More weight, faster descents??

wrote:
The little guy rolls down the hill at 27 mph as Chalo pulls away at 40
mph. (In real life, Chalo would have slightly more wind drag, so
probably he wouldn't pull away quite that fast, but his weight rises
much faster than his frontal area, so no one wants to challenge him to
a coasting race down a long, straight hill.)

And in equally fit riders, muscle mass increases much faster than
frontal area, so they not only have an advantage in higher terminal
velocity, they have a higher power/frontal area ratio.

That's why climbers usually beat descenders.

But the difference in muscle mass is why climbers rarely win the tdf.
A pure climber does not have the optimal muscle mass to win anything
but the mountaintop finishes. They _usually_ do not have the power to
maintain their lead over a rider with greater muscle-to-frontal area
ratio when the road starts descending. More importantly, they don't
even have the power to maintain their lead when the road is flat. In
other words, climbers (in general) don't beat descenders except when
they are all coasting down the mountain.

On Oct 1, 7:07 am, Mark
wrote:
DaveH wrote:
I've seen this notion in various forums. It typically takes the form
of "A heavier bike may be more work uphill, but is faster downhill due
to gravity..." Something like that.

The notion -- which I think is incorrect -- really should take the
form of "Greater total mass (rider + bike + stuff) may be more work
uphill, but is faster downhill..."

In any case, reviewing the elementary physics, doesn't mass cancel in
the equations? Same reason a rock and feather both accelerate at g in
a vacuum? Ergo, that heavier bike isn't getting you down the hill any
faster.
Dave

Why don't you go do some cycling in a vacuum and let us know how it
works out. Out here in the real world (no vacuum), heavier bikes (w/
same frontal area) go down hill faster.

Mark J.

I've been trying to figure why I accelerate faster downhill (coasting)
than my riding buddy. We are about the same weight, size, bike
position, tires. Is it my Campag Record hubs versus his Mavic Ksyrium
Elites?

I'm 5'10", 130ish lbs. I just got back from the 6 Gap ride in the N.
Georgia mountains. I was smoking people going uphill, but then they
smoked my ass going down and I couldn't catch up no matter how hard I
tried (save for a few with a high pucker factor).

There's a *lot* more to descending than rider weight. Otherwise, the TdF
guys would float downhill like a feather, but if you watch the coverage,
you'll find plenty of lightweight guys who can descend plenty fast.

My theory is that most of the bigger guys descend faster entirely by
accident. I was watching the coverage of the TdF a few years ago, and
noticed as they were flying down the hill just how fat some of the guys
were. Yet I knew they were anything but (fat). I even looked up some of
their weights, just to make sure. But they did look like they had big guts
hanging out.

And that, as it turns out, is the secret. You want to not only get low, but
bring your chest down and your knees up. Close up the airspace and your
aerodynamics improve dramatically. And the guys who really are big? Their
guts hang down whether they want them to or not. By accident they're often
more aerodynamic (despite thinking that their increased size would render
them less so).

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com


"Paul Myron Hobson" wrote in message
...
DaveH wrote:
I've seen this notion in various forums. It typically takes the form
of "A heavier bike may be more work uphill, but is faster downhill due
to gravity..." Something like that. The notion -- which I think is
incorrect -- really should take the
form of "Greater total mass (rider + bike + stuff) may be more work
uphill, but is faster downhill..." In any case, reviewing the elementary
physics, doesn't mass cancel in
the equations? Same reason a rock and feather both accelerate at g in
a vacuum? Ergo, that heavier bike isn't getting you down the hill any
faster. Dave

I'm 5'10", 130ish lbs. I just got back from the 6 Gap ride in the N.
Georgia mountains. I was smoking people going uphill, but then they
smoked my ass going down and I couldn't catch up no matter how hard I
tried (save for a few with a high pucker factor).

Mass does cancel out in elementary physics, but if you add fluid mechanics
into the picture (drag force), low weight loses going down.

\\paul

DaveH wrote:
I've seen this notion in various forums. It typically takes the form
of "A heavier bike may be more work uphill, but is faster downhill due
to gravity..." Something like that.
The notion -- which I think is incorrect -- really should take the
form of "Greater total mass (rider + bike + stuff) may be more work
uphill, but is faster downhill..."
In any case, reviewing the elementary physics, doesn't mass cancel in
the equations? Same reason a rock and feather both accelerate at g in
a vacuum? Ergo, that heavier bike isn't getting you down the hill any
faster.

Mark wrote :
Why don't you go do some cycling in a vacuum and let us know how it
works out. Out here in the real world (no vacuum), heavier bikes (w/
same frontal area) go down hill faster.

Donga wrote:
I've been trying to figure why I accelerate faster downhill (coasting)
than my riding buddy. We are about the same weight, size, bike
position, tires. Is it my Campag Record hubs versus his Mavic Ksyrium
Elites?

Do you tuck in your knees and elbows and drop your chin to the stem? You
might try descending position tweaks.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

In article ,
DaveH wrote:

I've seen this notion in various forums. It typically takes the form
of "A heavier bike may be more work uphill, but is faster downhill
due to gravity..." Something like that.

The notion -- which I think is incorrect -- really should take the
form of "Greater total mass (rider + bike + stuff) may be more work
uphill, but is faster downhill..."

In any case, reviewing the elementary physics, doesn't mass cancel in
the equations? Same reason a rock and feather both accelerate at g
in a vacuum? Ergo, that heavier bike isn't getting you down the hill
any faster.

No. The power to weight ratio favors the lighter rider on the way up,
and the mass to frontal area ratio favors the heavier riders on the way
down. You're not descending in a vacuum, so that issue is irrelevant.
Generally the advantage to the lighter rider when climbing is greater
than the advantage to the heavier rider on the descent- it's much easier
for the heavier rider to lose 15 minutes going uphill than to gain 15
minutes on the descent. FWIW, the mass to frontal area ration also tends
to favor larger riders in time trials, because the larger rider
generally has a higher total output.

On Mon, 01 Oct 2007 00:50:35 GMT, "Mike Jacoubowsky"
wrote:

I'm 5'10", 130ish lbs. I just got back from the 6 Gap ride in the N.
Georgia mountains. I was smoking people going uphill, but then they
smoked my ass going down and I couldn't catch up no matter how hard I
tried (save for a few with a high pucker factor).

There's a *lot* more to descending than rider weight. Otherwise, the TdF
guys would float downhill like a feather, but if you watch the coverage,
you'll find plenty of lightweight guys who can descend plenty fast.

My theory is that most of the bigger guys descend faster entirely by
accident. I was watching the coverage of the TdF a few years ago, and
noticed as they were flying down the hill just how fat some of the guys
were. Yet I knew they were anything but (fat). I even looked up some of
their weights, just to make sure. But they did look like they had big guts
hanging out.

And that, as it turns out, is the secret. You want to not only get low, but
bring your chest down and your knees up. Close up the airspace and your
aerodynamics improve dramatically. And the guys who really are big? Their
guts hang down whether they want them to or not. By accident they're often
more aerodynamic (despite thinking that their increased size would render
them less so).

--Mike-- Chain Reaction Bicycles
Is that gut fat, or a lot a abdominal muscle mass?

DaveH wrote:
On Sun, 30 Sep 2007 16:44:47 -0400, Paul Myron Hobson
wrote:

DaveH wrote:
I've seen this notion in various forums. It typically takes the form
of "A heavier bike may be more work uphill, but is faster downhill due
to gravity..." Something like that.

The notion -- which I think is incorrect -- really should take the
form of "Greater total mass (rider + bike + stuff) may be more work
uphill, but is faster downhill..."

In any case, reviewing the elementary physics, doesn't mass cancel in
the equations? Same reason a rock and feather both accelerate at g in
a vacuum? Ergo, that heavier bike isn't getting you down the hill any
faster.
Dave
I'm 5'10", 130ish lbs. I just got back from the 6 Gap ride in the N.
Georgia mountains. I was smoking people going uphill, but then they
smoked my ass going down and I couldn't catch up no matter how hard I
tried (save for a few with a high pucker factor).

Mass does cancel out in elementary physics, but if you add fluid
mechanics into the picture (drag force), low weight loses going down.

\\paul

Paul, this assumes that the heavier rider/bike combo (henceforth
referred to as moving mass) will always present an aerodynamic profile
with more drag. No?
Dave

If I understand you correctly: Yes, but:
-Linear dimensions (size) scale, well, linearly.
-Frontal area scales with the square of the linear dimensions.
-Weight or Volume (inertia) scales with the cube of the linear dimensions.

So a slightly bigger (L) guy has an more than slightly bigger frontal
area (L^2) but then even bigger weight (L^3), which is the force
counteracting the drag force (L^2). I'm undoubtedly doing a horrible
job of explaining this. I must admit, I'm pretty tired.

\\paul

DaveH wrote:
Assume same air resistance or drag for both scenarios -- identical
frontal area and configuration.

Air resistance is a function of speed. A heavier bike accelerates to a
greater speed, because the pulling force is larger
(Fgravity.sin(grade-angle)).

Lou

Right Lou -- It is clear now. I used to tutor this stuff in college.
Believe that? Embarrasing.
Dave

I was a hydraulics TA for three semesters

Crowning achievement: showing my student how to calculate P_cK (critical
keg pressure - the pressure at which the beer will come out foamy).

\\paul

Is that gut fat, or a lot a abdominal muscle mass

On me? Gut fat! But for the TdF riders, what they're doing is intentionally
letting their stomach sag down, countering the natural tendancy to kinda
suck it in. A cyclist isn't going to intentionally build abdominal muscle
mass, as it's not much good for anything having to do with cycling.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com


"DaveH" wrote in message
news
On Mon, 01 Oct 2007 00:50:35 GMT, "Mike Jacoubowsky"
wrote:

I'm 5'10", 130ish lbs. I just got back from the 6 Gap ride in the N.
Georgia mountains. I was smoking people going uphill, but then they
smoked my ass going down and I couldn't catch up no matter how hard I
tried (save for a few with a high pucker factor).

There's a *lot* more to descending than rider weight. Otherwise, the TdF
guys would float downhill like a feather, but if you watch the coverage,
you'll find plenty of lightweight guys who can descend plenty fast.

My theory is that most of the bigger guys descend faster entirely by
accident. I was watching the coverage of the TdF a few years ago, and
noticed as they were flying down the hill just how fat some of the guys
were. Yet I knew they were anything but (fat). I even looked up some of
their weights, just to make sure. But they did look like they had big guts
hanging out.

And that, as it turns out, is the secret. You want to not only get low,
but
bring your chest down and your knees up. Close up the airspace and your
aerodynamics improve dramatically. And the guys who really are big? Their
guts hang down whether they want them to or not. By accident they're often
more aerodynamic (despite thinking that their increased size would render
them less so).

--Mike-- Chain Reaction Bicycles
Is that gut fat, or a lot a abdominal muscle mass?

On Oct 1, 11:25 am, A Muzi wrote:
DaveH wrote:
I've seen this notion in various forums. It typically takes the form
of "A heavier bike may be more work uphill, but is faster downhill due
to gravity..." Something like that.
The notion -- which I think is incorrect -- really should take the
form of "Greater total mass (rider + bike + stuff) may be more work
uphill, but is faster downhill..."
In any case, reviewing the elementary physics, doesn't mass cancel in
the equations? Same reason a rock and feather both accelerate at g in
a vacuum? Ergo, that heavier bike isn't getting you down the hill any
faster.
Mark wrote :
Why don't you go do some cycling in a vacuum and let us know how it
works out. Out here in the real world (no vacuum), heavier bikes (w/
same frontal area) go down hill faster.
Donga wrote:
I've been trying to figure why I accelerate faster downhill (coasting)
than my riding buddy. We are about the same weight, size, bike
position, tires. Is it my Campag Record hubs versus his Mavic Ksyrium
Elites?

Do you tuck in your knees and elbows and drop your chin to the stem? You
might try descending position tweaks.
--
Andrew Muziwww.yellowjersey.org
Open every day since 1 April, 1971

The phenomenon has to do with not even trying to go fast in a casual
ride, e.g. when we've laboured up a hill and crested it, then start to
coast down. Even if I'm sitting up, turned around chatting or gasping,
with the aerodynamics of a garden shed, I have to brake to stay with
him.