what is a climbing wheel????and physics questions

[David L. Johnso]

On Thu, 02 Oct 2003 08:37:00 +0000, JP wrote:

> Why is it easier to accelerate a mass in a weightless state (almost the same as a level surface)
> than it is to accelerate it up a hill? I don't think anyone would argue that the same effort is
> required. The fact is that gravity itself is an acceleration, and riding up a hill at a steady
> pace is essentially a constant acceleration in terms of the impact of a bicycle's mass:

However, it is not acceleration as far as spinning the wheels is concerned. You have to push the
mass over the top, yes, but you do not have to use "all that" extra energy to increase the
rotational energy of the wheels.

The real test is the spin-the-pedals-on-the-stand test Mark mentioned. If there is so much
acceleration needed to get the wheels going, hou come you can do this with one hand, in one stroke
of a pedal, with the bike on the stand?

> The thread is about *climbing* wheels.

> Regardless of the impact of rotational inertia, even small differences in wheel weight can be
> significant in a climb.

Why fuss about 100g of wheel weight, until the rider's weight is absolutely minimal? It's even
cheaper for the rider to lose weight than not, rather than costing hundreds of dollars for
magic wheels.

--

David L. Johnson

__o | Accept risk. Accept responsibility. Put a lawyer out of _`\(,_ | business. (_)/ (_) |

 

[Jobst Brandt]

JP writes secretively:

>> Over the course of most rides, most of your energy goes toward overcoming air resistance, (or,
>> when riding uphill, to lift yourself and the bike). Acceleration isn't as important as a lot of
>> people make it out to be.

> Why is it easier to accelerate a mass in a weightless state (almost the same as a level surface)
> than it is to accelerate it up a hill? I don't think anyone would argue that the same effort is
> required.

It isn't and it isn't. Linear acceleration is the same regardless of whether it is horizontal,
vertical or any other direction. If there is an additional burden, such as wind or weight, in the
case of an upgrade, that takes part of the effort.

> The fact is that gravity itself is an acceleration, and riding up a hill at a steady pace is
> essentially a constant acceleration in terms of the impact of a bicycle's mass: your power output
> doesn't only work to accelerate the mass of the bicycle, it also works to counteract the
> acceleration of gravity against its mass and yours.

I think you have accelerations confused. Bicyclists do not accelerate rapidly enough in road riding
to have any effect from small changes in peripheral weight on a wheel. This is especially true when
hill climbing where no net acceleration takes place. As I mentioned, the flywheel effect of extra
heavy wheels would enhance time trial speeds on the flat although carrying the weight up hill would
be a detriment.

> The thread is about *climbing* wheels.

Or better, what a "climbing wheel" is, and we aren't there yet.

>> But for the sake of argument, assume I'm doing a lot of stop-and-go, and I really care about
>> accelerating. In round numbers, my bike and I weigh 200 pounds total. If I used rims that were
>> each 1/4 pound lighter than the ones I have, I'd use about .5% less energy to accelerate to a
>> given speed: not a dramatic difference.

> I tend to think that a .5% difference is fairly significant at any level of competition, or to
> look at it another way, if your conditioning is fairly evenly matched with your competitors, I
> don't think you would want to give away .5% in your bike. If you have ever won a sprint by a tire,
> no matter what the level of competition, you have won by a margin much smaller than .5%.

Do you tend to think or do you think so? Don't beat around the bush.

If you ride much you may have noticed that sprinting over a hill that is just a bit too long makes
clear that almost no acceleration takes place as speed from the flat is maintained, it is a matter
of power to maintain the speed. Speed change, if any, progresses at rates that demand minimal
additional effort in comparison to the rate of climb effort. Acceleration is not even visible to an
observer. When a rider pulls away on a hill, the rate of separation from the pack is essentially
constant once the effort is begun. It is not one of accelerating.

> Regardless of the impact of rotational inertia, even small differences in wheel weight can be
> significant in a climb.

Hold it! That's putting the cart before the horse. That is the initial contention. Repeating it
without supporting evidence doesn't do much in supporting it other than making it a repetitious
mantra. Bicycling is full of these.

Jobst Brandt [email protected]

 

[Mike S.]

<snip>

> Why fuss about 100g of wheel weight, until the rider's weight is absolutely minimal? It's even
> cheaper for the rider to lose weight than not, rather than costing hundreds of dollars for
> magic wheels.
>
> --
Because its easier to earn an extra few hundred $$ than it is to have willpower, to diet, etc.

>
> David L. Johnson
>
> __o | Accept risk. Accept responsibility. Put a lawyer out of _`\(,_ | business. (_)/ (_) |

 

[Tom Ace]

anerobic wrote:

> i'd love it if you just wrote out that equation so i could look at all the terms- how much ehergy
> it takes to move the 200 lb mass and how much to spin the rims....

Kinetic energy is calculated as ½ m v² If the special characters didn't come out right on your
screen, that's one half m v squared

Using mass in kilograms and velocity in meters/second, that formula gives energy in joules.

A 90 kg mass at rest has no kinetic energy. A 90 kg mass moving at 10 m/sec has 4500 joules of
kinetic energy.

Wheels not only have to be accelerated forward along with the rest of the bike, they also have to be
spun up. Rotational kinetic energy has its own formulas, but you don't have to bother with
calculating the moment of inertia and angular velocity of the wheels. You can use the ½ m v² formula
for rotational motion as well, if you use for v the tangential speed of a piece of the wheel. For
points on the outside of the wheel, tangential speed is equal to the forward speed of the bicycle.
Although the rim isn't exactly at the periphery of the wheel, it's close enough for a reasonable
approximation.

So, for a 0.5 kg rim:

accelerating the rim forward from 0 to 10 m/sec takes 25 joules of energy; spinning the rim from
rest up to [the rate it spins at when the bicycle is moving forward at 10 m/sec] also takes 25
joules of energy (actually a little less, because the rim isn't exactly at the outside).

That's the basis for saying that mass at the edge of the wheel counts twice.

Tom Ace

 

[Mike S.]

"Tom Ace" <[email protected]> wrote in message news:[email protected]...
> anerobic wrote:
>
> > i'd love it if you just wrote out that equation so i could look at all the terms- how much
> > ehergy it takes to move the 200 lb mass and how much to spin the rims....
>
> Kinetic energy is calculated as ½ m v² If the special characters didn't come out right on your
> screen, that's one half m v squared
>
> Using mass in kilograms and velocity in meters/second, that formula gives energy in joules.
>
> A 90 kg mass at rest has no kinetic energy. A 90 kg mass moving at 10 m/sec has 4500 joules of
> kinetic energy.
>
> Wheels not only have to be accelerated forward along with the rest of the bike, they also have to
> be spun up. Rotational kinetic energy has its own formulas, but you don't have to bother with
> calculating the moment of inertia and angular velocity of the wheels. You can use the ½ m v²
> formula for rotational motion as well, if you use for v the tangential speed of a piece of the
> wheel. For points on the outside of the wheel, tangential speed is equal to the forward speed of
> the bicycle. Although the rim isn't exactly at the periphery of the wheel, it's close enough for a
> reasonable approximation.
>
> So, for a 0.5 kg rim:
>
> accelerating the rim forward from 0 to 10 m/sec takes 25 joules of energy; spinning the rim from
> rest up to [the rate it spins at when the bicycle is moving forward at 10 m/sec] also takes 25
> joules of energy (actually a little less, because the rim isn't exactly at the outside).
>
> That's the basis for saying that mass at the edge of the wheel counts
twice.
>
>
> Tom Ace

Not to nitpick, but I thought the top of the wheel was going twice bike speed. How does that play
into your nifty equation for us non-math guys?

Mike

 

[Mike S.]

<[email protected]> wrote in message news:[email protected]...
> JP writes secretively:
>
> >> Over the course of most rides, most of your energy goes toward overcoming air resistance, (or,
> >> when riding uphill, to lift yourself and the bike). Acceleration isn't as important as a lot of
> >> people make it out to be.
>
> > Why is it easier to accelerate a mass in a weightless state (almost the same as a level surface)
> > than it is to accelerate it up a hill? I don't think anyone would argue that the same effort is
> > required.
>
> It isn't and it isn't. Linear acceleration is the same regardless of whether it is horizontal,
> vertical or any other direction. If there is an additional burden, such as wind or weight, in the
> case of an upgrade, that takes part of the effort.
>
> > The fact is that gravity itself is an acceleration, and riding up a hill at a steady pace is
> > essentially a constant acceleration in terms of the impact of a bicycle's mass: your power
> > output doesn't only work to accelerate the mass of the bicycle, it also works to counteract the
> > acceleration of gravity against its mass and yours.
>
> I think you have accelerations confused. Bicyclists do not accelerate rapidly enough in road
> riding to have any effect from small changes in peripheral weight on a wheel. This is especially
> true when hill climbing where no net acceleration takes place. As I mentioned, the flywheel effect
> of extra heavy wheels would enhance time trial speeds on the flat although carrying the weight up
> hill would be a detriment.
>
> > The thread is about *climbing* wheels.
>
> Or better, what a "climbing wheel" is, and we aren't there yet.
>
> >> But for the sake of argument, assume I'm doing a lot of stop-and-go, and I really care about
> >> accelerating. In round numbers, my bike and I weigh 200 pounds total. If I used rims that were
> >> each 1/4 pound lighter than the ones I have, I'd use about .5% less energy to accelerate to a
> >> given speed: not a dramatic difference.
>
> > I tend to think that a .5% difference is fairly significant at any level of competition, or to
> > look at it another way, if your conditioning is fairly evenly matched with your competitors, I
> > don't think you would want to give away .5% in your bike. If you have ever won a sprint by a
> > tire, no matter what the level of competition, you have won by a margin much smaller than .5%.
>
> Do you tend to think or do you think so? Don't beat around the bush.
>
> If you ride much you may have noticed that sprinting over a hill that is just a bit too long makes
> clear that almost no acceleration takes place as speed from the flat is maintained, it is a matter
> of power to maintain the speed. Speed change, if any, progresses at rates that demand minimal
> additional effort in comparison to the rate of climb effort. Acceleration is not even visible to
> an observer. When a rider pulls away on a hill, the rate of separation from the pack is
> essentially constant once the effort is begun. It is not one of accelerating.
>
> > Regardless of the impact of rotational inertia, even small differences in wheel weight can be
> > significant in a climb.
>
> Hold it! That's putting the cart before the horse. That is the initial contention. Repeating it
> without supporting evidence doesn't do much in supporting it other than making it a repetitious
> mantra. Bicycling is full of these.
>
> Jobst Brandt [email protected]

Y'know Jobst, if you'd back these things up with facts, figures, and charts, it'd go a long way
towards making you sound like you're not bashing someone just because.

I see lots of things you've disagreed with, but very little in the way of proof WHY you disagree.

Think of it like this: if you're going to ***** about something, you'd better be prepared to do
something about it. So far, all I see from you is *****ing, nothing about doing something about it.

So, Mr. Brandt, WHY exactly is it that the weight on the rim is NOT worth twice its weight
on the bike?

That goes for all of y'all, BTW. (Myself included! so here goes...)

My thought, is that maybe there's a way to calculate the force required to accelerate your wheel up
to speed while the bike is sitting on a stand. I'd like to see someone compare say a Cosmic, a GL330
wheel, and an Open Pro to see exactly how much it takes to get from 0 up to say 40kph.
(Alternatively, to what speed does a set amount of force accelerate the wheel?)

Since I don't have access to strain gauges (SRM/PowerTap??) maybe someone that does can try
it and see?

That should give us numbers in watts, right? Then everyone can see what we're talking about in
real numbers.

Anyone see any gaping holes in my test?

Mike

 

[Jobst Brandt]

Tom Ace writes:

>> i'd love it if you just wrote out that equation so i could look at all the terms- how much ehergy
>> it takes to move the 200 lb mass and how much to spin the rims....

> Kinetic energy is calculated as ½ m v² If the special characters didn't come out right on your
> screen, that's: ( m * v**2 ) / 2

> Using mass in kilograms and velocity in meters/second, that formula gives energy in Joules.

> A 90 kg mass at rest has no kinetic energy. A 90 kg mass moving at 10 m/sec has 4500 Joules of
> kinetic energy.

> Wheels not only have to be accelerated forward along with the rest of the bike, they also have to
> be spun up. Rotational kinetic energy has its own formulas, but you don't have to bother with
> calculating the moment of inertia and angular velocity of the wheels. You can use the ½ m v²
> formula for rotational motion as well, if you use for v the tangential speed of a piece of the
> wheel. For points on the outside of the wheel, tangential speed is equal to the forward speed of
> the bicycle. Although the rim isn't exactly at the periphery of the wheel, it's close enough for a
> reasonable approximation.

> So, for a 0.5 kg rim:

> accelerating the rim forward from 0 to 10 m/sec takes 25 Joules of energy; spinning the rim from
> rest up to [the rate it spins at when the bicycle is moving forward at 10 m/sec] also takes 25
> Joules of energy (actually a little less, because the rim isn't exactly at the outside).

> That's the basis for saying that mass at the edge of the wheel counts twice.

Therefore: 25/4500=0.00555 or 0.555%

... for acceleration. However, in a time trial, whether flat or on a hill, acceleration occurs once
at the start and is of little consequence there and even less thereafter. We like to believe we are
world champions, ACCELERATING to great speeds while wearing garish advertising all over our
clothing, pretending ala Walter Mitty, that these images are real. They are not!

Jobst Brandt [email protected]

 

[Jobst Brandt]

Mike Shaw writes:

> Not to nitpick, but I thought the top of the wheel was going twice bike speed. How does that play
> into your nifty equation for us non-math guys?

The bottom of the wheel is standing still with respect to the road to make up for the twice as fast
but that is only a problem with your frame of reference. You must be aware that the wheel is turning
about its own center and its peripheral speed is that of the forward motion of the bicycle. If this
were not the case, how would a speedometer be able to measure the speed of the bicycle by counting
revolutions?

Jobst Brandt [email protected]

 

[S. Anderson]

"Mike S." <mikeshaw2@coxDOTnet> wrote in message news:TZ1fb.45065$vj2.22000@fed1read06...
>
> So, Mr. Brandt, WHY exactly is it that the weight on the rim is NOT worth twice its weight on
> the bike?

<<snip..>>

> Mike
>

As can be seen in the www.analyticcycling.com page, when determining the force required to
accelerate a bicycle, component of the equation relating to the bicycle and rider is the sum of the
rider weight, the bike weight, the weight of the front and rear wheels, and the moments of inertia
for the front and rear wheels, which are computed by 4*I/dia.^2. The moment of inertia is a measured
value, we'll assume 0.8kg/m^2. So when comparing these values, the mass of the wheel is approx. 1kg?
Slightly less?? Well, the moment of inertia value for that equation is approx. 0.91kg. So you're
talking a slightly LESS importance attached to moment of inertia vs. overall mass of the wheel when
accelerating the bicycle. Generally, they're about equal I'd say. Again, we're REALLY splitting
hairs here..

Cheers,

Scott..

"1+1 is 2! That's mathematics boy!! Ya can't fight mathematics!!" -- Foghorn Leghorn....

 

[David Damerell]

onefred <[email protected]> wrote:
>>1. good acceleration. This is accomplished by focusing the weight as close as possible to the hub.
>> This lowers the moment of inertia (less energy required to accelerate\decelerate the rim).
>That's debatable.

If you mean that it's debateable that moving weight closer to the hub lowers the moment of inertia,
then you're wrong. There's no doubt about that whatsoever.

[Whether this effect is significant, now...]
--
David Damerell <[email protected]> Distortion Field!

 

[Tom Ace]

Peter Chisholm wrote:

> Tom-<< The original claim was
>
> A study I read said something along the lines that doubling the rim weight increases energy to
> spin the wheel by .1%..that's one tenth of 1 percent.
>
> Not enough information to give an exact answer (how much do the hub, spokes, tire and tube weigh)?
> >><BR><BR>
>
> Two identical wheels, one with a 300 gram rim and one with a 600 gram rim.

I wonder if you even want to understand this issue; you don't seem to be reading carefully, or
thinking the matter through for yourself.

I gave you an answer already. Please read the part of my posting that you didn't quote.

Tom Ace

 

[Jp]

[email protected] wrote in message news:<[email protected]>...
> JP writes secretively:
>
> >> Over the course of most rides, most of your energy goes toward overcoming air resistance, (or,
> >> when riding uphill, to lift yourself and the bike). Acceleration isn't as important as a lot of
> >> people make it out to be.
>
> > Why is it easier to accelerate a mass in a weightless state (almost the same as a level surface)
> > than it is to accelerate it up a hill? I don't think anyone would argue that the same effort is
> > required.
>
> It isn't and it isn't. Linear acceleration is the same regardless of whether it is horizontal,
> vertical or any other direction. If there is an additional burden, such as wind or weight, in the
> case of an upgrade, that takes part of the effort.

I didn't say otherwise; in fact it is implied in my statement about the similarity of accelerating a
mass in a weightless state versus a level surface.

Weight, I guess you know, is an acceleration applied to a mass.

> > The fact is that gravity itself is an acceleration, and riding up a hill at a steady pace is
> > essentially a constant acceleration in terms of the impact of a bicycle's mass: your power
> > output doesn't only work to accelerate the mass of the bicycle, it also works to counteract the
> > acceleration of gravity against its mass and yours.
>
> I think you have accelerations confused.

I don't think so, but maybe you do. My point is that mass is a factor in acceleration, whether it is
level in the spin up of a sprint, or gravity acting on a bicycle wheel while *climbing*.

> Bicyclists do not accelerate rapidly enough in road riding to have any effect from small changes
> in peripheral weight on a wheel.

I didn't say they did, but define small. I did say that a .5% advantage is significant, implying
that .5% decrease in the mass of bicycle/rider combination could be decisive. In fact I will go out
on a limb and say that much smaller advantages in total mass could be decisive.

> This is especially true when hill climbing where no net acceleration takes place.

Not exactly. The cyclist going up a hill is being accelerated by gravity in opposition to the
direction of travel for the entire climb. The combined mass of the bicycle and the cyclist is a
factor. I am not saying that rotational inertia is a significant factor.

> As I mentioned, the flywheel effect of extra heavy wheels would enhance time trial speeds on the
> flat although carrying the weight up hill would be a detriment.

But since we are talking about *climbing* wheels, I guess your point is not evident to me. I guess
you are saying that a heavy wheel is bad on a climb? I agree.

> > I tend to think that a .5% difference is fairly significant at any level of competition, or to
> > look at it another way, if your conditioning is fairly evenly matched with your competitors, I
> > don't think you would want to give away .5% in your bike. If you have ever won a sprint by a
> > tire, no matter what the level of competition, you have won by a margin much smaller than .5%.
>
> Do you tend to think or do you think so? Don't beat around the bush.

I think I was pretty clear. I think that you pretend otherwise as a debate tactic. But since you
seem to like this sort of thing, let me be clear about it: there are a lot of things that seem
apparent to me but I am not so stupid as to extrapolate certainty about them in every circumstance.

> If you ride much you may have noticed that sprinting over a hill that is just a bit too long makes
> clear that almost no acceleration takes place as speed from the flat is maintained, it is a matter
> of power to maintain the speed. Speed change, if any, progresses at rates that demand minimal
> additional effort in comparison to the rate of climb effort. Acceleration is not even visible to
> an observer. When a rider pulls away on a hill, the rate of separation from the pack is
> essentially constant once the effort is begun. It is not one of accelerating.

The cyclist is counteracting acceleration- the acceleration of gravity, which makes mass an issue
for the entire climb, exactly the same as if the cyclist were accelerating the entire time.

The point is that there is no difference between riding up a hill at a constant speed and
accelerating on level ground. The effect of the mass of the cyclist is *exactly* the same, dependent
on the magnitude of the acceleration.

> > Regardless of the impact of rotational inertia, even small differences in wheel weight can be
> > significant in a climb.
>
> Hold it! That's putting the cart before the horse. That is the initial contention.

There was not an initial contention, there was an initial question- what makes a climbing wheel? The
answer is low mass.

> Repeating it without supporting evidence doesn't do much in supporting it other than making it a
> repetitious mantra.

I think gravity has been sufficiently supported that we can treat it as a given.

We frequently talk in this sport about how a small change in drag will affect the theoretical
outcome of a time trial. Well, the same effect is present with mass in a ride up a hill. I don't
think I have to perform the calculations for us to understand that a small change in mass will be
decisive in a climb, all other things being equal. That's why small improvements are important-
competitive cyclists who are very closely matched physically know that a few ounces may be the
difference between winning and losing.

I personally suspect ("tend to think") that rotational inertia is a factor in climbs because there
is a micro acceleration and deceleration with each pedal stroke on a climb, depending on a variety
of factors, such as grade, speed and riding style. It could conceivably be a significant factor in
the overall fatigue factor at the end of a long ride up a hill. It *might* be why LA's spinning
climbing style has an advantage (if it really is an advantage), but that's just speculation.

All in all, I would guess that the effect of rotational inertia is relatively small but measurable
in competitive cycling. I would certainly not dismiss it altogether without strong evidence that it
is insignificant, let alone your mere insistence that it is insignificant just because it *is*
small, if I were competing at an elite level.

JP

 

[Gwhite]

Mark Hickey wrote:
>
> gwhite <gwhite@hocuspocus_ti.com> wrote:
>
> >Benjamin Lewis wrote:
>
> >> But the 3.8 nanoseconds you save could be the difference between winning and losing!
> >
> >I don't know about 3.8 nanoseconds bit, but the difference between winning and second place is
> >something that concerns competitors from the amateur to professional ranks. Good bike races are
> >loaded with acceleration after acceleration. The folks who view bike races uniformly as some sort
> >of homogeneous effort don't race bikes.
>
> But as much as we'd all like to pretend otherwise, those "drastic accelerations" are really only
> going from 23 to 28 (or maybe 30...)mph in three to five seconds - hardly the kind of thing that's
> going to cause the aluminum in the rim to melt... ;-) To me, the fact it takes only a light push
> on one pedal with my hand (err, the bike's in a stand at the time - my arms aren't THAT long...)
> to spin the wheel from a dead stop up to race pace tells me that the a few mph acceleration
> doesn't take enough energy to get too worried about (especially since we're not even talking about
> the total energy - just the delta which is normally not that large).

All the mass (rider + bike) is accelerated when going from 23 to 28 mph -- that's what matters most.
And of course, these multitudinous acceleration events during the race aren't so important in the
sense that the win line is not being crossed. As I see it, hard effort surges matter only in the
sense of cumulative fatigue. (Of course, just pedaling along builds fatigue too.) Relative fatigue
does make a difference when the victory line *is* close. I don't think anyone really knows the
marginal effects, such as those due to multiple mass accelerations, when they are all added up.
Because marginal effects are not well enough defined, the basic philosophy is to protect the margin
if it is reasonable _to the individual_ to do so.

> >Given resources and reasonable individual judgement about "what is important and what is it
> >worth," the rule for bikes is to make them as light and aerodynamic as possible given the all
> >counter-balancing constraints. That is pretty much it for any vehicle with severe horsepower
> >limitations.
>
> Yep... FWIW, I love the feel of really light wheels. My old tubular wheels (built with GL330 rims
> and light oval spokes) really feel different. Of course I know that the box section rims are
> actually slowing me down at anything approaching a race pace... but I won't be racing them unless
> it's an all-out hill climb.

If you break away, "more aero" wheels might buy you a bit. How many times have breaks gotten busted
right at the line? (Lots.) How many times have they barely made it? (Lots.) Tiny margins can
occasionally matter for racers. How much are tiny margins (of unclear) worth to you?

 

[Gwhite]

Ryan Cousineau wrote:
>

> > Given resources and reasonable individual judgement about "what is important and what is it
> > worth," the rule for bikes is to make them as light and aerodynamic as possible given the all
> > counter-balancing constraints. That is pretty much it for any vehicle with severe horsepower
> > limitations.
>
> Here's the problem: for most riders, given a US$1000 road bike as a starting budget, you can
> either work at your usual hourly rate to earn enough money to buy lightness and aerodynamics until
> you are at a pro-level, or you can take that same time and ride your bike.

Let's not confound the problem by taking away what has already been stated and the normal givens.
The given is that race fitness is present. Many people have much more than $1000 to spend on the
bike and easily enough money to simply pay someone else to spend time working on the bike -- buffing
the bike will not affect their time available for training. For those who don't have the money, then
to forgo proper training and concentrate on bike minutiae is to not practice the "reasonable
individual judgement about 'what is important and what is it worth'" that I already pointed out.

Whether or not some $4k bike is "worth" $4k is pretty much a pointless question/valuation in any
general sense. Worth to one is not the same as worth to another. Wonderbread may be worth $2/loaf to
you, that doesn't mean it is to me, and most importantly: neither one of us is "wrong" in our
individual valuations of Wonderbread. I would fully agree that a $1k bike will cover most of the
important bases when it comes to racing. That is, a bike budget limit of $1k will certainly not by
itself preclude someone from "decent" race performance. Everyone knows the motor comes first.

> A US$1000 bike is very close to what the pros ride in road races, both aerodynamically and
> weight-wise. Your body is not. Fix the body, not the bike.

This is a red herring going off-topic. But okay, I'll play. My body will never be a pro body no
matter what I do. That said, and for a single point as an example, my BMI will be around 20.7 to
20.8 next race season. What else would you propose for me, a low level 47 yo amateur with about
10-12 hours/week available for training, regarding this particular matter?

> Avoid diminishing gains,

Well sure, but it unfortunately is a matter of case by case subjective common sense, not some sort
of well defined formula for making decisions for all people and matters. For what has diminished too
much for one will not have diminished too far for another. Besides, if someone wants to put a 10 g
Ti bolt on their bike, so what? *Most* people aren't so stupid to believe the bolt really matters
when it comes down to riding fast. They are simply playing with their bike while it is in the
garage, and that is quite an aside from riding/racing. For those who confuse the two endeavors I
only have sympathy.

I can say that I, as an individual, choose to have a reliable training bike with 36 spoke DB wheels
and box rims that does not require much in the way of time for maintenance. That's one of the ways I
come up with those 10-12 hours/week for training. Then I have a light (5 lb less than the training
bike) race bike that is ready-to-go for race day. That is about as simple as I have been able to
make it. If you have other suggestions, I'm all ears.

 

[Jobst Brandt]

George White writes:

> All the mass (rider + bike) is accelerated when going from 23 to 28 mph -- that's what matters
> most. And of course, these multitudinous acceleration events during the race aren't so important
> in the sense that the win line is not being crossed. As I see it, hard effort surges matter only
> in the sense of cumulative fatigue. (Of course, just pedaling along builds fatigue too.) Relative
> fatigue does make a difference when the victory line *is* close. I don't think anyone really knows
> the marginal effects, such as those due to multiple mass accelerations, when they are all added
> up. Because marginal effects are not well enough defined, the basic philosophy is to protect the
> margin if it is reasonable _to the individual_ to do so.

The point you make is exactly where the misunderstanding arises. In a pack of riders in a race,
cruising along at close to endurance speed, any extra speed is difficult to muster because riders
are not rested. Accelerating from 23 to 28mph is a substantial change in power to overcome wind and
at the same time is equivalent work of accelerating to 25mph from a standstill (by 1/2 m*v**2). I
don't think that is not a good example. How much work it takes to accelerate the riders body and
bicycle, ignoring the rotation is the main effort to a degree that makes the whole (change in)
rotating weight argument insignificant.

>> Yep... FWIW, I love the feel of really light wheels. My old tubular wheels (built with GL330 rims
>> and light oval spokes) really feel different. Of course I know that the box section rims are
>> actually slowing me down at anything approaching a race pace... but I won't be racing them unless
>> it's an all-out hill climb.

> If you break away, "more aero" wheels might buy you a bit. How many times have breaks gotten
> busted right at the line? (Lots.) How many times have they barely made it? (Lots.) Tiny margins
> can occasionally matter for racers. How much are tiny margins (of unclear) worth to you?

The guys that talk about rotating weight the most are usually not racers, or at least not ones in
contention of doing much.

Jobst Brandt [email protected]

 

[James]

anerobic <[email protected]> wrote in news:[email protected]:

> i'd love it if you just wrote out that equation so i could look at all the terms- how much ehergy
> it takes to move the 200 lb mass and how much to spin the rims....

Lots of phuzzy physics in this thread about rotational inertia and wheel acceleration. I've had just
enough physics, statics and dynamics in college to be dangerous. Let's crank some numbers...

-----

Total Bike System = Translational Kinetic Energy + Rotational Energy

(TKE is bike moving forward. RE is wheels spinning around. Total bike energy is sum of the two).

-----

TKE = 0.5 x m v 2 Mass = 81.82 Kg (160lb rider plus 20lb bike) Speed = 8.94 m/sec (20 mph) TKE =
3269 Joules (J)

-----

Rotational Kinetic Energy of Wheels

RE = Omega x m x r 2 (FWIW i don't agree with analyticcycling.com formula)

Get Omega: Circumference of wheel 2.14 m Revolutions per second 4.18 rev/sec Radians per second
(Omega) 26.25

Rim/tire/tube .6kg at 0.32m radius 42.3 J Hub/cassette .8kg at 0.03m radius 0.5 J Spokes are
ignored 0 J

One wheel RE = 42.8 J

-----

Total Bike System 3311.6 J Ratio of RE/TKE 1.3%

-----

What happens if we shave 50 grams off of the rider or frame? What happens if we shave 25 grams off
of each wheel rim?

Cut 50 grams off of non-rotating part of bike:

Mass = 81.77 Kg Speed = 8.94 m/sec TKE = 3267 J Change in TKE = 2 J, or, if we hold 3269 J constant,
speed increases by .003 m/sec

For a 2-hour ride, shaving 50 grams puts the rider ahead by 21 meters.

If we shave 50 grams off of the rims (25 grams each rim), RE drops from
42.8 J to 41.1 J. Therefore, the Total Bike System drops by (2 J + 1.7 J) or 3.7 J. or, as a
percentage, 1.7/2.0 = 88%.

Or, 50g from a wheel rim is equivalent to 94g from the rider or frame.

CONCLUSIONS

Shaving one gram off of the wheel rim or tire is equivalent to removing
43.88 grams from the rider or frame. Keeping rims, tubes and tires as light as possible is a
worthwhile endeavor.

The "one gram off the wheel is like three off the bike" saying is exaggerated. Change the three to
two and we're in the ballpark.

Rotational energy considerations are minor, on the order of 1.3% of the total bike and rider system.

Small changes in the weight of bike or rider do make significant changes in the finish line position
for multi-hour events.

--- James

 

[Eric Holeman]

In article <TZ1fb.45065$vj2.22000@fed1read06>,
Mike S. <mikeshaw2@coxDOTnet> wrote:

>Y'know Jobst, if you'd back these things up with facts, figures, and charts, it'd go a long way
>towards making you sound like you're not bashing someone just because.

I'm not sure why you'd expect someone to post a physics text when there are so many excellent ones
available at academic bookstores.

>My thought, is that maybe there's a way to calculate the force required to accelerate your wheel up
>to speed while the bike is sitting on a stand.

As someone posted here some time ago, there's a crude but easy way to do
it: Put the bike on the stand and use your hand to turn the crank. Put it in the highest gear. See
how much force it takes to accelerate the wheel so that you're spinning the crank at whatever
your favorite cadence.

If you really want a measure of the force, go push your hand on the bathroom scale and then come
back to the wheel.

Once you've determined how little force is actually required to accelerate the wheel, you can then
think about how you'd go about measuring that force.

--
---
Eric Holeman Chicago Illinois USA

 

[Mark Hickey]

gwhite <gwhite@hocuspocus_ti.com> wrote:

>Mark Hickey wrote:

>> But as much as we'd all like to pretend otherwise, those "drastic accelerations" are really only
>> going from 23 to 28 (or maybe 30...)mph in three to five seconds - hardly the kind of thing
>> that's going to cause the aluminum in the rim to melt... ;-) To me, the fact it takes only a
>> light push on one pedal with my hand (err, the bike's in a stand at the time - my arms aren't
>> THAT long...) to spin the wheel from a dead stop up to race pace tells me that the a few mph
>> acceleration doesn't take enough energy to get too worried about (especially since we're not even
>> talking about the total energy - just the delta which is normally not that large).
>
>All the mass (rider + bike) is accelerated when going from 23 to 28 mph -- that's what matters
>most. And of course, these multitudinous acceleration events during the race aren't so important in
>the sense that the win line is not being crossed. As I see it, hard effort surges matter only in
>the sense of cumulative fatigue. (Of course, just pedaling along builds fatigue too.) Relative
>fatigue does make a difference when the victory line *is* close. I don't think anyone really knows
>the marginal effects, such as those due to multiple mass accelerations, when they are all added up.
>Because marginal effects are not well enough defined, the basic philosophy is to protect the margin
>if it is reasonable _to the individual_ to do so.

True enough - but also remember that it only applies after braking (something that doesn't happen
much in most races). Any extra energy that's put into the wheel is stored there, and will "pay back"
the effort when the rider eases up after the acceleration. At any rate, my point is that 100g
difference (which is a relatively huge difference in modern wheels) takes vanishingly little energy
to accelerate in bike racing terms. If you figure a 5mph (8km/h) acceleration, comparing a 400g rim
with a 500g rim, you're talking about the amount of energy needed to spin the rear wheel up to 2mph
(5mph x 20% weight difference x 2 wheels) - something you can do with a half-hearted swipe with your
pinky finger.

>> >Given resources and reasonable individual judgement about "what is important and what is it
>> >worth," the rule for bikes is to make them as light and aerodynamic as possible given the all
>> >counter-balancing constraints. That is pretty much it for any vehicle with severe horsepower
>> >limitations.
>>
>> Yep... FWIW, I love the feel of really light wheels. My old tubular wheels (built with GL330 rims
>> and light oval spokes) really feel different. Of course I know that the box section rims are
>> actually slowing me down at anything approaching a race pace... but I won't be racing them unless
>> it's an all-out hill climb.
>
>If you break away, "more aero" wheels might buy you a bit. How many times have breaks gotten busted
>right at the line? (Lots.) How many times have they barely made it? (Lots.) Tiny margins can
>occasionally matter for racers. How much are tiny margins (of unclear) worth to you?

Faster is always better... ;-) And aero always trumps light.

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame

 

[Jens Kurt Heyck]

Seems like getting real small radius wheels would also make you faster, according to these
equations. Smaller wheels have lower rolling resistance, too (see, for example:
http://www.physics.helsinki.fi/~tlinden/rolling.html)

So why aren't we all riding around on tiny little clown bicycle wheels?

--j

"James" <[email protected]> wrote in message news:[email protected]...
> anerobic <[email protected]> wrote in news:[email protected]:
>
> > i'd love it if you just wrote out that equation so i could look at all the terms- how much
> > ehergy it takes to move the 200 lb mass and how much to spin the rims....
>
> Lots of phuzzy physics in this thread about rotational inertia and wheel acceleration. I've had
> just enough physics, statics and dynamics in college to be dangerous. Let's crank some numbers...
>
> -----
>
> Total Bike System = Translational Kinetic Energy + Rotational Energy
>
> (TKE is bike moving forward. RE is wheels spinning around. Total bike energy is sum of the two).
>
> -----
>
> TKE = 0.5 x m v 2 Mass = 81.82 Kg (160lb rider plus 20lb bike) Speed = 8.94 m/sec (20 mph) TKE =
> 3269 Joules (J)
>
> -----
>
> Rotational Kinetic Energy of Wheels
>
> RE = Omega x m x r 2 (FWIW i don't agree with analyticcycling.com formula)
>
> Get Omega: Circumference of wheel 2.14 m Revolutions per second 4.18 rev/sec Radians per second
> (Omega) 26.25
>
> Rim/tire/tube .6kg at 0.32m radius 42.3 J Hub/cassette .8kg at 0.03m radius 0.5 J Spokes are
> ignored 0 J
>
> One wheel RE = 42.8 J
>
> -----
>
> Total Bike System 3311.6 J Ratio of RE/TKE 1.3%
>
> -----
>
> What happens if we shave 50 grams off of the rider or frame? What happens if we shave 25 grams off
> of each wheel rim?
>
> Cut 50 grams off of non-rotating part of bike:
>
> Mass = 81.77 Kg Speed = 8.94 m/sec TKE = 3267 J Change in TKE = 2 J, or, if we hold 3269 J
> constant, speed increases by .003 m/sec
>
> For a 2-hour ride, shaving 50 grams puts the rider ahead by 21 meters.
>
> If we shave 50 grams off of the rims (25 grams each rim), RE drops from
> 42.8 J to 41.1 J. Therefore, the Total Bike System drops by (2 J + 1.7 J) or 3.7 J. or, as a
> percentage, 1.7/2.0 = 88%.
>
> Or, 50g from a wheel rim is equivalent to 94g from the rider or frame.
>
> CONCLUSIONS
>
> Shaving one gram off of the wheel rim or tire is equivalent to removing
> 1.88 grams from the rider or frame. Keeping rims, tubes and tires as light as possible is a
> worthwhile endeavor.
>
> The "one gram off the wheel is like three off the bike" saying is exaggerated. Change the three to
> two and we're in the ballpark.
>
> Rotational energy considerations are minor, on the order of 1.3% of the total bike and
> rider system.
>
> Small changes in the weight of bike or rider do make significant changes in the finish line
> position for multi-hour events.
>
> --- James
>
>
>
>
>

 

[G.Daniels]

someone send JB a colorado cyclist catalog. before its too late.