Re: Re : Stopping Distance Calculation

[email hidden] wrote in message news:<[email hidden]>...

Quoted message said:

I think Mu, which I think was something to do with coefficient of friction
will need to be considered. eg glass tyres compared to rubber

The method of calculation used was purely kinetic - ie. he assumed a
deceleration of 0.5g and used that.

If you want to calculate the actual decleration then you would have to
factor in the friction coeffiecient for both the brakepad-rim
interface and the tyre-surface interface. A whole of other stuff comes
into play as well, such as weight of rider+bike, surface areas etc.

Coefficient of friction for the tyre/road interface only matters if
you're sliding, which usually means the wheel is stopped so you don't
need mu for brake/rim interface. Weight of rider and bike only matter
for that too (unless you're doing momentum/energy calcs) as they're not
a normal force for the brakepads. Surface areas don't matter much unless
you've got to calculate the forces from some pressure.

daniels said:

[email hidden] wrote in message news:<[email hidden]>...

Quoted message said:

I think Mu, which I think was something to do with coefficient of friction
will need to be considered. eg glass tyres compared to rubber

The method of calculation used was purely kinetic - ie. he assumed a
deceleration of 0.5g and used that.

If you want to calculate the actual decleration then you would have to
factor in the friction coeffiecient for both the brakepad-rim
interface and the tyre-surface interface. A whole of other stuff comes
into play as well, such as weight of rider+bike, surface areas etc.

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______________________________________

Tamyka Bell, PhD Student
School of Human Movement Studies
The University Of Queensland
w: +61-7-33656105
m: +61-4-00782972
e: [email hidden]
______________________________________

Tamyka Bell said:

Coefficient of friction for the tyre/road interface only matters if
you're sliding, which usually means the wheel is stopped so you don't
need mu for brake/rim interface.

Optimal braking occurs with a small amount of tyre slip. If the tyres aren't
slipping, you're not braking hard enough.

However, it depends on the bike, normal uprights will not have sliding front
brakes, you can't apply that much pressure without going over the handlebars.
However, the rear wheel assists a bit as well.

Shallow seat angle recumbents don't lift the rear wheel under heavy braking,
so more braking can be applied there without going for a tumble.

Quoted message said:

Weight of rider and bike only matter
for that too (unless you're doing momentum/energy calcs) as they're not
a normal force for the brakepads. Surface areas don't matter much unless
you've got to calculate the forces from some pressure.

Heavier rider weight places more pressure on the tyre/road surface area,
effectively improving the grip there.

And then there's the matter of braking under abnormal conditions, say down a
steep hill. Temperature can come into it, which would affect some types of
brakes more than others.

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