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Pedal weight...(25 posts)

Pedal weight...must_pedal_harder
Apr 30, 2001 6:39 PM
I've been thinking about pedal weight over the weekend when it came to me.

What exactly are the advantages of a lighter pedal? Wouldn't the effect just cancel eachother out? Here's what I'm saying...

Downstroke, pedal weight is helping you(?)
Up and over, pulling the pedal.

Obviously, when one pedal is being pulled the other is being pushed down and back so wouldn't the weight of the pedals just cancel eachother out?

Stop me if I'm wrong, but that's just how my simple mind works : /
re: Pedal weight...simstress
Apr 30, 2001 11:01 PM
Interesting thought. I have no idea if it is sound.

I don't worry about rotational weight on my pedals though. When I changed to Speedplay's, I think I wanted to reduce the gross vehicle weight while getting some double-sided pedals.
re: Pedal weight...Waylon Smithers
May 1, 2001 8:53 AM
Simplism: weight=mass=inertia

Don't you abhor inertia? (both rotaional and translational)
Yes and Nogrz mnky
May 1, 2001 3:17 PM
Yes the weight of the two pedals cancel each other out with respect to the center of the BB. The same is true with the wheels about their axles. The weight of these various components have a rotational factor which really only comes into play when the speed changes (positive or negative) and there is an acceleration. Finally there is a very important consideration in that you ultimately have to supply the energy to haul you and the entire bike up every single hill. F=ma rules the day. One would be tempted to consider this live weight since it is connected to your legs, but the mass is evenly split and not available to help you apply more force to the crank via gravity through your body. Hope this helps!
Yes and NoWaylon Smithers
May 2, 2001 9:36 AM
"F=ma rules the day" True, but only when accelerating

Simplism: Work = force X distance, and Work = Energy.

Thus when climbing a hill at a constant velocity we can simply state:

Work = Energy = weight X height climbed
Yeah So?grz mnky
May 2, 2001 1:25 PM
When climbing, by definition you are accelerating against gravity. We could also be a bit more precise and say that KE=mgh and carry the uits through and then have the fun discussion of the distinction between a pound force and a pound mass in the English System. We could then expand the discussion to include that Power = Work x Time. BFD. At some point it's just showing off and intelectual masturbation.

I didn't really want to go into all the analysis and free body diagrams - even thought it is one of my favorite topics. Those of us that are engineers or have a good physics backround have been down this road. Those that aren't techies are usually not entertained. However, I was trying to provide some insight as to what the effect of pedal weight was based on the original question stating that shouldn't it all be cancelled out - in layman's terms.

I'm pretty sure I've already been through all the lectures, problems sets, and exams.
Yeah So?Waylon Smithers
May 3, 2001 9:16 AM
"I'm pretty sure I've already been through all the lectures, problems sets, and exams."

Je suis un mecanique ingeieur assi!

BSME 1990, Summa Cum Laude, Northeastern University, Boston, Ma.
That's Too Badgrz mnky
May 3, 2001 10:36 AM
BSME Cornell Univ. 1984 - MBA '93

Northeastern was my no-brainer backup.
Even with Daddy's tuition moneyWaylon Smithers
May 3, 2001 2:21 PM
you sure have forgotten some basics: "When climbing, by definition you are accelerating against gravity."

This is NOT true.

Acceleration is change in the velocity vector (with respect to magnitude or direction).

The acceleration of (or due to) gravity is the acceleration of a FALLING body in the earth's gravitational field, a change in the body's velocity of 9.8m/s/s (32ft/s/s). A body at rest, or climbing at a constant speed (constant velocity) is not accelerating.

Your F=ma does not rule the day.
Naw - Your Daddy's Tax Moneygrz mnky
May 3, 2001 5:18 PM
Took the full ROTC schoolarship and used my student loans to buy toys - that would be YOUR daddy's tax money (as well as mine). It didn't cost him a dime. When I was done they trained me fly jets and burn more tax money (i.e. fuel). Why pay for a good school and fun if you don't have too? I guess the only thing worse is to pay for a poor one.

Actually, to put it in your words, acceleration is the RATE of change in velocity vector.

You're dead wrong about a body at rest not being under acceleration, otherwise we would have no weight. Think about it. Weight = mass x gravity = Force. It doesn't matter if you're moving with velocity or at rest - everything on the surface of the earth is under gravitational acceleration of 32.2 ft/s^2. If you don't think that F=ma then you should surrender your degree - they obviously made a mistake in giving it to you.
You have misunderstood some thingsWaylon Smithers
May 4, 2001 8:48 AM
"You're dead wrong about a body at rest not being under acceleration, otherwise we would have no weight."

Think of this:
There is a large spherical magnet and a smaller piece of iron on it's surface. (Now I know the force due to gravity is much, much weaker than magnetism). Both the sphere and the piece of iron on it's surface are at rest (in relation to the veiwer's frame of reference). Thus, they both are not moving. The piece of iron is experiencing an attractive force towards the spherical magnet, it's "weight". (again, I realize the magnetic attractive force is a thousand fold greater than the gravitational attractive force)

Now the question: Is the piece of iron under acceleration?

It is NOT accelerating.

You may replace the large spherical magnet with the earth and the small piece of iron with an object.

Is the object under acceleration?

It is NOT accelerating.

I am dead wrong however in retaliating to your insults. The other readers will notice that you first attacked not only my arguement, but also make degroatory statements about me. I relatiated, and should not have, although I really feel the urge to insult you.
Let me guess, minor in Frenchtommyb
May 4, 2001 1:00 AM
I normally frown on correcting spelling and grammar in web boards, but in this case, I can't resist.

Je suis un mecanique ingeieur assi!

should be:

Je suis un ingenieur mecanicien aussi!

tommyb
L'Institut National des Sciences Appliquees
Lyon, France
Let me guess, minor in French: Not even,Waylon Smithers
May 4, 2001 9:22 AM
Je parle Francais mal, n'est-ce pas?

I took a few courses in high school. If I could study another language again, it could very well be Latin!
Safe to Saygrz mnky
May 4, 2001 1:00 PM
Your knowledge of French is on par with your engineering. On the surface it's passable, but the details are another story. You should pay attention to what you sling.
Stopped with your engineering logic/knowlege?Waylon Smithers
May 4, 2001 3:19 PM
Why can't you defeat my last post on acceleration due to gravity?

Because you are wrong, and I have been correct.
You're New Here, Right?grz mnky
May 4, 2001 5:18 PM
Everyone knows I try to never beat up retards on Fridays. Just one of those things.

Actually, I'm running out of pee for our pissing contest. Fact of the matter is neither one of us is going to convince the other of anything. The rest of our audience, assuming anyone is still paying attention, couldn't really care. There are lots of other technical savy folks out there who know right from wrong, but for one reason or another don't want to march down this road. Any one of a number of them would love to jump into the fray on _your_ side if you had a leg to stand on. Even your French is bad. Never debate a fact is usually good advice.

What is true is that I've gotten under your skin and now you're taking it all quite personally. Check on the general message board - it's been proposed that one sign of being a "Fred" is to let Grz Mnky piss you off. This is probably true.

Lemme get back to you.....it's play time!
Grz mnky: You fool, you're Engineering Knowlege Sux !!!!!Waylon Smithers
May 4, 2001 7:40 PM
grz mnky,

The fact of the matter is this, YOU BACKED DOWN. I understand. You were all wrong about F=ma and acceleration due to gravity.

Your basic engineering aptitude is horrible. Your instructors would be ashamed to know that a school of engineering graduate would make such erroneous statements that you have done here. I bet most high school physics students would know more about the subject than you.

Good thing you are a bean counter. Your engineering sux. You fool.
Grz mnky: You fool, you're Engineering Knowlege Sux !!!!!mr tornado head
May 6, 2001 9:32 AM
Look, drop it already. You are getting annoying. And you've yet to really answer the pedal question.

Please, if you want to drag me into the pissing contest, do it by email. Don't wast the bandwidth here.
Grz mnky: You fool, you're Engineering Knowlege Sux !!!!!mr tornado head
May 6, 2001 9:33 AM
Waylon;

Look, drop it already. You are getting annoying. And you've yet to really answer the pedal question.

Please, if you want to drag me into the pissing contest, do it by email. Don't wast the bandwidth here.
I challange you to prove my statements wrong,Waylon Smithers
May 4, 2001 3:49 PM
or is it that you can not, thus you resort to further derogatory remarks?

Come on, go for it. prove me wrong.

Other readers themselves can try this easy experiment.

Place a simple bathroom scale on the floor of an elevator. Place a non-moving object on the scale while the elevator is stationary. Read the weight of the object. (The weight is actually the force the object experiences due to gravity).

When the elevator first starts to move up (accelerates up) there will be an initial increase in the bathroom scale's reading due to the acceleration on the object. When the elevator reaches a steady speed (consider it to be a smooth elevator) the reading on the scale will be the same as when the elevator was stationary. Same thing will happen while going down. (Except there will be an initial decrease in thw "weight" before the elevator reaches a steady speed.)

Simplism: Without motion, there can not be acceleration.

It matters not if the attractive force is gravity or magnetic or atomic.
simple demonstrationDuane Gran
May 2, 2001 10:29 AM
Others have given more technical answers, but there is a simple observational way to see how these forces don't equal out for the rider's purpose. Imagine taking a small weight and adding it to your ankles. Already you should have a mental image of working harder. Instinctively we know it to be true, and indeed it is.

Another mental model is to see that the pedal moves in a circle. While most of the force is in the downward direction, one must move the pedals through the 12 and 6 O'clock positions where gravity has less of an effect. At this point you are basically moving the pedal, light or heavy. Light is easier.

Another consideration is simply that the crank isn't a zero-sum system. I think I'm using the right term here, but corrections are welcome. In short, you can't get the pedal started in motion and expect the other pedeal to pull it through in perpetual motion. The crank system absorbes a lot of energy. In spite of it all, it is a pretty efficient system.

Now... none of this really scratches the surface of weather or not saving 100g on a pedal makes us much faster, but the thought of adding 100g sure seems slow, doesn't it?
simple demonstrationgrz mnky
May 2, 2001 1:28 PM
Your first paragraph is correct, but unfortunately your second and third are not. Your illustration with a weight attached to each leg is an excellent one and was how I mentally started my analysis.
simple demonstrationLC
May 3, 2001 1:06 PM
Here is something you can try to see if you can feel the difference. Put on some of those strap on ankle weights and see if you feel the difference. You will notice that it seems to take forever to spin up to speed, and the same thing is happening with heavier pedals or shoes too.
efficiency vs. weightDog
May 3, 2001 3:01 PM
I've tried a dozen kinds of pedals. While Speedplays no doubt are the lightest, I can't tell the difference in weight on the bike. While I like to think of myself as a weight weenie, I use Looks now, after using Speedplay X/1's for over 10,000 miles. The comfort and efficiency the Looks provide me, compared to the Speedplays, vastly outweighs the benefits of the Speedplays' lighter weight. But that's just me.

The increased weight will matter somewhat when climbing or accellerating hard (sprinting). But, there is a chance the weight can be offset by inefficiency.

Doug
(B.S. Philosophy; J.D.) <---that's supposed to be funny
Shoe weight?Hap
May 4, 2001 2:19 PM
I was looking at shoes in some mail order catalogs after reading this thread and it occured to me that none of the shoe weights were listed. Shoes are a critical peice of equipment and not an area I would want to skimp in, but why no weights listed?

Hap -> BS Marketing & Advertising (The study of the science of BS) :)