Low or high gear causes wheel slippage?

[Phil, Squid-in-Training]

In a.m-b, we've mentioned singlespeeds and how the wheel sometimes slips
with a quick-release skewer. We got into gear ratio discussion, and I
maintained that high gears cause more wheel slippage since less of the pedal
force is being turned into torque and more is being turned into wheel
translation force. Low gears cause more torque and therefore slip less.

This is what I think... is it correct? I'm sure none of you have had the
wheel slip at a high cadence (not the cause but the general effect).

--
Phil, Squid-in-Training

 

[Kinky Cowboy]

On Thu, 8 Sep 2005 18:23:26 -0400, "Phil, Squid-in-Training"
<[email protected]> wrote:

>In a.m-b, we've mentioned singlespeeds and how the wheel sometimes slips
>with a quick-release skewer. We got into gear ratio discussion, and I
>maintained that high gears cause more wheel slippage since less of the pedal
>force is being turned into torque and more is being turned into wheel
>translation force. Low gears cause more torque and therefore slip less.
>
>This is what I think... is it correct? I'm sure none of you have had the
>wheel slip at a high cadence (not the cause but the general effect).

Gear ratio is irrelevant, what matters is chain tension. For a given
pedal load, this increases for longer cranks and smaller chainrings.
You'll pull the wheel less on 40/20 than on 32/16; same ratio, but the
bigger ring reduces the chain tension by 20%. Slip occurs at low
speeds because this is when the human exerts the greatest pedal loads.

Kinky Cowboy

Modernity consists in the substitution
for the immediate of the instantaneous

 

[Jasper Janssen]

On Thu, 8 Sep 2005 18:23:26 -0400, "Phil, Squid-in-Training"
<[email protected]> wrote:

>In a.m-b, we've mentioned singlespeeds and how the wheel sometimes slips
>with a quick-release skewer. We got into gear ratio discussion, and I
>maintained that high gears cause more wheel slippage since less of the pedal
>force is being turned into torque and more is being turned into wheel
>translation force. Low gears cause more torque and therefore slip less.
>
>This is what I think... is it correct? I'm sure none of you have had the
>wheel slip at a high cadence (not the cause but the general effect).

Torque is *turning force*. It doesn't cause the wheel to move horizontally
at all. What causes the wheel to move horizontally is that the torque is
generated by the chain pulling to the front at a distance from the axle
(depending on cog there, distance is greater or smaller), and the axle
clamping providing a force (hopefully) equal and opposite (but not acting
at the same point). So to sum up, what matters is the (maximum) chain
tension, not torque. And maximum chain tension scales directly with the
chainring size. In small chainrings, you've got a lot of leverage, and you
can turn your weight into much more chain tension.

So: The front gear matters, the rear one doesn't.


Jasper

 

[Werehatrack]

On Thu, 8 Sep 2005 18:23:26 -0400, "Phil, Squid-in-Training"
<[email protected]> wrote:

>In a.m-b, we've mentioned singlespeeds and how the wheel sometimes slips
>with a quick-release skewer. We got into gear ratio discussion, and I
>maintained that high gears cause more wheel slippage since less of the pedal
>force is being turned into torque and more is being turned into wheel
>translation force. Low gears cause more torque and therefore slip less.
>
>This is what I think... is it correct? I'm sure none of you have had the
>wheel slip at a high cadence (not the cause but the general effect).

All transmission of energy from the cranks to the wheel is done by
linear tension in the chain; the higher the chain tension, the higher
the force pulling the wheel forward. Therefore, the smaller the front
sprocket (regardless of the rear sprocket size), the more force that
will be exerted to dislocate the rear wheel during highest-force
pedalling. It's a simple matter of leverage ratios.

(Addendum: the rear sprocket size can limit the highest force
actually achieved; the larger the rear sprocket, the greater the
leverage that it has on the wheel, which will presumably then rotate
and consume the transmitted power, limiting the amplitude of the
impulse. If the wheel cannot rotate, then the chain tention is
determined entirely by the magnitude and vector of the force applied
to the pedal, the crank position, and the front sprocket size.)
--
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