounds of lead strapped wire wrapped around the outside of the hoop. Which will require more energy to keep moving at a constant rate of speed up a 20 degree hill?

When you're riding you are constantly accellerating and decelerating, sometimes in minute increments. Going uphill these these accellerations more pronounced, requiring more energy to keep all things moving.

Regardless of gradient, it takes more energy to keep a heavier object in motion.

My comments also assumed that we were talking wheel weight on the same bike, not different bikes of equal weight.

At a spoke count of 18 for the front and 20 for the rear, I'm not sure if my Ksyrium SSCs are considered low-spoke count or not. However, earlier this year, I managed to bend one of the non-driveside spokes on my rear wheel and the rim stayed absolutely true.

http://www.neebu.net/~khuon/albums/m...CT0007_001.jpg

Some people criticise the Ksyriums for not being the lightest wheel on the market and their rims are certainly not very aero but I believe that the rims are plenty stiff and beefy and that's what made mitigated the effects of a failure of the one spoke. So yes, I will have to agree with others who say that many low-spoke count rims probably have to be made much stronger and will probably be heavier.

Unless the extra weight is spent making the object more aerodynamic, in which case the heavier object will require less power to keep it in constant motion the faster it goes, compared to the other object.
Which was my point in my previous post... :)

No. If the gradient is zero, an object in uniform motion (rotational or linear) will stay in uniform motion (minus frictional forces). The 100lb ball of lead may experience more ******ing forces due to friction becasue of its weight and the nature of lead (and therefore require more energy input to keep it going) but round objects of dissimilar weights, having similar coefficients of friction will be indistinguisable once they have been set in motion and achieved a set velocity.

The moment of inertia of a bicycle wheel is simple to calculate (I=mr^2, where "r" is the center of radial mass, not the radius of the wheel) and it works in *both* directions--just as it ******* acceleration, it also ******* decelleration. For all practical purposes, all bicycle wheels of similar weight and having similar tires will interact with the ground in the same way. Therefore, these same wheels will all experience idential ******ing frictional forces--regardless of how the weight within the wheel is distributed. Consequently, since a pair of wheels w/ different moments of inertia (ie, differing r's)rolling along at a constant speed CANNOT experience differing ******ing forces, they will therefore require EQUAL ENERGY inputs to maintain this constant speed.

These arguments are academic. Bikes don't really go at a constant speed. Every pedal stroke is an acceleration. Your bike (and especially your wheels) should therefore be as light as practical.
Tom with a BS in Physics from Kansas State University, 1977.

Your explanation is very good textbook physics, except that forgot to factor in the decelerating effects of gravity (on hills) and wind resistance. The work required to maintain a perfectly even speed is equal to the work required to counter the decelerating forces of wind resistance and gravity. The previous sentence agrees with your explanation except when you put it into the real world of constant changes in velocity and rate of acceleration. If we could maintain a perfectly even speed, the weight of the wheel would not matter. But we don't. We are always changing our rate of acceleration. Because of this real world factor, the lighter wheel is more advantageous because it takes less work to bring back up to speed.
BTW, acceleration seems to have been misused a little in this thread. Not only is it a change in the rate, but it is also a change in the direction of movement. Therefore, the rim is always accelerating because of the change in direction of movement of any given location on the rim.

I thought I was a lone voice of practical application here...

*Sniff*

I love you guys...

(Tears welling up)

I have both types of wheels. I really can't see an advantage either way. The high spoke count wheels are overall lighter and actually feel more responsive, especially when climbing. Unless you are pushing the limits of cycling or cycling fitness it really doesn't matter too much. Better to loose 5 lbs. from you gut than spend a lot of effort calculating the advantage of spoke count. The biggest advantage of low spoke count to me is the appearance. Someone ask me one time did I have a good ride and my answer was "No but I sure looked good doing it".
Disadvantage of low spoke count: Break one spoke and you are done for the day.

Welcome to the Top Gun School of cycling.....where we all ride 40 spoke wheels with bladed spokes angled the wrong way (to increase air resistance!) and lead weights stuck to the rim for our training rides.

Then when you throw on some regular wheels you feel like you constantly have a tailwind cuz pedaling became so easy...LOL.

P.S. When you see a "top gunner" pass a cyclist running American Classic 420's with the above mis-angled bladed 40 spoke wheels you know it's the hardcore dedication paying off. Nothing beats sweat and time in the Saddle!