Road surface temperature and grip

[slofox]

I have just spent some time trying to dig out information on the relationship between road surface temperature (as opposed to tyre temperature) and tyre grip. (Yep. It's another slow day in the wine shop...:yawn:)
Most of what I found with the aid of the "giggle" searching device deals with stuff like ice making the road slippery...(what? slippery? ice? bullshit! :Pokey:).
I have found little (nothing actually) that deals with the difference between say a road surface at 2C (dry, no ice) and a road surface at 20C. Which is what I am interested in given that the roads are bloody cold at present, especially at the time of day I mostly ride (early morning).
So, wise gurus, what do y'all think? Is there any significant difference in that temperature range? Like up until the tar melts anyway.
My own experiences so far do not suggest a huge difference but then what the hell would I know..? :drool:

[Blackshear]

Being totally uneducated, it is my theory that tyre core temperature will have a far greater effect on grip than road temperature. Rubber = softer/stickier, more grip.

Colder blacktop would just slow the heating process, is my thought.

[YellowDog]

Another glass of wine Mr Fox ?

It is a good question. The tyre temperature is critical however it is also relative to that of what it is attempting to grip.

I remember reading somewhere that 5 degrees is the optimal road surface temperature and after 12 degrees the grip reduces depending upon the expansion properties of the surface.

I will try and see of I can find a reference to it.

[Finn]

I have just spent some time trying to dig out information on the relationship between road surface temperature (as opposed to tyre temperature) and tyre grip.

Given that while riding, you don't know the temperature of either so don't lose too much sleep over it.

Shared a bottle of 00 Grange on the weekend. Of course I ruined it with a cigar. Pity cause is was a great year.

[Jantar]

I believe a lot will have to do with the tyre design, and how much heat transfer occurs between the rubber and the road. Naturally, a colder road will slow the heat buildup in the tyre, and may even prevent the tyre from reaching its optimum temperature. It all depends on what the tyre manufacture has calculated as optimum road temperature for a particular tyre.

I can state quite confidently that Trail Attacks do not reach their optimum temperature with road temperatures below freezing, and is without any ice on the road.

[CookMySock]

I can't get my tires to talk to me at all. The old bridgestones always had something to say, especialy in the wet (sqriggle, wriggle, twitch) but the Michelins just STFU and never say anything. I'm actually a bit baffled by it.. Like, just how fast do I have to GO to make these things SAY something? Unprovokable.

Steve

[Blackbird]

Jantar is right:Punk:. What keeps you on the road of course is friction (adhesion, deformation and wear). Heat does affect the friction in that you effectively soften your compound which increases friction so yes, heat up to a point does improve grip; hence tyre warmers on circuit bikes and cars. The design of the tyre, the compound itself plus any friction modifiers (silica etc) also have a huge bearing so heat is only part of the equation. You can find a nice "primer" on the principles of tyre grip here: http://insideracingtechnology.com/tirebkexerpt1.htm. It doesn't cover tyre design, but the principles of grip are excellent.

[slofox]

Thoreau said "simplify, simplify."

So to complicate the simplification: all I want to know is how the coefficient of friction of a road surface varies with temperature in the range already stated. Nothing more. Not looking at any practical applications here. Just what the road itself does.
I told you it was a slow day...:sleep:

[AllanB]

Those V8 supercar chaps are always warbling on about track temperatures - possibly more worried as to how this will affect tyre wear, opposed to grip.

As for friction (gawd love that friction) do two cold surfaces offer less friction than two warm ones?

[slofox]

Those V8 supercar chaps are always warbling on about track temperatures - possibly more worried as to how this will affect tyre wear, opposed to grip.

As for friction (gawd love that friction) do two cold surfaces offer less friction than two warm ones?

So do the Indycar dudes according to what I did find on giggle...

[DEATH_INC.]

It definatly has an effect, try riding taupo racetrack in the winter, the first two and last session are always a bit dodgy, due to very cold track temps.

[steve_t]

I'm gonna go with basically zero change to the coefficient of friction of the road between 2 degrees and 20 degrees celcius. As has been suggested, the major factor influencing grip is getting the tyre up to operating temperature, which takes a lot longer, if at all, when it's 2 degree on the road. If the road temperature is really high and takes the tyre temp above optimal, grip is also reduced. You must have had a really boring day... I'm off to the pub :sunny:

[slofox]

I'm gonna go with basically zero change to the coefficient of friction of the road between 2 degrees and 20 degrees celcius. As has been suggested, the major factor influencing grip is getting the tyre up to operating temperature, which takes a lot longer, if at all, when it's 2 degree on the road. If the road temperature is really high and takes the tyre temp above optimal, grip is also reduced. You must have had a really boring day... I'm off to the pub :sunny:

I'm still at bloody work....have a beer for me willya?

[Starky307]

It definatly has an effect, try riding taupo racetrack in the winter, the first two and last session are always a bit dodgy, due to very cold track temps.

I'd second that. The last time I was at Taupo the first two sessions were sketchy as, it was a cold crisp friday and the tires never really "came on". By the 3rd and 4th sessions it took nothing to warm up the tires and they had amazing grip the whole session through out.

So there must be a relationship there some where.

[jono035]

Colder roads could also be a little damp, even on a clear day.

I think surface temperature would be more useful than core temperature... I think core temperature is measured simply because it takes longer to heat and longer to cool, thereby giving you a better idea of what the average temperature of your tires while actually riding is....

Also if the road is cold then it'll be soaking any heat you build up in the tires straight back out again every time the rubber comes down.

[carver]

hot tires=grip

cold tires=most bins wins

[Blackbird]

Thoreau said "simplify, simplify."

Thoreau clearly wasn't a physicist:laugh::laugh:. Road temperatures are largely irrelevant in themselves other than their ability to keep your tyres hot and elastic, which is, as the good people have said; bloody important:innocent:. Of course, when the road gets too hot, you lose grip, tar goes everywhere and then you have to take to your bike with a rag and WD40 to get the stuff off.

Nothing's ever simple:innocent:

[Mikkel]

So to complicate the simplification: all I want to know is how the coefficient of friction of a road surface varies with temperature in the range already stated. Nothing more. Not looking at any practical applications here. Just what the road itself does.
I told you it was a slow day...:sleep:

The coefficient of friction describes how two surfaces interact - the road, in itself, does not have a coefficient of friction.
What Jantar and Blackbird said is spot on - but I would like to add to it:

Tyres warm up in two way:
1. Through friction with the surface during acceleration, braking and cornering.
2. Through deformation - i.e. the flexing of the tyre when travelling along the road.

Mechanism 1. happens only at the surface of the tyre whereas 2. happens throughout the entire cross-section of the tyre. On a cold road mechanism 1. will be less effective and if you are riding sedately on a cold day you may never gain any heat gain from 1. at all.

2. on the other hand takes place all the time that the wheel turns and since it happens throughout the tyre - not just at the surface - the heat will be retained for longer.
The larger the deformation of the tyre the greater the heat gain. Tyre deformation, generally speaking, depends upon the total weight of the vehicle, tyre volume and tyre pressure. The heavier the vehicle - the larger the deformation. The larger the tyre - the larger the deformation. Higher tyre pressure - smaller deformation.

So, on a cold surface it might be worth while dropping your pressures a little bit to allow more heat build-up in your tyres.

[cowpatz]

I would imagine the tyre pressure would have to be reduced significantly in order to get sufficient deformation to incease tyre temps by any noticeable margin. Any gains would be hard to measure as they would be offset by the effects of a consequential larger footprint area and the change to the handling characteristics due to tyre profile change and the increased sidewall flex.

[Blackbird]

I would imagine the tyre pressure would have to be reduced significantly in order to get sufficient deformation to incease tyre temps by any noticeable margin. Any gains would be hard to measure as they would be offset by the effects of a consequential larger footprint area and the change to the handling characteristics due to tyre profile change and the increased sidewall flex.

Yep:Punk:. With a lardy bike like the 'bird, the bike is really sensitive to tyre pressures because of carcass flex. The standard pressure of 42psi front and rear is higher than a true sports bike largely because the 'bird is 230 kg dry as opposed to (say) 170 kg for a sports bike. Even an incompetent like me can feel a deterioration in handling if the tyre pressure drops below 38-40 psi! It's also why I can't use a lot of tyres which are suitable for sports bikes because the carcass construction simply isn't strong enough. The attached photo shows a Dunlop D220 tyre I had on the 'bird about 6 years go. The weight of the 'bird and its tendency to "push" the front in standard trim, caused sidewall flex when cornering and the "triangling/cupping" wear pattern is really noticeable. When Avon released their "B" spec Azaro and later the Storm which both had additional sidewall reinforcing, the problem went away.

It's a complicated old world, innit?

[captain_andrey]

Of course the temperature of both surfaces is important. Road, believe it or not, also flexes under the load of the tyre. On a microscopic level, there is always a difference.
Google came up with this one study on static friction co-efficient of materials relative to temperature of the material.
http://www.idspackaging.com/Common/Paper/Paper_458/Material%20Friction%20Coefficient.htm
This will also be incredibly easy to test if you have some spare time.