Rotating Mass...

Discuss light weight issues concerning road bikes & parts.

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asphaltdude
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by asphaltdude

Whow! That's a pretty damn nice garage door!

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AMclassic-fan
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by AMclassic-fan

Racing Aardvark wrote:All I'll say is, what kind of education do you think most people working (or riding) for cycling teams have? Heck only a SMALL percentage of American pros have any college education. In Europe it's even worse(there are a few exceptions!

Now, remember that MOST people working for pro teams either were pros or have always been involved in cycling. How many business people or people with careers give it up to work for a team? Very damn few. So, given the limited pool of candidates, what do you think the average IQ is?

(I do know a few, for instance a mechanic with a Masters in Sports Psychology, and a team director with a degree in Physiology, and there's actually quite a few MTBers with college degrees in advanced fields, but they are the EXCEPTION).


:exactly:
I race in U19 in the Netherlands. There are only a few guys that are on VWO (is that the same as high school? I don't know anymore.) Most of the boys just make sure that they are ready with school when they are 16 (vmbo) so they have all time of the world to train and race. They all think they will be a pro in a few years. I hope it for them otherwise they can clean cars for the rest of there lifes or something like that, because they have no schooling at all.

by Weenie


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divve
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by divve

VWO is more like college level in the US.

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ultimobici
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by ultimobici

divve wrote: A heavier wheel will take more energy to accelerate, but it'll also store more energy, and susequently decellerate at a slower rate. The only time you actually loose that energy is when you brake. This doesn't happen much going uphill.
If you ride uphill on a bike with standard wheels and then freewheel, then do the same test with light wheels and an appropriate amount of ballast (so you still have the same mass) I suspect that you will stop sooner on the energy storing heavy wheels.
It won't be much of a difference but it will be there.
When you climb any road there are constant changes of gradient, some obvious, others more subtle. Consequently there are "micro accelerations" all the time so that you can maintain your speed. Find me a road that has a constant 10% gradient over the entire climb. It doesn't exist, if it did your argument would be valid.

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asphaltdude
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by asphaltdude

ultimobici wrote:If you ride uphill on a bike with standard wheels and then freewheel, then do the same test with light wheels and an appropriate amount of ballast (so you still have the same mass) I suspect that you will stop sooner on the energy storing heavy wheels.
It won't be much of a difference but it will be there.


Why on earth do you think that?????? :shock:

When you ride up a hill at a certain speed, and then stop pedaling, the KINETIC energy of you and your bike (0.5 x M x V^2) and wheels (0.5 x M x V^2 + 0.5 x I (moment of inertia of wheels) x W^2) will be converted into POTENTIAL energy (M (mass) x G (gravity) x H).


If you have wheels with very heavy rims (but the total bike+ rider weight) is the same, you have more kinetic energy at a certain speed, and when you stop pedaling this energy will be converted into potential energy.
E will be bigger, M ang G are the same, so H will be bigger, so you'll stop later en roll further up the hill.
Whow! That's a pretty damn nice garage door!

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yourdaguy
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by yourdaguy

This is true if you are rolling perfectly straight, but thinking of the total system, the wheels are actually a pair of gyroscopes and moving them in a straight line up the hill is easy, but as the bike moves around the heavier wheels (especially those with more weight at the rims) will actually try to stabilize the bike from side to side movement. This will cause a loss of angular momentum in the wheels. Since you have stored more energy in heavier rims there will be greater losses.
For certain parts stiffer is more important than lighter.

mises
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by mises

"micro accelerations" is also misleading. On my computrainer when the grade gets much above 7% the fluctuations are more on the order of 0.5-1.5 kph - far more than I would have thought and that's without changes in road surface, wind, reaching for a bottle, dodging debris, adjusting your shorts (like lance does all the time), reacting to other people's pace, etc.

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asphaltdude
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by asphaltdude

mises wrote:"micro accelerations"


With micro accelerations we only mean the minor changes in speed that occur with every pedal stroke.
Whow! That's a pretty damn nice garage door!

mises
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by mises

asphaltdude wrote:
mises wrote:"micro accelerations"


With micro accelerations we only mean the minor changes in speed that occur with every pedal stroke.


That's what I am talking about also - just pointing out they aren't necessarily micro regardless of how smooth you may feel pedaling. The fluctuations happen so rapidly it's easy to feel like you are maintaining a fairly constant speed when you aren't even close.

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allezkmiec
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by allezkmiec

mises wrote:
asphaltdude wrote:
mises wrote:"micro accelerations"


With micro accelerations we only mean the minor changes in speed that occur with every pedal stroke.


That's what I am talking about also - just pointing out they aren't necessarily micro regardless of how smooth you may feel pedaling. The fluctuations happen so rapidly it's easy to feel like you are maintaining a fairly constant speed when you aren't even close.

One need only look at the water in a half-full water bottle to prove how un-minor these accelerations really are. Even on a gradual, more constant climb, the water sloshes forward and back quite a bit, demonstration very clearly the acceleration/deceleration pattern.

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53-11
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by 53-11

divve wrote:Micro accelerations? Must be some sort of BS you heard from Dr. Ferrari. A heavier wheel will take more energy to accelerate, but it'll also store more energy, and susequently decellerate at a slower rate. The only time you actually loose that energy is when you brake. This doesn't happen much going uphill.

The reason for light wheels feeling so much "lighter" is a combination of several factors.

Less mass at the outer perimeter allows for easier directional changes.

Acceleration feels quicker, for most this more apparent than the energy you get back from heavier wheels when slowing down.

High-end carbon competition wheels are very stiff and often use a heavy gauge, relative short spokes, or composite such as Lightweight. This gives you the feeling of much more snap compared to a lightweight CX-Ray box rim type of wheel build.

Finally, what pros choose, Riis and CSC, or Cees Beers think, is hardly an argument supporting laws of physics. If you want to back up your statements bring in the math. Be prepared to disprove Newton's laws when you do so.

Knock yourself out. There's a Nobel prize waiting for you on this for sure.

http://csep10.phys.utk.edu/astr161/lect ... 3laws.html

http://www.analyticcycling.com/


Nice post. I've never seen it so well written before.

fdegrove
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by fdegrove

Hi,

The only time you actually loose that energy is when you brake. This doesn't happen much going uphill.


Somehow I think gravity combined with the combined weight of the rider and his bike make for a nice set of brakes. Ones that are constantly on for as long as the climb goes no less.....

As for micro-accelerations and micro-decelerations, well of course; bikes aren't perpetuum mobiles either.
The friction in the bearings of the hubs combined with stiction of tyres and even disregarding the exact nature of roadsurface and weather conditions are always going to try to slow you down.

If that weren't the case a bike would maintain constant speed, something it won't do even under the most ideal yet real life circumstances.
We need to keep on giving the bike a continuous series of impulses to keep it moving or we'll be slowing down, eventually coming to a halt.

As I said before in another thread regarding TT and heavy rims (heavier than usually used anyway) the flywheel effect of such a heavy wheel and if you like a heavier pedal and shoe, could be put to good advantage to transform the input from the pedal strokes into what appears to be a more steady train of forward pulses.
However, this is just a theoretical model that does not take unfavourable external conditions into account.

For going uphill, there's no doubt in my mind that the reduction of the weight at the rim and tyres are a major advantage as a continous series of impulses from the drivetrain are not only needed to keep going forward, they're needed to prevent the rider from coming to a grinding halt.
That's why you'd want to go uphill using a big cog so you can speed up the sequence of pulses and keep the energy flow as constant as possible.
To make it even easier you definetely don't want to drag unnecessary weight against the forces of gravity....
Hold on....
Gravity? Wasn't that the same good ole Isaac Newton again? Ah...Plus ca change.....

As for the advice not to swing the frame of the bike too much sideways; that has alot to do with the increase of rolling resistance as the bike is being swung away from the middle section of the tyre towards the sides.
In the old days (some manufacturers still do make them this way) tyres used a steel carcas and riding that way caused some concern as the flexing could well cause permanent damage to the metal carcas.
Nowadays I assume that the flexing of the sides of the tyres is still different enough to have a negative influence on the rolling resistance, enough so in fact to advise against it.
There probably are other unfavourable factors to are at play here but that's what I recall from it at the moment.

Oh, whilst I'm at it; a trainer worth his salt will always tell the rider to try to pedal in the most fluent way possible.
There's is a good reason for the latest tendency to keep cadence high and gears small, it maintains a pretty constant speed that can be kept high with seemingly little effort: impulses are relatively small but there's just a lot more of them within a set timeframe.
That's what makes it so much easier to maintain high speed and if ever someone would make a graph of that it will be obvious that the output would look much more like a straight line as opposed to the hilly landscape of the old brute force kind of school .

There points to be made in favour of the heavy rim, heavy tyre approach I'm sure but most definetely not for climbing with them....

Ciao, :wink:
Being a snob is an expensive hobby.

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by 53-11

allezkmiec wrote:
mises wrote:
asphaltdude wrote:
mises wrote:"micro accelerations"


With micro accelerations we only mean the minor changes in speed that occur with every pedal stroke.


That's what I am talking about also - just pointing out they aren't necessarily micro regardless of how smooth you may feel pedaling. The fluctuations happen so rapidly it's easy to feel like you are maintaining a fairly constant speed when you aren't even close.

One need only look at the water in a half-full water bottle to prove how un-minor these accelerations really are. Even on a gradual, more constant climb, the water sloshes forward and back quite a bit, demonstration very clearly the acceleration/deceleration pattern.


A glass of water?

That's almost too sensitive.

Nobody has a perfect pedal stroke, but how much of an impact will 50 grams at the rim have on this accel/decel pattern?

How much extra water sloshing etc will this 50 extra grams really produce?

Obviously it a light rim has an effect, but total weight is much more important.

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divve
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by divve

fdegrove wrote:Hi,

The only time you actually loose that energy is when you brake. This doesn't happen much going uphill.


Somehow I think gravity combined with the combined weight of the rider and his bike make for a nice set of brakes. Ones that are constantly on for as long as the climb goes no less......


For going uphill, there's no doubt in my mind that the reduction of the weight at the rim and tyres are a major advantage as a continous series of impulses from the drivetrain are not only needed to keep going forward, they're needed to prevent the rider from coming to a grinding halt.
That's why you'd want to go uphill using a big cog so you can speed up the sequence of pulses and keep the energy flow as constant as possible.
To make it even easier you definetely don't want to drag unnecessary weight against the forces of gravity....
Hold on....
Gravity? Wasn't that the same good ole Isaac Newton again? Ah...Plus ca change.....



....just for your information the other half of the equation:

Newton's third law of motion - For every action there is an equal and opposite reaction.

In other words, if a wheel requires more energy to accelerate, it'll also absorb more energy when slowed down....much like a bigger hammer....it takes more energy to lift one, but when it comes down on your head it hurts so much more :lol:

No need for bringing in all kinds of other external factors. We're talking about just the inertia factor. The fact that it requires more energy to lift a greater body of mass isn't disputed.

BTW, this applies to a common road climb. In other instances, such as a very short sprint with a finite distance, the time related factor may not allow for that energy to be returned effectively.

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by 53-11

fdegrove wrote:
For going uphill, there's no doubt in my mind that the reduction of the weight at the rim and tyres are a major advantage as a continous series of impulses from the drivetrain are not only needed to keep going forward, they're needed to prevent the rider from coming to a grinding halt.


I think the lighter weight tires and rims biggest contribution is total weight reduction. From an rotational inertia standpoint these "impulses" you speak of are quite small.

How much G acceleration do you think these impulses really account for?

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