# Would heavier wheels be faster on flat roads..



## DIRT BOY (Aug 22, 2002)

without much stoping and staring like a century? I fgure that once you accelerate, the heavier mass on the outside of the wheels will give you more momentum and speed on a flat road.

I wondring because I am going to be doing a competive pace century at the end of the month. I can go with my lighter wheels that are 1340g or mu Fulcrum wheels wich are just under 1800g. With the same tires and tubes, the Fulcrums fell a little more compliant (comfortable and smoother ride) but are heavier. After 119 miles in the last 3 days, I seem to be slighty faster at the same HR/Cadence. I will know later when I download the info from my Polar.

Ther are no hills what so ever on the century ride.I know lighter wheels are faster uphill due to weight and I love the feeling on how fast they accelerate, but I am wondering if I should go with the heavier ones?

Thoughts?


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## The Don (Feb 6, 2004)

*stops/starts*

maybe you have a point, theoretically. I'd be wary though. Are you sure there aren't going to be starts/stops or a need to accelerate in general? 

I just did a century on Saturday, skipped a couple of rest stops, and if there were no stops/starts at traffic lights then my average speed would have been 2-3 mph higher with Open Pro rims. YMMV...


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## Meatball (Sep 3, 2005)

If they are heavier because of aero characteristics, otherwise, no clue.


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## DIRT BOY (Aug 22, 2002)

The roads are pretty rual so lot's of open space. Sure there are corners and rest stops, but it flows really well.

To the other poster. Both are 24mm semi aero rims. The lighter set has bladed spokes, heaveir set round.


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## asgelle (Apr 21, 2003)

Except for specialized track applications (where there are no brakes to dissipate energy), heavier wheels will always be slower. Look at the terms in F=ma for a bicycle. Several forces are proportional to mass (e.g. rolling resistance) but none of them goes inversely with mass.


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## omniviper (Sep 18, 2004)

didnt we just say that aero is always better than weight? if the fulcrums are more aero then by all means.


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## rruff (Feb 28, 2006)

Heavy wheels won't gain you anything on a flat road at a steady speed. They will be very slightly slower due to the greater rolling resistance because of the higher total weight... but this is very tiny. Aero differences would likely have a greater effect... and durability might be an important factor to consider as well.


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## spookyload (Jan 30, 2004)

I am under the belief that once a wheel is accererated to speed, the weight of the wheel is irrelivant. The F=MA really doesn't apply here either. We are assuming the wheels are at a constant speed for this situation, so the acceration is a constant. It will take more effort to get them up to speed, but once there, all things become about the same. If aero isn't as important as weight, then how can teams justify a disk wheel? They weigh tons more than a deep dish aero wheel, but most pro's will use them on flat TT's. For that matter, why are Mavic sponsored teams using the heavier Cosmic Carbone instead of the lighter Ksyrium ES? That is almost a pound heavier wheel. It is obvious to me that aero is more important than weight unless the road is pointing up.

Dirt- as to your question, I would use the wheels that are the most comfortable. Ass comfort will be more important than the 30-40 seconds you would save choosing the "best" wheel. As long as you aren't doing something like the Horsey Hundred in Ocala that is constant rollers, or coming anywhere near Clearmont, you should be fine.


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## alienator (Jun 11, 2004)

spookyload said:


> I am under the belief that once a wheel is accererated to speed, the weight of the wheel is irrelivant. The F=MA really doesn't apply here either. We are assuming the wheels are at a constant speed for this situation, so the acceration is a constant. It will take more effort to get them up to speed, but once there, all things become about the same. If aero isn't as important as weight, then how can teams justify a disk wheel? They weigh tons more than a deep dish aero wheel, but most pro's will use them on flat TT's. For that matter, why are Mavic sponsored teams using the heavier Cosmic Carbone instead of the lighter Ksyrium ES? That is almost a pound heavier wheel. It is obvious to me that aero is more important than weight unless the road is pointing up.
> 
> Dirt- as to your question, I would use the wheels that are the most comfortable. Ass comfort will be more important than the 30-40 seconds you would save choosing the "best" wheel. As long as you aren't doing something like the Horsey Hundred in Ocala that is constant rollers, or coming anywhere near Clearmont, you should be fine.


yup. Pretty much. And human's accelerate bicycles slowly enough that wheel weight--or more specifically, wheel weight distriubtion--doesn't really matter either.

One things for sure, though: tires made from hook velcro would be a pain to accelerate on pile carpeted road.


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## asgelle (Apr 21, 2003)

spookyload said:


> I am under the belief that once a wheel is accererated to speed, the weight of the wheel is irrelivant.


No because there's a weight term in the rolling resistance force.



spookyload said:


> The F=MA really doesn't apply here either.


Why would you think the basic equation for all mechanics doesn't apply. It's been found to work accurately for hundreds of years. 



spookyload said:


> We are assuming the wheels are at a constant speed for this situation, so the acceration is a constant


. 
In which case the acceleration is not only constant but identically 0, but so what? That only means the sum of the forces is zero. The equation F=ma where a=0 is still perfectly valid.



spookyload said:


> It will take more effort to get them up to speed, but once there, all things become about the same.


About the same or exactly the same? See above for the rolling resistance term. The point is that as soon as braking is involved adding weight to wheels acts only so slow the bike down. There are terms which decrease speed with increasing weight (though they may be small) and no terms which show increasing speed with increasing weight (for level riding). Adding hills makes things a little more complicated since now the gravity term does introduce a term which increases with weight, but the result doesn't change.


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## FLbiker (May 21, 2005)

*Wheels*

First, I am not an engineer, nor do I have a physics degree.

With that said, why are we having this discussion? Dirt mentioned that the heavier wheels have the same rim profile and gave no indication that they are more aero. So, if the heavier wheels are not more aero, what possible advantage could they offer?'

If they were more aero then someone could start writing equations about how much aero advantage would be required to overcome a certain amount of weight increase based on the profile of the road. But I do not see that potential here.

Dirt, I like to look at this from my layman's point of view. Cycling is a constant game of acceleration, that is why you must continue to pedal. 

If heavier wheels with the same aerodynamic profile were better, why are we all riding Mavic Ksyrium SL instead of Mavic Aksium?


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## asgelle (Apr 21, 2003)

FLbiker said:


> Cycling is a constant game of acceleration, that is why you must continue to pedal.


Sorry, that's just not so. Cycling is a game of constantly overcoming the forces opposing motion, that's why you have to pedal. It's possible that all forces, including input pedal forces, are in balance and there's no acceleratation. It's also possible that going downhill, there is no acceleration even without pedaling if the force of gravity is exactly offset by aero drag, rolling resistance and any other possible retarding forces.


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## FLbiker (May 21, 2005)

*Acceleration*

Yes, you are correct. And I completely understand that while going downhill you can accelerate without any input, the sheer force of gravity will propel you faster.

My point was that cycling is not a game of constant 20 mph speed for 100 miles. The human body is not a robot and we do not cycle in a lab. The pack slows slightly, we have to accelerate back up to speed. We reach for a water bottle and slow, we have to accelerate back up to speed. We take a corner, we have to accelerate back up to speed. We slide off the front and slow and then have to catch onto the back, we have to accelerate back up to speed. We miss a stop light, we have to accelerate back up to speed. I could go on and on with this list. 

IMHO, anything heavier on the bicycle, whether it is wheels, seatpost, rider, anything that is heavier, that does not offer an aerodynamic advantage, will make you work harder. How much harder? I'll leave that up to the engineers and physicists. But it must be to some degree.


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## den bakker (Nov 13, 2004)

FLbiker said:


> IMHO, anything heavier on the bicycle, whether it is wheels, seatpost, rider, anything that is heavier, that does not offer an aerodynamic advantage, will make you work harder. How much harder? I'll leave that up to the engineers and physicists. But it must be to some degree.


yeah pretty much the mass increase divided by total mass. So 100 grams extra weight on a 80kg rider+bike turns out to be around 0.1/80=0.125%.


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## asgelle (Apr 21, 2003)

den bakker said:


> yeah pretty much the mass increase divided by total mass. So 100 grams extra weight on a 80kg rider+bike turns out to be around 0.1/80=0.125%.


And that's the greatest possible effect seen when climbing very steep hills. For all other conditions the effect will be even smaller.


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## physasst (Oct 1, 2005)

*Actually*



FLbiker said:


> If heavier wheels with the same aerodynamic profile were better, why are we all riding Mavic Ksyrium SL instead of Mavic Aksium?



I just saw some data that another poster here posted about Aksium's being MORE aero the ksyrium's...

http://forums.roadbikereview.com/showthread.php?p=779791#poststop


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## den bakker (Nov 13, 2004)

asgelle said:


> And that's the greatest possible effect seen when climbing very steep hills. For all other conditions the effect will be even smaller.


no, also for accelerations on flats. If you want to accelerate as fast with the heavier wheel you need a higher force as well. 
For a constant velocity you are right. 
One might want to put in a fudge factor for rotational weight but it's not going to make much of a difference.


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## turbogrover (Jan 1, 2006)

I always thought that, when riding at a steady rate on the flats, every single pedal stroke was required to overcome the forces opposing motion. So, if the wheels are identical except for weight, the lighter ones would be faster.
Now, coming back to reality, If I had to choose which wheels to ride a century on, I'd choose the more comfortable set. If I had to "race" a century, I'd choose the faster set.


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## Argentius (Aug 26, 2004)

*Use the fulcrums*

Because it doesn't matter, and I'm sure you have plenty of excuses to use the lightweight wheels.

The only time heavier wheels are BETTER are when you need to go fast under extremely controlled conditions for a sustained period -- Hour record setters have used heavy discs to good effect.


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## maximum15 (Feb 6, 2004)

*one advantage of heavier wheels*

is that they will coast farther and faster than lighter wheels assuming resistance to rotation by the bearings, tires, and spokes are the same. The exact opposite of trying to bring them up to speed (accelerating).


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## den bakker (Nov 13, 2004)

turbogrover said:


> I always thought that, when riding at a steady rate on the flats, every single pedal stroke was required to overcome the forces opposing motion. So, if the wheels are identical except for weight, the lighter ones would be faster.
> .


If your speed does not change, no term in the equation involves the mass of the bike and rider. So no


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## terzo rene (Mar 23, 2002)

Yes _assuming total bike weight was unchanged_ the heavier wheels would be faster, and it would also hold true going uphill.


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## turbogrover (Jan 1, 2006)

den bakker said:


> If your speed does not change, no term in the equation involves the mass of the bike and rider. So no


But your speed DOES change during every pedal stroke. Not enough to see it on your computer, but every pedal stroke is a surge in speed and then a deceleration. Otherwise there would be no need to pedal after you get up to speed. As soon as you stop pedaling, the bike loses speed. You don't pedal with 360 degrees of even power output. You have to accelerate the mass on every pedal stroke, or that's how it appears.

If you use a car engine's flywheel as an example, a big heavy one does a good job of smoothing out the engine pulses making a smoother running engine, but a lightweight replacement will make more horsepower, because there is less mass to spin.


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## den bakker (Nov 13, 2004)

turbogrover said:


> But your speed DOES change during every pedal stroke. Not enough to see it on your computer, but every pedal stroke is a surge in speed and then a deceleration. Otherwise there would be no need to pedal after you get up to speed. As soon as you stop pedaling, the bike loses speed. You don't pedal with 360 degrees of even power output. You have to accelerate the mass on every pedal stroke, or that's how it appears.
> 
> If you use a car engine's flywheel as an example, a big heavy one does a good job of smoothing out the engine pulses making a smoother running engine, but a lightweight replacement will make more horsepower, because there is less mass to spin.


ah yes the good old "micoraccelerations". make a search after them on RBR.


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## asgelle (Apr 21, 2003)

den bakker said:


> If your speed does not change, no term in the equation involves the mass of the bike and rider. So no


Really? How do you account for rolling resistance?


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## den bakker (Nov 13, 2004)

asgelle said:


> Really? How do you account for rolling resistance?


ok this is getting stupid. Yes the rolling resistance will change, especially if you don't compensate for the weight change with a change of tire pressure. Are we trying get as many significant digits as the fine structure constant here? Because you have got to be kidding me if you believe a change in wheel mass will be measureable in the total rolling resistance of bike+rider.


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## asgelle (Apr 21, 2003)

den bakker said:


> ok this is getting stupid. Yes the rolling resistance will change, especially if you don't compensate for the weight change with a change of tire pressure. Are we trying get as many significant digits as the fine structure constant here?


This has nothing to do with the number of significant figures. This is about someone claiming there are no (zero, zilch, nada, bupkas) terms with a mass dependence for level riding when in fact there is one. That means the relative error is infinite (1/0).


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## gibson00 (Aug 7, 2006)

bump..

So, science aside, can someone post some real world reviews, just describing how you liked carbone sl's vs Ksyriums, etc., for road racing (assuming no hill climbs longer than 1 km)??


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