Road Surface Effects

[Jersey Tom]

But firstly, what sort of track surfaces did you see this on?? Concrete aggregate? Textured concrete?? Asphalt? Dirt??

Asphalt.

As racing tyres employ soft compounds, a large degree of its CoF comes from mechanical keying and chemical bonding.

Not sure I particularly like the term "mechanical keying." Nor that I would necessarily say a large portion of force generation is from chemical bonding. I would say that force generation is largely proportional to hysteretic loss. But in that case, I can have a "harder" compound create more "grip" than a "softer" compound even if it has less indentation to the track.

Sure if a track has NEVER been run on, then aside from really poor track preparation, oils and debris could act as a lubricant and cause a lower grip level.

Well that's what we're talking about, no? A track that hasn't been run on? And I'd say it's more than just a dusty or dirty track. While that's part of it for the first few laps... I'd say my experience is that a racetrack will continue to get faster after days of hard running. The surface really needs to be burnished in for the grip level to become consistent.

In any event, this...

Several readings were taken from the machine, in order to ensure an accurate representation. Using these readings a virtual representation of the track from the tyre’s point of view can be created on computer.

Together with some asphalt samples from the new venue, this allowed Pirelli to calculate the likely wear rate and the effect of the asphalt and ambient temperatures on the tyres at different points on the circuit."

... my gut feeling is that's an awfully big stretch from their marketing department. Or I'm sure they can come up with a "calculation" but any degree of accuracy is a big mountain to climb.

In any event, my assessment is this: Brand new track is slow and will pick up speed as it's initially worn in and stabilizes. Until then it's very difficult to assess setup changes or performance relative to the field because any time you make an outing... even if you don't change the car at all... you'll go faster. From a tire company perspective repaves can be hell, as the speeds and loads wind up being high and the tires don't wear much or at all. As a result you end up with quite high tread temperatures and durability concerns.

Beyond that, it's been a while since I've read his book(s) but many of Paul's assertions with tires I've found to be questionable at best and incorrect at worst. As such, I'm wary of just about all of it.

[Jersey Tom]

I'll go a bit further and hand wave here some myself.

I'd say it is established in public domain literature on rubber tribology that a given tire will work best when excited in a specific frequency range or length scale of the track on which it's running. Perhaps it is that brand new asphalt is too fine and requires some running and use to wear off the ultra fine grit and expose some of the small aggregate to get maximum "grip." After this time as the track wears and you expose larger and larger aggregate, lose effective contact area maybe, and in any event lose traction.

That's not much more than speculation, but it's still directly opposite the assumption that a track gets smoother as you drive on it or wear it out.

[DaveW]

This:

http://www.racetechmag.com/articles/article.php?id=17

and following episodes might help, perhaps.

[hardingfv32]

If the track hasn't been prep'd Bernie won't let it run. If there's excess sand then there could be tantrums.

Does a "First Lap Ceremony" count as running? That is it for track time.

There is nothing Bernie can complain about. The ultra smooth surface/finish of a new asphalt roadway cannot be avoided. Chances are very good that the track will have a very narrow groove lined with the small sandy aggregate that is lifted from the new surface.

Brian

[aussiegman]

This:

http://www.racetechmag.com/articles/article.php?id=17

and following episodes might help, perhaps.

Thanks Dave you're a legend (+1 for you )

This was one of the articles I had remembered reading somewhere and I was looking for last night in the folders of Racetech mags I have sitting on the shelves behind me but to no avail. Cheers mate, saved me going insane trawling through back issues =D>

[aussiegman]

OK, let me start off by saying I am not trying to be a “d*ck”, I’m just having an interesting conversation with persons that seem to know something on the subject.

Asphalt

I wasn’t sure what track surface you NASCAR guys do most of your running on. I though NASCAR ran on concrete and asphalt tracks but it must be hard with varying surfaces etc.

Not sure I particularly like the term "mechanical keying."

OK, why??

If not described as mechanical keying or mechanical deformation, what would you call it?? As you rightly point out “force generation is largely proportional to hysteretic loss”. So how does this “hysteretic loss” physically manifest itself in a tyre? Primarily as heat energy in the tyre carcass while secondary energy is lost to sound production is my understanding.

So in undergoing the processes of hysteretic loss, this imparts to the tyre a higher energy state which alters the viscosity of polymers forcing it to undergo transitions into or through its higher energy viscous or molten states. This in turn sees a more fluid polymer which can undergo higher degrees of plastic deformation at the tyre tread/track surface interface. This in turn increases the surface area due to deformation and provides for mechanical keying into the surface.

So perhaps it’s my (limited) understanding of what actually hysteretic loss is, how it effect the tyre and how it changes the interaction of the tyre with the track surface.

In a tyre, (my understanding) hysteretic loss occurs where there exists an energy difference between the energy input (seen as tyre deformation of the tread face and sidewall) versus energy output (energy used to return the tyre to its previous state) and the difference is accounted for as heat and sound energy which is required by the law of conservation of energy.

As previously discussed in the “Define tyre grip” thread, tyres are made of deformable polymers which are designed for optimum temperature and time ranges where their plastic deformation due to hysteretic loss energies can be used to provide mechanical keying into and adhesion onto the track surface.

So as the tyre rotates, the tyre tread face impacts the track surface and the entire tyre carcass and tread face is distorted by the vertical and horizontal forces acting on the tyre. This forms an interface between the track surface and the polymer compound of the tyre where the tread face deforms around the irregularities in the surface. These can effects are seen in irregularities from sub-millimeter to millimeter sizes. This is what I understand to be mechanic keying. The Racetech editorial by Pat SYMONDS (thanks again Dave) describes this as “asymmetric deformation”. Mechanical keying or asymmetric deformation due to high energy visco-elastic polymers within the tread face due hysteretic loss would seem to be one and the same.

Pat’s editorial also goes some way to helping describe my example of wet track lines and there being more grip off line due to increased mechanical keying by showing this can take place in the presence of a water film (wet track) where film thickness is not sufficient enough to prevent indention of the rubber into the track surface. It also helps to show one of the reasons (not the only reason) as to why wet weather tyres are typically made of much “softer” or more deformable polymers as they rely to a greater degree on the effect of mechanical keying into the surface for friction or "grip".

Nor that I would necessarily say a large portion of force generation is from chemical bonding.

OK, so chemical bonding which I more simply described adhesion (which includes various forms of dispersive and chemical adhesion) is the interaction of the track surface and the tyre polymer. Again, the Racetech editorial described this more eloquently than me, providing that “molecular adhesion” was the Van Der Waals forces between the track surface and the tyre polymer and he equates this force as having an orders of magnitude of 10 to 100 times greater than that seen in more rigid non visco-elastic materials, like a cold tyre.

In addition to the Van Der Waals forces, a tyres dispersion adhesion is dependent on the effects of “wetting” between the viscous polymer and the track surface which is to various degrees further dependant on thermodynamic compatibility of two surfaces and surface “roughness” or texture. This interacts with the Van Der Waals force and can increase the adhesive strength.

The track surface consists of both high energy (the aggregate stones) and low energy (the bitumen matrix) surfaces, however the high energy aggregate forms the largest percentage of the surface for interaction. I have seen some modeling on this which was described as the wetting of non-ideal rough surfaces but it was years ago back at university so would struggle to talk intelligently on it without revision.

However again, the Racetech editorial seems to agree that “a large degree" of a tyres "grip" or CoF comes from mechanical keying described as asymmetric deformation and chemical bonding described as molecular adhesion. Pat SYMONDS specifically lists these two interactions under the sub heading of “Mechanisms of tyre grip”.

I would say that force generation is largely proportional to hysteretic loss.

There is a difference in defining the mechanisms of tyre CoF or “grip” as opposed to determining the proportionality of the effect on a tyre’s "grip" or CoF from the of various forces and energies enacted upon it.

So while force generation (seen as an increase or decrease in the tyres CoF) may be proportional to hysteretic loss, the energy involved influences the systems whereby the tyre enacts with its surroundings to generate a CoF in the first instance. Energy in, effect resulting from energy and energy out.

So while I don’t generally disagree that the hysteric losses proportionally effect force generation, I think your statement argues that hysteretic loss is the system from which the tyre's CoF is derived rather than only an influence on the mechanisms which the tyre derives its CoF.

A tyre's CoF is a result of chemical and mechanical interactions on a micro and macro scale that are directly impacted by energies imparted to the tyre from hysteric losses. Hysteric loss, which is only an energy state descriptor, does not in and of itself provide any actual CoF to the tyre but merely affects those systems that do.

But in that case, I can have a "harder" compound create more "grip" than a "softer" compound even if it has less indentation to the track.

How so?? The chemical bonding relies on surface area contact which increases with hysteretic loss due to heat energy input into the tyre allowing greater degrees of plastic deformation (flow) due to the polymers visco-elastic properties. A hard compound tyre will not indent to the same degree and so have a considerably lower lower surface area for bonding to take place and as such will generate a lower CoF or “grip”.

It is the same principle by which that the ubiquitous racer favorite, race tape / 100MPH tape / helicopter tape or duct tape works. Duct tape works better once you provide a force to press it in to or on to a surface. Use force to press it down and you increase the surface area of contact increasing the adhesive “chemical” bonding between the two surfaces. As said, these increase by orders of magnitude as surface area contact increases. Whereas, if you gently lay it on a hard surface without providing a force to it you can reasonably easily remove it as there is less adhesion.

So any hard compound tyre would only be “harder” when in it is in a low energy state prior to experiencing hysteretic loss through use which generates heat. If the tyre had a suitably high Glass Transition temperature then it would never undergo transition from a rigid solid to a molten or visco-elastic fluid and the required “asymmetric deformation" whioch increases surface area for chemical and mechanical bonding would not be able to take place and provide increases in the tyres CoF or grip.

Whereas if a softer compound tyres polymers, as an amorphous solid, have a sufficiently low Glass Transition temperature, whereby it starts as a generally rigid solid then transitions to a visco-elastic fluid once it has transited past the Glass Transition temp, it would be able to undergo greater degrees of plastic deformation and have a higher degree of indentation into the track surface due to the energy input from hysteretic loss in the tyre generating heat. This increases the surface area of the tyre/track surface interface increasing chemical bonding mechanisms of Van Der Walls and dispersion adhesion as well as the asymmetric deformation properties of the tyre.

Well that's what we're talking about, no? A track that hasn't been run on? And I'd say it's more than just a dusty or dirty track. While that's part of it for the first few laps...

I was under the impression there had been more running at COFA than Brian’s indicated “ceremonial laps” performed so far, but if you know otherwise I will bow to your first hand knowledge as I am only hearing this 3rd and 4th hand.

I'd say my experience is that a racetrack will continue to get faster after days of hard running. The surface really needs to be burnished in for the grip level to become consistent.

Again, I disagree with you but can understand what you’re saying and think what you are describing as "burnishing" is the "rubbering up" of the track over consecutive days of running. I think perhaps we are simply looking at different time horizons for the change. I absolutely agree a track gets faster as it rubbers up and as long it is doesn't rain of get oil, sand or other dumped all over it, tracks generally get faster over the course of an event.

However over a greater time horizon, a new track (less than 1 month old with little use and proper preparation) will have more grip than an older track (greater than 1 year, with regular use) due to aggregate wear. The quotes “delacf” provided seemed to generally indicate differences of tracks over a wider time horizon due to wear while also showing that a tracks characteristics change as it “rubbers up”.

In any event, this...

Several readings were taken from the machine, in order to ensure an accurate representation. Using these readings a virtual representation of the track from the tyre’s point of view can be created on computer.

Together with some asphalt samples from the new venue, this allowed Pirelli to calculate the likely wear rate and the effect of the asphalt and ambient temperatures on the tyres at different points on the circuit."

... my gut feeling is that's an awfully big stretch from their marketing department. Or I'm sure they can come up with a "calculation" but any degree of accuracy is a big mountain to climb.

Pirelli have photos of their staff at the track with measuring equipment and I have seen tyre manufacturers doing exactly the same thing at Australia’s Phillip Island before motoGP races.
Again Pat SYMONDS describes that Bridgestone “measures this (micro and macro roughness) using an optical device that determines the height of surface irregularities in representative parts of the track.”

So while they would likely be averaging the results, they would be measuring the sizes and “roughness” of the aggregate chips in the tarmac to properly assess a tracks ability to provide “grip”.

In any event, my assessment is this: Brand new track is slow and will pick up speed as it's initially worn in and stabilizes. Until then it's very difficult to assess setup changes or performance relative to the field because any time you make an outing... even if you don't change the car at all... you'll go faster. From a tire company perspective repaves can be hell, as the speeds and loads wind up being high and the tires don't wear much or at all. As a result you end up with quite high tread temperatures and durability concerns.

Beyond that, it's been a while since I've read his book(s) but many of Paul's assertions with tires I've found to be questionable at best and incorrect at worst. As such, I'm wary of just about all of it.

BTW, whose “Paul”?? Anyway, for a brand new, not prep’d, not washed, not dressed track maybe sure. I’ll concede that it might be slow and get faster over the weekend. However, compare the same track as with a sub 1 month aged surface and the same surface after use of say greater than 1 year or even 2 to 3 years constant use and I would expect the new track however prep’d to record faster times as was borne out in CART’s experience with ’96 the Laguna Seca resurface. I did a little more searching on this and the CART cars were apparently 1 to 3 seconds slower a six months later when they returned.

I would also agree that more aggressive surface could very well cause durability and heat issues as this is exactly what happens when you run on the high grip surfaces at Paul Ricard, it tears and overheats the tyres very quickly due to masses of inherent “grip”. But that’s a different discussion.

[aussiegman]

I'll go a bit further and hand wave here some myself.

I'd say it is established in public domain literature on rubber tribology that a given tire will work best when excited in a specific frequency range or length scale of the track on which it's running.

This is where I know only enough to be dangerous.

A polymers frequency is (as much as I know) determined in simplistic terms by the speed at which is can stretch vs, the speed at which it break. To fast it breaks, slow enough it stretches and reforms. Again (thanks Dave) the Racetech article describes this very eloquently and basically sets down that a tyres polymer can considered (in my words) as a Non-Newtonian Fluid whose viscosity rate is dependent on shear rate and/or shear rate history which renders it as a thixotropic or "shear thinning" visco-elastic fluid.

I do not see a correlation between induced harmonic frequencies due to surface structure as the descriptor here, more as described in the Racetech article it is the "molecular frequency" or the rate of change over time at which the polymer is expected to stretch and return to equilibrium before it looses its ability to deform which woudl seem to have more correlation to wheel rotational speed.

Again a simple example can be seen with a small amount of hair gel in between two fingers. Move the fingers apart slowly and long, thin strands will form as the fluid retains its visco-elastic properties. Move them apart quickly and the fluid ceases to be viscous and looses its visco-elastic properties and the strands snap or never form.

Perhaps it is that brand new asphalt is too fine and requires some running and use to wear off the ultra fine grit and expose some of the small aggregate to get maximum "grip." After this time as the track wears and you expose larger and larger aggregate, lose effective contact area maybe, and in any event lose traction.

That's not much more than speculation, but it's still directly opposite the assumption that a track gets smoother as you drive on it or wear it out.

This effect might be seen where the tyre polymer cannot deform on a small enough scale to undergo effective deformation into the track surface, however I doubt this to be the case as the post race markings on a race tyre should very small (sub-millimeter) imperfections on the tread face. There may indeed be a small time window where the asphalt binder can be worn off to expose more of the aggregate, however it is simple maths and physics that a rough irregular surface has a greater surface area than a smooth regular surface (ask any cartographer the issues this causes when measuring a coastline) and therefore presents a greater surface for the effects of mechanical and chemical adhesion to act upon.

A simple example is which has the greatest surface area, 1sq/m of glass or 1sq/m of track surface? The closer you get to the smooth glass surface the greater the reduction in surface area and the ability to create friction between surfaces reduces by orders of magnitude due to the inter-relation of force(s) to available surface area such as those from mechanical and chemical adhesion or bonding.

[aussiegman]

If the track hasn't been prep'd Bernie won't let it run. If there's excess sand then there could be tantrums.

Does a "First Lap Ceremony" count as running? That is it for track time.

There is nothing Bernie can complain about. The ultra smooth surface/finish of a new asphalt roadway cannot be avoided. Chances are very good that the track will have a very narrow groove lined with the small sandy aggregate that is lifted from the new surface.

Brian

Cheers Brain, I had been told there had been more running than that. V.interesting but at least with the practice sessions and support races a decent line should develop as you say over the event.

Also, if its as "sandy" as you indicate, then it will be like Bahrain is first thing in the morning when the dunes have blown back over the track. Be interesting to see the cars running and watch the aero pick up the grit as they go.

[ubrben]

My general experience with new surfaces is more abrasion and shorter tyre life. Sometimes more grip, but often it's dusty/dirty when a tracks been re-done, so it's hard to make generalisations. They patched parts of Estoril in 2006 before the MotoGP and the new bits were "slippery" according to our rider at the time. They did Daytona a few years back and the new surface had a lot more grip.

The abrasion is the common factor for me. Persson's friction modelling that JT's posted links to in the past is worth reading:

http://www.multiscaleconsulting.com/ind ... r-friction

Is a pretty good representation, and can explain the abrasion you get on new surfaces. Higher micro-roughness of a new surface will give you higher frequency inputs for a give sliding speed. This means you operate closer to the TG. Two things happen when you do this; firstly the compound will behave as if it's stiffer, and secondly it will be more brittle. If the compound is dynamically stiffer it's peak grip will occur at a higher temp, so if you can't achieve a higher temp then you might not have more grip. The more brittle to compound is, the more crack-prone it is, hence the abrasion.

I'm also with JT when it comes to mechanical keying and adhesion not necessarily being key factors in friction. However I'd put one major caveat on that; If the rubber is too hard when you go out you won't get enough keying into the surface to make the compound work at all, so initial grip is very dependant on dynamics modulus, and this is why some tyres work so much better with tyre warmers, because they eliminate the region close to the TG, which may be above zero degrees C in some cases. This is where I think Pirelli are in F1 - high TG, high dynamic modulus at low-temp, but then softening a lot with temp and loosing shear strength.

Ben

[Jersey Tom]

Too much text to quote and reply to. A few points-

1. Paul = Paul Haney.

2. "Mechanical keying" to me just means indentation (personally this is the first I've heard that phrase so perhaps that's where the disconnect is). Literally lack of stiffness. The difference between poking your finger into a sponge and a brick. That parameter however is NOT equivalent to loss rate (or what Pat S I guess is calling asymmetric deformation, in that a local strain doesn't result in a purely elastic or "symmetric" response - there is a loss or "asymmetry" to it). Never said that this parameter is the ONLY thing to "grip" - but it's really big. I would consider it the largest by a good margin. Opinions there may vary. You can most assuredly have a stiff tread rubber that blows the doors off a soft compound because the latter tries too much for "mechanical keying" and not enough for energy loss. Getting the most effective surface area isn't the end game (though it helps if you can get it without trading anything off). And hot race tires may feel sticky to the touch but don't misconstrue that as necessarily a direct attempt to make the rubber act like glue.

3. As far as the frequency range at which a polymer is excited with regard to force generation, it is indeed related to the small scale surface interaction (high freq.) rather than rotational speed of the tire (very low freq. by comparison). As Ben mentions, Persson's work on this topic is a good thing to read up on.

4. I don't doubt Pirelli have taken measurements of the track surface. That's easy. I don't doubt that they've made some calculation or prediction of what it will do to their tires. What PR never mentions is what the error bar is on that process. Maybe they have the whole thing down to an incredibly precise science (though given their product performance over the past 2 years I doubt this). In reality though I would expect the error bars are quite large. Wear is not a trivial thing to science out.

5. Interesting that my experience is on the other end of the spectrum when it comes to new surfaces and wear. My experience is that brand new pavement has extremely low wear rates - which is a bad, evil thing.

I don't at all disagree that newer track surfaces are generally much faster than old worn out ones. But I maintain that brand new, you can have very low grip and it's not just down to needing to hose the thing down to wash off "dirt and oil." In my experience the track has to be physically "worked" by hard running over several days or weeks to have any consistent performance... during which time it just gets faster and faster with every outing.

[ubrben]

Interestingly Valencia (not the F1 track...) has just been resurfaced and this weekend's MotoGP is the first proper event there since.

Valencia is also an interesting case because the old surface was quite light in colour and the new one is as black as the night. Historically you got very low track temps, particularly in the morning because it was so light. If a new surface is blacker that will help create temperature that will further alter the friction characteristics.

Ben

[olefud]

I don't at all disagree that newer track surfaces are generally much faster than old worn out ones. But I maintain that brand new, you can have very low grip and it's not just down to needing to hose the thing down to wash off "dirt and oil." In my experience the track has to be physically "worked" by hard running over several days or weeks to have any consistent performance... during which time it just gets faster and faster with every outing.

New asphalt has to cure to gain the strength and toughness to support higher grip. Curing involves cooking off the lighter hydrocarbons –like paint drying- and, I suspect, also involves cross linking of the bituminous binder. “Working” an at least partially cured surface could aid the former in a small way and the latter more substantially.

Of course laying down rubber is probably is the most significant.

[DaveW]

Another example - that might be worth repeating:

Late in 2004 (I believe) the Indianapolis track was resurfaced. An "Indy" car test revealed that the new surface lacked grip, so much so that the surface was "diamond grooved" early in 2005. A test following this revealed that the tyres would not last a stint (& they may have experienced failures). I was told that it took Firestone a couple of iterations to solve the problems, & Indy series eventually ran with "Indy-specific" tyres. WilliamsF1 posted some interesting images of the track and its affect on tyres.

Last time I heard, they still have "Indy-specific" tyres, by the feeling was that the track had over the years become more forgiving, & special tyres were probably no longer necessary.

I believe that Goodyear also had problems with that & similar surfaces, & Michelin (who had no prior knowledge of the surface) were famously (& expensively) caught out at the 2005 F1 non-race.

[delacf]

I'm a little frustrated. I have taken two hours to read your comments. I need to improve my English. It was worth it. I got much more than what I asked. Thank you

But firstly, what sort of track surfaces did you see this on?? Concrete aggregate? Textured concrete?? Asphalt? Dirt??

I think the confusion is caused by dirt that normally covers fresh asphalt. In addition to rubbering up of the track. The fresh asphalt micro-texture (sharp) improves adhesion. The way I see it adhesion mainly works with micro-texture and hysteresis mainly works with macro-texture.

I'd say my experience is that a racetrack will continue to get faster after days of hard running. The surface really needs to be burnished in for the grip level to become consistent.

But I think we do not speak of days, I think we talked about months in which the asphalt loses these micro-roughness [10^-1 mm] of the stones. In my opinion we have to speak at two levels of wear (of the asphalt).

I'd say my experience is that a racetrack will continue to get faster after days of hard running. The surface really needs to be burnished in for the grip level to become consistent.

Again, I disagree with you but can understand what you’re saying and think what you are describing as "burnishing" is the "rubbering up" of the track over consecutive days of running. I think perhaps we are simply looking at different time horizons for the change. I absolutely agree a track gets faster as it rubbers up and as long it is doesn't rain of get oil, sand or other dumped all over it, tracks generally get faster over the course of an event.
However over a greater time horizon, a new track (less than 1 month old with little use and proper preparation) will have more grip than an older track (greater than 1 year, with regular use) due to aggregate wear. The quotes “delacf” provided seemed to generally indicate differences of tracks over a wider time horizon due to wear while also showing that a tracks characteristics change as it “rubbers up”.

I agree with you 100 percent, aussie. I think this is the key.

Cheers

[ubrben]

So the new Valencia surface looks grippy. Pedrosa broke a 6-year old pole record (which was Rossi on a 990) having lost the vast majority of practice time to rain, so probably not with a perfect set-up.

Ben