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Short article on theory of tire/road friction


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#1 Widefoot2

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Posted 20 May 2015 - 20:15

http://www.aip.org/p...bber-meets-road

 

German scientist Bo Persson has been working on tire friction theories for 20 years, this article is a simplified view of his work.  Curious what people here think of it.



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#2 Greg Locock

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Posted 21 May 2015 - 00:08

Nothing to argue with, only problem I see is that it is the usual description as given in many books! Trick question - why does rubber wear?



#3 gruntguru

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Posted 21 May 2015 - 05:16

Exceeding the shear strength of the rubber at the local (micro) scale? (Just an intuitive guess)

 

eg only at the highest asperities in the road surface for low values of slip - increasing to most of the contacting surface at high slip values.



#4 mariner

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Posted 21 May 2015 - 11:45

I am no chemist, tyre engineer or any kind of engineer actually so my only thought is that any tyre friction model has to explain why the co efficient of grip is largely independent of rotational speed  - the grip doesnt seem to change much with wheel speed or small vs large tyres as far as I know - which isnt too much!

 

Does the molecular attraction, dis engagement -  reattachment proces he describes happen so fast that wheel speed wil never affect it?



#5 DaveW

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Posted 21 May 2015 - 13:23

Extract from the linked article: "The amount of lost energy is related to the texture of the road, which is why rough roads generally cause more slowing friction than smooth surfaces."

 

Comment: The dampers also dissipate energy, around 80 percent of energy consumed on a rig - for what that is worth...



#6 MatsNorway

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Posted 21 May 2015 - 13:29

is thats alot of heat? Does dampers ever run hot? ive never seen dampers with cooling ribs or anything else.



#7 munks

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Posted 21 May 2015 - 17:41

Nothing to argue with, only problem I see is that it is the usual description as given in many books!

 

Agreed, I thought most of this was pretty well known. In fact I thought Persson's main contribution wasn't really mentioned in the article (or at least not directly), which is the flash temperature stuff.

 

Trick question - why does rubber wear?

 

Mmm, ozone?



#8 Fat Boy

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Posted 21 May 2015 - 19:05

Trick question - why does one wear a rubber?

 

 

Honestly, Greg, get your mind out of the gutter.



#9 DaveW

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Posted 21 May 2015 - 20:29

is thats alot of heat? Does dampers ever run hot?

Not necessariy, though rally car dampers often do run hot.  In endurance testing it is common the run dampers with water cooling.

 

The actual figures for my road car example were 83% dampers and 10% tyres. The missing 7% was dissipated by everything else (mostly engine mounts).



#10 Greg Locock

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Posted 21 May 2015 - 22:27

Road car shocks do run hot, for example on corrugated roads, it is one of the sizing parameters we use, that is what volume of oil do we need and what outer tube diameter, hence surface area. 

 

In the little spaghetti diagram the end of the spaghetti that is welded to the asphalt breaks off, hence leaving rubber on the road.



#11 MatsNorway

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Posted 22 May 2015 - 09:08

There is allways some slip. Trains have slipage too. And that is often a issue with central europe trains. They have more slippage allowed to get going.. but in Norway all you do is uphill and downhill, tight corners left and right, add some snow too pretty much. So locomotives from central europe wears out their wheels in no time. Alot has to do with the load ofc.. so they try to replace the 6 axled locomotive with a new and fancy 4 axled locomotive that also is lighter.. on paper it does the trick.. as the wheelspinn stuff is not mentioned.


Edited by MatsNorway, 22 May 2015 - 09:09.