Rolling Resistance Test Rig

In Bill S said:

One of the problems in determining tire rolling resistance
is eliminating uncontrolled variables and producing
repeatable results.

Quoted message said:

How about using an inclined plane? Picture a ramp with
adjustable angle. You set a weighted bike on the ramp
(starting at a very low ramp angle) and you give it a little
push.

Are you planning to give it an ISO push or an ANSI push?

Mike

Bill S said:

One of the problems in determining tire rolling resistance is
eliminating uncontrolled variables and producing repeatable results.

How about using an inclined plane? Picture a ramp with adjustable
angle. You set a weighted bike on the ramp (starting at a very low ramp
angle) and you give it a little push. If the ramp angle is very low it
will stop rolling. You increase the ramp angle in small increments and
repeat. At some point the bike keeps rolling. At this point, the
rolling resistance coefficient (drag force/weight)is equal to the
tangent of the ramp angle. This technique has been used in the past to
determine coefficient of sliding friction.

One problem is keeping the bike upright while it's moving without
increasing friction. Using 3 wheels would solve it but there may be an
easier way.

Another consideration is that this is done at low speed. Does anyone
have data on variation of rolling resistance with speed?

It might be possible to make a bike or test rig stable by getting the
center of gravity below the ramp. Elevate the ramp and hang weights from
the bike and below the ramp.

A standardized push could be provided by a spring compressed a set
distance. Make sure the mass of the bike is constant.

Since the ramp will need to be narrow, the rolling surface might need to
be slightly concave.

Rather than search for the constant velocity slope, it would be easier
to time the bike over some distance. It will need to be a long ramp and
maybe indoors to eliminate wind.

A single wheel might be stable with under-slung weight.

Michael Wileman said:

In Bill S said:

One of the problems in determining tire rolling resistance
is eliminating uncontrolled variables and producing
repeatable results.

Quoted message said:

How about using an inclined plane? Picture a ramp with
adjustable angle. You set a weighted bike on the ramp
(starting at a very low ramp angle) and you give it a little
push.

Are you planning to give it an ISO push or an ANSI push?

I have this horrible fear that nobody's going to tell you just how
da**ed funny that was.

Consider that I just have.

ROTFL!

Having the CG below the ramp is a great idea. Reminds me of
the tight rope bike riders who have people hanging under the
bike.

My thought on the "pusher" was that the static drag might be
higher than the rolling drag, therefore the need to get it
rolling. The spring loaded pusher sounds like it should work.

Dan said:

It might be possible to make a bike or test rig stable by getting the
center of gravity below the ramp. Elevate the ramp and hang weights from
the bike and below the ramp.

A standardized push could be provided by a spring compressed a set
distance. Make sure the mass of the bike is constant.

Since the ramp will need to be narrow, the rolling surface might need to
be slightly concave.

Rather than search for the constant velocity slope, it would be easier
to time the bike over some distance. It will need to be a long ramp and
maybe indoors to eliminate wind.

A single wheel might be stable with under-slung weight.

Michael Wileman said:

In Bill S said:

One of the problems in determining tire rolling resistance
is eliminating uncontrolled variables and producing
repeatable results.

Quoted message said:

How about using an inclined plane? Picture a ramp with
adjustable angle. You set a weighted bike on the ramp
(starting at a very low ramp angle) and you give it a little
push.

Are you planning to give it an ISO push or an ANSI push?

The DIN push would doubtless provide greater precision, but it is not
documented as being applicable to this test.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

A treadmill would give you variable speed and adjustable angle. You could
measure the rolling resistance by the tension in a string tied to the bike,
and running parallel to the moving belt. (Deduct the component due to the
weight of the bike.)

On Thu, 08 Jun 2006 15:52:47 GMT, Bill S <[email hidden]>

Quoted message said:

One of the problems in determining tire rolling resistance
is eliminating uncontrolled variables and producing
repeatable results.

How about using an inclined plane? Picture a ramp with
adjustable angle. You set a weighted bike on the ramp
(starting at a very low ramp angle) and you give it a little
push. If the ramp angle is very low it will stop rolling.
You increase the ramp angle in small increments and repeat.
At some point the bike keeps rolling. At this point, the
rolling resistance coefficient (drag force/weight)is equal
to the tangent of the ramp angle. This technique has been
used in the past to determine coefficient of sliding friction.

One problem is keeping the bike upright while it's moving
without increasing friction. Using 3 wheels would solve it
but there may be an easier way.

Another consideration is that this is done at low speed.
Does anyone have data on variation of rolling resistance
with speed?

Dear Bill,

If I follow you, the idea is to put a weighted bicycle that somehow
stays upright on a tiltable surface, give it enough of a push to get
it going, and then adjust the downward tilt of the table until the
tire resistance stops the gently rolling bike:

"At this point, the rolling resistance coefficient (drag
force/weight)is equal to the tangent of the ramp angle."

I'm assuming that your trigonometry is correct, but this distance
amounts to less than a single spin on a spin-down drum test, so the
margin of error would be much larger, wouldn't it?

Here's a table of measured RR values for tires:

http://www.legslarry.beerdrinkers.co.uk/tech/JL.htm

Here are the tangents for some ramp angles in the 0.0040 to 0.0100
region that you'd be trying to measure:

(tilt) (rr)
degrees tangent
0.20 0.0035 good tire
0.25 0.0044
0.30 0.0052
0.35 0.0061
0.40 0.0069
0.45 0.0079
0.50 0.0087
0.55 0.0096
0.60 0.0105 bad tire

http://www.online-calculators.co.uk/functions/mathsfunctions.php

You'll have trouble getting a polished bicycle-sized tilt-table whose
slope is adjustable in 0.05 degree increments. A spin-down drum is
simpler, cheaper, and more likely to provide reliable results.

Cheers,

Carl Fogel

Bill S said:

One of the problems in determining tire rolling resistance
is eliminating uncontrolled variables and producing
repeatable results.

How about using an inclined plane? Picture a ramp with
adjustable angle. You set a weighted bike on the ramp
(starting at a very low ramp angle) and you give it a little
push. If the ramp angle is very low it will stop rolling.
You increase the ramp angle in small increments and repeat.
At some point the bike keeps rolling. At this point, the
rolling resistance coefficient (drag force/weight)is equal
to the tangent of the ramp angle. This technique has been
used in the past to determine coefficient of sliding friction.

One problem is keeping the bike upright while it's moving
without increasing friction. Using 3 wheels would solve it
but there may be an easier way.

Another consideration is that this is done at low speed.
Does anyone have data on variation of rolling resistance
with speed?

You're going to need a long table and lots of trials to reduce the signal to
noise ratio.
--
Phil

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

Quoted message said:

One of the problems in determining tire rolling resistance is eliminating
uncontrolled variables and producing repeatable results.

How about using an inclined plane? Picture a ramp with adjustable angle.
You set a weighted bike on the ramp (starting at a very low ramp angle)
and you give it a little push. If the ramp angle is very low it will stop
rolling. You increase the ramp angle in small increments and repeat. At
some point the bike keeps rolling. At this point, the rolling resistance
coefficient (drag force/weight)is equal to the tangent of the ramp angle.
This technique has been used in the past to determine coefficient of
sliding friction.

One problem is keeping the bike upright while it's moving without
increasing friction. Using 3 wheels would solve it but there may be an
easier way.

Another consideration is that this is done at low speed. Does anyone have
data on variation of rolling resistance with speed?

Well I think I would consider a frame assembly with a electric motor
powering the wheel via a chain drive and the sprockets.
You can then change the road surface under and put weight on the frame
simulating a rider's weight loading the wheel and tire combination.
You then measure the current flow through the motor from the start to finish
of the test run.
This would let you be better able to control all the variables, and see what
the different variables would do too.
You could also hook up a fan or wind tunnel affair to see if wind resistance
at different speeds would have any effect as well.