Cycling physics questions

Epetruk said:

1. When I'm cycling into a headwind, I usually bend as low as possible to
reduce the wind resistance. Does it make sense to keep my back as upright as
possible when I have a tailwind behind me (so as to maximise the area of my
body that is being 'pushed'😉? I ask, because I still find that being hunched
over the bars is a more comfortable position here as well.

It depends on relative velocity. If you're going faster than the
tailwind then you still have a net headwind, so you're better in a
crouch. If, OTOH, you want to freewheel with sind power then the
greater the area of "sail" the better. Any amount of pedalling will
probably mean that a crouch is more efficient, but if you /really/ want
to do this properly get a velomobile or other faired recumbent.

Quoted message said:

2. When I'm climbing a 10% hill, I can just about cope using a 38x20
combination of front/rear chainrings. Should this mean that to climb a 20%
hill with the same amount of effort, I should use a 19x20 combination?

The effort (work) required to get up a hill, irrespective of gradient,
is basically the height of the hill plus a bit more for frictional drag
along the road. What gearing you use, along with the cadence,
determines how fast you'll get up it, not the total amount of effort
you'll need. Trundling up something in 10 minutes in an ubergranny
actually requires the same amount of work as mashing it in top, but the
latter requires a lot of force applied on a few pedal strokes rather
than hardly any applied over very many. Steeper hills feel harder
because basically they require you to gain the height more quickly, so
your work /rate/ is quicker.

To get up hills best, just ask your legs and cardiovascular system what
works best for them. They'll be telling you with puffing and lactic
acid buildup...

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email hidden] http://www.dundee.ac.uk/~pjclinch/

Peter Clinch said:

The effort (work) required to get up a hill, irrespective of gradient,
is basically the height of the hill plus a bit more for frictional drag
along the road. What gearing you use, along with the cadence,
determines how fast you'll get up it, not the total amount of effort
you'll need.

Well, it also depends how fast you're going up the hill. The faster
you go, the more work done to overcome wind resistance. However, if
like me you head up hills pretty damn slowly, the additional work done
is likely to be negligable compared to the work done getting up the hill.

There's also the issue that if you go very slow indeed, there's likely
to be a degree of "wasted" effort from the increased wobbling :-)

R.

Peter Clinch said:

Quoted message said:

2. When I'm climbing a 10% hill, I can just about cope using a 38x20
combination of front/rear chainrings. Should this mean that to climb
a 20% hill with the same amount of effort, I should use a 19x20
combination?

The effort (work) required to get up a hill, irrespective of gradient,
is basically the height of the hill plus a bit more for frictional
drag along the road. What gearing you use, along with the cadence,
determines how fast you'll get up it, not the total amount of effort
you'll need. Trundling up something in 10 minutes in an ubergranny
actually requires the same amount of work as mashing it in top, but
the latter requires a lot of force applied on a few pedal strokes
rather than hardly any applied over very many. Steeper hills feel
harder because basically they require you to gain the height more
quickly, so your work /rate/ is quicker.

Actually Peter, when I said "same amount of effort", I actually meant the
same amount of exertion, i.e. huffing and puffing, muscle strain, etc. I'm
sure you'll agree that if you do a hill in low gears, this exertion is less
than if you do it in higher gears (even though you may go slower). Perhaps
the word I'm looking for is 'power' rather than 'work'.

Richard said:

There's also the issue that if you go very slow indeed, there's likely
to be a degree of "wasted" effort from the increased wobbling :-)

Trike with a supergranny and parking brake: no wobbles, stop whenever
you want without taking your feet off the pedals...

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email hidden] http://www.dundee.ac.uk/~pjclinch/

Epetruk said:

A couple of cycling physics questions:

Have a look at this power & speed calculator. A few minutes playing with
various input values will provide a lot of answers.

http://www.kreuzotter.de/english/espeed.htm

Mike

Epetruk said:

Hi all,

A couple of cycling physics questions:

1. When I'm cycling into a headwind, I usually bend as low as possible to
reduce the wind resistance. Does it make sense to keep my back as upright as
possible when I have a tailwind behind me (so as to maximise the area of my
body that is being 'pushed'😉? I ask, because I still find that being hunched
over the bars is a more comfortable position here as well.

In most situations you'll still be travelling faster than the average
tailwind, so a crouch is still in order. However, it's less critical to
crouch if the resultant headwind is only 5mph.

Quoted message said:

2. When I'm climbing a 10% hill, I can just about cope using a 38x20
combination of front/rear chainrings. Should this mean that to climb a 20%
hill with the same amount of effort, I should use a 19x20 combination?
(Experience tells me that there is no such linearity, but I was thinking
that since the second case meant doubling the amount of work I do, then I
should double my efficiency.)

For a given pedal rpm, it's true that 19x20 will give you the same force
on your knees than 38x20 on the shallower hill. You'll climb at half
the speed though.

Peter Clinch said:

Also note that speed is not absolute in a gear, because you can vary
your cadence. It may be better to spin a lower gear at a higher rate to
get a certain speed.

Unless you're on a fixie, when you must ATTACK! I've done 1 in 6 hills
in 48 x 18, and it's surprisingly easy. If your knees are well
conditioned, it's sometimes easier, at least for short hills, to stomp
up them in a big gear. Disclaimer = this isn't advisable all the time,
or you get fat heavy legs.

Zog The Undeniable said:

Unless you're on a fixie, when you must ATTACK! I've done 1 in 6
hills in 48 x 18, and it's surprisingly easy. If your knees are well
conditioned, it's sometimes easier, at least for short hills, to stomp
up them in a big gear. Disclaimer = this isn't advisable all the
time, or you get fat heavy legs.

The attack method also gives you the advantage of not having to accelerate
at the top of the hill.

--
Andy Morris

AndyAtJinkasDotFreeserve.Co.UK

Love this:
Put an end to Outlook Express's messy quotes
http://home.in.tum.de/~jain/software/oe-quotefix/

Zog The Undeniable said:

Peter Clinch wrote:

I've done 1 in 6 hills in 48 x 18, and it's surprisingly easy.

I have but one reply to this:

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Epetruk said:

Zog The Undeniable said:

Peter Clinch wrote:

I've done 1 in 6 hills in 48 x 18, and it's surprisingly easy.

I have but one reply to this:

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

In my young and foolish days I'd regularly ride round th eNorth Downs with a
63" bottom gear. 1 in 4 and 1 in 5 hills were hard work but doable, as long
as they weren't too long.

...d

Epetruk said:

Zog The Undeniable said:

Peter Clinch wrote:

I've done 1 in 6 hills in 48 x 18, and it's surprisingly easy.

I have but one reply to this:

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

When I was much younger all I had was a 52/48 and 12/14/16/18/21
freewheel. Did all the Pyrenees on that but perhaps that's why I
struggle now on my 30x23
All the best
Dan Gregory

Zog The Undeniable said:

Unless you're on a fixie, when you must ATTACK! I've done 1 in 6 hills
in 48 x 18, and it's surprisingly easy.

Indeedie.

My first real tour was done on gears bought for Cambridge, and was the
year I left (we did a run loosely described as Cambridge to Oxford via
Edinburgh:-) As we approached the Kirkstone pass, my cycling companion
bet me I wouldn't make it up without walking. So I did. No great
hardship; just take it gently. That was with a 42-22 bottom gear,
and with full touring/camping gear on the back.

I was a lot faster back then. Learning a bit of theory and dropping
into lower gears for the uphill really slows you.

--
Nick Kew