Tyre Temperatures and Degradation

[eSEA One]

Not sure anyone has done anything on this before but I would like to start something to get a data base on AC tyres Ok this first one "Lotus Exos T125 and the S1" came from some notes @Georg Siebert gave out a little while back I had some intentions to do it but forgot about it and only just came across it in my files today. So I would like to get this "wheel rolling!" I have opened this spreadsheet up for anyone to edit so feel free to add data to it.
So click on the link and add you favorite cars:
Tyre Temperatures and Degradation

Any ideas could expand on this are welcome and thanks for your collaboration!

 

[Joao Alves]

If this does end up taking off, make sure you back up that file in case someone decides it'd be fun to ruin it.

 

[eSEA One]

If this does end up taking off, make sure you back up that file in case someone decides it'd be fun to ruin it.

Good Idea, thanks mate

 

[Georg Siebert]

The Merc SLS is missing, rename the GP2 car into FC2 2014 season, like the new 0.9.9 version is.
You can grab the tyre info for the GT3 & GT2 cars here:

--------------------------------------------
4.10 Tyre compounds and optimal tyre temperatures (Source)

• Road legal tyres: mainly affected by thermal degradation, no exact value applicable
• Street tyres: 75 - 85°C, easy to overheat
• Semi-Slicks: 75 - 100°C, keep in that range for optimal performance, have linear wear
• GT2 Supersoft: 90 - 105°C, very high wear, keep in that range
• GT2 Soft: 90 - 105°C, high wear, keep in that range
• GT2 Medium: 85 - 105°C, low wear
• GT2 Hard: 80 - 100°C, after some laps stay stable for a long time
• GT2 Superhard: 80 - 100°C, same as Hard
• GT3 Soft: 80 - 110°C, very high wear
• GT3 Medium: 75 - 105°C, same as GT2 Hard
• GT3 Hard: 70 - 100°C, same as GT2 Hard
• Hypercar tyres (Zonda R / 599XX), no exact value applicable
• Vintage F1 '67 tyres: 50 - 90°C, low wear

-------------------------------------------

I'm not sure, if the street and semislick tyres and the vintage f1 tyre info are accurate. Your chart for each car would be more accurate.

 

[eSEA One]

Ok I have developed the spreadsheet further. I have made it easier to fill in. All you have to do in the "Sheet1" is use the drop down list to choose the preset lists for both tyre "Temp" and "Notes"
I made a second sheet "SHEET2" where the temps and note are, not to worry the notes and temp's have no relationship within the "SHEET2" this is just the "data validation lists" that are used to fill in the drop down lists in "SHEET1.
If you have any problems or if you can not find the correct "Temp" or "Notes" let me know and I will try and sort it out.

 

[Chronus]

Degradation is the rate at which a tyre looses grip.

Georg, degradation is not the "rate at which a tyre looses grip". Degradation does have an impact on grip, and can be seen as a "thermal performance loss" (what engineers/chemists mean by this is not what is commonly talked about), but it's not any grip loss rate.

The rubber compounds of tires degrade (breakdown, deteriorate chemically) during its life time due to exposure to heat, UV, rain and even microbial action.

Furthermore, in racing circles, it's generally recognized the following types of "degradation" (which Degradation Models take into account in various ways):
- linear, which is related to tire wear (a physical process, or tread surface process).
- graining: as Bridgestone's Motorsport Director of Tyre Development, Hamashita explains, "Tyre graining happens when the side-forces on the tyre cause the surface rubber to roll up and present a non-uniform contact patch with the road, which affects the grip level".
- blistering, as Haney and others explain, the tire rubber melts around or on the interface between the layer of laminated material and the rubber - the rubber reverts to its "natural" state, ie, it de-vulcanizes. When overheated, the tire does in fact form heat blisters which are afterwards separated/torn from the surface of the tire. This phenomenon is also tied to how the core temperature varies.

Different "types" of degradation that obviously effect changes to the performance of tires and inherently to lap times.

Explaining such processes as a mere "rate at which a tyre looses grip" is not the correct way of clarifying things, even from a "high level" point of view.

 

[Georg Siebert]

@Chronus
that means, the loss of grip (linear or progressive) is strictly 'tyre wear'
and the (thermal) deterioration of a tyre, which in turn affects the loss of grip, is 'tyre degradation'
is that right?

So tyre degradation is not a (fixed, variable) value that is influenced by compound or friction between surface and contact patch, but a term to describe the symptoms of (thermal) deterioration, right?

What adjectives are then appropriate to describe degradation? High, low, fast, slow, etc?

 

[Chronus]

that means, the loss of grip (linear or progressive) is strictly 'tyre wear'
and the (thermal) deterioration of a tyre, which in turn affects the loss of grip, is 'tyre degradation'
is that right?

Georg, I didn't say that. My objection was against the improper explanation of degradation as "the rate at which a tyre looses grip".

Performance falloff is significantly more complex than simply tread wear. Actually, data (lots of if) seems to indicate that tread wear is not as important an indicator of tire performance as other indicators.

Data suggests that the de-vulcanization of tires happens significantly at very high temperatures. Which points to overheating tires and successive heat cycles as the primary reasons for performance falloff (ie, loss of viscosity/rubber compound strength caused by heat). We could also mention the continued curing process (under successive heat cycles) due to excess of cross-linking agents left over in the rubber, which leads to harder rubber and wider areas of the tire with different hardness coeffs.

The process, from linear (tread wear) to thermal-based degradation, is largely not linear, and is surely hard to predict.

So tyre degradation is not a (fixed, variable) value that is influenced by compound or friction between surface and contact patch, but a term to describe the symptoms of (thermal) deterioration, right?

No. Though you cannot reduce degradation (from a scientific/engineering POV, that is) to a single variable, you shouldn't think of it as a list of "symptoms".

Degradation, as I explained earlier, happens due to many factors:
-exposure to heat,
-exposure to UV,
- exposure to rain
- and even due to microbial action

Under race conditions, stresses are obviously higher. We're talking about lateral and vertical deflections due to forces in the range of several thousands of newtons, and an inevitable gap between the tire surface temperature and its core.

There are 3 main degradation types:
- linear
- graining
- blistering

Everything in a tire is constantly changing when submitted to stress (or forces). The viscosity, flexibility and hysteresis of rubber vary significantly during a stint, and depend on temperature and stress frequency. If you increase temperature, rubber changes to a more rubbery state; on the other hand, increase stress frequency and rubber changes from a rubbery state into a more vitreous state. Getting closer to the glass transition temperature elicits higher hysteresis and flexibility (on the other hand, higher stress frequency is conducive to higher glass transition temperature).

With the right level of hysteresis and flexibility, friction coefficients (for a given compound over a given type of surface) are maximized.

So, with the onset of degradation, the above changes - and changes faster (though some anomalies may still occur as when drivers report that tires are beginning to "lose it" and suddenly seem to be "coming back"). How?

Lets consider this. Tyre grip is a function of the frequency excitation of rubber under the application of a certain type of stress - in particular, that resulting from slippage over a track surface. Degradation affects the two friction mechanisms - indentation and molecular adhesion:
- indentation: hysteresis changes over time, which means the ability to asymmetrically deform over road irregularities (thereby creating the inevitable force field) changes.
- molecular adhesion: rubber molecular chains, due to its viscosity properties, resist deformation, thereby creating a friction force which resists sliding. With degradation, the state of the rubber compounds change, which means molecular chains create less force to oppose skidding (they break and do not reattach).

Engineers do add special elements that retard the degradation of rubber and other tire compounds by increasing the tendency of these broken chains to reattach, but that's only retarding the progress of degradation, not preventing it or stopping it.

So, it's not a list of symptoms we're dealing with here, but very specific indicators (though hard to monitor) of both the performance of the tire and its state.

The interaction of all these factors and mechanisms is reflected on the level of grip (or rather, the friction coefficients).

 

[Georg Siebert]

@Chronus
I was able to follow most of it and I see now that my previous definition and understanding of tyre degradation was wrong - I'll change that in the setup guide.

Can you write down short definition of both tyre wear and tyre degradation for me to include in the setup guide and future articles?

Edit:
you can also include some graphics and charts to illustrate the wear and degradation process, for instance
- the function of friction coeff to excitation
- friction coeff to loss of molecular adhesion
- friction coeff to graining/blistering
for a typical tyre compound or a specific compound used in a Formula class

@Edwin Collingridge
I've changed degradation in the spead sheet into wear.

 

[Chronus]

Ok.

In simple terms, tire wear is a process affecting tread surface. We could understand this as a tire wearing out, running out of rubber - even in some cases through the cords. However, this is not the most important factor causing performance falloff.

Tire degradation comprises 3 different processes:
- linear degradation, which we know to be tread surface wear
- blistering
- graining

Blistering is caused essentially by overheating tires, which causes more and more of the tire rubber to revert to its "untreated state", i.e., it de-vulcanizes. With overheating and more heat cycles, blisters form and eventually those parts of the tire affected are torn from it.

Tyre graining occurs essentially when the tyre is sliding. The tread surface deforms, conforms to the track surface, and as the sliding progresses this causes the rubber to wear off and roll up, presenting an irregular contact patch to the road. The rolling up persists after sliding has stopped, leaving peaks (sharp, projected points) counter to the direction of motion.

If pressure is too high, the rubber is too stiff or temperatures are too low, graining occurs frequently. If you push harder on your tires, you'll eventually saturate them. Once you saturate them and still push them further, light graining begins and eventually serious graining sets in (which is why instead of saturating tires, one must ease off the throttle and decrease the steering angle).

Hope this helps, Georg.

 

[Georg Siebert]

ok to summerize

Definition
Tyre wear - linear reduction of tread on the surface, small performance impact

Tyre degradation - thermal - de-vulcanization of the rubber caused by overheating, high performance impact

Tyre degradation - graining - process of disintegration of the surface caused by sliding, progressive performance impact

Can 'tyre wear' be used as a generalization of both described tyre wear effects and both tyre degradation effects?

Is all of the above right?

 

[Chronus]

ok to summerize

Definition
Tyre wear - linear reduction of tread on the surface, small performance impact

Yes, though while some consider it linear (Y=ax+b), others believe it's not really linear and depends on other factors. For all practical purposes, consider it linear. It may haver a smaller or bigger impact, depending on tire construction and compounds used.

Tyre degradation - thermal - de-vulcanization of the rubber caused by overheating, high performance impact.

Tyre degradation - graining - process of disintegration of the surface caused by sliding, progressive performance impact

Note that graining and blistering are both thermal in nature - just on opposite sides.

In the case of graining pattern (a case of abrasion patterns, according to Paul Haney), we also see more of a compound effect. Tires are more prone to graining if:
- pressure is too high,
- the rubber is too stiff
- temperatures are too low

What happens when pressure is too high? For the same load on the tire, the contact patch is reduced. If you look at readings from temp probes, you see a general decrease in temperatures (though a relative increase can be detected in the centre of the tire tread).

If the rubber is too stiff (harder compounds, for one; but tires with higher pressure also have an effect on the tread), heat generation tends to decrease (roughly speaking). Harder compounds have more cross-links between long rubber molecules, which tends to reduce the length of the molecules that end up interacting with the track. Less interaction between rubber molecules and track molecules means...less heat generation.

If temperatures are too low (track temperatures, but also tire temps: in some tracks, there is enough distance from one corner to the next for the tire's surface temperature to decrease appreciably), the same applies - higher tendency to a graining pattern.

Curiously, as linear degradation increases, graining...may tend to disappear (sometimes, tires suffering from graining get progressively "cleaner" of the loose, peaks of rubber as the tread wears out).

Note: there is another type of abrasion pattern (graining-like) which is caused by tires too soft for the surface conditions or for the driver's style (too aggressive) when the said driver does not heat up tires properly and places high demands on them.

At the other end we have blistering, which requires rather high temperatures (actually, overheating).

Can 'tyre wear' be used as a generalization of both described tyre wear effects and both tyre degradation effects?

Not quite (and I suspect Stefano C. has this in the TM - maybe not as deep as heat cycles, but probably close).

Tire degradation comprises tread wear, graining and blistering - all of them processes with physical (and chemical) consequences, all of them with some sort of impact on performance.

I have talked to tire engineers and racing team engineers who look at it this way:
- tire wear, degradation of a more physical nature (they don't seem to worry about it too much)
- blistering and graining more of a heat & chemical nature

We could complicate things even more (as I hinted at earlier) with references to incomplete curing of tires and curing reversal (when the rubber reverts to its "natural state"). On top of that, different abrasion patterns, different damages to the internal structure of the tire, and to complicate things even more we could mention tires that degrade and look wet (oily) and dark and others degrade and look desert-dry and greyish.

A very very complicated subject. Imagine modelling it...

 

[Georg Siebert]

In general, does tyre temperature increase or decrease for more tyre pressue?

 

[Chronus]

Higher tire pressures lead to lower temperatures.

Higher tire pressures also decrease the possibility of standing waves (at high speeds); lower tire pressures increment the possibility of standing waves, which in turn lead to excessive heat accumulation.

All is interconnected.

 

[Georg Siebert]

Higher tire pressures lead to lower temperatures.

hugh? that's surprising - this stands in contrast to all testing and research I've done in the last 3 months.
It's quarter to 2 o'clock here, let's continue later.

Edit: Chronus, just to make sure, you are not trolling me, right? That would be purely evil.
Will link some charts and do some math later on.

@Edwin Collingridge
sorry for the thread hijack but this is one of the most interesting conversations I had recently

 

[Chronus]

hugh? that's surprising - this stands in contrast to all testing and research I've done in the last 3 months.
It's quarter to 2 o'clock here, let's continue later.

Really?

So, higher pressures do not mean lower temperatures (less "wrinkles", less deformation, less standing waves formation, less heat build-up), which means lower pressures do not contribute to heat build-up, more deformation, more resistance...Which means all of the following is "wrong":

Underinflation:

• Reduces tread life through increased treadwear on the outside edges (or shoulders) of the tire
• Generates excessive heat, which reduces tire durability and can lead to tire failure

http://www.michelinman.com/tires-101/tire-care/tire-maintenance/diagnostic-tool-solution-generator.page?categoryName=TIRE&subCategoryName=Wear on Both Edges

Or this:

The most common causes for tread separations are under inflation or overloading. Both of these conditions cause a tire to flex more than is should which creates excessive heat that breaks down a tire's internal components. Add in the high summer road temps and conditions are ripe for a catastrophic failure.

Blowouts are not as uncommon as you may think. Michelin reports approximately 535 fatalities and 23,000 collisions per year due to a tire blowout. - See more at: http://blog.tirerack.com/blog/letters-from-luke/im-back-from-gator-country#sthash.gZpu1Tt5.dpuf

- Tirerack

And this must also be wrong:

Underinflation contributes to rapid and uneven tread wear[...]poor vehicle handling and excessive heat buildup which may lead to tire failure.

- The Pneumatic Tire, U.S. Department ofTransportation, National Highway Traffic Safety Administration

And also this:

-Overinflation
Higher inflated tires cannot isolate road irregularities well and this leads to a harsher ride.
Tires can also be damaged more easily, lowering safety levels.
1-Safety - More susceptible to damage from external factors (potholes, debris)
2-Economy - Speeds up wear, in particular wear of central tread part

-Underinflation
Underinflation increases tire wear, creates excessive heat and causes the sidewalls to overflex. This diminishes the tires' integrity, making them vulnerable to premature failure.

- Hankook Tire USA
http://hankooktireusa.com/Serv/Inflation.aspx?pageNum=3&subNum=3&ChildNum=4

Not to mention Paul Haney being wrong, and other authors as well...and years of research of several people.

Interesting...3 month-research you got there.

It's quarter to 2 o'clock here, let's continue later.

I think not.

 

[Georg Siebert]

Interesting 3 month-research you got there.

I think not.

Bye.

No need to be sarcastic; I thought we had an honest conversation handling our position with mutual respect. Please refrain from those comments.

I mainly refered to the tyre model of Assetto Corsa - the game and forum section in which this very thread is located.
I don't know how close Kunos' own tyre model is accurate to reality, but it should be quite so. That is why we do the testing in the first place.

 

[Chronus]

Edit: Chronus, just to make sure, you are not trolling me, right? That would be purely evil.
Will link some charts and do some math later on.

"Purely evil"? "Trolling"? "Please refrain from..."

To be clear: I have been nothing but cooperative since my first post and giving up my own time to inform you. Plus, all the info I have has been given in good faith (to you, and anyone with an interest in these matters).

But...all right.

 

[Brad Merys]

Hi there guys. Interesting discussion. I have no technical expertise to share but I was thinking: doesn't the degradation/heat questions have to do with the AC tyre model, not necessarily real world conditions?

 

[Georg Siebert]

Yes, as I said a post earlier - I want to figure out the AC tyre model so we can make accurate predictions about tyre temps and pressures and incooporate suggestions into the next setup guide that i'm writing.