Re: How much power does an average recreational rider generate when climbing?

On Aug 6, 4:14 pm, carlfo...@xxxxxxxxxxx wrote:
Dear Dan,

Yikes!

Let's start with your last comment. Maybe you're overestimating the
steepness of the hills that you climb?

I must be overestimating the steepness of the hills I climb. What I
meant to say is that I rarely go under 10 MPH – I find my cadence gets
too slow and my bad knee bothers me. I am more likely to stand and
hammer to keep my cadence up. Since I really don’t know how to
estimate the grade of a hill, I’ll just assume I’m dead wrong on the
8% thing.


"Again, I don't tend to slow down a lot for hills, especially of that
grade, but they certainly take a lot more out of me."

That grade was 8%--Tour de France winners slow down an awful lot for
8% hills, even though it's only a rise of 8 feet in 100.

It's unlikely that a rider with a bad knee who talks about 18~25 mph
on the flats can climb 8% grades without tending to slow down an awful
lot.

There’s no doubt I slow down an awful lot – to me from 20+MPH to 10ish
MPH is an awful lot. What I meant to say is I don’t slow to 5MPH –
that would put my cadence far too low for comfort.


Either you're slowing down much more than you think, your hills aren't
anywhere near 8%, or you're the next TDF winner.

I’ll go for option B.


I expect that you're posting in good faith, so please understand that
I'm just trying to explain how unlikely it is for _anyone_ to talk
about not slowing down a lot on 8% grades.

Again, a lot is relative. I consider dropping to 10ishMPH from my
18-25 to be quite a bit. Still, I’m thinking I’m just off on the
grade estimate. Where I ride there are no grade signs, so I don’t
have much to judge by.


Have a look again at this side-by-side calculator:
http://bikecalculator.com/veloUS.html

The defaults and 200 watts will produce almost 20 mph for both sides.

Change one side to an 8% grade, and even 500 watts won't go 15 mph.

It's unlikely that you weigh 150 pounds and put out 500 watts for more
than a few seconds.

175ish, and have no idea the wattage I put out. I have strong legs,
but I’m willing to bet they’re not 500 watts of strong.


As for the mountain bike, even one in good repair is likely to be much
harder to ride because mountain bikes generally come with horrible
knobby tires (huge rolling resistance) and their flat bars force the
sit-up-and-beg position.

My point is that both bikes in question in the analogy referring to my
father are mountain bikes. The tires and sitting position are very
similar. One is a BST that weighs half a ton, and the other is a high-
end bike that is fairly light. I don’t think rolling resistance is
very different since his wheels will at least match if not outspin
mine in the upside-down wheel spinning test. There’s likely some
effort lost in the bottom bracket and derailers, but I doubt it’s a
whole lot. The difference in effort required to move each bike,
however, is a whole lot.


You can see this on the same side-by-side calculator:
http://bikecalculator.com/veloUS.html

Use the defaults and 200 watts on both sides, which should produce
19.67 mph. Now change the right side from hoods to drops, and the more
aerodynamic rider gains 1.63 mph and goes 21.30 mph. That 1.63 mph
doesn't sound like much, but it's 8.3% faster.

In other words, the calculator agrees with you--just ducking down on
the drops will make a fairly level paved ride much faster and easier.

The power needed to overcome wind drag rises with the cube of speed.
That is, if you double your speed, you need to devote 2^3 (2x2x2) as
much power to fighting wind drag. That's why aerodynamic improvements
pay off in road races and why Armstrong spent so much time in wind
tunnels.

(The _total_ power for twice the speed rises only ~6 times as much,
not 8 times as much, because the power spent on rolling resistance and
transmission losses doesn't need to rise anywhere near as fast as the
power spent on wind drag.)

You don't lose (or gain) as much speed due to head and tail winds as
the wind speed itself because part of the equation for wind drag and
power involves the distance.

When a headwind slows you down, you end up covering less distance in
the same time, so less power is needed, and you don't lose as much as
the total wind speed.

Similarly, when a tailwind speeds you up, you have to cover more
distance in the same time, so more power is needed, and you don't gain
as much as the total wind speed.

Again, the side-by-side calculator helps to illustrate this:
http://bikecalculator.com/veloUS.html

Use 200 watts with the defaults, and both sides go to 19.67 mph.

Change to 5 and -5 for the headwinds, and one side drops to 16.69, a
~3 mph loss, and the other side rises to only 22.90, a ~3 mph gain.

Neither side gains or loses the actual wind speed.

The slower you go, the less effect the wind will have, since wind drag
is tiny at low speeds--at 5 mph, you're putting your power into
deforming the tires, transmission losses, and (most likely) raising
your weight uphill.

***

Most of the speed gain that you notice between a mountain bike and a
touring-style drop-bar bike is likely to be due to better tires and
aerodynamics.

Again, I never compared road bikes to mountain bikes. The analogy I
used regarding my dad involves 2 mountain bikes, his and mine. Both
run similar tires and invoke similar riding position.


Consider the tires first:
http://bikecalculator.com/veloUS.html

Same old 200 watts with the defaults for both sides, same old 19.67
mph for both sides.

Now change from the default road-style clinchers to MTB tires.

Yikes! The speed drops from 19.67 mph to 17.85 mph, about 10% slower.
The tires deform as they roll, bulging outward as the rubber rolls
through the contact patch and then returning to the normal shape. The
more tire that you deform, the more power is lost--the "spring" of the
rubber never returns 100% of the power you put into deforming it.

Put a pair of high-pressure slick tires on a mountain bike, and the
speed rises. A few years ago, I rode a thousand miles in 4-mile daily
rides on a WalMart Fury RoadMaster with huge knobbies and then
switched to slicks--instant and sustained speed increase:
http://groups.google.com/group/rec.bicycles.tech/msg/d60e3ac9c2c9a35d

***

Now consider the weight of the mountain bike.

Even if one bike weighs 20 pounds and the other weighs 40, the
difference due to weight on the flats is tiny:
http://bikecalculator.com/veloUS.html

Use the defaults for both, plug in 200 watts, and change the bike
weights to 20 and 40--19.68 versus 19.53 mph. (For a rider who weighs
more than the default 150 pounds, the difference will be even less.)

The tiny difference in cruising speed on the flat is just the result
of the tiny increase in rolling resistance--the extra 20 pounds
deforms the tires a little more.

That's why a heavy single-speed can cruise at about the same speed on
the flat as a new multi-gear bike--weight means almost nothing on the
flat.

***

Uphill, an extra 20 pounds will slow things down more because you're
raising the weight, not rolling it on the flat.

Run the 20 and 40 pound bikes up an 8% grade at 200 watts, and one
goes 6.43 mph and the other goes only 5.80 mph, about 10% slower. When
you climb, more and more of your power goes into lifting raw weight
rather than overcoming wind drag.

While I don’t disagree with the speed difference at a given wattage, I
do wonder if we’re downplaying the effect this has on the endurance of
the cyclist. I’m not suggesting that 1/3lb will shave notable time
off of my commute, but it does seem to me that a bike that’s a few lbs
lighter requires less effort to get around, especially during
acceleration and going up hills.


But the effect of weight uphill is much less than our gram-counting
culture leads us to imagine. It's the _total_ weight that matters.
When you switch to a 40-lb bike from a 20-lb bike, you don't double
the weight that you have to pedal up the hill. You still weigh 150
pounds (using the default rider in the calculator), so you're going
from 150+20 to 150+40, which is from 170 to 190 pounds, a bit less
than a 12% increase in total weight, not a 100% increase.

You're probably not climbing 8% grades of any significant length on a
single-speed. In the early Tour de France, most of the single-speed
riders got off and walked for miles up such grades, pushing their
bicycles and cursing the organizers.

The 1910 TDF winner pushing up the Galibier:
http://magliarosa.files.wordpress.com/2007/08/lapize.jpg

Three 1920 TDF single-speed riders pushing up the Tourmalet:
http://i35.tinypic.com/fwq1hg.jpg

A 1934 TDF single-speed rider, pushing up the Izoard:
http://www.worldcycling.com/graphics/00000002/PSTP304.jpg

***

Anyway, you might look into the actual grade of the hills that you
ride and see if they're really 8%.

I think I’ll do this at some point, if nothing else to satisfy my
curiousity. I do wish we had signs around here like they have in some
other areas telling us these things.


For fun, you can make an inclinometer with some cheap plastic pipe and
a right-angle ruler-level combination:

"Intrigued, I cobbled together an inclinometer, having read Jobst
Brandt's comments on grade percentages. Instead of an effete
Euro-style meter-bar, I used a five-foot piece of heavy-wall
straight plastic plumbing pipe, carving a chunk out 50 inches from the
end and dropping an ordinary carpenter's square through a slit in the
lower half of the pipe. The built-in level and the pipe cradling
the square, along with the adjusting screw to lock the ruler, made it
more convenient for a clumsy oaf to use and the extra ten inches make
it more accurate than a meter stick.
__
| |
| |<--50"------------------------------->
______ | |______________________________________
| \____|__| |
| level visible inside pipe |
|_____________________________________________________|
| | /
| | 3" /
|__| /
\___touch road_____________________/

On an 8% grade, four inches of ruler would stick out below the pipe
when the bubble inside the pipe showed level.

A longer pipe will give even more accuracy.

I may have to give this a whirl. Thanks for taking the time to reply.
.

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