# Rotating weight of pedals



## rkb (Apr 4, 2007)

I am considering some upgrades on my bike one being the pedals. I currently run the new Ultegra 6620s, but they are heavy. I will have some extra bike cash coming in and would like to find the best place to invest it. With this in mind I am looking at the Look Keo Carbon Ti pedals. This would drop close to 140 grams of weight. The other option would be to change the brakes out to 0Gs. Right now I have Ultegra brakes and pedals and everything else Dura-ace. I will not have the cash to do both, and the weight savings is similar. So the question is static weight or rotating weight.


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## DM.Aelis (Jun 19, 2007)

*well...*

I've heard a lot about "static versus rotating" and quite frankly, I think a lot of it is a load of crap. It might apply in the sense of wheels, where a heavier wheel is less quick to accelerate, but your energy input is identical. 

That being said, if the weight savings from traditional brakes to ZeroG's, or your current pedals to the Looks are identical, I would probably do one of two things:

1) Get the pedals. I'm guessing, money/gram, that this is a cheaper way to drop weight.
2) Get the brakes. If the time ever came to resell, I'm assuming they would hold their value much better versus the pedals. And, once you've got em, you really probably will never need another set of brakes in your life (unless they break, however unlikely).

$.02


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## PigmyRacer (Oct 3, 2007)

Obviously, I have no idea what kind of setup you have as far as weight, but there are much better ways to spend money than buying Zero Gravity brakes. 

Pedals are not rotating weight in the sense you are thinking of. Wheels are rotating weight, pedals, for the purposes of a physical analysis are static. I would save up maybe and upgrade something more substantial, but otherwise I would go with the new pedals.


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## rkb (Apr 4, 2007)

Current setup-
Frame: 08 Lemond Tete de Course size 55cm -850grams
Fork: Bontrager XXX lite fork (heavy)
Wheels: Ksyrium SSC SLs
Saddle: Fizik Aliente braided carbon
Seatpost: Thomson Masterpiece w/Ti hardware
Stem: FSA OS115
Bars: FSA SLK carbon compact
Dura-ace drivetrain
Ultegra pedals and brakes
Pro2 Race tires
Zipp cages and Ti skewers

15.9lbs as ridden


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## android (Nov 20, 2007)

Why change pedals for no good reason? I've seen so many people change pedals and then end up with knee or foot issues. If you don't have a good reason to change pedals, don't do it unless you are moving to a different pedal of the same type. For example from Ultegra SPD-SL to DA SPD-SL.


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## iliveonnitro (Feb 19, 2006)

Just do both?


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## rkb (Apr 4, 2007)

iliveonnitro said:


> Just do both?


Love to but the bike budget will only allow one totally frivolous upgrade for the single minded purpose of dropping a few grams. Damn this weight weenie disease...........You get a crazy light frame and you turn into a monster!


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## MIN in PDX (Nov 29, 2007)

Huh? How come it's so much worse to ride when I have booties on vs just shoes? I vote for lighter pedals, fo' shizzle.


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## rkb (Apr 4, 2007)

MIN in PDX said:


> Huh? How come it's so much worse to ride when I have booties on vs just shoes? I vote for lighter pedals, fo' shizzle.


Yeah, thats where I'm heading for the same reason. 145grams times an average cadence of 90 times a minuet times one hour on a three hour ride is 2,249,000 grams or 5180 pounds, 2.59 tons, or 370 stone. PLUS look how cool they LOOK-


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## Forrest Root (Dec 22, 2006)

rkb said:


> 145grams times an average cadence of 90 times a minuet times one hour on a three hour ride is 2,249,000 grams or 5180 pounds, 2.59 tons, or 370 stone.


Just because a calculator will give you an answer doesn't mean that answer is worth anything.


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## MIN in PDX (Nov 29, 2007)

Forrest Root said:


> Just because a calculator will give you an answer doesn't mean that answer is worth anything.


True but light pedals are still better than heavy ones. (duh)


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## Forrest Root (Dec 22, 2006)

MIN in PDX said:


> True but light pedals are still better than heavy ones. (duh)


Yeah? How so? I'll bet any sum of money that it's next to impossible to feel a difference, on the road, between "heavy" pedals and light pedals. Heck, I'll bet you can't see the difference in ride data. 

A crankset weighs roughly the same as a rear wheel, even with pedals attached. The radius of wheel with a 700x23 tire is about 333mm, with a circumference of about 2090mm.
At 20 mph, such a tire goes 'round at about 257rpm. The energy of a rotating hoop is E=0.5*I*w^2. The crank isn't a hoop, but we'll say it is because it will tilt the approximation in favor of your "theory." The moment of inertia of said hoop, 'I' from the energy equation is M*R^2. As a result of that difference in radius, the crankset will have a total moment of inertia 1.8 times smaller than that rear wheel. If you're pedaling a 53/19 combo, that means at 20mph, your cadence is about 92rpm. In that energy equation w is the angular velocity, or RPMs. That means on the basis of angular velocity the cranks energy will be 7.8 times less than the wheels (for the same mass and MOI). Over all, that means for this little scenario, the cranks will have an energy *14 TIMES* smaller than the wheels. In the real world, that means pedal weight is insignificant.


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## johnmyster (Mar 13, 2003)

I think you should spend your time and money worrying about the rotating inertial component of pedals, cranks, chains, cassettes, hubs, and jockey wheels. Why not worry about the rotating inertia of stems, headset bearings and handlebars too? 

Me, I'll spend my time and money considering things that really matter.

Yeah, I have to lift a heavier pedal some 5 billion times over the course of the ride, but you forget that there's a pedal on the opposite crank falling. It's a balanced system. That contribution doesn't matter.


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## MIN in PDX (Nov 29, 2007)

FR-

You obviously paid more attention in math and science than I did. (I was a math major in college, ironically.) 

All I know is that when I wear booties, it suck compared to nuddies. Wet booties = worse than dry booties. 

I won't get into the issue of rotational weight, as that is not my forte. However, you can't serious argue that heavy is as good as light pedals. The entire package benefits from weight reduction.


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## johnmyster (Mar 13, 2003)

MIN in PDX said:


> FR-
> 
> You obviously paid more attention in math and science than I did. (I was a math major in college, ironically.)
> 
> ...


I don't notice my booties, other than the fact that I can actually feel my feet. Sure, lighter = better when going uphill. But the "I lift the pedal every revolution of the crank" arguement doesn't work, because it neglects that the pedal also falls every revolution. 

I also argue against getting bent out of shape over the crank/pedal/chain/cassette being rotational mass (although it is) because it's mass that stops and starts, every time you start pedaling. Plus, the rotational velocity of such items is low (okay, the cassette is at the same speed as the wheel) and the moment of inertia of items is slow (square of average mass radius is small).

Sure, lighter is better. But you don't get to claim that you lift your pedal every stroke.


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## android (Nov 20, 2007)

Yeah, and you got to lift you calf and foot too, how much do they contribute to the equation? Do you consider your foot to be rotating mass also?
I bet legs are around 1/3 of your body weight. Feet probably weight about 5 lbs each. 

And the reason you probably don't ride as fast with booties is because all that winter gear restricts movement AND the reason you're wearing it is becuase it's freakin' cold outside.


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## rkb (Apr 4, 2007)

Wow- I didn't mean to stir up a conversation of applied physics. Please understand that I thought I was posting on a weight weenie forum. I my mind that means we suspend all rational thought as too the true validity or necessity of a particular bike part. But rather we look at the part it a pure attempt to build a lighter bike. 

In my case I will have the bike part budget that will allow one of two upgrades. Brakes or pedals, numbers aside it seems to my basic math brain that less weight moving around is better than more weight. 

You guys have brought up some very interesting arguments that have successfully done two things- first, Forrest, you lost me shortly after "Yeah so-" and second lets not suck all the fun out getting some real cool bike parts.


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## MIN in PDX (Nov 29, 2007)

johnmyster said:


> Sure, lighter is better. But you don't get to claim that you lift your pedal every stroke.


I didn't make that claim.


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## android (Nov 20, 2007)

rkb said:


> In my mind that means we suspend all rational thought as too the true validity or necessity of a particular bike part. But rather we look at the part it a pure attempt to build a lighter bike.
> 
> In my case I will have the bike part budget that will allow one of two upgrades. Brakes or pedals, numbers aside it seems to my basic math brain that less weight moving around is better than more weight.


Oh, in that case, go with the brakes. Others will see and appreciate how light they are. Pedals are hidden under your feet and much less noticeable when you're riding. :thumbsup:


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## rkb (Apr 4, 2007)

android said:


> Oh, in that case, go with the brakes. Others will see and appreciate how light they are. Pedals are hidden under your feet and much less noticeable when you're riding. :thumbsup:


That a Boy! Now we're talkin' cool light bike parts that make you happy during these cold winter days. One thing though, I mostly ride alone and even when I do ride in a group I am more interested in the ride than the bling. That said, it is a goal of mine to build my version of the ultimate bike. Its not a Parlee or something like that but is a very sweet ride and I realize just how fortunate I am to have it. 

Thanks to all that have tossed in their two bits worth, even the theoretical physicists. I may not have understood a thing you said, but it was impressive none the less.


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## Guest (Jan 18, 2008)

Forrest Root said:


> In the real world, that means pedal weight is insignificant.


Hmmm. Is that the same world where ceramic bearings which save a fraction of a percentile of rider power output, are considered by many to be a worthy purchase?


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## laffeaux (Dec 12, 2001)

rkb said:


> Yeah, thats where I'm heading for the same reason. 145grams times an average cadence of 90 times a minuet times one hour on a three hour ride is 2,249,000 grams or 5180 pounds, 2.59 tons, or 370 stone.


Are you sure that math is correct? There's an equal weight on the opposite crank arm that's pushing down (via gravity). I'm not sure that any more effort goes into turning a heavy pedal versus a light one. I'd think that the weights canceled out as far as any "rotational weight" argument goes.

The pedals still add to the entire weight of the bike, and should be counted as static weight.


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## MIN in PDX (Nov 29, 2007)

laffeaux said:


> Are you sure that math is correct? There's an equal weight on the opposite crank arm that's pushing down (via gravity). I'm not sure that any more effort goes into turning a heavy pedal versus a light one. I'd think that the weights canceled out as far as any "rotational weight" argument goes.
> 
> The pedals still add to the entire weight of the bike, and should be counted as static weight.


Strap 5 lb weights to your shoes and tell me if that argument holds water.


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## Forrest Root (Dec 22, 2006)

laffeaux said:


> Are you sure that math is correct? There's an equal weight on the opposite crank arm that's pushing down (via gravity). I'm not sure that any more effort goes into turning a heavy pedal versus a light one. I'd think that the weights canceled out as far as any "rotational weight" argument goes.
> 
> The pedals still add to the entire weight of the bike, and should be counted as static weight.


First, yes his math is, well, not quite right. In fact, it has no connection with reality at all.

Second you can't cancel rotating mass as you've tried to do. It doesn't work that way. There is energy stored in the rotational motion of the system, whether or not weights are rising or falling. The amount of energy in the pedal crank system is really small, but it is still there.

FWIW, if you added 5lbs to each shoe, as someone suggested, in the system I modeled, the rear wheel would still have 2.2 times the energy of the crank/pedal system.


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## CleavesF (Dec 31, 2007)

Forrest Root said:


> A crankset weighs roughly the same as a rear wheel, even with pedals attached. The radius of wheel with a 700x23 tire is about 333mm, with a circumference of about 2090mm.
> At 20 mph, such a tire goes 'round at about 257rpm. The energy of a rotating hoop is E=0.5*I*w^2. The crank isn't a hoop, but we'll say it is because it will tilt the approximation in favor of your "theory." The moment of inertia of said hoop, 'I' from the energy equation is M*R^2. As a result of that difference in radius, the crankset will have a total moment of inertia 1.8 times smaller than that rear wheel. If you're pedaling a 53/19 combo, that means at 20mph, your cadence is about 92rpm. In that energy equation w is the angular velocity, or RPMs. That means on the basis of angular velocity the cranks energy will be 7.8 times less than the wheels (for the same mass and MOI). Over all, that means for this little scenario, the cranks will have an energy *14 TIMES* smaller than the wheels. In the real world, that means pedal weight is insignificant.


Just because a calculator will give you an answer doesn't mean that answer is worth anything.


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## MIN in PDX (Nov 29, 2007)

CleavesF said:


> Just because a calculator will give you an answer doesn't mean that answer is worth anything.


Oh boy, now we are getting into mutually circular logic. People, lighter pedals are better. End of story.


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## Guest (Jan 20, 2008)

So in conclusion we have learned that:

a) heavy pedals ARE rotating weight.
b) they are on the worst place on the crank arms, i.e the ends.
c) the only worse place the weight could be on is the wheels.


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## rkb (Apr 4, 2007)

Did I mention how cool looking the carbon pedals are............


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## Forrest Root (Dec 22, 2006)

CleavesF said:


> Just because a calculator will give you an answer doesn't mean that answer is worth anything.


Well, that's only because in your case you don't understand the answer. Mine is the physicaly real answer that uses the actual physics that describes said rotational motion. Bikes don't work because of some hidden, dark magic. The actually work because of this thing called "physics." The calculations I did directly give the energy put into the wheel and cranks by the rider, i.e. the energy he had to expend (not including, however, energy losses in his own body and the translational kinetic energy of the system, which is only a dc shift in the two values.).

If you have an intelligent response, please, give it.


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## Forrest Root (Dec 22, 2006)

MIN in PDX said:


> Oh boy, now we are getting into mutually circular logic. People, lighter pedals are better. End of story.


Better? How so? There is a point at which the returns are not worth the costs. That is the case, often, in the real world. Do you actually have anything factual and physically verifiable to back up your "better" assertion?


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## Guest (Jan 20, 2008)

Forrest Root said:


> Better? How so? There is a point at which the returns are not worth the costs.


Your are extrapolating his argument that lighter pedals are better, into an argument that one must lighten one's pedals.

Clearly the decision to buy lighter pedals involves lots of factors such as $ cost, durability, opportunity cost, type of riding one does, taste, how light one's existing pedals already are etc etc.

Just because one may not choose to buy lighter pedals, or instead spends that money on say...ceramic bearings...or an aero-helmet, does not mean that wattage cannot be saved through using lighter pedals (all other things being equal).


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## CleavesF (Dec 31, 2007)

Forrest Root said:


> If you have an intelligent response, please, give it.


In the American tradition of keeping it simple... and according to Anatole France on plagiarism... my conclusion is thus:

"Lighter is better."

I mean considering I was arguing with you (FR) about body weight vs bike weight and that I thought it was cheaper losing body fat over your bike losing weight hence my "worthiness argument" and I got flamed like crazy by you.

Now you're telling us that dropping an extra X amount of $$$ is wrong because it's insignificant to you by your calculations. 

I'm not saying the equations are wrong, or your calculations. But honestly, I'm no longer a Mechanical Engineer major, I'm Biological Systems Engineering with a crappy 2 years of physics. If you know more that's great! But most enthusiasts know that rotating weight is best to limit first then static weight. 

Maybe you don't care about acceleration... or you're only into TT's or something. Big deal! Just because you can't "feel" it doesn't imply insignificance. Nobody feels the aerodynamics of their bike's frame... but it makes a difference. 

Also I don't think you can say a crankset with pedals is always roughly equal to the weight of a rear wheel... because last time I checked, someone, I believe you Forest Root had a 900 gram wheel... 

If pedal weight is insignificant, why did you even argue that people can do whatever they want with their money in your "worthiness" argument. It's almost contradictory. 

I say yeah, spend your money one whatever you want. But if you have fat to lose, it's better losing that before losing static weight... rotating weight like pedals... I can't argue that at all yet YOU can which sorta baffles me. :mad2: Maybe I'm just stupid. Plenty of people think I am. 
________
Vvt-Ie


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## Forrest Root (Dec 22, 2006)

CleavesF said:


> I mean considering I was arguing with you (FR) about body weight vs bike weight and that I thought it was cheaper losing body fat over your bike losing weight hence my "worthiness argument" and I got flamed like crazy by you.


No, you got flamed for the asinine way you referred to "fatties." I never said losing body weight wasn't better. You should read more carefully. In fact, all of the flaming done by everyone in that thread was the result of your arrogance and the way you tried to make yourself superior to others by calling them fatties. Full stop.

The rest of your argument fails, completely. To think that any positive change in a parameter is beneficial and worthwhile is fanciful at best, especially when the magnitude of those changes is lost in the noise and likely indistinguishable from any of several different sources. Go to Weight Weenies. Over there, they're serious about bike weight issues, and there are more than a handful of current pro riders there, including the newly crowned Australian national TT champ. Almost no one over there believes that lighter parts impart significant performance changes. Frankly, all the math and science aside, my own experience aside, I'll put my money on what the pros believe as opposed to what you believe.


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## BunnV (Sep 7, 2005)

*Keep it fun!*



rkb said:


> Wow- I didn't mean to stir up a conversation of applied physics..... lets not suck all the fun out getting some real cool bike parts.


I HEAR THAT! Go with the fun and emotion of it. I like your choice of the Keo's because they are light and they look cool. The Zero Gravity brakes look WAY cool but according to many reviews I've read, they don't stop very well. I don't know because I've never tried them. I do feel that light parts are better only if they actually work in the real world. All that being said, I vote for the pedals. BTW, OF COURSE lighter is better! If weight didn't matter I'd still be riding my 35 pound Schwinn Varsity I had in high school!


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## BunnV (Sep 7, 2005)

rkb said:


> Did I mention how cool looking the carbon pedals are............


Whatever part you decide on, please post pictures in this thread. I'm excited for you. :thumbsup:


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## California L33 (Jan 20, 2006)

rkb said:


> Yeah, thats where I'm heading for the same reason. 145grams times an average cadence of 90 times a minuet times one hour on a three hour ride is 2,249,000 grams or 5180 pounds, 2.59 tons, or 370 stone. PLUS look how cool they LOOK-


I kind of see where you're coming from with the weight thing (though I'm assuming your calculations are linear) but think of it like this- that's moving 2.59 tons about 14 inches (the distance of your cranks) in three hours. It doesn't take a lot of energy to do that. You and a friend could push a 3 ton truck 14 inches in a couple of seconds. 

Like someone else mentioned, I'd only change pedals if you're having knee problems, and Zero-G brakes seem like quite an extravagance- but it's your money.


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## CleavesF (Dec 31, 2007)

Forrest Root said:


> I'll put my money on what the pros believe as opposed to what you believe.


No wonder some people don't question Rush Limbaugh's drug addiction. :aureola:
________
Marijuana sativa


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## PigmyRacer (Oct 3, 2007)

CleavesF said:


> I'm not saying the equations are wrong, or your calculations. But honestly, I'm no longer a Mechanical Engineer major, I'm Biological Systems Engineering with a crappy 2 years of physics. If you know more that's great! But most enthusiasts know that rotating weight is best to limit first then static weight.
> 
> Maybe you don't care about acceleration... or you're only into TT's or something. Big deal! Just because you can't "feel" it doesn't imply insignificance. Nobody feels the aerodynamics of their bike's frame... but it makes a difference.
> 
> ...


This is possibly the most incoherent argument I've ever heard. I think you missed several important things along the way. One is that this isn't really a rotating vs. static weight argument. The whole point is that the crank has such a small radius that, although it is rotating, the fact that it is rotating has no profound impact on acceleration, etc... Even then, losing a hundred grams in WHEEL weight doesn't have much significance, so think of how pointless it is to try and shave that much from your pedals. 

The whole point here is not could you or should you, but whether it will make a noticeable difference. The fact that you think you feel a difference doesn't mean there is.


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## rkb (Apr 4, 2007)

The decision is made! Scored a set of Dura-ace brakes on Ebay and I am looking at getting the Look Keo Carbon cro-mo pedals. Cheaper than the Ti version and only 30 grams heavier, they are still 120 grams lighter than the Ultegras. 

Thanks again to everyone for the great debate. In terms of math I'm just beyond beating rocks together to make fire, but I still learned from all the posts. 

When it is all said and done the bike will weigh around 15.5lbs complete. A heavy bike by many weight weenies out there, but I'm happy with it.


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## PigmyRacer (Oct 3, 2007)

Nice compromise. Good call.


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## Forrest Root (Dec 22, 2006)

rkb said:


> The decision is made! Scored a set of Dura-ace brakes on Ebay and I am looking at getting the Look Keo Carbon cro-mo pedals. Cheaper than the Ti version and only 30 grams heavier, they are still 120 grams lighter than the Ultegras.
> 
> Thanks again to everyone for the great debate. In terms of math I'm just beyond beating rocks together to make fire, but I still learned from all the posts.
> 
> When it is all said and done the bike will weigh around 15.5lbs complete. A heavy bike by many weight weenies out there, but I'm happy with it.


15.5 is a fine weight. Have fun. Go fast, take chances, and for the sake of the gods, don't use the brakes.


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## Guest (Jan 22, 2008)

Heavy pedals make your bike more stable due to gyroscopic effect...conversely light pedals given more responsive handling.

/Don't forget to include the effect of the Earths rotation in your wattage calculations, to a degree this depends upon the azimuth you are travelling...minor things such as the local density of the Earth crust (effects gravity), sun spot activity/magnetic storms, and the position of the moon/tidal effects, should also not be ignored.


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## rkb (Apr 4, 2007)

the_rydster said:


> Heavy pedals make your bike more stable due to gyroscopic effect...conversely light pedals given more responsive handling.
> 
> /Don't forget to include the effect of the Earths rotation in your wattage calculations, to a degree this depends upon the azimuth you are travelling...minor things such as the local density of the Earth crust (effects gravity), sun spot activity/magnetic storms, and the position of the moon/tidal effects, should also not be ignored.


Yes, and correct me if I'm wrong, but these calculations will have to be reversed in the southern hemisphere.


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## Guest (Jan 22, 2008)

rkb said:


> Yes, and correct me if I'm wrong, but these calculations will have to be reversed in the southern hemisphere.


The way to get around that is to put the drive side on the left.


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## California L33 (Jan 20, 2006)

rkb said:


> Yes, and correct me if I'm wrong, but these calculations will have to be reversed in the southern hemisphere.


Not at all, because in the Northern hemisphere you start with a pedal up and push it down, then up. In the Southern Hemisphere you start with a pedal down and pull it up, then down- it all cancels out.


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## Forrest Root (Dec 22, 2006)

the_rydster said:


> Heavy pedals make your bike more stable due to gyroscopic effect...conversely light pedals given more responsive handling.
> 
> /Don't forget to include the effect of the Earths rotation in your wattage calculations, to a degree this depends upon the azimuth you are travelling...minor things such as the local density of the Earth crust (effects gravity), sun spot activity/magnetic storms, and the position of the moon/tidal effects, should also not be ignored.


Exactly. You have to account for, on Earth, centripetal and coriolis forces. As mentioned, then you need to add in the Moon's gravitational effect. But, if you want to do that exactly, then you'll need to solve the Earth-Moon-Venus problem, and as it happens the three body gravity problem hasn't been solved yet. Oh, you'll also have to account for the forces caused by the non-gravitationally related movements of the 26 or so movements the Earth makes.

And if you really want to optimize everything as best as possible, so that you can save that extra tenth of an attosecond, you should account for the varying radius of the Earth along your chosen ride path.


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## Guest (Jan 22, 2008)

Forrest Root said:


> And if you really want to optimize everything as best as possible, so that you can save that extra tenth of an attosecond, you should account for the varying radius of the Earth along your chosen ride path.


I heard the new Trek Madone was designed to take into account the curvature of the Earth's surface?


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## Juanmoretime (Nov 24, 2001)

You can customize your own frame to account for the curvature of the planet. You just need to run into the rear bumper of a parked car at the right speed. If done correctly it will add this dimple to your top and down tubes and that dimple adds areodynamics breaking up the air flow. I stole this from Zipp. Whey spend big money on an aero frame when you can do it yourself?


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## RobbieTunes (Jan 21, 2008)

Let's not forget the Yuengling effect, which accounts for the inertia/momentum of the heavy pedals acting as a flywheel. To enhance this, one must tie bricks to the bottom of the pedals, and only ride in straight lines.


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