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[hpv] Are bents with larger rear wheels faster? Why?

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Peter Lewis

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Oct 11, 1999, 3:00:00 AM10/11/99
to
As a non-physicist and layman, I would like a simple understanding of the
reasons why a person would choose a recumbent with a 700C wheel over a 20"
wheel. Or vice-versa. I know that a smaller wheel supposedly climbs well and
accelerates well, but I would sure like an easy to understand explanation.

TIA,

Peter

Bill Volk

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Oct 12, 1999, 3:00:00 AM10/12/99
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Peter asks:

Easier to setup the gearing with a larger wheel. Don't need huge chain
rings, Mt Drives, or 3x7's.

There's an opinion that a 700c wheel rolls faster than the 20" wheels, but I
don't share it.

Bill Volk

Tim & Ally Smith

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Oct 12, 1999, 3:00:00 AM10/12/99
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I know several who go for the larger wheel to get the gearing.
A 20" needs something like a 3x7 Sachs on the rear to have tall enough
gearing at speed. (unless you have gigantic front cogs)

At 04:57 PM 11/10/1999 -0500, you wrote:
>As a non-physicist and layman, I would like a simple understanding of the
>reasons why a person would choose a recumbent with a 700C wheel over a 20"
>wheel. Or vice-versa. I know that a smaller wheel supposedly climbs well
and
>accelerates well, but I would sure like an easy to understand explanation.

<<<<<<<<<<<<>>>>>>>>>>
Tim & Ally Smith
Devonport, Tasmania, Australia
Web Page http://www.vision.net.au/~timotsc/index.htm
<<<<<<<<<<<<>>>>>>>>>>


Scott Talkington

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Oct 12, 1999, 3:00:00 AM10/12/99
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Peter:

I'll give this a shot. Bear in mind that I'm not an engineer, so be gentle.
If you have two people of the same height and weight and with the same
inseam and "gait," but different shoe sizes, then the person with the
smaller shoe size will need to have his shoes re-soled more often. By the
same token, a smaller diameter tire uses less surface to cover the same
distance, and will therefore wear faster than a larger diameter tire. Rims
will wear faster, and fade more quickly, for essentially the same reason. I
realize that the pneumatic characteristics of the tire could alter these
assumptions to some extent, but I'm assuming the contact patch will remain
the same.

As far as speed goes, there should not be any *net* difference between the
two; at least not in an ideal world. The smaller wheel will accelerate and
decelerate faster, so the ride will be more "nervous" but the average speed
would be the same, provided the mechanics were controlled by an "ideal"
monitor, like a computer. If you can slow down more quickly you can also
speed up more quickly. This assumes that you don't loose any speed as a
result of the need to monitor your exertion level and speed more carefully
due to the "nervous" quality of the smaller wheel. In the real world that
monitoring function usually causes people to overshoot and/or undershoot a
target speed and exertion level, so the efficiency of energy transfer is
less with a smaller wheel. This is entirely due to the limitations of human
cognition, however. There is no inherent mechanical advantage to having a
larger wheel as far as I know.

-Scott


----- Original Message -----
From: Peter Lewis <ple...@execpc.com>
To: <h...@ihpva.org>
Sent: Monday, October 11, 1999 5:57 PM
Subject: [hpv] Are bents with larger rear wheels faster? Why?


> As a non-physicist and layman, I would like a simple understanding of the
> reasons why a person would choose a recumbent with a 700C wheel over a 20"
> wheel. Or vice-versa. I know that a smaller wheel supposedly climbs well
and
> accelerates well, but I would sure like an easy to understand explanation.
>

> TIA,
>
> Peter
>
>


john Riley

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Oct 12, 1999, 3:00:00 AM10/12/99
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Don't know if this qualifies as "easy to understand" but this old message
(edited) reveals the theory and the basic question. - JR


The energy in a spinning wheel depends on the mass (or at least, a
similar quantity) and the square of the rpm.
At low speeds, the mass of a large wheel (say, 27") will make it
harder to turn than a smaller wheel. The smaller
wheel (say, 20") does have to spin faster to go the same linear-equivalent
speed, but there exists some range of low speeds where the velocity
contribution is insignificant.
At high speeds, the difference due to mass is still there, but the
difference due to rpm(27")^2 vs. rpm(20")^2 grows quickly. That is,
increasing the rpm of the 20" will take more energy than increasing the
rpm of the 27" to achieve the same increase in linear speed.
So I'm asking, what is a low speed and what is a high speed in
this case? is 10 mph high? or is it more like 100 mph?
_______________________________________________________________________________
Lou Hom >K '93
lh...@nature.berkeley.edu
http://www.ocf.berkeley.edu/~lhom

Kent Larson

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Oct 12, 1999, 3:00:00 AM10/12/99
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I know little, but wouldn't the larger wheel take bumps better?

Kent

DrRec...@aol.com

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Oct 12, 1999, 3:00:00 AM10/12/99
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I think we can all agree on the performance benefits of such bikes that
primarily use 700c wheels such as the Lightning SWB and Easy Racers LWB. When
the limits of recumbent design are pushed, say in the case of a lowracer, the
lines become more blurred. What I am finding in my years of recumbency is
that there is always a contradiction to any generalization that one makes.

My question as it relates to the above is with the recumbent subculture of
big wheelers. WHIRL's Mark Colliton rides his V-Rex (the original prototype
V-Rex) with dual 24's. I think I first rode it this way 3 or 4 years ago.
There are others who have converted their bikes to two full size wheels.
Vision now has the dual 24 Saber as their performance flagship. The theory
behind the design seems to be that big wheels roll faster. We are working on
an article on big wheel recumbents, and I was looking for some feedback.

My question is this: At what point do the supposed benefits of big wheel
rolling resistance overcome the negatives of more frontal area of a high bike.

Lastly, I am aware of the benefits of lowracers and don't want to turn this
into an article about them (we have a few of those coming up in RCN as well).
I don't think the larger US mfrs will be rushing to produce lowracers for
perceived safety reasons (another generalization).

Cheers
Bob Bryant
Recumbent Cyclist News
www.recumbentcyclistnews.com

Bill Volk

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Oct 12, 1999, 3:00:00 AM10/12/99
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Tim wrote:

> I know several who go for the larger wheel to get the gearing.
> A 20" needs something like a 3x7 Sachs on the rear to have tall enough
> gearing at speed. (unless you have gigantic front cogs)

Or spin. I have a 58 large ring.... that gives me (with the Comp Pool)
about a 100" top gear. I've spun it to 43mph .... but I did need a taller
gear with the full fairing .... I was maxing out at 33 mph before I
completely went into overheat.

Bill Volk

Scott Talkington

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Oct 12, 1999, 3:00:00 AM10/12/99
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Kent:

That makes sense to me. It would also tend to smooth any irregularities
(not just "bumps") that are either shorter and/or deeper than the arc of the
wheel. I had not considered that. So, with your comment, mine, and John
Riley's, there may be three independent sets of speed advantages to larger
wheels. Since there doesn't seem to be an interaction between them the
effect would be additive, and I guess the issue is whether, taken together,
they amount to very much.

It reminds me vaguely of the "big bat - little bat" slugging controversy in
baseball. Even though it appears that little bats have won the argument I
find it hard to swallow the notion that the primary difference between Ruth
(big bat) and McGuire & Sosa (little bat) is due to bat size. On the other
hand the average number of HRs per player seems to be higher now. (I don't
know this for sure. Just extrapolating from some other stats.) I heard the
other day that for either McGuire or Sosa to match the percentage of total
HRs hit by all players in the 1921 season achieved by Ruth (he hit 59)
either one would have to hit a whopping 357 home runs! Since there are
probably not six times as many players nowadays either pitchers have gotten
worse, players have gotten better, or there's something to the little bat
theory. On the other hand, perhaps there *are* six times as many players
taking the field now. Anyone know?

-Scott
----- Original Message -----

Bill Volk

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Oct 12, 1999, 3:00:00 AM10/12/99
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This ....

> The energy in a spinning wheel depends on the mass (or at least, a
> similar quantity) and the square of the rpm.
> At low speeds, the mass of a large wheel (say, 27") will make it
> harder to turn than a smaller wheel. The smaller
> wheel (say, 20") does have to spin faster to go the same linear-equivalent
> speed, but there exists some range of low speeds where the velocity
> contribution is insignificant

Is why my costly Ivy League Physics degree is not wasted. It allows me to
say:

Not Really Relevant. I mean what in the heck does:

"At low speeds, the mass of a large wheel (say, 27") will make it harder to
turn than a smaller wheel. "

mean? Harder to turn? Nope. Harder to accelerate, maybe.

At a constant speed the rotational energy of the wheel isn't a factor. Yes,
small wheel bikes tend to accelerate faster ... if the rims and tires are of
similar weight-per-unit-length as the larger wheels. But it has nothing to
do with TT speeds.

The inertia of the ride and hpv are quite a bit larger than the wheels.

Bill Volk

GSS...@aol.com

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Oct 12, 1999, 3:00:00 AM10/12/99
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Or ......Modern fields are not as deep. (I heard this on TV or NPR or
somewhere).

Gunther

Scott Talkington

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Oct 12, 1999, 3:00:00 AM10/12/99
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Bob:

I was under the impression that Mark's primary reason for preferring the
24/24 setup was handling rather than speed. The average wheel diameter of
the 20/26 setup is 23, and assuming the drive wheel dimension is more
important, and the smaller front wheel will have lower drag, then the 20/26
ought to be at least as "fast" as the 24/24, if not faster. There is at
least one guy with a 26/26 V-Rex in WHIRL. He's pretty fast.

I think we have a reasonable grasp of the general theories, but what leaves
me in the dark is some clue about magnitudes and sensitivities of various
design characteristics, including wheel size. Without those all we have is
BS. I feel like my gears are stripped.

I hasten to add that the "nervous ride" concept is something that seems to
have been overlooked in other discussions about wheel size. It may not be
insignificant at all, and it is not a mechanical advantage, per se. It is
therefore hard to model without some data on human reaction times. Knowing
that, or taking an educated guess, one might install some sort of mechanical
device, analogous to Bill Patterson's control spring, that dampens
acceleration/deceleration of smaller wheels. That would leave only the
mechanical advantages.

-Scott
----- Original Message -----
From: <DrRec...@aol.com>
To: <h...@ihpva.org>; <b...@recumbentcyclistnews.com>
Sent: Tuesday, October 12, 1999 11:01 AM
Subject: RE: [hpv] Are bents with larger rear wheels faster? Why?

Estes Wayne-W10191

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Oct 12, 1999, 3:00:00 AM10/12/99
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Here's my understanding of why large wheels are faster than small wheels in
"real world" conditions.

On an ideal smooth road, a small wheel has about the same rolling resistance
as a large wheel if the tires are really hard. But on a surface that is
less than perfectly smooth, the rolling resistance of a small wheel will
degrade more than the rolling resistance of the large wheel.

A good analogy is a suitcase with very small wheels. It rolls pretty well
on the smooth floor of the airport terminal building. But the rolling
resistance increases significantly when you roll the suitcase outside onto
asphalt which isn't nearly as smooth. You will notice much less difference
in rolling resistance if you ride your bike (larger wheels) from the airport
floor to the road outside. The larger the wheel, the less effect that
surface imperfections have on the rolling resistance.

Advantage of large wheels:
Lower rolling resistance on "real world" imperfect surfaces
Handles potholes better (less likely to crash)
More convenient gearing

Advantage of small wheels:
Lower mass (better climbing, more responsive acceleration)
Lower wind resistance
Stronger structure (stays true, lasts longer)

Which wheel is best depends on how you value these attributes.


Wayne Estes
Mundelein, IL, USA


john Riley

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Oct 12, 1999, 3:00:00 AM10/12/99
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Bill Volk wrote:
[...]

> At a constant speed the rotational energy of the wheel isn't a factor. Yes,
> small wheel bikes tend to accelerate faster ... if the rims and tires are of
> similar weight-per-unit-length as the larger wheels. But it has nothing to
> do with TT speeds.
>
> The inertia of the ride and hpv are quite a bit larger than the wheels.
>
> Bill Volk

Small wheels accelerate faster; do they not also decelerate faster? Isn't the
larger wheel better able to store energy?

Are you saying that if you had two flywheels of equal mass, a small diameter
one would be as good at storing energy as a large diameter one?

John Riley

Jeff Wills

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Oct 13, 1999, 3:00:00 AM10/13/99
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> I'm not disagreeing with you in any way, Bill. But what I don't
> understand
> is why when I cost at 32kph on a Rocket I slow down much faster
> than when I
> cost from 32 kph on a V-rex. please explain.
>

Are the tire pressures the same between the two bikes? Is the
seat/handlebar/crank _exactly_ the same.

Eliminate the variables- then report the results. Gotta be scientific here.
;-))


Jeff Wills

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Oct 13, 1999, 3:00:00 AM10/13/99
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>
> The radius that the mass travels at does affect the ride. A small radius
> wheel of the same mass, will not have as much gyroscopic effect.
> A small radius wheel that is lighter will have even less
> gyroscopic effect.
> Try riding no hands on a steel wheeled 10 speed, then an alloy
> wheel, then a
> 20 "
> bike. The small light wheels are far less stable.
> Ross
>

The two Bills (Patterson and Volk) will jump on you- and so will I.

Gyroscopic effect has _nothing_ to do with stability. People have created
stable bicycles with 17" wheels, 12" wheels, 2" skateboard wheels, or even
ice skates on the front. I challenge you to make a bicycle more stable by
substituting heavier wheels.

As long as the geometry (fork rake and head angle) is adjusted to compensate
for the smaller wheel, stability will be maintained.

Jeff

Jeff Wills

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Oct 13, 1999, 3:00:00 AM10/13/99
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Scott said:
>
> That makes sense to me. It would also tend to smooth any irregularities
> (not just "bumps") that are either shorter and/or deeper than the
> arc of the
> wheel. I had not considered that. So, with your comment, mine, and John
> Riley's, there may be three independent sets of speed advantages to larger
> wheels. Since there doesn't seem to be an interaction between them the
> effect would be additive, and I guess the issue is whether, taken
> together,
> they amount to very much.
>

OK, here's another way of thinking about it. Cut lateral grooves in a
roadway at right angles to your wheel's path. Make them X width. Now roll
two test wheels across these grooves at an arbitrary speed: the first wheel
is 3X diameter, the second wheel is 5X diameter.

Obviously, both wheels will fall into and climb out of the grooves the same
number of times in a given interval, so their frequency of fall/rise is the
same. But the smaller wheel will fall further and have to climb further
with every groove it passes. Thus the smaller wheel experiences falling &
rising of greater _amplitude_. Therefore, on a non-smooth surface, a
smaller wheel will use more energy than a larger wheel, all other factors
being equal.

Comments, anyone?

Jeff


RobHague

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Oct 13, 1999, 3:00:00 AM10/13/99
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john Riley said:

> Small wheels accelerate faster; do they not also decelerate faster? Isn't the
> larger wheel better able to store energy?
>
> Are you saying that if you had two flywheels of equal mass, a small diameter
> one would be as good at storing energy as a large diameter one?
>

When I was reading up on flywheel research a while back (NASA - energy storage for space systems) they were greatly in
favour of small, light flywheels (for obvious reasons) and keen to point out that kinetic energy is mass*velocity
squared (ok, the physics were explained in layman terms, I can't remember the rotational equations!!!). They argued that
increasing rotational speed was a far better way of increasing the amount of energy that may be stored. The remainder of
the paper discussed how to design a flywheel that doesn't break up under such extreme conditions, destroying the vehicle
and causing a navigational hazard.....

Don't spin too fast out there guys!!!

Rob.
--
Rob Hague
Westcountry Recumbents, Somerset, UK
Voice: 0870 7401227 (UK National Rate)
Fax: 07050 695561 (UK 'K' rate)
NEW WEB PAGE ---> http://www.wr.hpv.co.uk


RobHague

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Oct 13, 1999, 3:00:00 AM10/13/99
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Estes Wayne wrote:

> Advantage of large wheels:
> Lower rolling resistance on "real world" imperfect surfaces
> Handles potholes better (less likely to crash)
> More convenient gearing
>
> Advantage of small wheels:
> Lower mass (better climbing, more responsive acceleration)
> Lower wind resistance
> Stronger structure (stays true, lasts longer)
>
> Which wheel is best depends on how you value these attributes.

(Assuming large wheel equates to narrow section tyres and small wheel equates to wider section tyre use...)

More advantages, and what about the disadvantages...?

Advantages of large wheels.
Wider selection & availability of fast tyres/tubes?

Advantage of small wheels.
See Zach Kaplan notes on 'safer' large section tyres (RCN etc.)
Work better with hub brakes due to shorter leverage.
Less mechanical loading (especially for trikes)

Disadvantages of large wheels:
Prone to pinch punctures when small section tyres used.
Can be difficult to remove/fit tyres - tools required

Disadvantages of small wheels:
Tyres with built-in puncture resistance strip hard to find (only Vredestein?)

john Riley

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Oct 13, 1999, 3:00:00 AM10/13/99
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Jeff Wills wrote:
[...]

> Gyroscopic effect has _nothing_ to do with stability. People have created
> stable bicycles with 17" wheels, 12" wheels, 2" skateboard wheels, or even
> ice skates on the front. I challenge you to make a bicycle more stable by
> substituting heavier wheels.
>
> As long as the geometry (fork rake and head angle) is adjusted to compensate
> for the smaller wheel, stability will be maintained.

I believe that, but does not the wheel size (and gyroscopic effect) affect the
feel of the bike's steering? Perhaps in terms of perceived "responsiveness"?
If you hold a spinning wheel by the axle (and you only need to hold it by one
end if you rotate slowly!) and move it about, you can feel forces. They don't
seem insignificant when I have the wheel in my hands.

John Riley

Fred Larimer

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Oct 13, 1999, 3:00:00 AM10/13/99
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Been following this discussion with much interest. This analogy makes
sense. Although real world conditions rarely have grooves parallel to the
wheels' path but all manner of surface irregularities that the tires have
to roll over. Wouldn't the fact that we typically use a wider tire on the
smaller wheels help them roll over at least some of the surface
irregularities that would otherwise catch them?

Fred

At 08:41 PM 10/12/99 -0700, Jeff Wills wrote:
snip


>OK, here's another way of thinking about it. Cut lateral grooves in a
>roadway at right angles to your wheel's path. Make them X width. Now roll
>two test wheels across these grooves at an arbitrary speed: the first wheel
>is 3X diameter, the second wheel is 5X diameter.
>
>Obviously, both wheels will fall into and climb out of the grooves the same
>number of times in a given interval, so their frequency of fall/rise is the
>same. But the smaller wheel will fall further and have to climb further
>with every groove it passes. Thus the smaller wheel experiences falling &
>rising of greater _amplitude_. Therefore, on a non-smooth surface, a
>smaller wheel will use more energy than a larger wheel, all other factors
>being equal.
>
>Comments, anyone?
>
>Jeff
>
>
>

Fred. 95 Vrex, 94 Kowal ultra SWB Tandem

Scott Talkington

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Oct 13, 1999, 3:00:00 AM10/13/99
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Bill:

As long as there are no imperfections or irregularities in the road surface,
or events that occur with a different frequency than the cadence of the
pedal stroke. In that case a wider variation presents more opportunity for
loss of energy. And you say you're getting that rattling of the Rans bag
for free? There are other mechanisms on the bike itself that lose energy
with greater variation, where the forces and vectors are not in the same
line as the pedal stroke. And we're also not necessarily talking about a
constant variation either, as with the constant repeated pressure of the
pedal stroke (or a smooth curve, at least). Why would there not be larger
*overall* variations in amplitude, at irregular intervals? With less
capacity to maintain a constant pace you have to lose more energy, not just
to bumps in the road, but to any and all impinging events.

-Scott
----- Original Message -----

From: Bill Volk <bv...@inetworld.net>
To: Scott Talkington <freewh...@home.com>; hpv list <h...@ihpva.org>
Sent: Tuesday, October 12, 1999 5:35 PM
Subject: Re: [hpv] Re: Are bents with larger rear wheels faster? Why?


> Scott wrote:
>
> > This is basically what I thought was going on, until John Riley started
> > talking about "harder to turn" wheels. If the issue is purely one of
> > acceleration/deceleration then the only difference that makes sense is
the
> > one concerning a "nervous" ride. The wider the variation around the
mean
> > cruising speed the more energy is wasted in maintaining that speed
>
> And the energy loss mechanism in the acceleration and deceleration of the
> wheels is?????
>
> (answer: none, the energy in accelerating the wheel is returned during the
> deceleration or coasting part of the pedal stroke).
>
> Interesting note: You do tend to "surge" more with smaller light wheels.
> That is the change in speed as a result of the pedal stroke is more
> pronounced. I can feel the Rans bag rocking against the seat back when I
> pedal with a good bit of effort.
>
> Bill Volk
>


Gary King

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Oct 13, 1999, 3:00:00 AM10/13/99
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Often wheel size gets blamed when other factors are the cause. I can argue
some CLWB have more rolling resistance than SWBs & LWBs because of weight
distribution. My SWB has very close to 50/50 weight distribution while my
CLWB is 70/30 biased to the back wheel. Tyre contact patch and therefore RR
is proportional to weight on the tyre (among other factors). So the back
tyre of the CLWB needs 40% MORE pressure than on the SWB to keep rolling
resistance the same. The SWB runs 100psi in both tyres but unfortuantely I
don't know of any 20" tyre rated at 140psi for the CLWB so you can see that
design of bike is handicapped from the start.

BTW my CLWB has 20/20" wheels and the SWB is 26/20 (not that this matters).

The arguement for better rolling over bumps is interesting, maybe true for
wheel size potholes? A semi rural road I sometimes ride has a very coarse
chip asphalt and slows all my bikes down, I estimate, by 3 or 4km/h. The
vibration and slowness is just as bad on my 700C racer as it is on the 20/20
CLWB. However the Moulton (with full suspension & 16" wheels!!) glides over
it.

Keep the wheel size theories coming, I don't think any of them are right.

ciao
--
Gary King

Ed Gin & Shirleen Kajiwara

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Oct 13, 1999, 3:00:00 AM10/13/99
to
Have been following this thread and is a good one for arguments.
However my 2 cents regarding which wheel sizes are faster.......

To run real world tests would create a nightmare requiring a "mule" type
to bike to maintain exact rider positioning with adjustable frames to
accomodate the different wheels. Wayne's references to differing road
conditions throws in more variables. I have found that adding
suspension to a bike gives higher speeds though greater weight is
obviously involved, counterintuitive huh?

In the overall scheme of things, rolling resistance IMO is only one
small factor in the formula for overall speed especially at higher
speeds above 20mph. Total frontal area, bottom bracket height, seat
height, bike length, chain line orientation, seat angle, arm
positioning, head positioning, clothing worn, types of hubs/bottom
brackets used 3speed/rohlhoff/ Schumpf, etc. are all other components to
consider when discussing what is "faster."

Amonst the bikes I've owned, 700/451 V-Rex, 700/16inch, 26inch/406 Stock
and Fully Faired P-38's, 26inch/moulton Windcheetah, 406/406 Tailwind,
and 406/406 Tiger, I can't tell and wouldn't venture to guess which has
the best rolling wheelset. There are just "too many" other factors to
consider which will affect conclusions.

Tailwinds and cheers,

Ed Gin

---------------------------------------------------
CHICAGOLAND RECUMBENT RIDERS
web site.... http://www.mcs.net/~gkpsol
email.... gkp...@mcs.net
---------------------------------------------------

Bill Patterson

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Oct 13, 1999, 3:00:00 AM10/13/99
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IMHO we are talking about the control spring. How hard it is to turn the handle
bar.

The main equation for the control spring is K2 times velocity squared. THe
largest contributor to K2 is the centrifugal acceleration of the bike when the
handlebar is turned. THe second is the angular acceleration of the frame about the
contact point of the wheels.
Bicycle wheels are not massive enough for angular momentum to predominate.
Motorcycles with massive front wheels must include the angular momentum of the
front wheel and perhaps bikes with a steel rimmed 26 inch wheel or larger. K2 is
increased by only 10 percent or so for small wheeled recumbents.

Its the sideward friction force acting on the moment arm of the trail vector that
is important for most bikes.

john Riley wrote:
I believe that, but does not the wheel size (and gyroscopic effect) affect the

> feel of the bike's steering? Perhaps in terms of perceived "responsiveness"?
> If you hold a spinning wheel by the axle (and you only need to hold it by one
> end if you rotate slowly!) and move it about, you can feel forces. They don't
> seem insignificant when I have the wheel in my hands.
>
> John Riley

--

Bill Patterson mailto:wy...@lightspeed.net
Assoc. Prof. Mechanical Eng. CALPOLY SLO

"Lords of http://www.calpoly.edu/~wpatters/
the Chainring" Handling qualities theories for bicycles
and motorcycles (90+ spiral-bound pages)
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mailto:DrRec...@aol.com
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+ book reviews mailto:no...@praxcomm.com
Australia http://www.greenspeed.com.au/
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1998 class photos (student web site showing prototypes)
http://www.geocities.com/SouthBeach/Inlet/5986/bike.html

Bannister, Wade

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Oct 13, 1999, 3:00:00 AM10/13/99
to
Let me summarize this thread:

Differences between large dia/small dia (in general):

Given that it takes energy to spin a bearing, and that it will take more
energy for a faster rotation, a large wheel will require less energy to spin
at the same ground speed as a small wheel. My engineering handbook implies
that this is a linear property, and that ball bearings are 99% efficient:
the faster spin required for smaller wheels is a function of the radius so a
20" has to spin 13.5/10=1.35 times faster than a 27 for the same speed.
This implies that the bearing friction will also be 1.35 times higher so a
20" wheel would be consuming 1%x1.35 power Vs the 27 .35% is not much more
but is 1/3 more than the large wheel. It has been noted previously that air
resistance (which increases geometrically with speed) far exceeds this
effect.

Larger wheels burn less power on rough surfaces. A linear effect with the
same proportions as above.

Large wheels are easier to gear for faster speed ranges, small ones for slow
speeds/climbing. Purely aesthetic/personal.

Conclusion: Larger wheels are a little more efficient, but the difference is
small enough that it depends on your preferences. Many recumbents require
small wheels for clearance/packaging reasons, particularly on the front.

Handling stability:
Smaller wheels respond faster! but this also means that more base
stability (trail, basically) needs to be built into the frame geometry. I
note that if you take a bike and put a larger front wheel on it, you will
also increase the trail and therefore stability. This works if you
increase both or just the front, tho just the front will also kick the head
angle back (increases trail and fork flop).

Actually this works like the gearing argument: You have to slow the
response of a small wheel design down for your comfort level, or speed it up
on a large wheel design for the same.

Conclusion: If your bike is too responsive for you, put on a larger diameter
front wheel and it will slow it down some. Putting on a longer fork or one
with less forward rake would do the same.


Ross or Judy

unread,
Oct 13, 1999, 3:00:00 AM10/13/99
to
Stability of smaller wheeled bikes can be compendsated for
by changing steering geometry. The physics can not be changed.
The large wheel has to move the mass a greater distance for an
equal angle change. Spin a large wheel in your fingers and change
the direction that it is pointed. Then spin a small
wheel in your fingers . Try light wheels and heavy wheels.
It makes sense when you consider the physics. To do
a similar change in direction , the different size wheels
would have to deflect different amounts.
Ross

I challenge you to make a bicycle more stable by
>substituting heavier wheels.
>
>As long as the geometry (fork rake and head angle) is adjusted to
compensate
>for the smaller wheel, stability will be maintained.
>

>Jeff


If the circumferences of the equal mass flywheels are traveling
at the same speed (small one spining faster) they will have the
same amount of stored energy. But it would take
more energy to change the direction of the larger wheel.


>Are you saying that if you had two flywheels of equal mass, a small
diameter
>one would be as good at storing energy as a large diameter one?
>

>John Riley
>

William Volk

unread,
Oct 13, 1999, 3:00:00 AM10/13/99
to
Wade wrote:

>Given that it takes energy to spin a bearing, and that it will take more
>energy for a faster rotation, a large wheel will require less energy to
spin
>at the same ground speed as a small wheel.

See Wilson's "Bicycle Science" for just how important the bearing losses
are...

hint "almost negligible".

Bill Volk


William Volk

unread,
Oct 13, 1999, 3:00:00 AM10/13/99
to
Mark wrote:


>I'm not disagreeing with you in any way, Bill. But what I don't understand
>is why when I cost at 32kph on a Rocket I slow down much faster than when I
>cost from 32 kph on a V-rex. please explain.

Higher cranks (in relation to the seat) on the V-Rex perhaps? Seat back
angle? Better aero.

What 20" tires are you running on the Rocket? Primo Comets? Tioga Comp
Pools?

If it's any consolation, with Thorn-Tubes the Comp Pools are not that low in
rolling resistance.

>This leads me to believe that it takes more of MY energy to keep the same
>speed on a Rocket as a V-rex. At least I feel like I'm working harder and
>can't rest. This further leads me to believe that A larger rear wheel is
>faster in the long run. Maybe not in a sprint, but over a 100k, yes.

Aero is a much bigger effect, even at 32kph, then rolling resistance.
Really.

The best way to compare rolling resistance is at low speeds. Like 10kmph.
See how far the bike will coast.

I also agree with the posting that on bumpy roads the larger wheels may be a
better bet since they are effected less by bumps.

Bill Volk

William Volk

unread,
Oct 13, 1999, 3:00:00 AM10/13/99
to
Ross wrote:

>The small light wheels are far less stable.

>Try riding no hands on a steel wheeled 10 speed, then an alloy wheel, then
>a 20 "

My last 700c upright (Myata 1000LT) could NOT be ridden no-hands. My old
1975 Bob Jackson TT bike with sewups and very light wheels could ...

My dual 20" recumbent can be ridden no hands easily. Not only by me.

Much more to that than just the wheel sizes and gyroscopic effects.

Bill

Tim & Ally Smith

unread,
Oct 14, 1999, 3:00:00 AM10/14/99
to
A friend on mine says he had markedly more stability in a turn on his LWB
USS bike when loading lead weights around the 16" front wheel.
They're mounted on the spokes and covered by reflectors. See
http://sunsite.anu.edu.au/community/ozhpv/tas/richard.htm


Jeff Wills wrote:
[...]
> Gyroscopic effect has _nothing_ to do with stability. People have created
> stable bicycles with 17" wheels, 12" wheels, 2" skateboard wheels, or even

> ice skates on the front. I challenge you to make a bicycle more stable by


> substituting heavier wheels.
>
> As long as the geometry (fork rake and head angle) is adjusted to compensate
> for the smaller wheel, stability will be maintained.


<<<<<<<<<<<<>>>>>>>>>>
Tim & Ally Smith
Devonport, Tasmania, Australia
Web Page http://www.vision.net.au/~timotsc/index.htm
<<<<<<<<<<<<>>>>>>>>>>


F.Lenk

unread,
Oct 14, 1999, 3:00:00 AM10/14/99
to
Interesting. I encountered a similar increase in slow speed stability on
my LWB OSS Pursuit when a full large water bottle was stored on the
long, rearward tilting steering column. I reproduced and enhanced that
slow speed stability fulltime with a piece of bungy stretched between
the steering column and frame (and still have the excellent highspeed
stability Pursuits are known for).
fred lenk.

Tim & Ally Smith wrote:
>
> A friend on mine says he had markedly more stability in a turn on his LWB
> USS bike when loading lead weights around the 16" front wheel.
> They're mounted on the spokes and covered by reflectors. See
> http://sunsite.anu.edu.au/community/ozhpv/tas/richard.htm
>
>

--
Rotator Pursuit, Thunderbolt Trike
website->www.lenk.net, email->le...@vcnet.com

Jeff Wills

unread,
Oct 14, 1999, 3:00:00 AM10/14/99
to
Ummm... I think I see what's happening. The mass of steered assembly has
been increased. This can damp steering by reducing PIO: pilot-induced
oscillation.

I bet your friend could get the same effect by taking the lead weights out
of the wheel and mounting them rigidly at the same distance from the
steering axis- say, on a fender or rack.

I think Jim Blackburn (of Blackburn racks fame) did this experiment many
years ago: as long as weight was rigidly attached to the fork, adding more
weight added stability. They ended up with 60 pounds in their front
panniers: the bike steered like a pig, but boy, was it stable!

So, in that sense, a heavier wheel _can_ make a bike more stable. It's the
mass, not any "gyroscopic effect".

Jeff


> -----Original Message-----
> From: h...@ihpva.org [mailto:h...@ihpva.org]On Behalf Of Tim & Ally Smith
> Sent: Wednesday, October 13, 1999 5:30 PM
> To: h...@ihpva.org
> Subject: Re: [hpv] Re: Are bents with larger rear wheels faster? Why?
>
>

> A friend on mine says he had markedly more stability in a turn on his LWB
> USS bike when loading lead weights around the 16" front wheel.
> They're mounted on the spokes and covered by reflectors. See
> http://sunsite.anu.edu.au/community/ozhpv/tas/richard.htm
>
>

Marcel Wijkstra

unread,
Oct 14, 1999, 3:00:00 AM10/14/99
to
Ed Gin wrote:
>Amonst the bikes I've owned, 700/451 V-Rex, 700/16inch, 26inch/406 Stock
>and Fully Faired P-38's, 26inch/moulton Windcheetah, 406/406 Tailwind,
>and 406/406 Tiger, I can't tell and wouldn't venture to guess which has
>the best rolling wheelset. There are just "too many" other factors to
>consider which will affect conclusions.

Then I guess we should go mainstream: anybody have a Bike Friday (20"),
a trialthlon bike (26") and a (what you american call) road bike (28")
to compare? I think these DF configuration hardly differ.

Marcel (still slower on his M5 20/28 than on his 3speed Gazelle)

/ \ ----------------------------------------------------
/`|,\ Marcel Wijkstra mar...@medialab.lostboys.nl
\ | / Lost Boys media lab +31-20-5356164
\ / ----------------------------------------------------

____HPVert Alert____

unread,
Oct 14, 1999, 3:00:00 AM10/14/99
to
Writes Tim Smith:

> A friend on mine says he had markedly more stability in a turn on
> his LWB USS bike when loading lead weights around the 16" front
> wheel. They're mounted on the spokes and covered by reflectors.
> See http://sunsite.anu.edu.au/community/ozhpv/tas/richard.htm


This has nothing to do with wheel size but with bad frame
geometry. The front wheel on many LWBs is so lightly loaded
that any weight placed up front will result in better traction,
ergo better cornering (st)ability. My equally light in front
Roulandt is pretty unstable at low speeds, esp. in gravel.
Turning in such conditions is not for the lightheaded[sic].

Tell your friend to remove the lead weights from the spokes
and mount his bikelock, an iron bar or similar heavy element
on the frame close to or above the steering tube... the result
should be the same at less energy input (= lesser rotational
mass).


__Ian

William Volk

unread,
Oct 14, 1999, 3:00:00 AM10/14/99
to
Marcel wrote:

>Then I guess we should go mainstream: anybody have a Bike Friday (20"),
>a trialthlon bike (26") and a (what you american call) road bike (28")
>to compare? I think these DF configuration hardly differ.


Actually I hear very good things about the Bike Friday road racers.
Typically with 451/451 wheelsets they are supposed to be climbing and
sprinting demons. Saw a really pretty one this morning, the model with the
beam (Ti tube) suspension.

At the local TT series the dual 571 bikes seem to be appearing in every
larger numbers.

Bill Volk

Bill Patterson

unread,
Oct 14, 1999, 3:00:00 AM10/14/99
to
I think Jeff has a good point, but I disagree.

I don't include the gyroscopic term to the control spring becuase it is small
for bicycles. It is there and can be enhanced with lead weights on the wheel.

Adding weight to the front assembly increases mass and reduces front end
acceleration.

IMHO it isn't the same as adding the mass to the wheels.

WE are talking apples and oranges.

change in force with respect to control deflection is Control spring.
change in force with respect ot control speed is control damping
change in force with respect to control acceleration is control mass.

I think control spring is all important. Control mass is interesting and large
but it doesn't have the importance of the control spring.

Adding angular momentum to the wheels changes control spring Adding mass to the
front fork changes control mass.

So adding mass to the front wheel does much the same as adding a bungee like
Fred's Bike. They both change the effective control spring.

Jeff Wills wrote:

>
> I bet your friend could get the same effect by taking the lead weights out
> of the wheel and mounting them rigidly at the same distance from the
> steering axis- say, on a fender or rack.

Bill Patterson mailto:wy...@lightspeed.net

Jeff Wills

unread,
Oct 15, 1999, 3:00:00 AM10/15/99
to
Hmmm... I think I'm going to defer to the Perfesser. Gyroscopic forces exist
and can afffect the handling. However, I think they're a minor compared to
the frame geometry- "control spring" in the Professor's terms.

BTW: Did you happen to see the Koski Ski-Bike at InterBike? It's a bike
frame with skis subsituted for wheels. How'd your students like to analyze
the geometry of it??

Jeff

> Subject: [hpv] Control spring vs control mass

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