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

[Kraig Willett]

At the risk of ruining great speculation, I would like to submit real data to the discussion of
accelerations during a ride (solo ride up/down Palomar Mtn in the San Diego area):

http://www.biketechreview.com/power/accel_temp.htm

IIRC, the recording interval was 1 second.

--
==================
Kraig Willett www.biketechreview.com
==================

 

[Mike S.]

"Eric Holeman" <[email protected]> wrote in message
news:[email protected]...
> 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.
>
Yeah, a textbook is great IF you a. know what it is saying, and 2. know what to do with the
knowledge. I need someone to translate these things for me 'cause I'm mathematically challenged (and
have been since HS).

There's lots of great formulas, which one do you use to calculate what we're looking to find out?

> >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.

So you don't have an SRM/Powertap either huh? Seems to me that that would be the quickest/most
accurate way available to mere mortales to test what we're looking to find out... I know my hand
isn't the most accurate force measuring device, that's why I was thinking SRM/Powertap.
>
> 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

 

[Benjamin Lewis]

Mike S. wrote:

> Eric Holeman wrote:
>>
>> 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.
>
> So you don't have an SRM/Powertap either huh? Seems to me that that would be the quickest/most
> accurate way available to mere mortales to test what we're looking to find out... I know my hand
> isn't the most accurate force measuring device, that's why I was thinking SRM/Powertap.

The nice part about the spinning-the-crank-by-hand method is that it allows you to directly
experience how little force is required to accelerate the wheel, and it becomes immediately obvious
how unimportant (small) this effect is, without trying to figure out what the numbers mean.

--
Benjamin Lewis

Your lucky number is 3552664958674928. Watch for it everywhere.

 

[Dave Lehnen]

Mark Hickey wrote:

<snip>
>
> 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.
>

The energy to accelerate from 23 to 28 mph isn't the same as the energy to accelerate from 0 to 5
mph; the first case takes 10.2 times as much energy, or is equivalent to the energy to go from 0 to
12.6 mph. It still isn't much when compared to the energy a bicyclist expends pushing air out of the
way while he is accelerating, if he's starting from a fairly high speed.

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

...unless the hill is really steep. Aero doesn't mean much at 6 or 7 mph.

Dave Lehnen

 

[Mike S.]

"Benjamin Lewis" <[email protected]> wrote in message news:[email protected]...
> Mike S. wrote:
>
> > Eric Holeman wrote:
> >>
> >> 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.
> >
> > So you don't have an SRM/Powertap either huh? Seems to me that that would be the quickest/most
> > accurate way available to mere mortales to test what we're looking to find out... I know my hand
> > isn't the most accurate force measuring device, that's why I was thinking SRM/Powertap.
>
> The nice part about the spinning-the-crank-by-hand method is that it
allows
> you to directly experience how little force is required to accelerate the wheel, and it becomes
> immediately obvious how unimportant (small) this effect is, without trying to figure out what the
> numbers mean.
>
I don't know about the rest of y'all, but I can certainly feel a difference trying to go from
30-35mph when riding my Cosmics vs. riding my Ritchey Pro wheels (or either of my OP wheels). The
Cosmics take a little more force on the pedal to make them go faster. The Cosmics are easier to keep
at the top speed because they're more aero.

Going from 0-5mph is a different critter. It don't take nearly as much effort...

Now, I don't know how much of what I'm feeling is just trying to get through the wind and how much
is wheel-related, but there's a difference between my two aero wheels. How do I know this? Well, the
Thursday night Fiesta Island ride tops out at around 35-37mph most evenings during the summer.
Groveling in the gutter at 35mph is a tough thing even with a tailwind!

Aero AND light! Now that's the ticket! Now if someone wants to buy me a Zipp 404 wheelset,
I'd be a Pro!

Mike

 

[James]

I made an error in my post below:

Rotational Energy = Omega^2 x m x r^2

I left out the exponent after the Omega.

The smaller radius wouldn't make you faster due to rotational energy -- at any given speed
the rotational energy is the same regardless of wheel radius. (Play with the equation and
you'll see why.)

You're right, smaller wheels would have some advantages. Less tire and tube weight. Shorter and
therefore lighter spokes.

A disadvantage would be larger chainrings. The extra weight alone might cancel any advantages
smaller wheels might bring.

--- James

"Jens Kurt Heycke" <[email protected]> wrote in
news:[email protected]:

> 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 0.003 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
>>
>>
>>
>>
>>
>>
>>
>>
>

 

[Peter]

Jens Kurt Heycke wrote:

> 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?

The data at the cited website generally shows the opposite - i.e. that rolling resistance is larger
for the smaller diameter tires if other factors are kept constant. Unfortunately the tires tested
generally differed in other respects besides just the diameter, but the Schwalbe Standard GW HS tire
was tested with 47 mm width in both 406 and 622 mm rim sizes. Their results showed 37% greater
rolling resistance for the smaller diameter tire. This is also what would be expected by elementary
considerations of the amount of flex seen by the tire/tube in the vicinity of the contact patch.
Smaller diameter wheels will have greater flex and therefore greater energy losses and higher
rolling resistance if other factors (pressure, width, construction) are kept equal. Whitt & Wilson
reach the same conclusion in their book, Bicycling Science, where it's stated that rolling
resistance is inversely proportional to wheel diameter. So increased rolling resistance is one
reason we don't ride around on little clown bicycle wheels. Susceptibility to bumps in the road
surface is another. OTOH, larger wheels are heavier and have greater air resistance.

 

[David L. Johnso]

On Sun, 05 Oct 2003 00:20:15 +0000, James wrote:

> You're right, smaller wheels would have some advantages. Less tire and tube weight. Shorter and
> therefore lighter spokes.
>
> A disadvantage would be larger chainrings. The extra weight alone might cancel any advantages
> smaller wheels might bring.

The added weight of a couple more teeth on a chainring is far less than the saved weight of the
smaller wheels -- if that were all that were involved.

Take a look at any decent small-wheeled bike. Most of them have suspension forks, and many have rear
suspension (usually a rubber damper) as well.

Perhaps there is something more than simply weight considerations involved.

--

David L. Johnson

__o | A foolish consistency is the hobgoblin of little minds, adored _`\(,_ | by little statesmen
and philosophers and divines. --Ralph Waldo (_)/ (_) | Emerson

 

[Onefred]

> >>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...]

Well, that's it. I've always understood its greater efficiency to be very minor. I doubt we would
see riders like Jan Ulrich climbing mountains with considerably heavier aerodynamic rims if they
sapped THAT much more energy. Though, if I were in his shoes, I'd be going for as light as possible.

Dave

 

[Bruce]

For accurate computations go to http://www.analyticcycling.com/WheelsInertia_Page.html

The equations are there if you want to see the physics & dynamics behind it. Or you can just look at
the results and trust them.

As for your feeling the difference between wheels, if there are any perceptable differences they are
most likely aero. I doubt even those can be percieved.

-Bruce

"Mike S." <mikeshaw2@coxDOTnet> wrote in message news:56Ifb.47308$vj2.29440@fed1read06...
> I don't know about the rest of y'all, but I can certainly feel a
difference
> trying to go from 30-35mph when riding my Cosmics vs. riding my Ritchey
Pro
> wheels (or either of my OP wheels). The Cosmics take a little more force
on
> the pedal to make them go faster. The Cosmics are easier to keep at the
top
> speed because they're more aero.
>
> Going from 0-5mph is a different critter. It don't take nearly as much effort...
>
> Now, I don't know how much of what I'm feeling is just trying to get
through
> the wind and how much is wheel-related, but there's a difference between
my
> two aero wheels. How do I know this? Well, the Thursday night Fiesta Island ride tops out at
> around 35-37mph most evenings during the summer. Groveling in the gutter at 35mph is a tough thing
> even with a tailwind!
>
> Aero AND light! Now that's the ticket! Now if someone wants to buy me a Zipp 404 wheelset, I'd
> be a Pro!
>
> Mike

 

[Mark Hickey]

Dave Lehnen <[email protected]> wrote:

>Mark Hickey wrote:
>
><snip>
>>
>> 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.
>
>The energy to accelerate from 23 to 28 mph isn't the same as the energy to accelerate from 0 to 5
>mph; the first case takes 10.2 times as much energy, or is equivalent to the energy to go from 0 to
>12.6 mph. It still isn't much when compared to the energy a bicyclist expends pushing air out of
> the way while he is accelerating, if he's starting from a fairly high speed.

You missed my point. We're talking about the energy to incrementally accelerate the extra (small)
mass of the wheel - and that's linear (meaning that the energy we're talking about is the same
whether that acceleration is from 0 to 5 or 100 to 105mph). I'd have to be a pretty naive bike rider
to think I could go from 23 to 28 as fast as from 0 to 5 (wish I COULD though... errr, unless it
means that I can't go from 0 to 5 very quickly).

>> Faster is always better... ;-) And aero always trumps light.
>
>...unless the hill is really steep. Aero doesn't mean much at 6 or 7 mph.

I think that's about the right "break even point" - of course, it's a pretty unusual ride that
averages that kind of gradient - if the course flattens out even a little bit, you're still ahead
with the aero wheels.

Besides, they look cool... ;-)

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

 

[Dave Lehnen]

Mark Hickey wrote:
> Dave Lehnen <[email protected]> wrote:
>
>
>>Mark Hickey wrote:
>>
>><snip>
>>
>>>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.
>>
>>The energy to accelerate from 23 to 28 mph isn't the same as the energy to accelerate from 0 to
>>5 mph; the first case takes 10.2 times as much energy, or is equivalent to the energy to go
>>from 0 to
>>12.6 mph. It still isn't much when compared to the energy a bicyclist expends pushing air out of
>> the way while he is accelerating, if he's starting from a fairly high speed.
>
>
> You missed my point. We're talking about the energy to incrementally accelerate the extra (small)
> mass of the wheel - and that's linear (meaning that the energy we're talking about is the same
> whether that acceleration is from 0 to 5 or 100 to 105mph). I'd have to be a pretty naive bike
> rider to think I could go from 23 to 28 as fast as from 0 to 5 (wish I COULD though... errr,
> unless it means that I can't go from 0 to 5 very quickly).
>
>

Well, no, I didn't miss your point. The energy to accelerate the extra mass is not linear, it's
proportional to velocity squared.
(1/2 m v^2). For 0 to 5, it's proportional to 25, for 23 to 28 it's proportional to (28^2 - 23^2) =
255, and for 100 to 105 it's proportional to (105^2 - 100^2) = 1025. Not the same, or even close.

Dave Lehnen

 

[Mark Hickey]

Dave Lehnen <[email protected]> wrote:

>Mark Hickey wrote:

>> You missed my point. We're talking about the energy to incrementally accelerate the extra (small)
>> mass of the wheel - and that's linear (meaning that the energy we're talking about is the same
>> whether that acceleration is from 0 to 5 or 100 to 105mph). I'd have to be a pretty naive bike
>> rider to think I could go from 23 to 28 as fast as from 0 to 5 (wish I COULD though... errr,
>> unless it means that I can't go from 0 to 5 very quickly).
>
>Well, no, I didn't miss your point. The energy to accelerate the extra mass is not linear, it's
>proportional to velocity squared.
>(1/2 m v^2). For 0 to 5, it's proportional to 25, for 23 to 28 it's proportional to (28^2 - 23^2) =
> 255, and for 100 to 105 it's proportional to (105^2 - 100^2) = 1025. Not the same, or even
> close.

The energy required is non-linear not because of weight, but because of aerodynamics. The comparison
is between two aerodynamically identical rims of different weight.

It would be the same as adding extra passengers to a car - the difference in acceleration would be
linear based entirely on weight.

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

 

[Joe Riel]

Mark Hickey <[email protected]> writes:

> Dave Lehnen <[email protected]> wrote:
>
> >Mark Hickey wrote:
>
> >> You missed my point. We're talking about the energy to incrementally accelerate the extra
> >> (small) mass of the wheel - and that's linear (meaning that the energy we're talking about is
> >> the same whether that acceleration is from 0 to 5 or 100 to 105mph). I'd have to be a pretty
> >> naive bike rider to think I could go from 23 to 28 as fast as from 0 to 5 (wish I COULD
> >> though... errr, unless it means that I can't go from 0 to 5 very quickly).
> >
> >Well, no, I didn't miss your point. The energy to accelerate the extra mass is not linear, it's
> >proportional to velocity squared.
> >(1/2 m v^2). For 0 to 5, it's proportional to 25, for 23 to 28 it's proportional to (28^2 - 23^2)
> > = 255, and for 100 to 105 it's proportional to (105^2 - 100^2) = 1025. Not the same, or even
> > close.
>
> The energy required is non-linear not because of weight, but because of aerodynamics. The
> comparison is between two aerodynamically identical rims of different weight.

Aerodynamics has nothing to do with it. Assume the drag coefficient were zero. Kinetic energy is

KE = 1/2*m*v^2.

The kinetic energy difference between two velocities v1 and v2 is

dKE = 1/2*m*(v2^2-v1^2)
= 1/2*m*(v2+v1)*(v2-v1)

Note that the last factor in the product (v2-v1) equals the difference in velocities. Also note that
the factor (v2+v1) is proportional to the mean velocity. It takes more energy to accelerate the
faster vehicle.

However, also note that required energy is linear with mass, regardless the velocities.

Joe Riel

 

[David L. Johnso]

On Sun, 05 Oct 2003 13:42:54 +0000, Qui si parla Campagnolo wrote:

> I think the bottom line is that when a wheel maker says in their advert that the wheel is so much
> 'faster' cuz the weight is at the hub rather than the rim.

This nonsense is common in advertising. It was one of the big "features" of the Spinnergy Spox
wheels that the spoke tensioning do-dads were at the hub rather than the rim, so they would
accelerate faster. Lame.

--

David L. Johnson

__o | Become MicroSoft-free forever. Ask me how. _`\(,_ | (_)/ (_) |

 

[Dave Lehnen]

Mark Hickey wrote:
> Dave Lehnen <[email protected]> wrote:
>
>
>>Mark Hickey wrote:
>
>
>>>You missed my point. We're talking about the energy to incrementally accelerate the extra (small)
>>>mass of the wheel - and that's linear (meaning that the energy we're talking about is the same
>>>whether that acceleration is from 0 to 5 or 100 to 105mph). I'd have to be a pretty naive bike
>>>rider to think I could go from 23 to 28 as fast as from 0 to 5 (wish I COULD though... errr,
>>>unless it means that I can't go from 0 to 5 very quickly).
>>
>>Well, no, I didn't miss your point. The energy to accelerate the extra mass is not linear, it's
>>proportional to velocity squared.
>>(1/2 m v^2). For 0 to 5, it's proportional to 25, for 23 to 28 it's proportional to (28^2 - 23^2)
>> = 255, and for 100 to 105 it's proportional to (105^2 - 100^2) = 1025. Not the same, or even
>> close.
>
>
> The energy required is non-linear not because of weight, but because of aerodynamics. The
> comparison is between two aerodynamically identical rims of different weight.
>
> It would be the same as adding extra passengers to a car - the difference in acceleration would be
> linear based entirely on weight.
>
> Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame

The non-linearity is not in mass, but in velocity. Velocity is a second-power (squared) term in
kinetic energy, not a linear term. This is why it takes more energy, in the absence of aerodynamic
drag, rolling friction, etc, to increase speed by some fixed increment when starting from a higher
speed, and why your original calculation was in error.

Aerodynamic drag is nonlinear in velocity, as has often been discussed on this NG, and is the
largest power-consuming factor on level ground after roughly 10 mph. But even if you could eliminate
aerodynamic and other drag sources, acceleration is not constant with constant power, but is
proportional to the inverse of the current speed.

Dave Lehnen

 

[Mike S.]

"David L. Johnson" <[email protected]> wrote in message
news:[email protected]...
> On Sun, 05 Oct 2003 13:42:54 +0000, Qui si parla Campagnolo wrote:
>
> > I think the bottom line is that when a wheel maker says in their advert that the wheel is so
> > much 'faster' cuz the weight is at the hub rather than the rim.
>
> This nonsense is common in advertising. It was one of the big "features"
of
> the Spinnergy Spox wheels that the spoke tensioning do-dads were at the hub rather than the rim,
> so they would accelerate faster. Lame.
>

Ditto with the Cane Creek Crono wheels.

The minute difference of where the nipples are located may mean tenths to hundredths of a second,
but as a marketing tool, well, now that's priceless!

Mike
> --
>
> David L. Johnson
>
> __o | Become MicroSoft-free forever. Ask me how. _`\(,_ | (_)/ (_) |