If nothing else, I thought a super heavy rear wheel would be awesome on a trainer and give it that "road feel"

As long as you have a tri course that has no stops. The inertia required to restart might be significant.
That hour record was a rolling start, right?

it would be a great thing to study.

i suspect that if rolling resistance increases due to the greater weight could be negligible, that it would help to have heavy wheels on super flat courses with no turns or acceleration.

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Where would you want to swim ?

Or a lightweight wheel but with a significant weight added at one position.

but then it would be very unbalanced.

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Where would you want to swim ?

First, the vast majority of the momentum of a bike-rider combination is the non-rotating weight, so it would take quite a bit of weight to make any significant difference I think.

Second, counter forces acting on the bike do not change. If we add weight so that it takes more energy (or longer period) to slow the bike, then it just takes more energy to speed it back up.

Do you believe a loaded truck or freight train gets better gas milage than an empty one? I don't, so I don't see how this could do anything but decrease performance.

[reply]The hour record this year (admittably achieved on a flat surface) was achieved by adding weights to the wheels to create a flywheel effect. Wouldn't this be an advantage on rolling style road courses for us as well ?

Discuss.[/reply]

Yes, it would be an advantage unless the course had a large elevation gain where the overall weight would be a disadvantage.

Why would it be an advantage. Well, the natural power variations in the pedal stroke cause natural speed variations (this is how spin scan works) and the wind resistance varies with the square of the speed, so the average wind resistance for any given average speed is actually more than one would see with a steady speed, making the rider work more. The more momentum (weight, amplified in the wheel weight, especially the rim) in the bike the less this speed variation, so the faster the rider can go for the same work. It is another reason spinning should result in faster speeds, for the same effort, over mashing, everything else being equal.

It is simple physics (mechanics).

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Frank,
An original Ironman and the Inventor of PowerCranks

On the surface, it seems like a good idea. I don't know physics in enough depth to know if it really works or not (or if lighter wheels help you). It may come down to the course or type of race- a tight crit with lots of accellerations might favor light rims/tires, while flat courses, or those with gradual uphills/downhills might favor heavier rims/tires. In the end, though, I don't think either wheel will affect your outcome in a race. I have gotten the fastest bike split of the day on (relatively) heavy, non-aero wheels, and had crummy days on my light/aero wheels.

What Frank Day makes sense. Another point- your riding style would be more at odds with those around you on the course. A lot depends on the length and degree of the grade, but in general, you would find yourself maintaining speed better at the bottom of a downhill and immediately after the descent, whether it be on another climb or a flat sections. On the other hand, you might go slower in the later stages of a hill and at the peak. It would also take you longer to accelerate back up to speed after the crest. My riding riding style tends to follow this anyway, and I find that I end up jockeying back and forth with those riding about the same average speed.

[reply]What Frank Day makes sense. Another point- your riding style would be more at odds with those around you on the course. A lot depends on the length and degree of the grade, but in general, you would find yourself maintaining speed better at the bottom of a downhill and immediately after the descent, whether it be on another climb or a flat sections. On the other hand, you might go slower in the later stages of a hill and at the peak. It would also take you longer to accelerate back up to speed after the crest. My riding riding style tends to follow this anyway, and I find that I end up jockeying back and forth with those riding about the same average speed.[/reply]

This weight gain advantage would probably only work on TT efforts without a lot of turns and would help a masher more than someone with a smoother pedaling stroke. It is a steady state advantage that comes from many very tiny advantages multiplied 90 times a minute or so for an hour.

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Frank,
An original Ironman and the Inventor of PowerCranks

hmmm...actually, it makes no sense at all, unless you have a lack of understanding of physics.

The ONLY advantage a heavier "flywheel" would have is going downhill-- even then the effect would be minimal.

As far as Sosenka's hour record, I've seen/read/heard so much conflicting information regarding it that I'm beginning to wonder if he even did it! Maybe it's just urban legend?? (Maybe it's trouble with the translation!).

He's going to be over 8 feet tall and riding a 60 pound bike by the time the story is finished.....

 
I would imagine the heavy "fly" wheels were used to keep the speed consistent, carrying more speed through the corners, as to keep the cadence optimum at all points on the course. (Remember that they would be using a single speed bike.) This would be the only time that I think heavy wheels may be preferable.

Not just a single speed, but a fixie...

Ick, a simple question creates such discourse...

I'm at the office right now, in a building full of physicists, and I asked around, and I have THE answer to this question:

take two wheels, one weighing 2 times as much as the other; spin them up to the same rotational velocity (this is the point I think most everyone has missed); place them both on the same surface and let them go; the heavier wheel will travel further before stopping because it has more energy stored up as angular momentum; not to be forgotten however is that the energy input required to spin-up both wheels to the same angular velocity is larger for the heavier wheel.

So to answer the question from a riding perspective, a heavier wheel- once spun up- requires less energy input per unit time (power) because the energy loss by the wheel from friction is appreciably offset by the stored angular momentum; thus, to replace the instantaneous loss of energy from friction becomes smaller as wheel weight increases, BUT you better be strong as a bear to get that wheel moving.

The major point here is that the energy input averaged over the time period that the wheel is spinning is equal in both cases. Argue away if this makes a difference in the case of muscles because I don't know; but I have seen the efficiency of muscles decrease over the course of an hour but have never seen the analog in a car engine over 100miles (meaning a car doesn't get slower because gas is being removed from the tank, it slows when the gas is gone).

[reply]
So to answer the question from a riding perspective, a heavier wheel- once spun up- requires less energy input per unit time (power) because the energy loss by the wheel from friction is appreciably offset by the stored angular momentum; thus, to replace the instantaneous loss of energy from friction becomes smaller as wheel weight increases, BUT you better be strong as a bear to get that wheel moving.[/reply]

I think the time it takes to spin it up is insignificaant to the hour record. Oh, and ask all those physicists the energy cost of constantly accelerating and decelerating (albeit slightly) 90 times a minute seen in a bicycle but not in a car and the effects of wind resistance on same.

and, I might add, the more substantial speed reductions and accelerations twice each time around the track, those must be considered also.

the man was going for the hour record. What is the most efficient use of his available energy to achieve the goal?

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Frank,
An original Ironman and the Inventor of PowerCranks

My comment on being strong as a bear was more directed at wheel weighing like 1/2ton, such as in a locamotive or earth mover. For two bike wheels, one with mass M and the other 2*M, the change in spin-up time for equal energy input is also twice as long, so if it takes a rider 30sec (exaggeration here) to get wheel of mass M to max speed, then a wheel of mass 2*M will take 1min, so the difference is negligible especially if the goal is to keep the wheel moving at that max speed for an hour.

I guess the point being, if someone wants to ride a bike under very flat, controlled conditions (like at a track for an hour record) make the wheel heavier, it reduces the amount of power needed to turn the wheel for the all the time after spin-up. I guess someone should actually crunch the numbers but I'd guess for a wheel of 2000g maybe 1-2watts savings which should translate into like a few secondsin 1hr...?

[reply]My comment on being strong as a bear was more directed at wheel weighing like 1/2ton, such as in a locamotive or earth mover. For two bike wheels, one with mass M and the other 2*M, the change in spin-up time for equal energy input is also twice as long, so if it takes a rider 30sec (exaggeration here) to get wheel of mass M to max speed, then a wheel of mass 2*M will take 1min, so the difference is negligible especially if the goal is to keep the wheel moving at that max speed for an hour.

I guess the point being, if someone wants to ride a bike under very flat, controlled conditions (like at a track for an hour record) make the wheel heavier, it reduces the amount of power needed to turn the wheel for the all the time after spin-up. I guess someone should actually crunch the numbers but I'd guess for a wheel of 2000g maybe 1-2watts savings which should translate into like a few secondsin 1hr...?[/reply]

For a wheel of 2 m the spin up time is really much less than double since the mass of the wheels is only a small part of the whole when one takes into account the mass of the rider and the bike. Doubling the mass of the wheel probably only adds a few seconds to getting to top speed.

And, your analysis is neglecting the energy cost of the varying speed in the wind resistance as the speed varies. That is where the real savings from the excess weight is, from smoothing out the speed profile.

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Frank,
An original Ironman and the Inventor of PowerCranks

Your forgetting the energy cost of bringing the wheel back up to speed and the effects that has on the performance of the engine. I just look at history. If heavy wheels worker we would be riding them.

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customerjon @gmail.com is where information happens.

[reply]
For a wheel of 2 m the spin up time is really much less than double since the mass of the wheels is only a small part of the whole when one takes into account the mass of the rider and the bike. Doubling the mass of the wheel probably only adds a few seconds to getting to top speed.[/reply]

You're correct, I'm treating this experiment as just a wheel, I'm assuming everything else is equal and looking only at how weight effects wheel rotation. Thinking that way establishes an upper-bound, basically an overestimation, of the real world quantities that would be effected by wind resistance, rolling resistance; the point being, the benefit of a heavier wheel will only get better.

Tibbs, we're imagining this on a flat course.

I was under the impression that the Campagnolo Ghibli wheel was very popular because of the "flywheel effect". Clearly a heavier wheel than the zipp disk.