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#1
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Which wheel travels furthest?
On 9 July, 09:54, TrailRat wrote:
The front one or the back one? Surely the front one as the back one follows on behind. Ahhh, but the back starts in the same location as it finishes, the exact same distance behind the front one. Anyway, the point of this madness. I got a little bored and decided a little experiment. Before I set out I made sure both wheels had the valves pointing straight up. The wheels, tyres and the inner tubes are identical back and front (apart from that big block of cogs on the back one, duh!). Both are disc braked. I also made sure the pressure was the same. Then I set off on a gentle 10 mile ride. All road and cycle paths. Any loose paths will make for more rear wheel rotation due to slippage under drive. Nothing to strenuous. I made sure to use access ramps and not just bounce off the kerbs. I kept my speed below 15mph. Anyway on my return, I inspected the valves expecting to find them still aligned and was surprised to find that front one was about 4" in front of the rear one. and how many rotations? Are you sure rear wheel is behind the front? About 40" is the usual amount. Typographical error? So, I turn the scientific analysis to my peers and ask that ultimate scientific question, huh?? Although the rear wheel usually takes a slightly shorter route around bends so resulting in fewer revolutions, it is also subject to the driving force which amounts to a little slippage, resulting in more revolutions than the front. I don't know whether there is a typical value on this. |
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#2
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Which wheel travels furthest?
On 09/07/2010 19:58, thirty-six wrote:
Although the rear wheel usually takes a slightly shorter route around bends so resulting in fewer revolutions, it is also subject to the driving force which amounts to a little slippage, resulting in more revolutions than the front. I don't know whether there is a typical value on this. I'd guess about the square root of feckall .. if the rear spun that much then you'd be skidding all over. Maybe on sheet ice ... -- Paul - xxx '96/'97 Landrover Discovery 300 Tdi Dyna Tech Cro-Mo comp |
#3
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Which wheel travels furthest?
On 9 July, 20:16, Paul - xxx wrote:
On 09/07/2010 19:58, thirty-six wrote: Although the rear wheel usually takes a slightly shorter route around bends so resulting in fewer revolutions, it is also subject to the driving force which amounts to a little slippage, resulting in more revolutions than the front. * I don't know whether there is a typical value on this. I'd guess about the square root of feckall .. if the rear spun that much then you'd be skidding all over. *Maybe on sheet ice ... Drive-slip occurs at the centre of the wheel tread only, not like wheelspin which is slip across the whole of the tread. |
#4
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Which wheel travels furthest?
On 10/07/2010 04:48, thirty-six wrote:
On 9 July, 20:16, Paul - wrote: On 09/07/2010 19:58, thirty-six wrote: Although the rear wheel usually takes a slightly shorter route around bends so resulting in fewer revolutions, it is also subject to the driving force which amounts to a little slippage, resulting in more revolutions than the front. I don't know whether there is a typical value on this. I'd guess about the square root of feckall .. if the rear spun that much then you'd be skidding all over. Maybe on sheet ice ... Drive-slip occurs at the centre of the wheel tread only, not like wheelspin which is slip across the whole of the tread. ? How does that work then? How can the centre of the tread slip without the rest of the tread? -- Paul - xxx '96/'97 Landrover Discovery 300 Tdi Dyna Tech Cro-Mo comp |
#5
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Which wheel travels furthest?
On 10 July, 06:29, Paul - xxx wrote:
On 10/07/2010 04:48, thirty-six wrote: On 9 July, 20:16, Paul - *wrote: On 09/07/2010 19:58, thirty-six wrote: Although the rear wheel usually takes a slightly shorter route around bends so resulting in fewer revolutions, it is also subject to the driving force which amounts to a little slippage, resulting in more revolutions than the front. * I don't know whether there is a typical value on this. I'd guess about the square root of feckall .. if the rear spun that much then you'd be skidding all over. *Maybe on sheet ice ... Drive-slip occurs at the centre of the wheel tread only, not like wheelspin which is slip across the whole of the tread. ? *How does that work then? How can the centre of the tread slip without the rest of the tread? It is longer in the centre with a round section tyre. The wheel is under drive and so any slip will be the centre of tread going backwards. The sides of the tread still grip the road fully and are not subjected to the same amount of wear. That the centre of the rear tyre of a bicycle slips is quite obvious when you examine the wear pattern. |
#6
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Which wheel travels furthest?
On Sat, 10 Jul 2010, Phil W Lee wrote:
Paul - xxx considered Sat, 10 Jul 2010 06:29:52 +0100 the perfect time to write: How can the centre of the tread slip without the rest of the tread? How can a tyre with a larger diameter in the middle than at the sides NOT slip, when both the middle and the edge of the tyre are spinning at the same rate, and the centre of the tread is therefore traveling faster than the sides? Are you assuming the tyre leaves a groove in the road surface? I think all points on a line across the contact patch are at the same radius (for the case of a wheel perpendicular to the road surface, but that seems to be the simplified case under discussion). That is, the middle of the contact patch does not have a larger radius than the edge of the contact patch. The radius at front and back of the contact patch varies, but it varies along the patch, not across, and the centre therefore does not slip relative to the edges. regards, Ian SMith -- |\ /| no .sig |o o| |/ \| |
#7
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Which wheel travels furthest?
On 10 July, 22:15, Ian Smith wrote:
I think all points on a line across the contact patch are at the same radius (for the case of a wheel perpendicular to the road surface, but that seems to be the simplified case under discussion). Then you are a fool. The contact patch is flat, it has no radius. That is, the middle of the contact patch does not have a larger radius than the edge of the contact patch. *The radius at front and back of the contact patch varies, but it varies along the patch, not across, and the centre therefore does not slip relative to the edges. regards, * Ian SMith -- * |\ /| * * *no .sig * |o o| * |/ \| |
#8
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Which wheel travels furthest?
On Sun, 11 Jul 2010 04:48:20 +0100, Phil W Lee wrote:
Ian Smith considered Sat, 10 Jul 2010 21:15:31 +0000 (UTC) the perfect time to write: On Sat, 10 Jul 2010, Phil W Lee wrote: Paul - xxx considered Sat, 10 Jul 2010 06:29:52 +0100 the perfect time to write: How can the centre of the tread slip without the rest of the tread? How can a tyre with a larger diameter in the middle than at the sides NOT slip, when both the middle and the edge of the tyre are spinning at the same rate, and the centre of the tread is therefore traveling faster than the sides? Are you assuming the tyre leaves a groove in the road surface? I think all points on a line across the contact patch are at the same radius (for the case of a wheel perpendicular to the road surface, but that seems to be the simplified case under discussion). I hadn't made the assumption that it was the simplified case - on an average or typical ride the tyre will act as a taper in both directions, and the tread has to move slightly against the road for this to happen. This does happen on both tyres, of course, but with one significant difference: No, that's not the same simplified case under discussion. The case I am talking about is that the wheel is perpendicular to the road surface and there is not scrubbing going on. You are not addressing scrubbing either - you are talking about the same simplified case that I am. If the tyre is inclined, then there is a differing radius, but that's not the case you're talking about because you say "larger diameter in the middle than at the sides" and in the inclined wheel case, the diameter is larger at one side than at the middle. With drive taking place through the rear, and braking largely through the front, tyre drift (one part of the contact patch slipping but with no overall loss of grip) has a tendency to be biased in opposite directions at the two wheels, and the rear will move very slightly faster than the front for the same distance covered. That's all irrelevant to the particular point, being different radii across the width of the contact patch. I don't think there are. Were you assuming the tyre indents the road? If not, how do you conclude that the tyre in contact with the road has a different radius at the middle of the contact patch than at the edges? regards, Ian SMith -- |\ /| no .sig |o o| |/ \| |
#9
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Which wheel travels furthest?
On 07/11/2010 12:25 AM, thirty-six wrote:
On 10 July, 22:15, Ian wrote: I think all points on a line across the contact patch are at the same radius (for the case of a wheel perpendicular to the road surface, but that seems to be the simplified case under discussion). Then you are a fool. The contact patch is flat, it has no radius. The same distance from the hub kind of radius you dolt! -- www.slowbicyclemovement.org - enjoy the ride |
#10
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Which wheel travels furthest?
On 11 July, 04:48, Phil W Lee wrote:
Ian Smith considered Sat, 10 Jul 2010 21:15:31 +0000 (UTC) the perfect time to write: On Sat, 10 Jul 2010, Phil W Lee wrote: *Paul - xxx considered Sat, 10 Jul 2010 *06:29:52 +0100 the perfect time to write: How can the centre of the tread slip without the rest of the tread? *How can a tyre with a larger diameter in the middle than at the sides *NOT slip, when both the middle and the edge of the tyre are spinning *at the same rate, and the centre of the tread is therefore traveling *faster than the sides? Are you assuming the tyre leaves a groove in the road surface? I think all points on a line across the contact patch are at the same radius (for the case of a wheel perpendicular to the road surface, but that seems to be the simplified case under discussion). I hadn't made the assumption that it was the simplified case - on an average or typical ride the tyre will act as a taper in both directions, and the tread has to move slightly against the road for this to happen. *This does happen on both tyres, of course, but with one significant difference: With drive taking place through the rear, and braking largely through the front, tyre drift (one part of the contact patch slipping but with no overall loss of grip) has a tendency to be biased in opposite directions at the two wheels, and the rear will move very slightly faster than the front for the same distance covered. This will be the opposite to the effect of the front tyre covering a greater distance due to steering, so the overall difference (and therefore which wheel turns further) will depend on route, tyre pressure, tyre load, weight distribution, riding style, rider strength, grip level between the road and tyre, and probably some other things I've missed. It's very likely the case that they rarely, if ever, rotate at precisely the same speed for very long. If they were to do so over the length of a few miles ride it probably would be only due to an amazing coincidence. Like going downhill on the down slope side of a hill, like, if you know what I mean! That is, the middle of the contact patch does not have a larger radius than the edge of the contact patch. *The radius at front and back of the contact patch varies, but it varies along the patch, not across, and the centre therefore does not slip relative to the edges. regards, * Ian SMith |
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