question of weight on a bike

wrote:
On Tue, 23 Feb 2010 16:30:58 -0600, Mark Cleary
wrote:

wrote:
On Tue, 23 Feb 2010 07:36:35 -0800 (PST), raamman
wrote:

On Feb 22, 11:06 pm, Mark Cleary wrote:
I am not an engineer but I gather lighter bikes help climbing but what
about on the flats. In other words I ride around the flatlands here no
real hills a few ups over the bridges, does weight become almost non
issue within reason.

In other words on a road bike that weights say 21 pounds, is there any
real advantage if the bike is say 20, 19, 18, or 17 pounds? If your bike
weighs a little more do you generate more speed going down? I really
don't know this but it does seem if the bike is heavier I should go down
faster. At what point do you think it would matter in weight or does
that all have to do with big hills and long grades up the mountain. I
could see this being an advantage to have a light bike.

If I ride say a 50 mile route or time trial for 2.5 hours would I gain
much having a bike that weighs less on a flat course or just gentle
rolling hills. Any idea the difference? Naturally it is all in the
engine and if you want to get faster you need to work the engine but I
just wondered.

I ask this because my road bike weighs 21 pounds fully load with pedals
and 2 h20s cages in a 61 cm size. I really don't need to lose weight so
do give me that option. I am not looking to get rid of bike weight just
want the facts on this.
--
Deacon Mark Cleary
Epiphany Roman Catholic Church
Galileo theorized equal acceleration of bodies of different mass; this
was later demonstrated on the moon where a feather and a hammer were
dropped and fell at the same rate; he was persectuted by the catholic
church some 400 years ago. It astounds me to no end that people
continually repeat the notion that heavier objects fall faster. They
don't.It is a physical law.
Dear R,

In a vacuum, feathers and hammers fall at the same rate.

In air, the heavier object with the same frontal area and wind drag
hits the ground much sooner.

For bicyclists, mass increases faster than wind drag and rolling
resistance, so a heavier bicycle and rider coasts faster downhill.

Here's a typical bicycle speed calculator that includes those factors
and lets you compare things side by side:
http://bikecalculator.com/veloUS.html

With the defaults, the two riders go 15.00 mph on level ground by
putting 100 watts into the pedals.

Down a -6% grade, their predicted speed, assisted by their 100 watt
effort, rises to 32.51 mph.

Turn one of the 150 lb riders into a 180 lb rider, and the extra 30
pounds increases his speed to 34.74 mph, 2.23 mph faster.

That extra 2.23 mph doesn't sound like much.

But at 34.74 mph, wind drag and rolling resistance increase so much
that the lighter rider has to put out 220 watts to catch up with the
heavier rider putting out only 100 watts--more than twice as much
power.

Increase the heavy rider to 220 pounds, and the extra 70 pounds
increases his speed to 37.55 mph, 5.05 mph faster.

At 37.55 mph, wind drag and rolling resistance are so powerful that
the lighter rider has to raise his power from 100 watts to 402.5 watts
to catch up--over 300 watts.

A calculator can only approximate how much the actual wind drag and
the real rolling resistance will increase with a heavier bike or
rider, but experience and testing show that heavier riders do indeed
roll downhill faster, given reasonably similar bikes and postures.

To get back to Mark's original question about a 4-lb lighter bike, go
back to the 150 lb riders rolling down the 6% grade at 100 watts.

On a 21 lb bike, the rider hits 32.43 mph.

On a 17 lb bike, the rider hits 32.12 mph, 0.31 mph slower.

To make up that tiny 0.9% speed difference 0.31 mph, the rider on the
4-lb lighter bike needs to raise his power 15%, from 100 watts to 115
watts. That's how important wind drag is when you pedal downhill.

Cheers,

Carl Fogel
Carl,

You win the prize I like that answer made sense. So ho much to I lose
going up the 6 grade?

Dear Mark,

It depends on power, weight, position, and so on:
http://bikecalculator.com/veloUS.html

Differences are greater for a lower total weight, so try 200 watts up
a 6% grade with tubulars (for that calculator roughly as good as
modern clinchers) on the hoods for a 150 lb rider and 10 miles.

150 lb rider
200 watts
tubulars
10 miles
6% grade 21 lb 17 lb 21 lb 17 lb seconds
mph mph minutes minutes faster

on hoods 9.98 10.17 60.11 59.02 -65.4

on drops 10.16 10.35 59.08 57.96 -67.2

on drops
1.37 mph hw 9.98 10.17
1.40 mph hw 60.11 59.02

The 4 lb difference makes about as much difference as the wind drag at
~10 mph on the hoods versus on the drops.

A headwind less than 1.5 mph that you can't detect cancels out the
advantage of going onto the drops in still air.

In other words, what you ate for breakfast, the vagaries of the wind,
and any slight changes in your posture and cadence (sneezing, raising
your head, swerving here and there) are likely to obscure a 4/171
weight reduction amounting to 2.3% that may give you about a minute
per hour on a ten-mile 6% climb.

Downhill, the heavier bike won't make up the minute that it lost on
the climb for two reasons.

First, you spend far less time going back down because you go so much
faster, so there isn't enough time to make up the difference

On the drops with 200 watts back down the ten-mile 6% grade:

mph minutes
21 lb bike 38.80 15.46 8.4 seconds faster
17 lb bike 38.47 15.60

Second, on real downhills it takes forever to get up to terminal
velocity and then you throw most of it away when you brake for a
corner, as opposed to getting up to 10 mph climbing almost immediately
and never touching the brake on a 6% climb.

Cheers,

Carl Fogel

Cheers,

Carl Fogel
Too much math makes preaching seem like piece of cake, but of course to
practice it is another story.
Thanks!!!!!

--
Deacon Mark Cleary
Epiphany Roman Catholic Church

In article ,
says...


I am not an engineer but I gather lighter bikes help climbing but what
about on the flats. In other words I ride around the flatlands here no
real hills a few ups over the bridges, does weight become almost non
issue within reason.

In other words on a road bike that weights say 21 pounds, is there
any
real advantage if the bike is say 20, 19, 18, or 17 pounds? If your
bike
weighs a little more do you generate more speed going down? I really
don't know this but it does seem if the bike is heavier I should go
down
faster. At what point do you think it would matter in weight or does
that all have to do with big hills and long grades up the mountain. I
could see this being an advantage to have a light bike.

If I ride say a 50 mile route or time trial for 2.5 hours would I gain
much having a bike that weighs less on a flat course or just gentle
rolling hills. Any idea the difference? Naturally it is all in the
engine and if you want to get faster you need to work the engine but
I
just wondered.

I ask this because my road bike weighs 21 pounds fully load with
pedals
and 2 h20s cages in a 61 cm size. I really don't need to lose weight so
do give me that option. I am not looking to get rid of bike weight just
want the facts on this.
--
Deacon Mark Cleary
Epiphany Roman Catholic Church
I am certainly not an expert or engineer. My sense is that once up to
speed more mass would tend to stay in motion; it would be more
dificult than a smaller mass to get up to speed. So its possible that
given all else a heavier bike may be an advantage on flat surfaces only.
As others pointed out, the more speed and the more aerodynamics
come into play. Bottom line is that a few pounds in your situation will
probably make no differnece at all. Except for you wallet. The closer
you get to that magical 15 pounds the cost of each ounce lost goes up
logrithmetically.

Keep riding, stay safe!

On Tue, 23 Feb 2010 17:46:27 -0800, Ronko
wrote:

In article ,
says...


I am not an engineer but I gather lighter bikes help climbing but what
about on the flats. In other words I ride around the flatlands here no
real hills a few ups over the bridges, does weight become almost non
issue within reason.

In other words on a road bike that weights say 21 pounds, is there
any
real advantage if the bike is say 20, 19, 18, or 17 pounds? If your
bike
weighs a little more do you generate more speed going down? I really
don't know this but it does seem if the bike is heavier I should go
down
faster. At what point do you think it would matter in weight or does
that all have to do with big hills and long grades up the mountain. I
could see this being an advantage to have a light bike.

If I ride say a 50 mile route or time trial for 2.5 hours would I gain
much having a bike that weighs less on a flat course or just gentle
rolling hills. Any idea the difference? Naturally it is all in the
engine and if you want to get faster you need to work the engine but
I
just wondered.

I ask this because my road bike weighs 21 pounds fully load with
pedals
and 2 h20s cages in a 61 cm size. I really don't need to lose weight so
do give me that option. I am not looking to get rid of bike weight just
want the facts on this.
--
Deacon Mark Cleary
Epiphany Roman Catholic Church
I am certainly not an expert or engineer. My sense is that once up to
speed more mass would tend to stay in motion; it would be more
dificult than a smaller mass to get up to speed. So its possible that
given all else a heavier bike may be an advantage on flat surfaces only.
As others pointed out, the more speed and the more aerodynamics
come into play. Bottom line is that a few pounds in your situation will
probably make no differnece at all. Except for you wallet. The closer
you get to that magical 15 pounds the cost of each ounce lost goes up
logrithmetically.

Keep riding, stay safe!

Dear R,

A slightly greater mass increases the rolling resistance slightly.

So the same power won't push the bike up to quite the same speed.

Given exactly the same power and wind drag, the heavier bike loses
steadily on the flats.

You can see the point he
http://bikecalculator.com/veloUS.html

With the defaults, both bikes go 15.00 mph.

Change one bike from the default 22 pounds to 18 pounds.

The lighter bike cruises 0.04 mph faster because of the reduced
rolling resistance--with less weight, the tire flexes less.

But as you say, the difference is unlikely to make any difference in
Mark's situation. The heavier bike can keep up by increasing the power
from 100.0 to 100.7 watts. At 200 watts and just under 20 mph, the
heavier bike needs just 200.8 watts to keep up.

Cheers,

Carl Fogel

On Feb 23, 4:21*pm, thirty-six wrote:
On 23 Feb, 20:42, Frank Krygowski wrote:

On Feb 23, 3:23*pm, thirty-six wrote:

If you already have your shoulders below your backside with your
forearms horizontal, what advantage does the forward bar give?

Significantly less frontal area, by virtue of getting the arms more
inboard. *Seehttp://www.vintagebicyclepress.com/images/BQ61cover.jpg

That's not a view of either position being discussed.

You're right. I grabbed the wrong picture. But what I said is still
true: with clip-on aero bars, the arms move inward and frontal area is
reduced.

I find them to also be more comfortable than the equivalent low
position with hands on the drops. *And I think most people get lower
on aero bars, as shown in that photo.

There are no aero bars there. ..

My mistake.

I dont see significant less frontal area.

I recall riding with a friend (another engineer) one of the first
times I used the low & forward position of aero bars. He was drafting
me when I switched from the more standard position on the drops. He
told me he was amazed at how much lower I got. And it certainly feels
like I'm getting lower.

In any case, there can be no question they really work - unless, I
suppose, you've never tried them or ridden with somone else who used
them. And if they work, they can work by reducing frontal area, by
reducing drag coefficient, r both. I've read that it's primarily the
former.

- Frank Krygowski

Frank Krygowski wrote:

I recall riding with a friend (another engineer) one of the first
times I used the low & forward position of aero bars. He was drafting
me when I switched from the more standard position on the drops. He
told me he was amazed at how much lower I got.


Did he notice a difference in the strength of the draft then?


--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.liamg\100cm.j.dat/"

raamman wrote:

Galileo theorized equal acceleration of bodies of different mass; this
was later demonstrated on the moon where a feather and a hammer were
dropped and fell at the same rate; he was persectuted by the catholic
church some 400 years ago. It astounds me to no end that people
continually repeat the notion that heavier objects fall faster. They
don't.It is a physical law.

I know from observation that on a downhill, I can coast effortlessly
past people who are pedaling furiously, just because I am heavier.
Frontal area (which dictates aero drag) is proportional to the square
of height, while mass (which dictates downhill thrust) is proportional
to the cube of height.

I used to hit 55mph regularly on the way to work, when that route
included a straight, smooth half-mile grade of 8%.

Chalo

On Feb 23, 12:37*pm, AMuzi wrote:
-snip gravity-

thirty-six wrote:
I think that being heavy, a rider will usually take better care of his
equipment and be able to have complete confidence in it.

A quick perusal of any active bicycle service department
would disabuse one of that notion.

My commuter bike is a prime example -- I broke a shift cable coming in
to work this morning (at the head, in an STI lever). Total neglect.
The only good part is that downtown PDX is riddled with bike shops. I
bought a replacement cable and threw it in over lunch. Helpful tip:
do not do mechanical work on a dirty commuter bike while wearing a
suit. Kudos to Bike Gallery for giving me some grease in a tiny
ziplock bag instead of making me buy a big, expensive tube. -- Jay
Beattie.

On Feb 23, 8:56*pm, Frank Krygowski wrote:
On Feb 23, 4:21*pm, thirty-six wrote:

On 23 Feb, 20:42, Frank Krygowski wrote:

On Feb 23, 3:23*pm, thirty-six wrote:

If you already have your shoulders below your backside with your
forearms horizontal, what advantage does the forward bar give?

Significantly less frontal area, by virtue of getting the arms more
inboard. *Seehttp://www.vintagebicyclepress.com/images/BQ61cover.jpg

That's not a view of either position being discussed.

You're right. *I grabbed the wrong picture. *But what I said is still
true: with clip-on aero bars, the arms move inward and frontal area is
reduced.

I find them to also be more comfortable than the equivalent low
position with hands on the drops. *And I think most people get lower
on aero bars, as shown in that photo.

There are no aero bars there. ..

My mistake.

I dont see significant less frontal area.

I recall riding with a friend (another engineer) one of the first
times I used the low & forward position of aero bars. *He was drafting
me when I switched from the more standard position on the drops. *He
told me he was amazed at how much lower I got. *And it certainly feels
like I'm getting lower.

In any case, there can be no question they really work - unless, I
suppose, you've never tried them or ridden with somone else who used
them. *And if they work, they can work by reducing frontal area, by
reducing drag coefficient, r both. *I've read that it's primarily the
former.

- Frank Krygowski

I remember riding behind a stranger using aero bars and he *was* fast.
He was also sooo crooked that I let him go just to protect life and
limb in case he wiped out on the downhill, where he continued
synchronizing random bar movement with his punchy pedal strokes. This
is not a condemnation of aero bars per se. It's a condemnation of aero
bars used by people who used them because Greg Lemond used them, and
not because they knew what the hell to do whilst riding a bicycle. As
an aside, I suspect his waistline provided as much advantage over me
as did his aero bars, but before the top of the subsequent uphill we
were even again.

sa

On 2010-02-24, Tim McNamara wrote:
[...]
Galileo theorized equal acceleration of bodies of different mass;
this was later demonstrated on the moon where a feather and a hammer
were dropped and fell at the same rate; he was persectuted by the
catholic church some 400 years ago. It astounds me to no end that
people continually repeat the notion that heavier objects fall
faster. They don't.It is a physical law.

It astounds me to no end that people continually misrepresent Galileo's
point and then cite foolish things to support that notion. Get a hammer
and a feather, drop them off the roof, and get back to us about the
results. Then go learn something about terminal velocity.

The hammer will overtake the feather before either of them reach
terminal velocity (on Earth, not on the Moon of course).

On 24 Feb, 01:17, Tim McNamara wrote:
Then go learn something about terminal velocity.

Caveat, just in case ... .

Terminal velocity is _not_ a fundamental constant of physics.
It was _not_ hypothesized by Alfred.

Sergio
Pisa