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Here's a bit of a test for these ideas. Get two big water bottles, fill 'em up, put 'em in your bottle cages and go for a short ride including a hill or two. Now, put the bottles in your rear pockets secure enough so they're not moving around on your back. Do the same ride. Which feels better?Here's my guess. If you've got a really light bike, the bottles on the bike will make it feel heavy and sluggish, making you feel faster with them on your back. The heavier you and the bike are, the less you would notice any of this. I really thinkthat weight questions like this have a lot to do with bike weight relative to rider weight.
 
Kerry Irons said:
Simple physics will tell you that rotating weight is only meaningful when you accelerate...This is a simple, physical fact, and not something that is debateable.
simple physics seems to ignore friction and wind resistance. the simple, physical fact is that a cyclist is constantly decelerating due to these facts - unless countering them with an applied force.
 
jaekormtb said:
Here's a bit of a test for these ideas. Get two big water bottles, fill 'em up, put 'em in your bottle cages and go for a short ride including a hill or two. Now, put the bottles in your rear pockets secure enough so they're not moving around on your back. Do the same ride. Which feels better?Here's my guess. If you've got a really light bike, the bottles on the bike will make it feel heavy and sluggish, making you feel faster with them on your back. The heavier you and the bike are, the less you would notice any of this. I really thinkthat weight questions like this have a lot to do with bike weight relative to rider weight.
I definitely sense something is there on my MTB carrying two large water bottles. I don't throw around my road bike nearly enough to "really" feel anything. My full suspension MTB is 23.3lbs and the road bike is about 16.3lbs.
 
Coolhand said:
You will notice dropping a pound of bike weight much more readily, because the percentage change is huge in comparison to dropping a pound of body weight. .

It doesn't matter, because you have to haul both the rider and the bike up the hill. If the rider and bike together weigh 200 lbs, 1 pound is 0.5% of the weight of the system. Take the weight from where you will, it's the same thing. Taking it off the bike will be more noticeable, but I bet if you averaged your times up some of your favorite hills over a period of a few weeks, youl'd notice little or no change.

Considering that, for us recreational riders, or even non-elite racers, physical performance can vary by large amounts, maybe up to 10%, spending money on a 1 or 2 percent improvement seems silly.

Just remember, a burrito and a beer weighs three pounds.

--Shannon
 
Kerry Irons said:
Simple physics will tell you that rotating weight is only meaningful when you accelerate. IOW, a pound of wheel weight is the same as a pound of water bottle weight at constant speed. If your speed is going up and down, then you take double the energy to accelerate the wheels (compared to non-rotating weight) but you get that energy back when you decelerate. Unless you're constantly braking, wheel weight is the same as other bike or rider weight when you average things out. This is a simple, physical fact, and not something that is debateable.
Kerry, I always read your posts in the threads we are both in. The simple fact is that riders in many typical group ride, race or hill climbing situations are constantly changing speeds (as the pull out and off, in and out of corners, on different slopes of the climb, whenever they attack, or react to attacks, whenever they sprint for the line or the town line sign, ect.). Only if you are doing lots of long solo rides without climbs or stop signs and long TT's does this become less of an issue and the aero aspects become more important. You were right about one thing- the importance of rotating weight isn't debatable. For most riders, rotating weight is king- those pedals, cranks and wheelsets are what you are going to have to spin, so the lighter they are, the easier it will be.

Coolhand
 
A better test

jaekormtb said:
Here's a bit of a test for these ideas. Get two big water bottles, fill 'em up, put 'em in your bottle cages and go for a short ride including a hill or two. Now, put the bottles in your rear pockets secure enough so they're not moving around on your back. Do the same ride. Which feels better?Here's my guess. If you've got a really light bike, the bottles on the bike will make it feel heavy and sluggish, making you feel faster with them on your back. The heavier you and the bike are, the less you would notice any of this. I really thinkthat weight questions like this have a lot to do with bike weight relative to rider weight.
Interesting. The better test would be two indentical bikes. One with a wheelset which is a pound lighter. The other carrying a pound of water (not for drinking) in the bottles. So overall, the bikes and rider have the same weight each time. Assuming (as we must to make the test work) that the rider is able to put out the exact same effort on both climbs of the course, will he have the same time for each bike?

I say no- the lighter wheelset equipped bike will have the better time. But I am curious to see if it actually holds true or not and what the difference in time would be percentages wise. I know I climb better with a lighter wheelset, as do the other riders in my club- and most racers in general. But it would be fun to quantify the difference, wouldn't it?

:)
 
Physics, one more time

Unless you are using your brakes to burn up the rotational kinetic energy in your wheels, you GET IT ALL BACK when you coast. Therefore, the total energy expenditure over the ride is the same whether the weight is in the wheels, in a water bottle on the frame or in your back pocket, or in your body. It may FEEL faster by shifting weight from wheels to someplace else, it may FEEL faster to have weight on your body than on your bike, but the physics is immutable - it IS NOT faster. This is easy to prove, and it has nothing to do with how fast you are going, how much wind resistance there is, what your tire, chain, or bearing friction is, etc. The extra energy it takes to spin up a heavier wheel is returned when you coast, whether that coasting is down a long hill, or just the "micro coasting" that takes place in tiny speed fluctuations during each pedal revolution.

And another point - the kinetic energy of accelerating wheels IS double that of the KE of any other mass in the bike-rider system. This is because the wheels (rim and tire) are rotating at the same speed as the bike. Pedals, shoes, cranks, hubs, and BB axles are rotating so slowly that the additional KE from spinning them is infintesimal. I know that lots of people BELIEVE that wheel mass is super significant compared to everything else, but unless you are in a crit where you are braking for every corner, wheel (rim and tire) mass is EXACTLY the same as any other. Full stop.

I'd be happy to present the physics equations that prove this, if there's interest.
 
Kerry, thanks for your post. First, while simple equations are good for academic discussion, if they do not factor in all of the real world factors, such as wind, grade, group riding and taking pulls, pulling off and accelleration back onto the group the proposed model is flawed and worthless. Rather then dealing in abstractions, lets deal with the actual racing world. Outside of TT's (were aero is more important then anything else), teams, coachs and althletes have all found that lighter rotating parts are key, especially in any sort of climbing situation. Even rec level racers have felt the major difference of going from training wheels and tires to their race setups. Now maybe all these decades of experience could be mistaken (heavens knows it wouldn't be the first time), but you will need more evidence then a self devised physics model.

If you can find any studies which prove your assertion, please provide me a link and I will read them. I will try and do the same for you. Deal?
 
Coolhand said:
If you can find any studies which prove your assertion, please provide me a link and I will read them. I will try and do the same for you. Deal?
Some quick things I found already:

http://www.cptips.com/energy.htm

Finally, weight is a factor in sprints where inertia (the resistance to setting an object into motion - why it is harder to get up to speed on a bike than to maintain that speed) comes into play. It definitely takes more energy to accelerate a heavier rider/bike combination in a sprint. And extra weight in some bike components (rims for example) may require twice as much energy to accelerate as an equal weight in the frame. This is a result of the fact that with rotational speed you are accelerating these components much more quickly. (Note: this means you should upgrade your tires, rims, crankset, and shoes before you spend your extra $$ to decrease your frame weight an equal amount).
Looking for a more accurate model- check this out (not for the faint of heart):

http://www.analyticcycling.com/WheelsConcept_Page.html

More fun:

http://search.bikelist.org./ term "inertia"

I am an engineer working at Cane Creek Cycling components and have measured
the moments of inertia of many wheels. Here's some numbers for you:

Cane Creek Aerohead with Ti Spokes (24 front/28 rear):
Front wheel mass: 675 g
Front wheel MOI: 45.5 g*m^2
Front wheel "equivalent mass": 1080 g
Rear wheel mass: 892 g
Rear wheel MOI: 44.3 g*m^2
Rear wheel "equivalent mass": 1287 g
Combined "equivalent mass": 2367 g (5.22 lb)

Cane Creek Carbon:
Front wheel mass: 659 g
Front wheel MOI: 42.2 g*m^2
Front wheel "equivalent mass": 1037 g
Rear wheel mass: 928 g
Rear wheel MOI: 43.6 g*m^2
Rear wheel "equivalent mass": 1317 g
Combined "equivalent mass": 2354 g (5.18 lb)

Rolf Vector Pro:
Front wheel mass: 795 g
Front wheel MOI: 56.2 g*m^2
Front wheel "equivalent mass": 1296 g
Rear wheel mass: 1006 g
Rear wheel MOI: 56.4 g*m^2
Rear wheel "equivalent mass": 1509 g
Combined "equivalent mass": 2804 g (6.18 lb)

Mavic Ksyrium:
Front wheel mass: 740 g
Front wheel MOI: 48.7 g*m^2
Front wheel "equivalent mass": 1174 g
Rear wheel mass: 933 g
Rear wheel MOI: 51.1 g*m^2
Rear wheel "equivalent mass": 1388 g
Combined "equivalent mass": 2562 g (5.65 lb)

All of the above values were from random production wheels.

My term equivalent mass is a combination of the mass and the moment of
inertia. The moment of inertia, I, can be converted to a simple mass, m,
by converting the equation T=I*alpha into F=m*a. Since T=F*r and
alpha=a/r, T=I*alpha is equivalent to F*r=I*(a/r) or F=I/r^2*a. So I/r^2
acts like an additional translated mass and accounts for the rotational
inertia. Using a typical 700c wheel outer radius, 1/r^2 is a constant and
is 8.91 when using the units of grams and meters. [For those not familar
with the formulas; T=torque, I=moment of inertia, alpha=angular
(rotational) acceleration, F=force, m=mass, a=acceleration (translational).
These equations are from Newton's 2nd Law.]

>From the combination, it can be stated, for example, that using a Rolf
Vector Pro wheelset has the effect of adding 0.44 kg (1 pound) additional
mass during acceleration versus the use of a Cane Creek Aerohead wheelset.

You are correct in your assumption that the relatively heavier rim causes
the MOI to be higher than an equivalent mass wheel using more spokes. This
logic is exactly why we place even our spoke nipples at the hub, where they
contribute significantly less to the MOI. So when comparing the masses of
wheels, pay attention not only to the mass, but where it is distributed.
If you add 1g to a rim (at 300 mm radius) it has the same effect on MOI as
adding 225g to a hub (at 20 mm radius)!

Rob Tison
Cane Creek Cycling Components
another point made on the list:

I suspect you haven't raced much if you think acceleration is not a factor
in road racing. I am an active USCF Category 2 racer and have experienced
accelerations as a significant factor in every race except for straight and
flat time trials. As a category 2 racer, I've had the privilege of racing
in many US National Calendar races with the best racers in the US. The
accelerations at this level are fierce and often. If you can't accelerate
hard enough to close the slightest gap to maintain a draft during a race,
you can quickly be off the back. Races are either won by a field sprint,
or a by riders in a breakaway group. Acceleration is a major factor in a
sprint where it is essential to accelerate away from a pursuer trying to
stay in your slipstream. Acceleration is also how a breakaway group
establishes itself with an attack on the field of riders. Most attacks are
unsuccessful requiring repeated attacks before success. These attacks can
occur repeatedly during a road race lasting several hours. In races, there
is nearly always an acceleration out of every turn as well. Lower mass and
MOI mean one can accelerate with less effort, conserving valuable energy.
Or, lower mass and MOI can enable better accelerations with a given
effort. Opponents are "dropped" during quick accelerations to which they
cannot respond. Since there is such a great aerodynamic advantage in
drafting, it is impossible to ride someone off of your wheel by increasing
the pace by a small percent.

In road races differing from the traditional road race accelerations can be
even more important. A good example is racing a criterium (the most common
road races in USA) where a typical race may last 1 hour, and be ridden on a
typical course with 6 right angle turns per kilometer lap. With a
reasonable average speed of 28 mph (45 kph), this results in more than 270
hard accelerations per race. To think acceleration is not a factor here is
unimaginable.
There are good people arguing your side as well. Take a look, its is a fun (if nerdy) discussion by some of the luminaries of the cycling world.

For example, Keith Bontrager makes a good point here:

The issue for optimizing the characteristics for a racing wheel
is also subtle. The compromise between aerodynamics (which is
a significant parameter for many events), weight (important in
a mountain TT where speeds are slower) and the wheel's M.O.I.,
is not an easy one to work out in order to optimize a wheel for
a given event.
:)
 
Are you jumping in the deep end?

coreyb said:
simple physics seems to ignore friction and wind resistance. the simple, physical fact is that a cyclist is constantly decelerating due to these facts - unless countering them with an applied force.
F=ma, if all forces are balanced, netF=0, a=0.

What you wrote was correct, but irrelevant. Physics (even simple physics) does not ignore friction (mechanical or fluid). When a riders forward velocity is constant, his acceleration is zero, regardless of friction, gradient, or time of day.

Now, if we want to talk about rotating mass, and the resultant forces caused by centripital acceleration at constant rpms, we can really drift this thread!
 
Isn't this pointless to argue about?

Unless you are a Pro/Elite you probably CAN afford to lose 10lbs of fat and/or lose some upper body muscle. I know there are lots of people who like to just say they are "heavy" or "dense" or "I just have too much muscle" or something but IMO most of that is BS. Most of those people that I've met are just fat and could lose lots of weight without losing strength at all. It seems to be an overall thing with American men, everyone automatically thinks heavier is stronger.

And like someone said 10lbs of fat loss blows away any bike changes. It's the difference between struggling in your lowest gear up a hill and blasting over it in the big ring in a lot of cases.

Ben
 
Again, the physics is simple

You are just calculating the kinetic energy of rotation at different conditions. You can set the conditions to anything you want - any rim/tire weight, any speed, any change of speed. The KE of a rotating wheel is mV^2, and the KE of everything else is 1/2mV^2. Grade is not a factor, wind is not a factor, group riding is not a factor, etc. You are just looking at the KE required to accelerate.

If your case is a sprint, then of course lighter wheels are more important, because you never get the stored energy back through coasting. Same situation if you are using the brakes to slow down rather than coasting, because you never get the stored energy back.

However, if you accelerate to pass someone, you have to generate the power to increase your system KE. When you return to the group's speed, you get that KE back. Ifyou drop to the back of the group, you lose some KE (and so don't have to pedal as hard) and then have to regenerate it when you accelerate back to group speed. Your KE balance is zero. Whether it is windy or not makes no difference, as that drag doesn't change as a result of changes in wheel or bike/rider weight. Whether you are on a hill or not makes no difference because KE is strictly a function of speed and weight - there is no "g" term in the KE calculation.

Weight is important in climbing hills, no question. The question is whether transferring the weight between the rim/tire and the rest of the bike/rider system makes a difference. It does not and there is no physical principle you can cite that would suggest that it does. The AnalyticCycling site uses the KE equations noted above. I am not aware of any studies ever done to test the physics. If you believe that such a study would prove your point, then it would require something like lead filled wheels vs. lead filled water bottles to get a difference large enough to rise up out of the noise inherent in such measurements. I suggest you go to the AnalyticCycling site and plug in a 10 lb. weight shift between rim/tire and bike/rider for a hill climbing case and see what you get.
 
Interesting..................

Bacco said:
I was discussing with my LBS owner whether or not losing 1 lb body fat (mine) would provide the same end results in performance for me as buying a bike that weighed 1 lb less? Of course, he believed that having a lighter bike would be more advantageous. What do you think?

I can understand that lighter wheels would make more of a difference due to the rotational dynamics involved, but just considering the weight of the frame, I can't see any difference between body weight and frame weight.
Bicycling Magazine (I realize they get slagged a lot but bear with me) had an interesting
graph/chart showing the time it takes to climb a hill at a certain height and weight and
certain bike weight, but showed how long it tooks as that person gained 10 pounds, then
10 more pounds. It was pretty illuminating. I've lost about 22 pounds this year and I know
that I feel like I've been shot out of a cannon when riding lately so, yeah, it's a good thing.
Losing weight and having a light bike will both help.
 
djg said:
There is absolutely no way--NO WAY--you can simply substitute a pound of frame for a pound of fat when you are baking. Disaster--don't do it.

Yeah, you're right on that one. Those cookies tasted horrible. . .

;)
 
Biology at work

To me, biology is a much bigger deal than simply physics.

An overweight person losing 1 pound may bring more benefit to his body (hence fitness for cycling) than just being a bit lighter. Less clogged blood vessels, for example, will make him a more efficient athlete. A smaller gut, will facilitate a more aero riding position, hence less drag, etc... But for a 120lb climber at the end of Vuelta, losing 1 pound means quite the opposite. It might kill him.

Therefore what losing weight does to a cyclist is far more complicated than the physical body mass reduction.

For a bike, losing weight will involve a lot of factores like, cost, compatibility, dependability, function, etc. (thinner tires could be more puncture prone, hence losing you time), so this question can ultimately be answer in context and not standing alone.

Bacco said:
I was discussing with my LBS owner whether or not losing 1 lb body fat (mine) would provide the same end results in performance for me as buying a bike that weighed 1 lb less? Of course, he believed that having a lighter bike would be more advantageous. What do you think?

I can understand that lighter wheels would make more of a difference due to the rotational dynamics involved, but just considering the weight of the frame, I can't see any difference between body weight and frame weight.
 
If you weight 200 lbs. and you carry your 20 lb. gargage can to the curb it takes x amount of energy.

If you lose 10 lbs and you carry your 20lb. garbage can to the curb it will still take x amount of energy

If the garbage can looses 10 lbs it will take less energy to move it regarless of what you weigh...........
 
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