what makes a light bike really light?

Weight is overrated, but if you want to reduce it, go for the highest
stuff first, as that will lower your center of gravity and give a
lighter feel when standing. Saddle, bars, stem, seatpost, brifters.

-Mike

<[email hidden]> wrote: (clip) Would cranks and road cassettes also
count as "rotating weight"? Possibly anything that "rotates" while pedaling,
like pedals as well?
^^^^^^^^^^^^^^^
As you accelerate, the parts of a bike that rotate have an extra inertial
component called "moment of inertia." This uses up a little of your
pedaling energy while you accelerate. But moment of inertia depends on the
diameter as well as the weight. The wheels have most of their weight (mass)
at the outside, so the effect is larger (though not large.) Things like the
crank and chainrings are small in diameter by comparison. I'm not sure how
to think about the pedals--they don't spin on their axis, since they are
pressed against your foot, but they do go around in circles. I think I
would include their weight with the cranks.

One of the best places to remove weight, for many of us, though it doesn't
rotate. is the waistline. :-)

Mike Reed said:

Weight is overrated, but if you want to reduce it, go for the highest
stuff first, as that will lower your center of gravity and give a
lighter feel when standing. Saddle, bars, stem, seatpost, brifters.

-Mike

I can't quantify this, but my beater (Reynolds 531) has horribly heavy
rims. My nicer bike (Columbus tubing from '87) has Velocity Aeroheads
that are incredibly light (to me). The difference is amazing in both
the heft of the whole bike and how easily it accelerates uphill. Also,
I notice quite in the difference in stopping as well (when not using
brakes as they are fixies).
\\paul
--
Paul M. Hobson
Georgia Institute of Technology
..:change the f to ph to reply:.

Tires are a great and fairly cheap way to shave off a few hundred
grams. Then, if you can find a scale, pull your stem, your saddle, and
your seat post and weigh them. Often you can replace such parts for
even rather inexpensive new stuff, and knock off a pound.

I'm not obsessive about weight myself, but dropping nearly 750g by
going from Brooks to Flite saddle (and it's more comfy for me) made my
bike feel like a new much faster version, especially in the hills, as
it's "swung" weight.

Saving weight via wheels can get expensive and unreliable, start with
the basics as I said. Sometimes you can drop 200g with a new $20
seatpin you found at Nashbar on sale, a lot more friendly to the pocket
than spending $500 to drop that same 200g via wheels.

Leo Lichtman said:

<[email hidden]> wrote: (clip) Would cranks and road cassettes also
count as "rotating weight"? Possibly anything that "rotates" while pedaling,
like pedals as well?
^^^^^^^^^^^^^^^
As you accelerate, the parts of a bike that rotate have an extra inertial
component called "moment of inertia." This uses up a little of your
pedaling energy while you accelerate. But moment of inertia depends on the
diameter as well as the weight. The wheels have most of their weight (mass)
at the outside, so the effect is larger (though not large.) Things like the
crank and chainrings are small in diameter by comparison. I'm not sure how
to think about the pedals--they don't spin on their axis, since they are
pressed against your foot, but they do go around in circles. I think I
would include their weight with the cranks.

One of the best places to remove weight, for many of us, though it doesn't
rotate. is the waistline. :-)

What really matters is the speed relative to the bike speed. The outside
of the rim, independent of wheel diameter, rotates at a speed equal to the bike
speed (approximately). The ratio of pedal speed to bike speed is
crank length / effective wheel radius * rear cog teeth / front cog teeth.
Since kinetic energy is proportional to the square of speed, pedal rotational
kinetic energy is small. A larger factor is shoe weight, since shoes must
be supported isometrically.

Dan

mxd1007 said:

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 :-) ),

A light steel frame is half a pound heavier than a typical Ti or carbon
frame, although the lightest carbon frames are half a pound lighter still.
So all else being equal, that's the difference in having a steel frame.

If you want to go faster, ride more.

Quoted message said:

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?

The rotating weight issue is severely overblown. If bike salesmen really
understood physics, do you think they'd be selling bikes for a living?
Most of the weight savings in light wheel sets is in the hubs anyway.

However, it's easy to save some weight with a lightweight wheel set.
Carbon cranks are several ounces lighter than aluminum ones too.

There's a website devoted to bike weight freaks:

www.weightweenies.starbike.com

Matt O.

Mike Reed said:

Weight is overrated, but if you want to reduce it, go for the highest
stuff first, as that will lower your center of gravity and give a
lighter feel when standing. Saddle, bars, stem, seatpost, brifters.

Let's say you lighten the bike by two pounds via the installation of a
lighter saddle, lighter bar and stem, etc. (not likely, but let's
pretend)

Now, take a 160lb rider standing whilst pedaling a 17lb bike. Where is
the center of gravity, and how much did the loss of those two pounds
lower it?

Quoted message said:

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?

It's really pretty incremental, there's no obvious single place to drop
a lot of weight (or everyone would). Like the man said: "light,
reliable, reasonably priced -- pick any 2".

"Rotating weight" arguments are overstated, but it's not unreasonable to
have a spare set of wheels with light tires & tubes. Some things make a
bike feel lighter, without actually doing much.

Outside of climbing hills, aerodynamic drag is the most important thing
to improve for speed. I'm always surprised by riders with very light and
expensive bikes who wear flappy jackets and/or have very upright
positions on the bike.

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

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

Ozark Bicycle said:

Mike Reed said:

Weight is overrated, but if you want to reduce it, go for the highest
stuff first, as that will lower your center of gravity and give a
lighter feel when standing. Saddle, bars, stem, seatpost, brifters.

Let's say you lighten the bike by two pounds via the installation of a
lighter saddle, lighter bar and stem, etc. (not likely, but let's
pretend)

Now, take a 160lb rider standing whilst pedaling a 17lb bike. Where is
the center of gravity, and how much did the loss of those two pounds
lower it?

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

Quoted message said:

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).

Drilling holes in your water bottle has been known to save a pound or
more of weight.

Seriously, unless you can save a couple of pounds, it's not going to
make much difference. Calculate the combined weight of you and the
bike.Then calculate the amount of bike weight you want to save. The
percentage of saved weight to "total package" weight will probably be
about 1 percent. And that will only make a difference when climbing.

In many (if not most) cases, cutting weight will reduce reliability.
Unless you're into competition, don't worry about an extra pound or
two.

Art Harris

"Dan Connelly" wrote: (clip) A larger factor is shoe weight, since shoes
must be supported isometrically.
^^^^^^^^^^^^^^^^^
I don't know what you mean by "isometrically."

I see the shoe weight being lumped in with the pedal weight. But when you
get your thinking to that point, where do you stop. Rotating weight would
include the foot, and part of the lower leg.

Quoted message said:

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?

If you want to make your bike lighter, take it apart, weigh the
components, and then shop for alternate components that have less
mass. You may discover that there's a specific area in which your
current bike is already at the limits of practical lightness, and/or
you may find that there's no one place where a change is going to make
a big difference. You may also discover that there's a hidden boat
anchor that you can change out for something more svelte which will
bring the total weight down a lot. Until you know what's heavy and
what's light among the bits you have, however, it's pointless to
speculate.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

IMHO the bottom, farthest from the center of gravity, is more
important. The role of the bike is basically to move back and forth to
support the rider and maintain balance. Light bikes are similar to
light pogo sticks -- easier to get them where they need to be under the
rider.

Mike Reed said:

Weight is overrated, but if you want to reduce it, go for the highest
stuff first, as that will lower your center of gravity and give a
lighter feel when standing. Saddle, bars, stem, seatpost, brifters.

On a bicycle, a low C of G is actually a disadvantage. Balancing a bike
is a bit like swinging an upside-down pendulum, or (a closer
approximation) balancing a stick on your hand with a weight fixed to the
one end. If you slide the weight nearer your hand, balancing it becomes
more difficult because the period of its natural oscillation has reduced
and you have to react quicker to catch it before it tilts too far. In
the same way, a high C of G makes the bike wobble more slowly,
increasing stability.

[email hidden] mused:

Quoted message said:

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).

Exactly correct. Remove the wheels and install an antigrav
conversion, but make sure that you get one with an interial damper
field as well; the conversion kits have substantial mass in the
quantum black hole that supplies their power, and without the inertial
damper field, the energy required to move them around can be
substantial. Beware of cheap units from Beta Aurigae IV; they have
lousy quality control, 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.

Of course, in theory you could simply install an inertial damping
field generator and leave the wheels in place, but why bother? The
damping field's power drain means that you'll need the power
generation capability of the quantum black hole unit anyway, and once
you've got that, there's no really good reason to do without the
antigrav...and you get a better deal on the setup as a bundle than you
would on the individual pieces. Swapping to antigrav also eliminates
the issue of having to repressurize your tires for different planetary
gravitational field strengths and local atmospheric densities.

Quoted message said:

Would cranks and road cassettes also count as
"rotating weight"?

Only if they're spinning at the time. Once you eliminate the wheels,
this is no longer an issue.

Ozark Bicycle said:

Let's say you lighten the bike by two pounds via the installation of a
lighter saddle, lighter bar and stem, etc. (not likely, but let's
pretend)

Now, take a 160lb rider standing whilst pedaling a 17lb bike. Where is
the center of gravity, and how much did the loss of those two pounds
lower it?

I said it would lower the center of gravity, and it will. Ranting about
how much difference it makes is pointless when I qualified it by saying
that weight is overrated. Your argument is obvious and applies to
weight in general, not just center of mass.

-Mike

Quoted message said:

IMHO the bottom, farthest from the center of gravity, is more
important. The role of the bike is basically to move back and forth to
support the rider and maintain balance. Light bikes are similar to
light pogo sticks -- easier to get them where they need to be under the
rider.

I see where you're coming from. It's kind of like balancing a vertical
broom on your fingertip, it's much easier with weight on the end (like
the Chinese spinning plates).

But as another poster pointed out, moving the center of mass of the
bike lower doesn't have significant effect on the bike/rider system. It
does, however feel a little nicer when you're swinging the bike while
standing.

-Mike

Leo Lichtman said:

"Dan Connelly" wrote: (clip) A larger factor is shoe weight, since shoes
must be supported isometrically.
^^^^^^^^^^^^^^^^^
I don't know what you mean by "isometrically."

The weight needs to be in part supported without doing any active work. A static force must
be supplied to support the shoe, preventing it from rotating to its position with the
COM vertically aligned with the pedal axis.

Quoted message said:

I see the shoe weight being lumped in with the pedal weight. But when you
get your thinking to that point, where do you stop. Rotating weight would
include the foot, and part of the lower leg.

The kinetic energy of the feet is negligible, so treating them as "rotating"
is misleading.

Dan