Physics question (1)

Triathlon Forum
21

BTW, to answer the OP:

Power to over come rolling resistance = CrrM9.8*V. So, weight plays a role in overcoming rolling resistance.

Power to overcome gravity = M9.8V*sin(arctan(road_grade))

You can mess around with these formulas and determine the marginal wattage needed to overcome a marginal amount of additional weight.

Of course, the full set of equations is needed to do a complete analysis because each little change in one part affects some of the others (via velocity). There is also the aerodynamic part of the equation, delta-kinetic energy (which deals with starting/stopping, etc.* ), and drive-train losses.

**Frank thinks this is a big number on flat ground at a constant speed, but refuses to actually provide the formula or any calculations based on actual cycling dynamics. Extraordinary claims require extraordinary proof. You can’t just make stuff up or compare some rowing calculations to cycling by just guessing at numbers. *

22

**Frank thinks this is a big number on flat ground at a constant speed, but refuses to actually provide the formula or any calculations based on actual cycling dynamics. Extraordinary claims require extraordinary proof. You can’t just make stuff up or compare some rowing calculations to cycling by just guessing at numbers. *

Did I say this was a big number? No, I said it was a factor.

I did some calculations since you seem to lazy to do them yourself. I calculated that this effect may slow the average 20 mph rider about 1 minute over a century. The variation in speed from fastest to slowest as I calculated it is about 0.02 fps. It is a tiny variation but it occurs lots of times, hence the effect.

It is a small effect. It is not trivial (although some might consider it so - hardly worth the effort unless you lose by 45 seconds). Thanks for your attention to this matter.

23

Did I say this was a big number? No, I said it was a factor.

I did some calculations since you seem to lazy to do them yourself. .

No, I’m not lazy. Remember – the guy making the claim needs to do the math. Since you are so proud of your familiarity with publication standards, use those standards now. Show us the formula and its solution. When I made claims about rolling resistance, I posted the raw data, the formula(s) and method of solving it(them).

Speaking of which – what’s your raw data? What pedal torque profile did you assume – did you use a continuous model or did you assume discreet arcs? If you used arcs, how many radians was each one? Naturally, since you are comparing two riders, you used two sets of assumptions. Would you be so kind as to post both?

Inquiring minds want to know whether this is a real, actual effect or if you’re just blowing smoke.

24

Phoeey. I am not submitting this for peer review.

My claim was that speed variation slows overal time and that most cycling calculators ignore this. If you want the proof that the variation affects time is the rowing slide, they already did the work and they are not me - the principle is the same. Another real world example is the difference in gas mileage one gets on cruise control or manual throttle control for the same average speed. The variations in speed are much greater there but there will usually be a difference in gas mileage on the order of 10%. It is pretty straight forward physics and if you don’t understand it now my putting some calculations here isn’t going to convince you.

The proof that analytic cycling doesn’t consider it is there is no variable for that even though they have one variable for changes that are usually (but not always) trivial such as air density (which usually only is important if at altitude or trying to set a new world record at Battle Mountain when temperature and humidity can affect the speeds even though the altitude is constant).

Whatever, it is really a small effect but it is an effect. Believe it or not.

25

The easiest way (apologies if this was covered somewhere already) is to just factor in rolling resistance. So if you want to be very specific, you can get an exact Crr for the tires you use. Or, you can just ballpark it and use 0.0050 as a reasonable “average” tire Crr value.

Then it is just Crrmgv
m=mass in kg
g=9.81m/s^2
(or weight in lbs. * 4.44 replaces mg)
v=speed in meters-per-second (divide by 2 from miles per hour for a rough calculation)

That will give you a close enough approximation.

So dropping 15lbs. would save you about 4 watts at 20mph on level ground. The real savings, of course, factor in when you start to go uphill…

You can head over to analyticcycling.com if you want to get really technical and factor in road grades, etc.

26

Frank, I’ve never posted on a PC thread (so what has happened to my judgment some may wonder) and am intrigued by your product (despite my concerns about lack of scientific validation of value). Now, however, I have no interest because you have made such silly statements above.

FYI, I think that your theory was debunked (with calculations) here earlier. I think it was in response to some thread about a heavy disk wheel being used for some track record. Without running any numbers, anyone who has coasted on a bike and rowed a boat can tell that the decelaration force while cycling is insignificant compared to rowing. Not surprising since in one case primary resistance comes from a FLUID and in other case from a GAS. Also speed in cycling is higher, resulting in greater inertia, and cycle time for force application (pedal stroke v. oar stroke) is quicker. In short, the mystery loss is trivial.

Do you really think the physics whizzes making the calculators would ignore something significant?

27

Well, you don’t need to prove anything through math to me. It is intuative that a constant, say, 250W applied to the rear wheel will be faster than an average 250W varying from say 220 to 280, or whatever. Accelleration always costs more energy than maintaining a given speed. The affect on your bike split may be insignificant or not, but it is certainly there.

However, you imply that cyclist are best served by maintaining this consistent power, and here I am not in agreement. I believe you are best served by using and developing the strong muscles just as much as the weaker muscles.

Take this analogy. There is no doubt in my mind that I can leg press much more weight than I can leg curl, so if someone challenged me to lift as much weight as possible in 30 minutes using a combination of leg presses and curls, I would do nearly all of it on the leg press machine. If I put say 50lbs on the leg curl machine (about the most I can do for high reps) and 50lbs on the leg press machine, and did 50% on each one, I’d fall way short of my maximum, since I could probably do (guessing) well over 100lbs of leg presses nearly indefinitely. Maybe with enough training I could get my leg curls up to 60 or 70 lbs, but equal training would probably improve my leg presses a similar percentage.

Similarly, I can maintain much more power on the downstroke than I can the rest of the pedal cycle. So if I focus all my training and energy on improving the weak part of my stroke, I am neglecting my strength. I believe in challenging my muscles in training all the way around the stroke, not just on the upside.

My guess is you’ve heard this arguement before, and are preparing your canned response. I’ve probably already heard that too. It’s like the story where the guys in prison all memorized the same joke book, so instead of telling the whole joke they just said “Joke 143” and everybody laughed. You can just respond with “power cranks thread #43454”. Your device is a good tool for training for those who can afford it to supplement the other training they are doing…I’ll leave you with that.

Dan

28

Frank, I’ve never posted on a PC thread (so what has happened to my judgment some may wonder) and am intrigued by your product (despite my concerns about lack of scientific validation of value). Now, however, I have no interest because you have made such silly statements above.

FYI, I think that your theory was debunked (with calculations) here earlier. I think it was in response to some thread about a heavy disk wheel being used for some track record. Without running any numbers, anyone who has coasted on a bike and rowed a boat can tell that the decelaration force while cycling is insignificant compared to rowing. Not surprising since in one case primary resistance comes from a FLUID and in other case from a GAS. Also speed in cycling is higher, resulting in greater inertia, and cycle time for force application (pedal stroke v. oar stroke) is quicker. In short, the mystery loss is trivial.

Do you really think the physics whizzes making the calculators would ignore something significant?

The principle still applies. Usually the math/physics whizzes will caclulate everything they think applies then comment that the effect of one thing or another is trivial. They have not done so in any equation I have ever seen discussed so I presume they haven’t thought to look. This is probably because the effect as they observe it is so small they cannot discern there is any difference so they presume pedaling is smooth and there would be no effect. As I noted earlier I calculated the variation would be 0.02fps, a seemingly trivial amount.

Whether the effect is small (even to the point of being trivial) the math says the effect should be there. The change of mass when a uranium atom divides is also trivial when taken one atom at a time. But, when lots of them happen to divide at nearly the same time the effects are noticeable. The only question is the magnitude, not whether it exists or not.

I will accept your conclusion the effect is trivial (after all trivial is in the eyes of the beholder, even I think it is a small effect). I will not accept your or anyone elses conclusion the effect does not exist.

But, this is ST, where people argue over trivial savings and minutiae. How much time do people save leaving their shoes on their bike in T1 for an Ironman. Is that savings trivial in your opinion?

What a shame we don’t all think the same. Then we would ust all agree and go out for a beer, in stead of disagreeing and going out for a beer. Oh wait, we would all still be riding penny farthings (although Cervelo would make the best ones I am sure) and there would be no such thing as ironman if we all thought the same.

I clearly think about some of these things a little differently than the average person or I would have never come up with the PC idea (or participated in the first IM). Anyhow, my product asks your forgiveness for my having the kind of personality that allows me to express some of my “different” views in some of these discussions without apology (except when I am shown to be wrong)

Cheers.

29

Whatever, it is really a small effect but it is an effect. Believe it or not.

Read more carefully and don’t insult my intelligence. I never said there is no such effect. All I have been saying is that you need to back up your claim. You allege that the effect has a specific value. I said, prove it. You just made up the number, and you know it. So does everyone else here.

There is such an effect. It can, in fact, be calculated. You didn’t calculate it with anything approaching rigor, yet you throw out a guess anyway. That’s cool – nothing wrong with guessing. You just need to say, “I just guessed. I really have no idea.” Look, plenty of people on ST guess and make conjectures and report lore as fact all the time. No big deal. You, on the other hand, are selling something with every post, and that means you get held to a higher standard. If you want to make factual claims in an attempt to sell your product, you’re going to have to back it up.

There is a reason the AC.com people don’t have a variable for the effect you are speculating about. Believe it or not, they are real, actual smart people running that site. They know about the delta-KE force acting on a bicycle. There is a term of art used to describe what you find when you do go through the trouble to calculate it:

*Vanishingly small. *

We get bigger effects by worrying about humidity, altitude and other minutiae.

30

Whatever, it is really a small effect but it is an effect. Believe it or not.

Read more carefully and don’t insult my intelligence.

Read carefully and don’t insult my intelligence. I never implied that there was a specific value for this effect nor was I trying to sell anything with the post. This is what I wrote that brought on your wrath: “I would agree but this is not strictly a weight effect. Actually, there is another element that would slow you down overall despite the same average power output and it is ignored by all the calculators. It is the energy required to constantly speed up the bike after the wind slows it down 180 times a minute or so from the irregular application of pedal force we all have. The more irregular the application of pedal force (more of a “masher” or a lower the spinscan number) the bigger this effect will be.”

I only said it was an effect that was ignored by most. You asked for a specific value and I gave what I thought was probably a good order of magnitude guessimate without doing specific calculations, and I said so. What is your heartburn with me? I mean, this is a discussion group and someone asked what the effect of changing weight might be. And, the post was made without regard to selling anything. This supposed smoothing would be a tiny benefit and hardly worth $800 if that was all they did, but this smoothing has almost nothing to do with the major benefit of the product and was not the point of the post.

If the people at AC have considered this effect it is not clear from the site. You now acknowledge it is real as are the effects of humidity (which is included on the site). You also acknowledge these calculations have been done. The ball is in your court now. Put up or shut up.

I want to see the calculations (and the assumptions upon which they are based) that show this effect to be “vanishingly small compared to changes in humidity”. You’ve done them and have stated this to be the case. Now it is your time to prove it. Of course, the analysis has to allow for differing applications of force and differing cadences. Surely there would be an effect if the speed were 25 mph, the cadence were 10, and the power on portion of the stroke were only 25% of the time. At what combination of speed, cadence, and irregular power application does the effect become “vanishingly small”?

If my analysis was wrong I will admit it. Show me the analysis. Again, your turn to put up or shut up.

31

Well, you don’t need to prove anything through math to me. It is intuative that a constant, say, 250W applied to the rear wheel will be faster than an average 250W varying from say 220 to 280, or whatever. Accelleration always costs more energy than maintaining a given speed. The affect on your bike split may be insignificant or not, but it is certainly there.

However, you imply that cyclist are best served by maintaining this consistent power, and here I am not in agreement. I believe you are best served by using and developing the strong muscles just as much as the weaker muscles.

Take this analogy. There is no doubt in my mind that I can leg press much more weight than I can leg curl, so if someone challenged me to lift as much weight as possible in 30 minutes using a combination of leg presses and curls, I would do nearly all of it on the leg press machine. If I put say 50lbs on the leg curl machine (about the most I can do for high reps) and 50lbs on the leg press machine, and did 50% on each one, I’d fall way short of my maximum, since I could probably do (guessing) well over 100lbs of leg presses nearly indefinitely. Maybe with enough training I could get my leg curls up to 60 or 70 lbs, but equal training would probably improve my leg presses a similar percentage.

Similarly, I can maintain much more power on the downstroke than I can the rest of the pedal cycle. So if I focus all my training and energy on improving the weak part of my stroke, I am neglecting my strength. I believe in challenging my muscles in training all the way around the stroke, not just on the upside.

My guess is you’ve heard this arguement before, and are preparing your canned response. I’ve probably already heard that too. It’s like the story where the guys in prison all memorized the same joke book, so instead of telling the whole joke they just said “Joke 143” and everybody laughed. You can just respond with “power cranks thread #43454”. Your device is a good tool for training for those who can afford it to supplement the other training they are doing…I’ll leave you with that.

Dan

I understand your argument. I only suggest it is better to use all the muscles equally according to their ability. If you are riding at 70% effort all the muscles should be working at 70% of their ability, not some at 80% and other “smaller” muscles at 50%.

Anyhow, the data someday will speak for itself. Stay tuned.

32

Anyhow, the data someday will speak for itself. Stay tuned.

Geez Frank. Are you for real?

Someday we’ll all be dead.

33

Ok I agree with you. We should have a beer. If I’m so lucky to meet you,it would be an honor to buy you one. You are a gentleman

While I don’t believe we lose much energy to acceleration/deceleration, I’m still intrigued by PCs, mainly as a way to work running muscles w/out the pounding of running.

Best of luck to you.