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Henry Dorset Case
Mangled
Joined: Apr 10, 2002
Posts: 10,326
Location: Talos IV
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 Posted: Tue 1/Jul/08 2:43pm Post subject: |
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Ive read a really good article about this in the context of motorcycle tyres. I will see if I can find linkage.
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Oli
Mangled
Joined: Aug 03, 2005
Posts: 32,945
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| Posted: Tue 1/Jul/08 2:48pm Post subject: |
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| Henry Dorset Case wrote: | | I think we're talking about HOW tyres grip at the molecular interface level, yes? |
I'm not. I'm talking about how in the real world tyres with less pressure in will grip better on ice that tyres pumped up to 140psi.
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danose
Mangled
Joined: May 27, 2004
Posts: 10,986
Location: Nose City
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| Posted: Tue 1/Jul/08 3:02pm Post subject: |
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| Oli wrote: | How do the tyres melt the ice, Danose? What a bunch of horsetihs!  |
exact same physics that floats glaciers down mountains on a thin film of water - obviously physics wasn't your fave subject at school eh!?
http://www.buzzle.com/editorials/8-30-2004-58620.asp
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Oli
Mangled
Joined: Aug 03, 2005
Posts: 32,945
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| Posted: Tue 1/Jul/08 3:06pm Post subject: |
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Er, that's a hamburger, Danose.
Tell me what physical force melts the ice under your road tyres. Is it heat? If so, where from? Friction? A glacier moving is a slightly different array of forces, it would seem to me.
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danose
Mangled
Joined: May 27, 2004
Posts: 10,986
Location: Nose City
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| Posted: Tue 1/Jul/08 3:07pm Post subject: |
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| Oli wrote: | Er, that's a hamburger, Danose.
Tell me what physical force melts the ice under your road tyres. Is it heat? If so, where from? Friction? A glacier moving is a slightly different array of forces, it would seem to me. |
it's pressure - jesus wept oli, why do you think it's called pressure melting
go cut an ice cube with a piano wire if you don't believe me
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CaptainCaveman
Mangled
Joined: Jun 18, 2004
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| Posted: Tue 1/Jul/08 3:09pm Post subject: |
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pb
Thrashed
Joined: Jul 31, 2005
Posts: 1,887
Location: Christchurch
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| Posted: Tue 1/Jul/08 3:09pm Post subject: |
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Wait a minute, more pressure gives more water, gives more lubrication. So higher contact pressures give more slippage.
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mfw
Scuffed
Joined: Nov 22, 2007
Posts: 339
Location: Out of breath in the port hills
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| Posted: Tue 1/Jul/08 3:10pm Post subject: |
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This demo uses ice cubes and string - a bit more convenient than the glaciers:
http://dimdima.com/Science/science_common/show_science.asp?q_aid=184&qblahblahblah
I suppose you want either the largest contact patch possible to get some grip on a slippery surface, or the smallest contact patch possible which will may melt ice, and avoid no mans land inbetween (where I was this morning).
I guess if you look at rally cars and they use super skinnies in some conditions
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Oli
Mangled
Joined: Aug 03, 2005
Posts: 32,945
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| Posted: Tue 1/Jul/08 3:11pm Post subject: |
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How about you go and ride on some ice with tyres at varying pressures? That's what I'm talking about, not glaciers or piano wires.
I simply don't believe there is enough pressure to melt the ice away from a tyre tread.
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pb
Thrashed
Joined: Jul 31, 2005
Posts: 1,887
Location: Christchurch
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| Posted: Tue 1/Jul/08 3:11pm Post subject: |
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I think the melting theory would only apply if you could melt all the ice under the tire, not just the top layer.
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crossalis
Dusty
Joined: Mar 07, 2007
Posts: 126
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| Posted: Tue 1/Jul/08 3:15pm Post subject: |
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 I like kittens!
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JohnnyC
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Joined: Jan 31, 2003
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Location: Christchurch
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| Posted: Tue 1/Jul/08 3:16pm Post subject: |
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| danose wrote: | | JohnnyC wrote: | This is right but last time I checked, road bike tyres sliding was a bad thing
I don't see how that principle increases grip |
but roadie tires don't spin out climbing dyers in the wet though
tyres melts ice, water gets displaced by tyre, tyre grips (nearly dry) tarmac |
So in the moment the tiny contact patch is touching the ice it melts all the way through and grips the tarmac? I can understand how that would work on a little bit of frost but not on a frozen puddle
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inzane
Wrecked
Joined: Feb 23, 2005
Posts: 6,642
Location: churchur
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| Posted: Tue 1/Jul/08 3:18pm Post subject: |
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just because of the nature of rubber, I dont think that enough pressure will ever be applied to a tyre to melt the ice underneath from pressure... and even if it did the water would be melted under a flat plane of the tyre making it slip just as easily.
There is never going to be a rubber edge sharp enough to melt a divot into the ice to give you grip. Little metal spikes sitting out of the rubber in the tyre, sure I can see those melting the surrounding ice due to pressure and gripping... but I am with Oli here. Lower pressure tyre causing more surface area will give you better traction on the ice.
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CaptainCaveman
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Joined: Jun 18, 2004
Posts: 11,500
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| Posted: Tue 1/Jul/08 3:21pm Post subject: |
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| inzane wrote: | just because of the nature of rubber, I dont think that enough pressure will ever be applied to a tyre to melt the ice underneath from pressure... and even if it did the water would be melted under a flat plane of the tyre making it slip just as easily.
There is never going to be a rubber edge sharp enough to melt a divot into the ice to give you grip. Little metal spikes sitting out of the rubber in the tyre, sure I can see those melting the surrounding ice due to pressure and gripping... but I am with Oli here. Lower pressure tyre causing more surface area will give you better traction on the ice. |
I think you are both half right - raising pressure won't have any real world affect - neither will lowering the pressure. Ice is just too slippery.
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inzane
Wrecked
Joined: Feb 23, 2005
Posts: 6,642
Location: churchur
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| Posted: Tue 1/Jul/08 3:25pm Post subject: |
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| CaptainCaveman wrote: | | inzane wrote: | just because of the nature of rubber, I dont think that enough pressure will ever be applied to a tyre to melt the ice underneath from pressure... and even if it did the water would be melted under a flat plane of the tyre making it slip just as easily.
There is never going to be a rubber edge sharp enough to melt a divot into the ice to give you grip. Little metal spikes sitting out of the rubber in the tyre, sure I can see those melting the surrounding ice due to pressure and gripping... but I am with Oli here. Lower pressure tyre causing more surface area will give you better traction on the ice. |
I think you are both half right - raising pressure won't have any real world affect - neither will lowering the pressure. Ice is just too slippery. |
Yes, lowering the pressure will probably give you only the tiniest fraction more traction... which is quite likely to not be enough to keep you on your bike... but that is beside the point!! It is the principle of the matter!!
I am right, Danose is wrong 
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