Wheel weight and acceleration
inox
total weight of bike stays the same?
-inox
Qui si parla Campagnolo
total weight of bike stays the same? >>
I am not a physicist, don't even play one on TV, but I have read that the
energy required to accelerate a bicycle depends on the mass of the bike and
rider. Rotational mass, altho a measureable item, is small compared to the mass
of the 'package'-
Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl ST.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
Mark Hickey
>Is it true that wheel weight has no effect on acceleration or braking, if
>total weight of bike stays the same?
I've seen arguments that weight on the wheels takes very slightly more
energy to accelerate than on the frame - but the effect is vanishingly
small. Here's the test I suggest to people who buy into the "I can't
ever win a sprint with these wheels" argument...
Take your front wheel, hold it by the QR, hook your index finger into
the spokes and give it a firm push for about half a revolution. You
probably spun the wheel up to ~10mph (16km/h). That's how much energy
it takes to accelerate that wheel from 20mph to 30mph during an
all-out sprint (minus aerodynamics, which is another issue
altogether). If you managed to find wheels with only HALF the
rotating mass (good luck!) the amount of energy you expended would
cover the difference in both wheels.
That said, you CAN feel the difference between a very light and a
not-so-light pair of wheels / tires by the way they react to every
pedal stroke - however the disadvantage in acceleration is offset by
an almost exactly equal predisposition to decelerate more slowly
(bicycle wheels make great flywheels).
Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame
bob...@hotmail.com
Please read the article at
http://www.bike.com/template.asp?date=8%2F1%2F2001&lsectionnumber=6
Mr. Willet does a nice job of quantifying the effects of mass, inertia
and aerodynamics.
Bob
Harris
> Is it true that wheel weight has no effect on acceleration or braking, if
> total weight of bike stays the same?
Within reason, wheel weight has very little effect on acceleration in most
on-road situations. The old wives tale that "one ounce saved on the
rim/tire is equivalent to two ounces saved on the frame" is baloney.
There are two kinds of acceleration. Translational acceleration refers to
getting the mass of the rider and bicycle moving down the road from one
speed to another. Rotational acceleration refers to getting the wheels
spun up from on speed to another.
The translational acceleration of getting the bike and rider's mass
moving down the road requires far more energy than that required to spin
up the wheels.
Try this: Put your bike in a workstand so that the rear wheel is free to
turn. Put the bike in a medium high gear. With one hand, give the cranks a
quick turn or two and see how fast the wheel spins. You can probably
accelerate the wheel speed from "zero to 20 mph" in about a second with
one hand.
Switching to a lighter rim and tire may make a 10 percent difference
in the energy required to spin up the wheel, but that's still a tiny
fraction of the total energy required to accelerate you and the bike.
Art Harris
David Damerell
>"inox" <inox...@hotmail.com> wrote:
>>Is it true that wheel weight has no effect on acceleration or braking, if
>>total weight of bike stays the same?
>I've seen arguments that weight on the wheels takes very slightly more
>energy to accelerate than on the frame
Weight on the very edge is worth twice as much, but of course wheel weight
is a pretty small fraction of bike weight anyway, and most of it is closer
to the hub than that.
>Take your front wheel, hold it by the QR, hook your index finger into
>the spokes and give it a firm push for about half a revolution. You
>probably spun the wheel up to ~10mph (16km/h). That's how much energy
>it takes to accelerate that wheel from 20mph to 30mph
To be fair, that's not true, because kinetic energy varies with the square
of velocity.
--
David Damerell <dame...@chiark.greenend.org.uk> flcl?
Steve Blankenship
bikes. At one point years back I had a Cannondale for crits and a Vitus for
long rides, along with a set of GEL280-based racing wheels and a set of
stout clinchers for training. The heavy wheels felt OK accelerating on the
Vitus, but horrible on the CD; like absolute boat anchors. On the other
hand, the light wheels didn't seem to shine as much on the Vitus as on the
CD. I always assumed that the flex in the Vitus damped out the peak efforts
of accelerating the heavy wheels, while the super-stiff CD gave more of a
hi-fi feeling at the pedals of what your effort was. The wheelsets
definitely felt more different on the stiffer bike, as it didn't flex and
return the energy at sub-peak points in my pedal stroke. It would sure
leave my legs more sore from a sprint workout, as well. But that's another
thread... ;-)
SB
"Mark Hickey" <ma...@habcycles.com> wrote in message
news:3d6cc497....@netnews.att.net...
> "inox" <inox...@hotmail.com> wrote:
<snip>
gsk
bob...@hotmail.com wrote:
Please read the article at
http://www.bike.com/template.asp?date=8%2F1%2F2001&lsectionnumber=6Mr. Willet does a nice job of quantifying the effects of mass, inertia
and aerodynamics.Bob
Good article Bob. Thanks for the post.
g.daniels
> inox <inox...@hotmail.com> wrote:
> > Is it true that wheel weight has no effect on acceleration or braking, if
> > total weight of bike stays the same?
>
> Within reason, wheel weight has very little effect on acceleration in most
> on-road situations. The old wives tale that "one ounce saved on the
> rim/tire is equivalent to two ounces saved on the frame" is baloney.
*****************
my experience is not that of a bike mechanic but a schwinn, dad's
raleigh, my raleigh progression, machine oil, triflow, CC, with two
rebuild's and no special equipment for ten years. so when I bought my
first real bicycle tubes and too discount small for the tire/rim combo
on the front rim replacing the walmart tube that's actually a combo
27"-28" tube, the effect was quite a surprise and the answer to the
question of why all the listed weights in colorado cyclist. a savings
of NINE GRAMS!! was an apparent spin savings of 25% effort. just
remarkable!
David J. Bockman
'polar moment of enertia'.... meaning that a heavier rim takes more force
(as it has greater inertia) to get to speed x, however it will also spin
longer because of the heavier weight.
--
David J. Bockman, Fairfax, VA (USDA Hardiness Zone 7)
Bunabayashi Bonsai On The World Wide Web: http://www.bunabayashi.com
email: d...@bunabayashi.com
"inox" <inox...@hotmail.com> wrote in message
news:j92b9.12942$ZE1.2...@news1.nokia.com...
bob...@hotmail.com
While you are correct it is important to point out that these effects
are minscule as related to bicycle wheels.
http://www.bike.com/template.asp?date=8%2F1%2F2001&lsectionnumber=6
Bob
bob...@hotmail.com
<dame...@chiark.greenend.org.uk> wrote:
>
>Weight on the very edge is worth twice as much, but of course wheel weight
>is a pretty small fraction of bike weight anyway, and most of it is closer
>to the hub than that.
>
No, it doesn't count twice as much
Mark Lee
"g.daniels" <data...@yahoo.com> wrote in message
> my experience is not that of a bike mechanic but a schwinn, dad's
> raleigh, my raleigh progression, machine oil, triflow, CC, with two
> rebuild's and no special equipment for ten years. so when I bought my
> first real bicycle tubes and too discount small for the tire/rim combo
> on the front rim replacing the walmart tube that's actually a combo
> 27"-28" tube, the effect was quite a surprise and the answer to the
> question of why all the listed weights in colorado cyclist. a savings
> of NINE GRAMS!! was an apparent spin savings of 25% effort. just
> remarkable!
You've lost me.
It's the lack of punctuation.
Mark Lee
Spoldi
Mass at the rim of a wheel will store twice as much kinetic energy per pound
than stationary mass on the frame when you accelerate up to speed. Going up a
hill at constant speed will store the same amount of potential energy per
pound per vertical foot in either the wheel or the frame however.
The 2 for 1 analogy comes from the fact that a 7 pound bike with 2 pound rims
(9 pound total) requires the same energy and force from the rider to
accelerate up to an arbitrary speed as a 10 pound bike with 1 pound rims (11
pound total). The lighter bike is still easier to climb up hill however.
Steve.
Jon Isaacs
>Mass at the rim of a wheel will store twice as much kinetic energy per pound
>than stationary mass on the frame when you accelerate up to speed. Going up a
>hill at constant speed will store the same amount of potential energy per
>pound per vertical foot in either the wheel or the frame however.
>
>The 2 for 1 analogy comes from the fact that a 7 pound bike with 2 pound rims
>(9 pound total) requires the same energy and force from the rider to
>accelerate up to an arbitrary speed as a 10 pound bike with 1 pound rims (11
>pound total). The lighter bike is still easier to climb up hill however.
>
>Steve.
The important thing to point out is that one needs to include the total mass of
the system, bicycle, rider, water bottles, clothing etc.
So say that the total system has a mass of 80 kg, that would be 10 kilos for
the bike, and 70 kilos for the rider. Then it is pretty easy to see that real
world rim mass differences are inconsequential in relation to the system mass.
Say there is a 400 gram difference in total rim and tire mass (which is huge)
then in accelerating the bike this difference will make a 1% difference in
acceleration. (2 x 400 grams/80 kg = 1%)
The total energy stored in those 400 grams at 10 m/sec (22.4 mph) is about 40
joules. Since riding at 10 m/sec requires an output of something like 250
joules per second (watts) it says that the energy stored in those wheels at
22.4 mph requires about 1/10 of a second of output.
Now when you consider how long it takes to reach 22.4 mph, it is pretty clear
that the energy stored in the added wheel mass is insignificant for all but the
most critical applications.
And in those applications, aerodynamic drag is normally far more important
because it is a constant energy drain rather than a one time expendature.
That is why the sprinters at the velodrome use disk wheels rather than
lightweight spoke wheels.
jon isaacs
Jon Isaacs
>raleigh, my raleigh progression, machine oil, triflow, CC, with two
>rebuild's and no special equipment for ten years. so when I bought my
>first real bicycle tubes and too discount small for the tire/rim combo
>on the front rim replacing the walmart tube that's actually a combo
>27"-28" tube, the effect was quite a surprise and the answer to the
>question of why all the listed weights in colorado cyclist. a savings
>of NINE GRAMS!! was an apparent spin savings of 25% effort. just
>remarkable!
>
Even more remarkable is the "apparent spin savings" that can be achieve by
adjusting a dragging brake. <g>
jon isaacs
Pat
David Damerell
><dame...@chiark.greenend.org.uk> wrote:
>>Weight on the very edge is worth twice as much, but of course wheel weight
>>is a pretty small fraction of bike weight anyway, and most of it is closer
>>to the hub than that.
>No, it doesn't count twice as much
Er, yes, it does. The rotational kinetic energy of a wheel with all its
mass at the edge is equal to its kinetic energy from moving in a straight
line at a given speed. Hence, the energy needed to accelerate that wheel
up to speed is twice as great as that needed to accelerate the same mass
if it does not rotate.
Jon Isaacs
>
>Er, yes, it does. The rotational kinetic energy of a wheel with all its
>mass at the edge is equal to its kinetic energy from moving in a straight
>line at a given speed. Hence, the energy needed to accelerate that wheel
>up to speed is twice as great as that needed to accelerate the same mass
>if it does not rotate.
>--
Of course Bob is correct because the factor of 2 is only truly applies to mass
that is at the radius of the contact patch.
Since the radius of gyration of the rim mass is at least an inch less than
this, the actual factor is close to 2 but is not 2. Since the energy is the
second power of the velocity, the rotational energy stored in the rim will be
approximately (for a 700C rim with a rolling circumference of 83 inches and a
1 inch difference between the radius of gyration and the contact patch, maybe
more) 86% of the linear kinetic energy.
Nit picking you say? Well this whole discussion is nit picking because for
normal riders (and this includes just about all of us) the rotational kinetic
energy stored in the rim is of no consequence.
jon isaacs
David Damerell
>David Damerell:
>>'Bob'
>>>No, it doesn't count twice as much
>>Er, yes, it does. The rotational kinetic energy of a wheel with all its
>>mass at the edge is equal to its kinetic energy from moving in a straight
>>line at a given speed. Hence, the energy needed to accelerate that wheel
>>up to speed is twice as great as that needed to accelerate the same mass
>>if it does not rotate.
>that is at the radius of the contact patch.
That would be a lot clearer if you didn't delete attribution lines.
As you will see, my original article says;
"Weight on the very edge is worth twice as much, but of course wheel
weight is a pretty small fraction of bike weight anyway, and most of it
is closer to the hub than that."
And my subsequent article explicitly discusses a wheel with all its mass
at the edge.
So, why am I wrong, again? Perhaps you are going to tell me that when I
write 'on the very edge' I don't mean it?
Jon Isaacs
>And my subsequent article explicitly discusses a wheel with all its mass
>at the edge.
>
>So, why am I wrong, again? Perhaps you are going to tell me that when I
>write 'on the very edge' I don't mean it?
Whatever you want to say is OK.
However the fact is that there is no such thing as a wheel with all its mass at
the edge and therefore in the real world the rim weight does not count as a
factor of two but as a factor of about 1.85
This might have been Bob's contention.
Jon Isaacs
Carl Sundquist
"Jon Isaacs" <joni...@aol.com> wrote in message
news:20020829143655...@mb-fc.aol.com...
>
> However the fact is that there is no such thing as a wheel with all its
mass at
> the edge and therefore in the real world the rim weight does not count as
a
> factor of two but as a factor of about 1.85
Jon,
Do you remember a short-lived product about ten years ago called the "Black
Hole"?
It was a rim that rolled around on a 'fork' that filled the back side (front
to back) of the wheel. The rim traveled on bearing system attached to the
fork. The front between the fork and rim was open to minimize the effect of
the wind turning the front wheel. I only saw one on Brian Walton's track
bike in Trexlertown and the thing was noisy as hell.
Joshua Zlotlow
>From: "Carl Sundquist" car...@cox-internet.com
>Date: 8/29/2002 4:28 PM Pacific Standard Time
>Message-id: <umtb9s4...@corp.supernews.com>
>Jon,
>
>Do you remember a short-lived product about ten years ago called the "Black
>Hole"?
>
>It was a rim that rolled around on a 'fork' that filled the back side (front
>to back) of the wheel. The rim traveled on bearing system attached to the
>fork. The front between the fork and rim was open to minimize the effect of
>the wind turning the front wheel. I only saw one on Brian Walton's track
>bike in Trexlertown and the thing was noisy as hell.
>
I recall seeing it in Bicycling magazine. I can't recall whether or not it was
an April issue though. It seemed like a goofy idea that wouldn't go anywhere.
Was the noise bad enough to encourage people to stay off his wheel? if so,
then it wasn't soo bad after all.
Josh Zlotlow
JAZl...@aol.com
Sacramento, California
Sacramento Golden Wheelmen
www.sacgw.com
Carl Sundquist
news:20020829193155...@mb-fy.aol.com...
Considering it was on his front wheel and loudest to him, perhaps the
motivation was to get to the finish as quickly as possible, just to silence
the darn thing.
BTW, somebody just listed a set of Shamals on ebay _starting_ at $400.
Mike Murray
"Carl Sundquist" <car...@cox-internet.com> wrote:
"Do you remember a short-lived product about ten years ago called the "Black
Hole"?"
There was a local bike shop that had one of these on display. I don't
believe he ever sold it and it was probably destroyed when the shop burned
down.
I thought that they were an amazingly bad idea. Even if the aerodynamics
were excellent it seems that any gain would be offset by the increased drag
from the multiple bearings that were out towards the rim.
--
Mike Murray
David Damerell
>However the fact is that there is no such thing as a wheel with all its
>mass at the edge
That is why I wrote "most of it is closer to the hub than that.", to make
it clear that, while mass on the edge counts twice, this tells us little
about real wheels.
>This might have been Bob's contention.
Then it would help if he - and you - read articles before criticising
them.
Tim McNamara
David Damerell <dame...@chiark.greenend.org.uk> wrote:
> Jon Isaacs <joni...@aol.com> wrote:
> >However the fact is that there is no such thing as a wheel with all its
> >mass at the edge
>
> That is why I wrote "most of it is closer to the hub than that.", to make
> it clear that, while mass on the edge counts twice, this tells us little
> about real wheels.
I think the real contention is whether mass at the edge of the wheels
really "counts twice." I personally doubt it highly, given that bicycle
wheels simply aren't accelerated all that quickly. Humans don't produce
much power and bicycle acceleration is pretty negligible. Granted our
egos don't like to admit this, but bicycles aren't going from 0-100 mph
in 5.5 seconds. More like 0-25 mph in 30 seconds.
My suspicion is that mass at the edge of the wheels counts about 1.05x
mass on the rest of the bike, not 2x.
jobst....@stanfordalumni.org
> I think the real contention is whether mass at the edge of the
> wheels really "counts twice." I personally doubt it highly, given
> that bicycle wheels simply aren't accelerated all that quickly.
> Humans don't produce much power and bicycle acceleration is pretty
> negligible. Granted our egos don't like to admit this, but bicycles
> aren't going from 0-100 mph in 5.5 seconds. More like 0-25 mph in
> 30 seconds.
There is no doubt that mass on the periphery of the wheel counts
twice. The problem is that weight savings on tires are not entirely
on the periphery and they are tiny compared to the rest of the bicycle
and rider.
> My suspicion is that mass at the edge of the wheels counts about
> 1.05x mass on the rest of the bike, not 2x.
As we have thrashed out before on this subject, bicycles do not
accelerate except at the start. Even a sprint out of the turn of a
criterium is dismally low, the main effort being wind drag and the
weight of the rider. On hill climbs, the notion that "he accelerated
ahead and dropped the pack" is misleading. If you consider the rate at
which the gap opened, it is dismally low acceleration of a second or so
and then it's a speed difference of about 1/2 mph.
Therefore, all this talk of acceleration is academic, not perceptible
in bicycling. It's mainly an excuse for buying some esoteric
equipment or lightweight tires or tubes, meanwhile no one worries
about the rotation mass increase of aerodynamic rims. The don't need
any defense, they are obviously such an advantage, it appears.
Jobst Brandt <jobst....@stanfordalumni.org> Palo Alto CA
David Damerell
>I think the real contention is whether mass at the edge of the wheels
>really "counts twice."
I said only that it counts twice in that it takes twice as much energy to
accelerate it to a given speed. No-one should be contending that.
I agree that that's not actually very significant in terms of the effects
on riders, but I've never said otherwise.
warren
<jobst....@stanfordalumni.org> wrote:
> Tim McNamara writes:
>
> > I think the real contention is whether mass at the edge of the
> > wheels really "counts twice." I personally doubt it highly, given
> > that bicycle wheels simply aren't accelerated all that quickly.
> > Humans don't produce much power and bicycle acceleration is pretty
> > negligible. Granted our egos don't like to admit this, but bicycles
> > aren't going from 0-100 mph in 5.5 seconds. More like 0-25 mph in
> > 30 seconds.
>
> There is no doubt that mass on the periphery of the wheel counts
> twice. The problem is that weight savings on tires are not entirely
> on the periphery and they are tiny compared to the rest of the bicycle
> and rider.
>
> > My suspicion is that mass at the edge of the wheels counts about
> > 1.05x mass on the rest of the bike, not 2x.
>
> As we have thrashed out before on this subject, bicycles do not
> accelerate except at the start. Even a sprint out of the turn of a
> criterium is dismally low, the main effort being wind drag and the
> weight of the rider. On hill climbs, the notion that "he accelerated
> ahead and dropped the pack" is misleading. If you consider the rate at
> which the gap opened, it is dismally low acceleration of a second or so
> and then it's a speed difference of about 1/2 mph.
I don't know the physics but does it matter that the rim and tire are
spinning around at a speed much higher than the speed of the bike?
-WG
jobst....@stanfordalumni.org
>> As we have thrashed out before on this subject, bicycles do not
>> accelerate except at the start. Even a sprint out of the turn of a
>> criterium is dismally low, the main effort being wind drag and the
>> weight of the rider. On hill climbs, the notion that "he
>> accelerated ahead and dropped the pack" is misleading. If you
>> consider the rate at which the gap opened, it is dismally low
>> acceleration of a second or so and then it's a speed difference of
>> about 1/2 mph.
> I don't know the physics but does it matter that the rim and tire
> are spinning around at a speed much higher than the speed of the
> bike?
That's where the factor 2 comes from. The wheel periphery must be
accelerated to traveling speed and the whole system as well. The top
of the wheel is moving forward twice the vehicle speed but the bottom
is stationary, so it is still rotation as fast as the forward motion.
Another way to visualize this is on the stationary bicycle on a
treadmill (moving belt) where the wheel is accelerated to a speed
indicated by a bicycle speedometer. I think that makes the inertia of
the wheel and it's speed more evident. The periphery of the wheel is
traveling at ground speed.
El Senor
> As we have thrashed out before on this subject, bicycles do not
> accelerate except at the start.
But what about city riding where stops/starts at traffic lights are
frequent? Wouldn't rim/tire mass have a noticable effect here?
-Mike
Jon Isaacs
>frequent? Wouldn't rim/tire mass have a noticable effect here?
>
> -Mike
The key word here is "noticeable."
Mathmatically, twice zero is still zero.
Some points of reference:
1. Superlight weight wheels will probably save no more than 400 grams over
standard wheels. These will have about the same effect on accelertaion as the
removal of 1 full water bottle. Climbing the effect will be half that water
bottle.
2. Put a bike equipped with a rear wheel pickup cyclometer on a trainer without
any load. Put bike in high gear and take 1/2 pedal stroke. You should reach
over 30 mph. Then think how many strokes it takes to get to 30 mph.
jon isaacs
Bill
> >But what about city riding where stops/starts at traffic lights are
> >frequent? Wouldn't rim/tire mass have a noticable effect here?
> >
> > -Mike
>
> The key word here is "noticeable."
>
> Mathmatically, twice zero is still zero.
>
> Some points of reference:
>
> 1. Superlight weight wheels will probably save no more than 400 grams
over
> standard wheels. These will have about the same effect on accelertaion as
the
> removal of 1 full water bottle. Climbing the effect will be half that
water
> bottle.
Provide a reference soure for the above please.
Bill
9sDura-Ace
"Racing wheel".
I think this is Wear and Tear's "Black Hole". See
"Carl Sundquist" <car...@cox-internet.com> wrote in message news:<umtb9s4...@corp.supernews.com>...
jobst....@stanfordalumni.org
>> As we have thrashed out before on this subject, bicycles do not
>> accelerate except at the start.
> But what about city riding where stops/starts at traffic lights are
> frequent? Wouldn't rim/tire mass have a noticable effect here?
Next time you get the opportunity, either put your bicycle in a repair
stand at your local bicycle shop or have someone hold the rear end off
the ground and see how easy it is to spin up a rear wheel to 30mph
with one hand. Then consider how much effort this is in the realm of
a bicycle with rider and how hard you need to pedal to achieve the
speed you want in city traffic. I think you'll see that a few grams
off the wheel are less than a couple of swigs from a water bottle.
jobst....@stanfordalumni.org
> 2. Put a bike equipped with a rear wheel pickup cyclometer on a
trainer without > any load. Put bike in high gear and take 1/2 pedal
stroke. You should reach over 30 mph. Then think how many strokes
it takes to get to 30 mph.
Oops! I didn't read this before I pulled that old advice from the bag
of practical explanations and offered it as a response.
Jon Isaacs
>
>Bill
Yes Bill, and if I do will you read it?
For the wheel mass issue, Damon Rinard's site has a large list of complete
wheel masses. One only has to put a water bottle on a scale to see that a full
standard large size bottle weighs about 800 grams.
The limiting factor of 2 has been nicely explained several times in this
thread.
Jon Isaacs
David Damerell
>>But what about city riding where stops/starts at traffic lights are
>>frequent? Wouldn't rim/tire mass have a noticable effect here?
>standard wheels.
And much of that mass will be at the hub, not at the rim.
Bill
> >Provide a reference soure for the above please.
> >
> >Bill
>
> Yes Bill, and if I do will you read it?
Yes.
>
> For the wheel mass issue, Damon Rinard's site has a large list of complete
> wheel masses. One only has to put a water bottle on a scale to see that a
full
> standard large size bottle weighs about 800 grams.
I checked for "Damon Rinard's" site but he seems to have turned the reins
over to someone else. But thanks for the information.
I did find a picture of you from one of the links, you are looking pretty
spiffy! :)
http://www.damonrinard.com/tt/00mar19/jonisaacs.jpg
Bill
Jon Isaacs
>over to someone else. But thanks for the information.
>
g.daniels
>
> Even more remarkable is the "apparent spin savings" that can be achieve by
> adjusting a dragging brake. <g>
>
> jon isaacs
**********
plus the improbable idea that psychologic advantage(s) beats newton
across the line! have you read the book? centripitally yours
**********