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What makes soft tires creep on rims?
What is the process by which soft tires creep on rims when the
tire is underinflated, even with no applied torque? I have a CycleTote trailer that uses standard 26" wheels. I tend to keep the tires quite soft, just a few psi, partly out of neglect and partly because the trailer is less inclined to bounce at low tire pressure. The beads seem firmly seated, the tire can't be slipped on the rim by hand. Over time, the valve stems become inclined in a direction that suggests the rim is rotating backwards relative to the tube. There's no torque applied to either tire or rim, so what is driving the motion? Thanks for reading, bob prohaska |
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What makes soft tires creep on rims?
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What makes soft tires creep on rims?
On Wed, 12 Jul 2017 01:12:30 -0000 (UTC), bob prohaska
wrote: What is the process by which soft tires creep on rims when the tire is underinflated, even with no applied torque? I have a CycleTote trailer that uses standard 26" wheels. I tend to keep the tires quite soft, just a few psi, partly out of neglect and partly because the trailer is less inclined to bounce at low tire pressure. The beads seem firmly seated, the tire can't be slipped on the rim by hand. Over time, the valve stems become inclined in a direction that suggests the rim is rotating backwards relative to the tube. There's no torque applied to either tire or rim, so what is driving the motion? When you under-inflate the tire, the inner tube loose contact at a few points with the inside of the tire. That creates a situation where the circumference of the inner tube and the tire are slightly different. Visualize what happens when two circles of unequal diameter and a common point of contact on the ground. As they roll forward, the inner circle rotates at a different rate than the outer circle causing the two circles to change relative position. The difference in circumferences are very small, but large enough to cause creep. When the inner tube and tire are properly inflated, the inner tube and tire are locked together by the tire pressure, so no relative rotation (creep) is possible. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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What makes soft tires creep on rims?
Week wrote
The contact surface piles a rubber wall. That resistance or pressure ahead is greater than the pressure before contact or during contact, exerting the systems retro motion. Found whrr 'grip' is more effective than 'roll' The motion is energy loss or energy soak off n should be designed or applied out of the total system. I guess finding it is misapplication of tire n rim |
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What makes soft tires creep on rims?
On 7/11/2017 8:12 PM, bob prohaska wrote:
What is the process by which soft tires creep on rims when the tire is underinflated, even with no applied torque? I have a CycleTote trailer that uses standard 26" wheels. I tend to keep the tires quite soft, just a few psi, partly out of neglect and partly because the trailer is less inclined to bounce at low tire pressure. The beads seem firmly seated, the tire can't be slipped on the rim by hand. Over time, the valve stems become inclined in a direction that suggests the rim is rotating backwards relative to the tube. There's no torque applied to either tire or rim, so what is driving the motion? It's not specific to torque[1]. The deformation at the bottom where your tire squishes out is cyclical, changing the pressure outward against the inner face of the rim, briefly higher, then lower. This effect is seen more dramatically at below-optimal tire pressures. One might suspect torque because the rear is usually more pronounced but I believe that's proportional to load. [1] Wheelbarrows and other carts do this as well. -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
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What makes soft tires creep on rims?
On Tuesday, July 11, 2017 at 7:46:46 PM UTC-7, Jeff Liebermann wrote:
On Wed, 12 Jul 2017 01:12:30 -0000 (UTC), bob prohaska wrote: What is the process by which soft tires creep on rims when the tire is underinflated, even with no applied torque? I have a CycleTote trailer that uses standard 26" wheels. I tend to keep the tires quite soft, just a few psi, partly out of neglect and partly because the trailer is less inclined to bounce at low tire pressure. The beads seem firmly seated, the tire can't be slipped on the rim by hand. Over time, the valve stems become inclined in a direction that suggests the rim is rotating backwards relative to the tube. There's no torque applied to either tire or rim, so what is driving the motion? When you under-inflate the tire, the inner tube loose contact at a few points with the inside of the tire. That creates a situation where the circumference of the inner tube and the tire are slightly different. Visualize what happens when two circles of unequal diameter and a common point of contact on the ground. As they roll forward, the inner circle rotates at a different rate than the outer circle causing the two circles to change relative position. The difference in circumferences are very small, but large enough to cause creep. When the inner tube and tire are properly inflated, the inner tube and tire are locked together by the tire pressure, so no relative rotation (creep) is possible. Errr, no. The creep is a rather simple thing. It's when the coefficient of drag (traction) of the tire on the ground exceeds that of the tire on the inside edge of the rim. You don't need power in nor braking power for this to occur. The tire is generally locked onto the inside edge of the rim by the inflation pressure. |
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What makes soft tires creep on rims?
On Wednesday, July 12, 2017 at 9:12:00 AM UTC-4, AMuzi wrote:
On 7/11/2017 8:12 PM, bob prohaska wrote: What is the process by which soft tires creep on rims when the tire is underinflated, even with no applied torque? I have a CycleTote trailer that uses standard 26" wheels. I tend to keep the tires quite soft, just a few psi, partly out of neglect and partly because the trailer is less inclined to bounce at low tire pressure. The beads seem firmly seated, the tire can't be slipped on the rim by hand. Over time, the valve stems become inclined in a direction that suggests the rim is rotating backwards relative to the tube. There's no torque applied to either tire or rim, so what is driving the motion? It's not specific to torque[1]. The deformation at the bottom where your tire squishes out is cyclical, changing the pressure outward against the inner face of the rim, briefly higher, then lower. This effect is seen more dramatically at below-optimal tire pressures. One might suspect torque because the rear is usually more pronounced but I believe that's proportional to load. [1] Wheelbarrows and other carts do this as well. -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 all said with math perfect models in mind gradually moving to degrade after dropping the wheel into a sewer grate air pressure moves around from contact ...prob doesn't take much degrade setting it in substantial motion I never notices a prob here always riding in advanced degrade |
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What makes soft tires creep on rims?
On Wednesday, July 12, 2017 at 10:06:17 AM UTC-7, Jeff Liebermann wrote:
On Wed, 12 Jul 2017 07:26:17 -0700 (PDT), wrote: On Tuesday, July 11, 2017 at 7:46:46 PM UTC-7, Jeff Liebermann wrote: On Wed, 12 Jul 2017 01:12:30 -0000 (UTC), bob prohaska wrote: What is the process by which soft tires creep on rims when the tire is underinflated, even with no applied torque? I have a CycleTote trailer that uses standard 26" wheels. I tend to keep the tires quite soft, just a few psi, partly out of neglect and partly because the trailer is less inclined to bounce at low tire pressure. The beads seem firmly seated, the tire can't be slipped on the rim by hand. Over time, the valve stems become inclined in a direction that suggests the rim is rotating backwards relative to the tube. There's no torque applied to either tire or rim, so what is driving the motion? When you under-inflate the tire, the inner tube loose contact at a few points with the inside of the tire. That creates a situation where the circumference of the inner tube and the tire are slightly different. Visualize what happens when two circles of unequal diameter and a common point of contact on the ground. As they roll forward, the inner circle rotates at a different rate than the outer circle causing the two circles to change relative position. The difference in circumferences are very small, but large enough to cause creep. When the inner tube and tire are properly inflated, the inner tube and tire are locked together by the tire pressure, so no relative rotation (creep) is possible. Errr, no. The creep is a rather simple thing. It's when the coefficient of drag (traction) of the tire on the ground exceeds that of the tire on the inside edge of the rim. You don't need power in nor braking power for this to occur. The tire is generally locked onto the inside edge of the rim by the inflation pressure. Yep, that's another explanation. Please note that the OP mentioned that: I tend to keep the tires quite soft, just a few psi, partly out of neglect and partly because the trailer is less inclined to bounce at low tire pressure. The beads seem firmly seated, the tire can't be slipped on the rim by hand. As far as I can recall, the only tube type tires that I've seen creep were on under-inflated tires. There may also have been a problem where someone used far too much baby powder, or smooth surface rim tape. I don't recall those. It is possible that the tire is slipping on the rim with under-pressure. However, it's my contention that the tube is what is moving relative to the tire, and that the rim and tire remain in place. It would be easy enough to test by putting simply marks on both the tire and rim to see they move relative to each other. Jeff, the exact same thing will happen if you use the locking screw on the filler value. Test it. Install the tire with the name centered on the filler. Ride it with less than minimum pressure for any distance the tire tube will remain vertically though because of sticking to the rotating tire it CAN tear the filler out. But the name can move a long way from where it started. |
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What makes soft tires creep on rims?
On Wednesday, July 12, 2017 at 6:12:00 AM UTC-7, AMuzi wrote:
On 7/11/2017 8:12 PM, bob prohaska wrote: What is the process by which soft tires creep on rims when the tire is underinflated, even with no applied torque? I have a CycleTote trailer that uses standard 26" wheels. I tend to keep the tires quite soft, just a few psi, partly out of neglect and partly because the trailer is less inclined to bounce at low tire pressure. The beads seem firmly seated, the tire can't be slipped on the rim by hand. Over time, the valve stems become inclined in a direction that suggests the rim is rotating backwards relative to the tube. There's no torque applied to either tire or rim, so what is driving the motion? It's not specific to torque[1]. The deformation at the bottom where your tire squishes out is cyclical, changing the pressure outward against the inner face of the rim, briefly higher, then lower. This effect is seen more dramatically at below-optimal tire pressures. One might suspect torque because the rear is usually more pronounced but I believe that's proportional to load. [1] Wheelbarrows and other carts do this as well. How about underwear? Is this the same mechanism by which, when you're pretending you're mario andretti, and driving 95 up such-and-such canyon-road, your underwear creeps up until you are in a wedgie, about to be strangled? |
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