what makes a light bike really light?

[Leo Lichtman]

"Harry Kim" wrote: (clip) and if you're not lucky they can induce a nasty
phase variance that will leave you stuck a couple of microseconds away from
the rest of the universe.
^^^^^^^^^^^^^^^^
But, if you ARE lucky, you can use this effect to tunnel through hyperspace
and arrive at the finish line a couple of microseconds ahead of the pack.
Trouble is, bicycle races are not measured that close. so a lead of a few
microseconds might not be detected--and if they figure out what you did you
are sure to be disqualified.

 

[Matt O'Toole]

On Mon, 27 Feb 2006 09:52:06 -0800, mxd1007 wrote:

> well I was poking fun by saying I want to make my bike lighter so I can
> go faster it seems thats the reason why most people switch to
> lighter parts...I'm a firm believer, 80% of riding has to do with the
> rider him/herself, how fit they are, how often they ride, how they
> ride, how the bike fits rather than spending a lot of $$$ on parts. But
> as a quick and easy way to shave some "dead weight" is to start with
> the wheels. Then "work your way up" the bike if you have some left over
> $$$ and get a lighter stem or seat or seat post. Most people say to
> start with the wheels first....kind of interesting to see how others
> would focus on other components

Actually I confess to owning a pretty light bike. I haven't weighed it
but I guess it's under 18 LB. This was an accident of a good bargain
though. I almost traded the light wheels for stronger ones, but so far
so good. I was ready to pay extra for cheaper ones, so to speak.

> hopefully this strict weight training regimen I have been doing over the
> winter will pay off once the snow is gone and I can ride again I
> envy you people in Southern Cali and Arizona

Excuses, excuses! Many on this forum ride year-round in climates
similar to yours. Congrats on the weight training program though. The
main cycling discipline I have is a need for groceries.

As a southern CA expat I can say climate is no cure either. As many
people there hibernate in cool weather as they do anywhere else. Of
course "cool" is relative. In AZ there's the opposite problem.

Matt O.

 

[[email protected]]

Well, any system will be easier to rotate with the mass closer to the
CG, in this case higher on the bike. But I agree that it's less of an
issue than the overall weight of the bike, and the height of the
overall CG above the ground.

The other issue is simply turning the front wheel laterally in the
headset. Virtually all balancing and steering maneuvers begin by
flicking the front wheel to one side or the other, so a lighter front
wheel (specifically, the rim) will manifest itself in lighter steering
action, somewhat independently of the other forces on the bike.

 

[Tim McNamara]

[email protected] writes:

> Hello
>
> being that I'm into steel road frames only and don't wish to get
> suckered into the buying frenzy of putting carbon and titanium and
> other exotic materials on my bike just to make it lighter(in order to
> make me go faster ), I was told by my LBS that if you wanted to
> lighten up your bike, the most important part to upgrade would be the
> wheels (rotating weight). Would cranks and road cassettes also count as
> "rotating weight"? Possibly anything that "rotates" while pedaling,
> like pedals as well?

Weight is weight. There is the argument that weight on the periphery
of the wheels counts double, and the math is available to show why
that is, but we're talking about pretty miniscule amounts of weight to
begin with. How much faster do you think you're going to get by
saving 40 grams or even 100 grams on a wheel?

IMHO if you are not racing and your bike weighs under 25 lbs, don't
worry about it. Just enjoy the ride. If you're racing and every
millisecond counts as far as you're concerned, then you'll feel a need
to lighten the bike.

Look at real weights, not claimed weights, and look at them very
carefully. With wheels, for example, it is often possible to build a
lighter pair of wheels than many expensive high-cost fancy wheels that
your LBS might want to sell you.

The heaviest part of the bike is usually the rider. :-D That's
usually the place where the greatest weight savings are to be had. I
could lose an entire bike's worth of weight!

 

[Vee]

[email protected] wrote:
> Hello
>
> being that I'm into steel road frames only and don't wish to get
> suckered into the buying frenzy of putting carbon and titanium and
> other exotic materials on my bike just to make it lighter(in order to
> make me go faster ), I was told by my LBS that if you wanted to
> lighten up your bike, the most important part to upgrade would be the
> wheels (rotating weight). Would cranks and road cassettes also count as
> "rotating weight"? Possibly anything that "rotates" while pedaling,
> like pedals as well?

Seems like other people have covered the oh-so-exciting physics, so all
that remains is the summary:

1. Money makes a bike really light.
2. A really light bike doesn't make you fast.

-Vee

 

[Ron Ruff]

[email protected] wrote:
> being that I'm into steel road frames only and don't wish to get
> suckered into the buying frenzy of putting carbon and titanium and
> other exotic materials on my bike just to make it lighter(in order to
> make me go faster ), I was told by my LBS that if you wanted to
> lighten up your bike, the most important part to upgrade would be the
> wheels (rotating weight). Would cranks and road cassettes also count as
> "rotating weight"? Possibly anything that "rotates" while pedaling,
> like pedals as well?

In the rate-of-acceleration equation, the rim and tire weight counts as
double... other rotating components are less since their rotational
speed is quite a bit slower than the ground speed.

This *only* effects rate-of-acceleration... and that by a tiny amount.
For instance if you and your bike weigh 200 lbs now and you reduced the
rim and tire weight by 1 lb (which is a lot) you would improve your
rate of acceleration by a massive 1% compared to 0.5% for losing 1 lb
elsewhere. That isn't the difference in speed by the way, only the rate
of change in speed... there will be no difference in the eventual speed
attained.

Light wheels tend to be weaker than heavy ones (for similar quality)...
same for all other components. The best place to lose weight is on your
body... cheaper, and possibly "stronger" as well.

 

[Ron Ruff]

Mike Reed wrote:
> We corner hard in the drops instead of the hoods to
> lower our center of gravity in case we have to react to something.
> Imagine the sacriest cornering you've ever done, and imagine doing it
> with a riser stem and moustache handle bars, sitting nearly upright.
> Eeek.

I don't care about the cg being lower in fast turns, but I want the
best grip on the bars and the brakes ... hence the drops. High would be
fine... in fact better than low.

 

[[email protected]]

Ron Ruff writes:

>> We corner hard in the drops instead of the hoods to lower our
>> center of gravity in case we have to react to something. Imagine
>> the scariest cornering you've ever done, and imagine doing it with
>> a riser stem and mustache handle bars, sitting nearly upright.
>> Eeek.

> I don't care about the cg being lower in fast turns, but I want the
> best grip on the bars and the brakes... hence the drops. High would
> be fine... in fact better than low.

I'll go along with a better grip, but I believe there is another
aspect to being down in the hooks,which is what runners or wrestlers
do starting in a crouch. That is a more versatile position from which
to move, be that shifting body weight fore and aft or aside, or to
jump the bicycle over a road hazard. In that position unloading the
saddle without loss of control is also easier. This could be
interpreted as a lower CG, but I don't believe that is important
because crouching, my CG is still higher than most riders and it
doesn't seem to affect control.

Beyond that, crouching reduces frontal area enabling higher speed.
The descending picture on Sheldon's site is hardly imaginable to me in
an upright position with hands on high bars.

Jobst Brandt

 

[John Forrest Tomlinson]

On 27 Feb 2006 21:56:14 -0800, "Ron Ruff" <[email protected]>
wrote:


>
>I don't care about the cg being lower in fast turns, but I want the
>best grip on the bars and the brakes ...

Why? Are you riding on super bumpy roads? In general, on a road bike
at least, it takes very little strength to hold the bars.

JT

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[Art Harris]

Ron Ruff wrote:

> This *only* effects rate-of-acceleration...

Only _affects_ rate-of-acceleration. Safer to use "impacts."

Art

 

[Qui si parla Campagnolo]

[email protected] wrote:
> Hello
>
> being that I'm into steel road frames only and don't wish to get
> suckered into the buying frenzy of putting carbon and titanium and
> other exotic materials on my bike just to make it lighter(in order to
> make me go faster ), I was told by my LBS that if you wanted to
> lighten up your bike, the most important part to upgrade would be the
> wheels (rotating weight). Would cranks and road cassettes also count as
> "rotating weight"? Possibly anything that "rotates" while pedaling,
> like pedals as well?

Energy to accerrate a bicycle and rider is the mass of the bicycle and
rider. Rotating weight, altho measureable, is teeny tiny. A 300 gr rim
and a 600 gr rim difference is lost in the noise.

What makes a cyclist 'fast' is
-fit-bike fit
-fitness-being fit
-finesse-riding, training and racing smart
-fat-lackthereof on the rider

WAY to much importance placed on the machine. It is a small part of the
equation. It is mostly there to get you there.

 

[Qui si parla Campagnolo]

p.k. wrote:

>
> Errm, I'm 230lb, i know the best way to lighten my bike - make it as heavy
> and inefficient as possible and work the weight off my waistline!
>
> pk

Bing, bing, bing, we have a winner!!

Not trying to be personal, PK, but the vast majority of american
cyclists, including me, could afford to lose some portion of or an
entire BW(bike weight, equaling 20 pounds).

BUT americans don't train and ride lots, that is hard. They look to buy
equipment to make them better. Whether it be cycling, golf, tennis,
etc.

 

[Mike Reed]

Ron Ruff wrote:
> I don't care about the cg being lower in fast turns, but I want the
> best grip on the bars and the brakes ... hence the drops. High would be
> fine... in fact better than low.

Ok, so let's say we make you a special road bike with an infinitely
rigid 20-foot seatpost and 20-foot high stem. Then we throw on some
stoker cranks/chain for you.

You believe you would corner better in a crit on a circus bike like
that?

-Mike

 

[Mike Reed]

Qui si parla Campagnolo wrote:
> Energy to accerrate a bicycle and rider is the mass of the bicycle and
> rider. Rotating weight, altho measureable, is teeny tiny. A 300 gr rim
> and a 600 gr rim difference is lost in the noise.

Exactly. For a demonstration of this, think about how quickly your
measly arm can accelerate a "heavy" front wheel to 20 mph when the bike
is in a workstand. You can do it with one stroke, in 1/4 second. Try it
with a lightweight wheel and it feels about identical. Then lower the
acceleration rate to something like 20 mph over 5 seconds, and it the
difference just doesn't matter.

-Mike

 

[Callistus Valerius]

> BTW, I don't eat that much (three meals, no soda, rarely eat fast
> food). I think that some people are just victims of a very efficient
> metabolism. Yeah, that's the problem, my metabolism ;-)
>
> Well, that and my affection for custard, stouts and porters, 15 year
> single malt, beef, barbecue, doughnuts and coconut curries.
>
>
> D'ohBoy
-----------
I think age has a lot to do with it. When a person is young his
metabolism is like a roaring fire. The old folk's furnace amounts to just a
pilot light. Easy way to verify this is go to a group ride on a cold day,
and compare how the old people dress, to the young people. And after the
initial miles, see which group still have their coats on, and who have taken
theirs off.

 

[Paul Hobson]

Callistus Valerius wrote:
>>BTW, I don't eat that much (three meals, no soda, rarely eat fast
>>food). I think that some people are just victims of a very efficient
>>metabolism. Yeah, that's the problem, my metabolism ;-)
>>
>>Well, that and my affection for custard, stouts and porters, 15 year
>>single malt, beef, barbecue, doughnuts and coconut curries.
>>
>>
>>D'ohBoy
>
> -----------
> I think age has a lot to do with it. When a person is young his
> metabolism is like a roaring fire. The old folk's furnace amounts to just a
> pilot light. Easy way to verify this is go to a group ride on a cold day,
> and compare how the old people dress, to the young people. And after the
> initial miles, see which group still have their coats on, and who have taken
> theirs off.

Or, you could touch my skin after a big meal. If the room in at a
typical room temperature (my college slum house is at around 55 deg. F
right now) I will sometimes start to sweat after a really good (big) meal.

I suppose this is good b/c I can eat what I want and not really worry
about it. But it also means that I'm spending a lot on food b/c it just
doesn't last long with me. Also, before embarking on a really big ride
with a road-ish crowd, I really have to make sure the three previous
meals were good, or I just bonk. Between cycling around town ~1 - 2
hrs/day and working out three/four days a week, one word describes me
above all others: "hungry"

 

[(PeteCresswell)]

Per Callistus Valerius:
> The old folk's furnace amounts to just a
>pilot light.

When I saw an interview with Jacques Cousteau (famous oceanographer, inventor of
the aqualung, author of "The Silent World") he was somewhere in his mid-to-late
sixties.

When I heard him telling the interviewer that he felt "the same as I did when I
was in my twenties", I remember thinking "Jacques, baby, you've either been
sitting on that boat too much, or you just weren't exploring the envelope when
you were in your twenties..".
--
PeteCresswell

 

[D'ohBoy]

Quoth QSP:

> ok, and?...........

Not to wax pedantic, but you had made the following double
condemnation/generalization of/about US sports enthusiasts:

> > Not trying to be personal, PK, but the vast majority of american
> > cyclists, including me, could afford to lose some portion of or an
> > entire BW(bike weight, equaling 20 pounds).

> > BUT americans don't train and ride lots, that is hard. They look to buy
> > equipment to make them better. Whether it be cycling, golf, tennis,
> > etc.

I just wanted to clarify that despite my personal (1e-10)*(3,584,000
gm) bulk and my enjoyment of high quality, low weight "go-fast" bikes,
I didn't fit into you category of not training or riding a lot and
shopping for equipment that will make me better.

I train and ride a lot and enjoy mucking about with bikes and I could
stand to lose at least 10% of my body weight. But I know that the
difference between my 21 lb Schwinn SuperSport and my 16 lb Fuji is
probably manifests almost completely in how much I enjoy riding each of
the bikes.

So there ;-)

D'ohBoy

 

[Mike Reed]

Yep, materialism is what keeps the high-end parts market in business.
Certainly keeping up with the latest widget in any hobby can become a
hobby in itself. Quite fun for a lot of people, but always annoying to
the grass-roots participants in said hobby.

Cycling: lightweight vs. practical speed
Backpacking: minimalist vs. $500/month spent at REI
Astronomy: homemade light buckets vs. computer-controlled mid aperture
catadioptrics
and so on...

 

[Michael Press]

In article
<[email protected]>,
"Qui si parla Campagnolo" <[email protected]> wrote:

> [email protected] wrote:
> > Hello
> >
> > being that I'm into steel road frames only and don't wish to get
> > suckered into the buying frenzy of putting carbon and titanium and
> > other exotic materials on my bike just to make it lighter(in order to
> > make me go faster ), I was told by my LBS that if you wanted to
> > lighten up your bike, the most important part to upgrade would be the
> > wheels (rotating weight). Would cranks and road cassettes also count as
> > "rotating weight"? Possibly anything that "rotates" while pedaling,
> > like pedals as well?
>
> Energy to accerrate a bicycle and rider is the mass of the bicycle and
> rider. Rotating weight, altho measureable, is teeny tiny. A 300 gr rim
> and a 600 gr rim difference is lost in the noise.
>
> What makes a cyclist 'fast' is
> -fit-bike fit
> -fitness-being fit
> -finesse-riding, training and racing smart
> -fat-lackthereof on the rider
>
> WAY to much importance placed on the machine. It is a small part of the
> equation. It is mostly there to get you there.

Agree that fitness is paramount. Here is the energy calculation.

Wheel radius: r = 0.330 m
mass of rim, tire, tube: m = 0.5 + 0.3 + 0.1 kg = 0.9 kg
mass of bicycle: M = 9 kg
angular speed of wheel: w

Kinetic energy of transverse motion: 1/2 * M * r^2 * w^2
Kinetic energy of rotational motion: 2 * 1/2 * m * r^2 * w^2

Ratio of rotational energy to transverse energy of motion: 2 * m / M.
Typicallly this ratio is about 1:5.
How much mass can we remove from rim, tire, and tube?
Can we get it down to 0.5 kg, making the ratio 1:9?.
This could be a noticable optimization while
accelerating into a sprint, attacking, or countering an
attack.

I opine that the weight of the rider does not count
fully as much as the simple account of his mass may
suggest, since the active rider is not entirely a dead
load. By throwing himself forward on pedal strokes it
may be that he can accelerate himself independently of
the acceleartion of the bicycle. This is a vague
account, and indefensible in its current form.

--
Michael Press