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Rolling Resistance Test Rig
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? |
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#2
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Rolling Resistance Test Rig
In Bill S writes:
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. Are you planning to give it an ISO push or an ANSI push? Mike |
#3
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Rolling Resistance Test Rig
Bill S wrote:
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. |
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Rolling Resistance Test Rig
On Thu, 8 Jun 2006 16:38:38 +0000 (UTC), Michael Wileman
wrote: In Bill S writes: 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. 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! |
#5
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Rolling Resistance Test Rig
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 wrote: 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. |
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Rolling Resistance Test Rig
On Thu, 8 Jun 2006 16:38:38 +0000 (UTC), Michael Wileman
wrote: In Bill S writes: 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. 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. |
#7
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Rolling Resistance Test Rig
On Thu, 08 Jun 2006 15:52:47 GMT, Bill S
wrote: 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 measu (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/...sfunctions.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 |
#8
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Rolling Resistance Test Rig
Bill S wrote:
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 |
#9
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Rolling Resistance Test Rig
"Bill S" wrote in message
.. . 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. |
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