Jack Ruby Jr.



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Sky Fly

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Archimedes was reported to have said, "Give me a place to stand I will move the earth". Presumably,
he was referring to the possibility of moving anything he wanted, provided he had the place to
position the appropriate lever and pivot.

Is there a similar rule with cycling? Could I say "Give me a gear, and I will climb a vertical rock
face"? Somehow I doubt it, even with at 10x100 gear. But at what point does the gearing on my bike
become irrelevant to the slope I'm climbing?

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Akin

aknak at aksoto dot idps dot co dot uk
 
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Tony Raven

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Sky Fly <[email protected]> wrote:
> Archimedes was reported to have said, "Give me a place to stand I will move the earth".
> Presumably, he was referring to the possibility of moving anything he wanted, provided he had the
> place to position the appropriate lever and pivot.
>
> Is there a similar rule with cycling? Could I say "Give me a gear, and I will climb a vertical
> rock face"? Somehow I doubt it, even with at 10x100 gear. But at what point does the gearing on my
> bike become irrelevant to the slope I'm climbing?

The limit is a combination of factors but the three limits are the slip limit of the rear tyre, the
torque limit of flipping out backwards and how slow you can go without falling off.

You can only move forward by driving the rear wheel and as the slope gets steeper more of your
weight goes towards pushing the bike backwards and less on pushing it towards the ground. If you
think of a vertical slope, there is no horizontal force to push the tyre against the ground so no
tyre/ground friction so no drive and the wheel will slip. Meanwhile your whole weight is pushing the
bike downwards and the tyre will simply slip down the surface. Most climbing is a balancing act; you
want your weight back to maximise rear tyre grip but that means there is not much weight on the
front wheel which lifts under the drive torque. So you have to compromise between the back wheel
slipping and the front wheel lifting. If you go to Moab in Utah the rocks there are very grippy and
you can climb incredible slopes before the rear wheel slips.

Tony

http://www.raven-family.com

"The single biggest problem in communication is the illusion that it has taken place" George
Bernard Shaw.
 
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Peter B

Guest
"Call me Bob" <[email protected]> wrote in message
news:[email protected]...
> On Sun, 12 Jan 2003 14:52:33 -0000, "Sky Fly" <[email protected]> wrote:
>
> >Archimedes was reported to have said, "Give me a place to stand I will move the earth".
> >Presumably, he was referring to the possibility of moving anything he wanted, provided he had the
> >place to position the appropriate lever and pivot.
> >
> >Is there a similar rule with cycling? Could I say "Give me a gear, and I will climb a vertical
> >rock face"? Somehow I doubt it, even with at 10x100 gear. But at what point does the gearing on
> >my bike become irrelevant to the slope I'm climbing?
>
> Balance, surely? At some point your gearing will become low enough that even though you may spin
> at a high rate you are moving so slowly that you can't actually stay upright.

There may also be the problem that if you can't spin smoothly you may stall when the pedals are at
TDC/BDC, application of power could then lift the front wheel causing problems alleviated by
shifting body weight forward which then causes the back wheel to unstick. This is a problem when
trying to climb uneven surfaces off-road, weight back = front wheel lift and loss of steering,
weight forward = loss of traction.

My 10p Pete
 
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Call Me Bob

Guest
On Sun, 12 Jan 2003 14:52:33 -0000, "Sky Fly" <[email protected]> wrote:

>Archimedes was reported to have said, "Give me a place to stand I will move the earth". Presumably,
>he was referring to the possibility of moving anything he wanted, provided he had the place to
>position the appropriate lever and pivot.
>
>Is there a similar rule with cycling? Could I say "Give me a gear, and I will climb a vertical rock
>face"? Somehow I doubt it, even with at 10x100 gear. But at what point does the gearing on my bike
>become irrelevant to the slope I'm climbing?

Balance, surely? At some point your gearing will become low enough that even though you may spin at
a high rate you are moving so slowly that you can't actually stay upright.

You could get past that by riding a trike I suppose, so the next obstacle you'd hit would be grip.
You could definitely (although not with standard kit) have gearing which would allow you to climb a
vertical slope but a bike just wont stay on that kind of incline. Even with super sticky tyres the
bike would just fall off backwards.

Bob
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Ian Smith

Guest
On Sun, 12 Jan 2003, Call me Bob <[email protected]> wrote:
> On Sun, 12 Jan 2003 14:52:33 -0000, "Sky Fly" <[email protected]> wrote:
>
> >Is there a similar rule with cycling? Could I say "Give me a gear, and I will climb a vertical
> >rock face"? Somehow I doubt it, even with at 10x100 gear. But at what point does the gearing on
> >my bike become irrelevant to the slope I'm climbing?
>
> Balance, surely? At some point your gearing will become low enough that even though you may spin
> at a high rate you are moving so slowly that you can't actually stay upright.

That's not the limit (not for me, anyway). I have an mtb with a microdrive chainset and a
non-microdrive quite large back block. Most of the gears on teh smallest chainring result in the
back wheel turning slower than the cranks.

Either losing traction or the front wheel lifting and falling off the back happen before I fall
sideways. Which happens depends on where my weight is and the available grip, but I've never fallen
sideways. I can, however, balance it completely stationary for a while and only need a tiny tiny
speed to stay upright indefinitely.

regards, Ian SMith
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S

Sky Fly

Guest
"Tony Raven" <[email protected]> wrote in message news:[email protected]...
> Sky Fly <[email protected]> wrote:
> > Archimedes was reported to have said, "Give me a place to stand I will move the earth".
> > Presumably, he was referring to the possibility of moving anything he wanted, provided he had
> > the place to position the appropriate lever and pivot.
> >
> > Is there a similar rule with cycling? Could I say "Give me a gear, and I will climb a vertical
> > rock face"? Somehow I doubt it, even with at 10x100 gear. But at what point does the gearing on
> > my bike become irrelevant to the slope I'm climbing?
>
>
> The limit is a combination of factors but the three limits are the slip limit of the rear tyre,
> the torque limit of flipping out backwards

Could you explain this 'torque limit' in more detail, please?

> and how slow you can go without falling off.

<snippage of post explaining how steeper slopes increase the component of the cyclist's weight that
pulls the cyclist back>

So at what slope might this slippage occur, if we assume that the person is riding a trike (to deal
with balance problems) on a surface that will offer maximum traction and with as low gearing as
possible? According to what you say, it should be 1:1 since at that point the component of your
weight acting downwards is equal to the component pulling you back - is this right? My O-level
physics is a bit rusty...
 
J

James Annan

Guest
Call me Bob wrote:
> On Sun, 12 Jan 2003 14:52:33 -0000, "Sky Fly" <[email protected]> wrote:
>
>
>>Archimedes was reported to have said, "Give me a place to stand I will move the earth".
>>Presumably, he was referring to the possibility of moving anything he wanted, provided he had the
>>place to position the appropriate lever and pivot.
>>
>>Is there a similar rule with cycling? Could I say "Give me a gear, and I will climb a vertical
>>rock face"? Somehow I doubt it, even with at 10x100 gear. But at what point does the gearing on my
>>bike become irrelevant to the slope I'm climbing?
>
>
> Balance, surely?

For us (on a tandem), rear wheel traction is the first to go with our
24/32 gearing (front/rear). Sometimes we would do better with a lower gear, especially at altitude
or at the end of a long day, but it would smash the hub and cassette even more frequently. I
don't see balance as a significant limitation around these speeds, and with lower gearing and
less grunt it would if anything be easier to maintain our poise and elegance...

James
 
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Call Me Bob

Guest
On Sun, 12 Jan 2003 23:08:42 -0000, "Sky Fly" <[email protected]> wrote:

>> The limit is a combination of factors but the three limits are the slip limit of the rear tyre,
>> the torque limit of flipping out backwards
>
>Could you explain this 'torque limit' in more detail, please?

Newton's 3rd Law: Every action has an equal and opposite reaction.

As you apply a turning force (torque) at the pedals the bike is subject to an equal and opposite
turning force. Basically the bike "wants" to turn the opposite way to your pedalling motion. In
normal cycling conditions this isn't a problem because you are on a (relatively) flat surface and so
gravity provides the force necessary to anchor the bike and rider to the ground.

However, if you are trying to ride up a very steep incline gravity is no longer acting straight down
through the bike and so it's ability to resist the torque generated at the pedals is reduced. Ride
up a slope steep enough and basically you'll wheelie the bike over backwards before you're able to
pedal forward.

This is something that hadn't occurred to me when I originally replied to your post.

>So at what slope might this slippage occur, if we assume that the person is riding a trike (to deal
>with balance problems) on a surface that will offer maximum traction and with as low gearing as
>possible? According to what you say, it should be 1:1 since at that point the component of your
>weight acting downwards is equal to the component pulling you back - is this right?

I've got no idea how to calculate this, but I'd guess the slope would have to be steeper than
1:1 before loss of grip would be the limiting factor (assuming dry, grippy surface and soft,
slick tyres).

Bob
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T

Tony Raven

Guest
"Sky Fly" <[email protected]> wrote in message news:<[email protected]>...
>
> So at what slope might this slippage occur, if we assume that the person is riding a trike (to
> deal with balance problems) on a surface that will offer maximum traction and with as low gearing
> as possible? According to what you say, it should be 1:1 since at that point the component of your
> weight acting downwards is equal to the component pulling you back - is this right? My O-level
> physics is a bit rusty...

Depends on too many variables to give an answer - coefficient of friction between the tyres and the
surface, position of riders weight and centre of gravity on the bike, tyre pressure (contact area)
etc etc. Your 1:1 supposition is not correct - it depends not on your weight down alone but weight
and coefficient of friction. For example a polished ice surface would have you slipping at much
less than 1:1.

Tony
 
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