Technical queries on tires [Archive]

atenza63

10th July 2009, 13:29

Jakg

10th July 2009, 13:36

1 - Peak Temp - Temperature at which the grip is optimum.

danthebangerboy

10th July 2009, 13:41

Use the F9 display ingame to see the tyre stats.

Colour codes are as follows...

Blue - Cold
Green - Optimum
Orange - Starting to overheat
Red - Cooked!

amp88

10th July 2009, 14:13

2. As a tire wear down, it starts to releases some of the heat and start to go down in temperature. In what way does this cool off effect have an impact on performance?

The impact on the performance will really depend on how low the temperature of the tyre falls as it wears. How low it falls depends on your car setup and driving style. You only need to really consider tyre wear if you're in quite a long race. depending on the track length, car type, driving style etc it can take anywhere from 10-20 or so laps for the tyre tread to start wearing significantly. What I try to do when I modify a setup for a long distance race is to have the tyres at their optimal performance (i.e. optimum temperature) at about 75% of the race distance. If you try to get the optimum performance sooner (say 25-50% race distance) then when you get to towards the end of the race you'll probably find your tyres have cooled too much and you'll be very slow. If you try to get optimum performance at the end of the race then you're wasting the best bit of the tyres. Something else to consider is that when you create a setup that's going to give you optimum temperatures at 75% distance your tyres will be above that temperature (and liable to overheat) for the start of the race. You will need to keep this in mind so you can alter your driving style to keep the tyres within a reasonable temperature range. There are a few things you can do to alter your driving style to try to keep the tyres in range:

Brake slightly earlier than the limit (this will reduce the chances of brake lockups which can create hotspots on the tyres)
Apply the throttle smoothly (reduce wheelspin and power oversteer)
Carry slightly less speed through the apex of corners than possible (decreasing stress)

As the tyre tread wears down you'll be able to push harder while keeping tyres within a reasonable range. This is because with less tread depth there's less rubber to move around on the surface of the tyre which creates less temperature.

Something to bear in mind with the above is that it can be much easier in theory than in practice. When you're battling for position you can forget optimum temperature ranges and conservative driving.

3. A tire with a higher pressure has better handling but sacrifices traction. Handling here refers to how quickly it reacts to driver's input. Am i right to say that?

Up to a point, yes. Higher tyre pressure normally gives better precision.

4. Besides pressure & temperature, do tire profile(sidewall) contributes to the car's cornering performance and how are they affected?

Yes. Sidewall strength (and thus how much it flexes) has an impact on tyre performance. If you take a look at this video (http://www.youtube.com/watch?v=v-DMkO3g2SI&fmt=18) you can see how much the tyre sidewall crushes under braking and deforms through right hand corners. The amount of deformation in the sidewall will effect the contact patch of the tyre. The more contact patch the more grip, obviously. A softer sidewall will deform more so give more grip, but may feel less precise to the driver (same thing as the tyre pressure). A stiffer sidewall will give less grip but more precise feeling.

JasonL220

10th July 2009, 15:50

what amp said, but just to elaborate on 3.

the higher the pressure that more responsive the handling of the car, as there is less rubber in contact with road, therefore less resistance to turning and also less tyre flex. low pressure will make the tyre respond slowly, but will increase the contact patch and therefore grip.

another thing to consider is how the pressure affects the tyre temperature, general rule high pressure = less heat

Riel

10th July 2009, 16:52

I never really feel the difference between a green inside of tire and just the green contact patch.

Can anyone shine a light on that?

danthebangerboy

10th July 2009, 17:09

something to do with camber angles or something, im not very technical lol.

amp88

10th July 2009, 17:34

I never really feel the difference between a green inside of tire and just the green contact patch.

Can anyone shine a light on that?

I don't understand the question. Can you provide more details please? Include screenshots of the F9 display if possible.

something to do with camber angles or something, im not very technical lol.

What was the point of this post?

danthebangerboy

10th July 2009, 17:38

The point was, presuming i understood what he was saying correctly, is that you will end up with the inside edge of the tyre green before the rest of it if the camber is set too much, Shit, thats not what he means is it, i think he might mean the difference between the actual air temp inside the tyre and the temp of the contact patch. Whoops.

So if i have got the meaning of the question right this time :hide: Then if the inside of the tyre and the contact patch are both green, then your tyres are nicely up to a good racing temperature, but if the inside of the tyre is blue and the contact patch is blue, then the whole tyre is still cold, and if middle is blue and the contact patch is green or orange or red, then the heat is only on the surface of the tyre and not the whole thing, indicating scrubbing tyres or excessive wheelspin.

If the whole tyre is green but one side or one spot of the contact patch is orange or red and the rest of the contact patch is green, then its either a flat spot due to locking the wheels under braking, or too much camber or toe in/out, depending on which side is hotter.

There is a guide somewhere on here that explains it all better than i can, and as soon as i find it again i will post a link in here. :thumbsup:

EDIT: this isn't the guide, but tyre physics are discussed fairly in depth in this thread... http://www.lfsforum.net/showthread.php?t=57041

logitekg25

10th July 2009, 18:12

Greetings all, i have a few doubts pertaining tires and i've listed the questions below.
I appreciate to aquire all relevant help and advices which i will be applying to both simracing and real racing.

1. What does a peak temp of a tire represents? Is it the highest temp a tire can get or is it the point the tire has the most traction? Is it related to overheating point? the temp at mamimum grip, not related to overheating point

2. As a tire wear down, it starts to releases some of the heat and start to go down in temperature. In what way does this cool off effect have an impact on performance? the closer to optimum temperature the better overall, nomatter what the amount of tread TO A POINT

3. A tire with a higher pressure has better handling but sacrifices traction. Handling here refers to how quickly it reacts to driver's input. Am i right to say that? a tire with less pressure has less reaction time but more of a footprint, so more grip. but a higher pressure heats up less, with less grip but a more immediate affect

4. Besides pressure & temperature, do tire profile(sidewall) contributes to the car's cornering performance and how are they affected? if you go overe a bump, the more side-wall or profile the tire has, the more of the bump the tires take compared to the suspension and compared to the passengers

hope i answered all of them correctly :schwitz:

NightShift

10th July 2009, 19:55

What was the point of this post?

As I read it, he's asking the difference between having the inside of the tyre heated up and having green on the contact patch.

While it's quite easy to bring the contact patch to optimal temperature, the inside of the tyre (which I suppose represent the temperature of the air, color coded wrt the optimal temp of the compound) can be harder to warm up. E.g. in the LX4/LX6.

His problem is he can't feel any change in the handling.

Riel

11th July 2009, 11:39

NightShift

11th July 2009, 12:26

There are some cars where you can end up with a blue outer band while the inside is green, surely restricted ones where the tyre is supposed to withstand much more power and speed, as the Baby-R which I was practicing with yesterday :D but I think there could be more.

My guess is the inside of the tyre provides heat inertia to the tyre, e.g. it slows down contact patch heating in the warm up phase and then slows down its cooling in later stages. The same could be said of the rim too (if you look closely on some cars that warms up too) though I suppose to a limited degree.

The XFG is a great car to do some testing about this, it's easy to bring the patch up to temperature and then the inside will come up as well.

NB: in LFS there's no such thing as 'cold' tyres out of the pits. They're already above ambient temperature, and an easy way to check this is to let the car sit parked along the track for some time, the tyres will cool down to about 20 °C IIRC.

This has been the source of some arguing since tyre blankets may only regarded as realistic for the faster race cars.

bbman

11th July 2009, 14:06

That indeed was my question: the inside of tires compared to the green outside.

So, when I want to conclude that:

1: Both Blue:
Tires still cold

2: Outside green, inside blue:
I am not driving smooth. The outside heats up due to wheelspin and scrub, and not by general rubber deformation. Less pressure to gain deformation and better driving lines are important.

3: Both green:
Perfect. GOod combination of tirepressure and driving style.

4: Inside green outside blue:
Won't happen but well looks like driving like grandpa on soft pressure :)

My REAL question now was:
How do I feel the difference between situation 2 and 3? I mostly don't mind a blue inside, as long as my outside stays green ... But, is this the right way of thinking ?

The question is wrong as you got the base of your question wrong: the air temperature inside the tyres is probably the most irrelevant on the whole F9-display... It only affects tyre pressure (as you know pressure increases with heat in a closed environment)... In fact if the air inside stays cool, it will cool the tread from the inside...

And as the only way the air temperature rises in LfS is by heat from the tread transferred to the inside your situation 4 will never arise...

@NightShift: That's the sidewall, not the rim...

AndRand

11th July 2009, 18:01

I never really feel the difference between a green inside of tire and just the green contact patch.

Can anyone shine a light on that?
tire warms up at the contact point, right? so it differs where is your contact patch in given setup.
The question is wrong as you got the base of your question wrong: the air temperature inside the tyres is probably the most irrelevant on the whole F9-display... It only affects tyre pressure (as you know pressure increases with heat in a closed environment)... In fact if the air inside stays cool, it will cool the tread from the inside...
I was always wondering how LFS simulates cooling from the outside becasue I always had the feeleing that tires once hot cant be cooled down driving competetive - I would have to go 5s a lap slower to get them cooled down for3 laps at least. So I have a feeling that cooling down with speed should work better.

bbman

11th July 2009, 22:40

I was always wondering how LFS simulates cooling from the outside becasue I always had the feeleing that tires once hot cant be cooled down driving competetive - I would have to go 5s a lap slower to get them cooled down for3 laps at least. So I have a feeling that cooling down with speed should work better.

There is a cooling from the outside as well, you can see this very well if you set the wind to orcan-like, but I agree the temperature model is grossly flawed - there should be much more fluctuation than there is currently, not just faster cooling...

Bob Smith

11th July 2009, 23:26

The tread on race tyres is typically a third of the thickness of a road tyre. If LFS does not adjust for this, then race tyres will store too much heat energy and thus heat and cool too slowly.

NightShift

11th July 2009, 23:51

@NightShift: That's the sidewall, not the rim...

I know where the sidewall is ;)

Take a look at the attached screenshot, you'll notice there's an additional part under the sidewall, the temperature is different as well (this you'll see well by taking a look at each wheel) - if that part is not the rim then I don't have a clue about what it is, the shape looks correct to me.

logitekg25

12th July 2009, 07:00

I know where the sidewall is ;)

Take a look at the attached screenshot, you'll notice there's an additional part under the sidewall, the temperature is different as well (this you'll see well by taking a look at each wheel) - if that part is not the rim then I don't have a clue about what it is, the shape looks correct to me.

the bead :shrug:

AndroidXP

12th July 2009, 08:04

It is in fact the rim and LFS also models its heating.

Riel

12th July 2009, 10:30

It only affects tyre pressure (as you know pressure increases with heat in a closed environment)... In fact if the air inside stays cool, it will cool the tread from the inside...

And as the only way the air temperature rises in LfS is by heat from the tread transferred to the inside your situation 4 will never arise...

Ah.
So my setupped-tirepressure is pressure @ cold tires, and the CURRENT pressure is the pressure next to it ...

AndroidXP

12th July 2009, 11:27

The setup pressure is pressure at optimum air temp, not cold temp AFAIK.

RasmusL

12th July 2009, 14:04

That's really stupid, how the hell do you set up pressure at optimal temperature like that.. IMO not realistic if that's true :shrug:

Bob Smith

12th July 2009, 23:13

Maybe so, but isn't it easier? As we don't have to worry about how pressure changes with temperature as much.

Ball Bearing Turbo

13th July 2009, 00:54

Hogwash. Should come out of the pits with ambient temp tires and have to worry about your pressures properly.

No more EZmode.

Keling

13th July 2009, 06:55

Some people say that the devs make LFS tyre model in this way (especially in Patch Y/Z) so that there will be fewer drifters. Is that true ?

Bob Smith

13th July 2009, 07:04

Should come out of the pits with ambient temp tires and have to worry about your pressures properly.
I can only think that tyres in LFS are preheated because Scawen is not confident about the effect on grip once the temperature gets for from the optimum.

Becky Rose

13th July 2009, 08:24

I can only think that tyres in LFS are preheated because Scawen is not confident about the effect on grip once the temperature gets for from the optimum.
Indeed it's not right. The closest real world example I can give you was during an endurance go kart race. I was flying before a fuel stop, it was a night stint, and after the fuel stop I belted out the pits and into the first turn and almost understeered straight off the track, the tyres had completely cooled and the lines and braking points I took before the stop no longer applied and it felt like driving on ice, literally I turned the wheel and nothing happened. By the end of the lap things where almost back to normal.

In LFS the surface tyre temperature raises and falls too slowly, you should be able to cool your tyres right off with 3-4 laps of easy driving, and currently that cant be done. Also, you should be able to get heat into your tyres in a lap or so of hard driving, and right now that isnt so.

My experience of tyre temperatures in karting seems consistent with observations of big car motorsports, slick tyre technology is afterall the same regardless of wheel size.

Bob Smith

13th July 2009, 09:13

Naturally a smaller tyre will have less heat capacity, so will heat and cool more rapidly than a larger tyre, but then seeing as a kart weighs so much less, I'd imagine that would go some way to cancelling out the heating side of things, and the reduced surface area will do the same for the cooling. That said, the general consensus is still that tyres heat and cool too slowly.

That wasn't the point I was getting at though. I was thinking more about how much grip is affected, and how optimum slip changes with it (as I'd expect temperature to have at least a little effect on cornering stiffness).

AndRand

21st July 2009, 17:12

In LFS the surface tyre temperature raises and falls too slowly, you should be able to cool your tyres right off with 3-4 laps of easy driving, and currently that cant be done. Also, you should be able to get heat into your tyres in a lap or so of hard driving, and right now that isnt so.
I wonder if the heating up and cooling down is symmetrical? I dont know how accurate is calculation and what factors are taken in. But if devs made it longer to heat up but also slower to cool down to make cars drivable - then it is in fact drivable but the balance between is I think very important to weight it.

logitekg25

21st July 2009, 17:15

maybe off topic, but i wonder if they made some things the way they did, so the cars would be drivable, and easy. (not for realism)

AndRand

21st July 2009, 17:48

maybe off topic, but i wonder if they made some things the way they did, so the cars would be drivable, and easy. (not for realism)
in a sim you always do - some things have to be assumed as approximation to get wanted effect.

logitekg25

21st July 2009, 17:56

in a sim you always do - some things have to be assumed as approximation to get wanted effect.

im saying they make it un-realistic in some way on purpose to make it either funner, or easier to play.

AndRand

21st July 2009, 18:03

well, it is not about being unrealistic, it about not taking into account all the aspect that should be calculated - for optimalization reasons. So if not all the factors in tire temperature changes are calculated (rubbing, tire pressure, air temp, heat capacity) some of them have to be approximated

Surprisingly, this is also discussed here :nod:

AndRand

23rd July 2009, 17:01

Hallen

23rd July 2009, 17:37

Frankly speaking I am curious if devs took mass of air into account in thermodynamical formulas, and in fact that is another thing that gives a lot of possibilities to set - but in the same time time-consuming thing to check. That is the amount of air flow under the fenders.

It is obviously possible to simulate the airflow and some kind of effect of that airflow on tire cooling.

But, the airflow on each car is going to be different based of the geometries and the aerodynamic features of each car. That's a lot of stuff to deal with. I would guess that some general formula could be used.

There is always going to be compromises in how things are done in the sim. Some stuff will be modeled dynamically, and others will probably use a general formula... a one size fits all kind of thing. I would think that airflow cooling of the tires would be one of those kinds of things.

AndRand

23rd July 2009, 17:53

But, the airflow on each car is going to be different based of the geometries and the aerodynamic features of each car. That's a lot of stuff to deal with. I would guess that some general formula could be used.
kg/s per car or axis?

Keling

24th July 2009, 06:17

kg/s per car or axis?
Plus speed factor, angle factor, susp travel factor, draging, .................

AndRand

24th July 2009, 18:59

Plus speed factor, angle factor, susp travel factor, draging, .................
consider pipe in airflow (where stream is Q=V/t - capacity per time - and speed of fluid is U= 4Q/pi*d^2 where d is diameter) - it is the same situation (compression level could be a kind of coefficient - the goal is not to simulate brake discs airflow intake cooling system but to simulate brake disc cooling effect), at least this representation is sufficient - angle factor could be easily taken into acount, susp travel could be probably neglected.

Some roumors say the next patch will bring rotating brake discs - I hope brake disc temps also (and brake fading) - the model is the same so I hope we'll get proper tyre temp changes also.

amp88

24th July 2009, 19:03

Some roumors say the next patch will bring rotating brake discs - I hope brake disc temps also (and brake fading) - the model is the same so I hope we'll get proper tyre temp changes also.

If we do get advanced brake simulation (like what I discussed here (http://www.lfsforum.net/showthread.php?p=1163342#post1163342)) then not only would air cooling effect brake temperatures but there could even be water cooling on the GTRs.

logitekg25

24th July 2009, 19:07

take pipe in airflow (where stream is Q=V/t - capacity per time - and speed of fluid is U= 4Q/pi*d^2 where d is diameter) - it is the same situation, at least this representation is sufficient - angle factor could be easily taken into acount, susp travel could be probably neglected.

Some roumors say the next patch will bring rotating brake discs - I hope brake disc temps also (and brake fading) - the model is the same so I hope we'll get proper tyre temp changes also.
settle down with your complex math, and your rock and roll music:geezer::gandalf:

AndRand

26th July 2009, 07:28

Well, I think it isnt complex math - it is few quite simple formulas that will result with mass of air per second taken from speed and some assumed coeficient for air intake property. And I reckon it as piece of cake comparing to physics problems Scawen did sorted out. :smileypul

What could be quite complex is a model for heat transfers in segmented tyre. Every segment transfers heat with every 5 to 8 neighbouring segments plus air inside and outside the tyre :schwitz:And the calculations for heat balance could be quite resource consuming so I think some simplistic model would be welcomed. :scratchch

logitekg25

26th July 2009, 14:59

Well, I think it isnt complex math - it is few quite simple formulas that will result with mass of air per second taken from speed and some assumed coeficient for air intake property. And I reckon it as piece for cake comparing to physics problems Scawen did sorted out. :smileypul

What could be quite complex is a model for heat transfers in segmented tyre. Every segment transfers heat with every 5 to 8 neighbouring segments plus air inside and outside the tyre :schwitz:And the calculations for heat balance could be quite resource consuming so I think some simplistic model would be welcomed. :scratchch
which is why i think scawen needs an assistant or two, of people who are just as smart as he is (if possible) to help him out...he must be stressed!

AndRand

27th July 2009, 10:46

short reconsideration - there is no need to simulate heat transfer between the neighbouring segments. They are too small comparing to contact patch. Second - there is no need to simulate heat transfer between each segment and air inside the tyre - it is better to get global factor for every segment. Third - the same applies for heat transfer between segments and outer environment. It will just look cool when with car standing still couple of minutes the contact patch (on i.e. hot tarmac) would be warmer than the rest of the tyre. But with expense of CPU usage :) edit: frankly speaking I didnt notice how does heat transfer between tyre and inside tube air work now - but I think the transfer between neighbouring segments could be done that way around: the whole tyre trades heat with air inside tube, thus each segment is affected.

edit: this latest idea would give strange effect - one flatspot could for a moment cool down the rest of the tyre till it settles in balance with air inside the tyre :) so it is not the bestest idea :)
and what I can think about is that every sector transfers heat with 3 environments: inner-tube air, outer air and average heat of the tyre thus the heat would be distributed to all the segments.

AndRand

3rd August 2009, 18:24

well, Im pretty sure devs will still make one of the best physics-best optimized sim out there. And brake fade would change a lot - especially at those long-straight-hairpin tracks :) where you will not smell the brakes but the next corner could be bit scary :) plus different characteristics and tricks for steel, ceramic and carbon discs.

Neilser

7th August 2009, 13:19

It is in fact the rim and LFS also models its heating.
Wow, I had never noticed those teeny weeny blips in the corners of the tyre-temp pic.

How do you know for sure it's the rim and that it's modelled? Did you find it mentioned in docs somewhere? Does the whole wheel get modelled (heat reservoir with hugely more mass than the air in the tyre)?

Two things to add to this:
1) I'm interested in the tyre-wear vs. grip (and temperature) effect. LFS doesn't provide a wear-level indicator but wear does seem to influence the grip. I recently saw a guy do a spectacular lap (and some WR HLs do the same) after about fifteen minutes of abusing his tyres and then letting them cool down. And in a recent long race I clearly saw my tyres cooling down (with wear I guess) so I could abuse them more and not have them go red (wasn't 100% sure I had more grip though). [This, despite the fact that slicks have no tread pattern to move around less as the tread-depth drops. But OK, I guess less tyre-thickness might also provide less mechanical deformation and thus less heating.]

SO, I really want to understand how LFS models this tyre-wear effect. Anybody know? Does a high-wear tyre really give more grip? I've searched the forum and found little on this.

2) Tyre cooling: I have sometimes wondered if a car driven slowly (in LFS) cools its tyres more quickly than one left stopped on the track (and if the piece touching the track for the stopped car cools more quickly still :)). Some half-hearted checks I made suggested that it made no difference (of course it should, as forced air cooling should be massively more effective at removing heat, no?). This point has come up already in this thread, but it's not clear if people are sure about it being absent. Anyone know for sure if this effect is modelled in LFS?

JasonL220

7th August 2009, 13:26

1. a worn down tyre, does not produce more grip, BUT it will loose/gain temperature quicker as with the correct driving and can keep it in the max grip temp range for longer.

2. not sure had a few beers :)

AndroidXP

7th August 2009, 14:43

Wow, I had never noticed those teeny weeny blips in the corners of the tyre-temp pic.

How do you know for sure it's the rim and that it's modelled? Did you find it mentioned in docs somewhere? Does the whole wheel get modelled (heat reservoir with hugely more mass than the air in the tyre)?

I know this mainly by messing around with Tweak and the tyre sizes. With a different rim size you see different parts of the tyre in the F9 view and it becomes more apparent. Also driving around in a high HP & several ton car heats the tyres just by driving (especially the sidewalls) which made me first notice that there's a rim down there on the F9 view. Seeing that a bit later the rim suddenly had the same colour as the sidewall made it clear that its heating is modelled.

Two things to add to this:
1) I'm interested in the tyre-wear vs. grip (and temperature) effect.

As far as I know tyre wear does not affect grip at all. It does, however, affect the weight of the tyre (relatively sure) and the heat capacity (100% sure), the former meaning that with worn tyres you drive a lighter car which goes faster through corners, the latter allowing you to punish the tyres more since they can't hold heat as well and therefore won't overheat as readily.

The temperature however does have an affect on grip (duh) (http://www.lfsforum.net/showthread.php?t=7757), though the graphs are most likely outdated by now.
LFS doesn't provide a wear-level indicator
It does (http://en.lfsmanual.net/wiki/Display#Tyre_temperature.2Fwear_.26_clutch_tempera ture) (click the picture on the right). Just not a numerical one.

JasonL220

7th August 2009, 14:49

dammit, i thought i forgot something, the tyre get lighter doh

Bob Smith

7th August 2009, 15:01

I'm not sure if it gets lighter but it should get smaller.

Ball Bearing Turbo

7th August 2009, 15:52

With less rubber why wouldn't it get lighter?

I bet it's so marginal that you'd never notice it though.

This point has come up already in this thread, but it's not clear if people are sure about it being absent. Anyone know for sure if this effect is modelled in LFS?

It's definitely there. More noticeable in open wheelers. If you really want to test it, take one out with a setup & on a trak you're very familiar with & crank the wind to full speed.

Neilser

7th August 2009, 18:26

It's definitely there. More noticeable in open wheelers. If you really want to test it, take one out with a setup & on a trak you're very familiar with & crank the wind to full speed.

Hmm, you sound like you mean it affects downforce (since you mention setup and track familiarity) but I meant tyre cooling. If wind affects tyre cooling wouldn't you prove that by just leaving the car stationary on a windy day and see how long it takes for tyres to cool? :)
I'm sure wind must affect the handling somehow (or why have it?) but I've actually never tried high wind :)

I'm not sure if it gets lighter but it should get smaller.Indeed. I agree worn=lighter tyres should make almost no diff to the car but a smaller rolling radius should be trivial to spot. But I think this effect is definitively absent or I'd (surely!) have noticed it by now...

I know this mainly by messing around with Tweak and the tyre sizes.
Must have a play with Tweak. Where did you find it? Don't suppose source code is available? :)

As far as I know tyre wear does not affect grip at all. It does, however, affect the weight of the tyre (relatively sure) and the heat capacity (100% sure), the former meaning that with worn tyres you drive a lighter car which goes faster through corners, the latter allowing you to punish the tyres more since they can't hold heat as well and therefore won't overheat as readily.

Hmm, that explanation seems a bit fuzzy to me. For a given heat input, thinner tyres should actually overheat *more* quickly (and cool down more quickly), no? So perhaps the point is that the heating *is* less on a thinner tyre (hence we observe it's harder to keep it hot) and therefore you can drive it at a higher slip angle for the same equilibrium tyre temperature and get more grip out of it as a result.... ??

The temperature however does have an affect on grip (duh) (http://www.lfsforum.net/showthread.php?t=7757), though the graphs are most likely outdated by now.

It does (http://en.lfsmanual.net/wiki/Display#Tyre_temperature.2Fwear_.26_clutch_tempera ture) (click the picture on the right). Just not a numerical one.Wow. Had NEVER spotted that the tread bars get thinner with time. Sheesh. Could have sworn I'd read that Wiki page properly before; in fact the text mentions "Wear" in the section title but nowhere else... And that pic makes it seem like the Wiki authors are (like me) unaware of the wheel rim temperature being part of the tyre-temp info :)

And double-wow. Those graphs are superb. Something I've been wanting to find/make for ages now. Thanks a mil. Will have to have a proper look when I get home in a few days. I've been pondering how to try and automate a procedure for generating stuff like this (maybe there's a way to write an AI for LFS to drive a car in controlled circles...?). OR, WAY easier, Scawen could just make the tyre models (and other stuff like torque curves) public... (Big hint there Scawen, if you ever read this ;))

AndRand

7th August 2009, 20:59

As far as I know tyre wear does not affect grip at all. It does, however, affect the weight of the tyre (relatively sure) and the heat capacity (100% sure), the former meaning that with worn tyres you drive a lighter car which goes faster through corners
cmon, it doesnt make the car significantly lighter, I wonder if those few grams in revolving mass of the tyre make a difference really?
The temperature however does have an affect on grip (duh) (http://www.lfsforum.net/showthread.php?t=7757), though the graphs are most likely outdated by now.
It does (http://en.lfsmanual.net/wiki/Display#Tyre_temperature.2Fwear_.26_clutch_tempera ture) (click the picture on the right). Just not a numerical one.
btw. Android - I reckon you took maximum points of grip vs. slip. Do you maybe have bundle of graphs for the type of tyre - grip vs. lateral force at given temp to see not the optimum tyre temp but the characteristic of the tyre at given temp? Just curious.
Hmm, that explanation seems a bit fuzzy to me. For a given heat input, thinner tyres should actually overheat *more* quickly (and cool down more quickly), no? So perhaps the point is that the heating *is* less on a thinner tyre (hence we observe it's harder to keep it hot) and therefore you can drive it at a higher slip angle for the same equilibrium tyre temperature and get more grip out of it as a result.... ??
well, it is not symmetrical - lots of heat in couple of seconds in the corners and cooling down on straights. So the shorter transition the easier optimum equlibrium to achieve. And I will have to do this test to see if my feeling that tyres cool down too long has some points.

AndroidXP

7th August 2009, 21:39

Indeed. I agree worn=lighter tyres should make almost no diff to the car but a smaller rolling radius should be trivial to spot. But I think this effect is definitively absent or I'd (surely!) have noticed it by now...
Now that I think about it I'm not so sure about the weight reduction anymore, since as you've all pointed out the difference would be minuscule.

However the radius of the tyre changes and that is even quite easy to verify. Simply make a setup with ridiculous brake strength, get some speed on a straight and mash the brakes to create an enormous flatspot. Instead of being a real flatspot, LFS simulates this (rather poorly if you think about it) by wearing down the affected tyre pads. If you then drive very slowly - preferably in wheel-only view - you'll see the tyre bounce up and down as it rolls over the worn-down pads/section. Actually, this is what I'm talking about: 22637

No idea about Tweak though, I haven't been keeping up with LFS for quite some time now. Heh, two seconds later I find this (http://www.lfsforum.net/showthread.php?t=50010).

@AndRand: I don't have the source graphs for that anymore, no, though I don't believe the heat changes the grip characteristics much at all. It seems to be more of a static grip modifier scaling the grip/slip curve up and down the G-force axis.
What makes quite a difference is tyre air pressure relative to the weight of the car. At low weight/high pressure the rising grip line to the peak/plateau is steep and the transition sharp, whereas a high weight/low pressure the grip rise is flatter and the transition much more gradual and smooth.

10772 - This is how a grip/slip curve looks in LFS in general. Note that these are all lateral grip curves - the longitudinal grip curve looks pretty much like the pre-U lateral curve to the right.

10778 - Here I found an old tyre pressure grip curve comparison, see that on a high pressure the grip peaks at about 6° slip whereas on the lowest pressure it reaches the maximum at about 10°. The difference visually doesn't look too great here mainly because the line was probably taken with the FOX, which is pretty lightweight so the tyre pressure had less of an effect.

Ball Bearing Turbo

7th August 2009, 22:07

Hmm, you sound like you mean it affects downforce (since you mention setup and track familiarity) but I meant tyre cooling. If wind affects tyre cooling wouldn't you prove that by just leaving the car stationary on a windy day and see how long it takes for tyres to cool? :)
I'm sure wind must affect the handling somehow (or why have it?) but I've actually never tried high wind :)

I know you meant cooling. I suggested the open wheeler because there is more exposure to ambient air, and the velocity thereof is not shielded by a wheel well. I suggested the setup/track familiarity because if you are real comfortable with it you'll notice that your heating/cooling cycles are noticably modified by a high wind setting.

Neilser

8th August 2009, 00:10

...LFS simulates this (rather poorly if you think about it) by wearing down the affected tyre pads. If you then drive very slowly - preferably in wheel-only view - you'll see the tyre bounce up and down as it rolls over the worn-down pads/section.
Wow, never noticed that. But I guess it doesn't modify the circumference? In other words, what I'd have expected to notice already if it's actually happening is that tyre wear would then raise the RPM for top speed on the straights. Since I've not noticed it (many of my sets would redline with only a modest increase in revs) I had assumed it was absent, but come to think of it I'm notoriously good at *not* noticing things :)
No idea about Tweak though, I haven't been keeping up with LFS for quite some time now. Heh, two seconds later I find this (http://www.lfsforum.net/showthread.php?t=50010).
Nice. Look forward to trying that when I am reunited with my wheel... (I'm so bad with a mouse it's pointless!)
This is how a grip/slip curve looks in LFS in general. Note that these are all lateral grip curves - the longitudinal grip curve looks pretty much like the pre-U lateral curve to the right.
Here I found an old tyre pressure grip curve comparison, see that on a high pressure the grip peaks at about 6° slip whereas on the lowest pressure it reaches the maximum at about 10°. The difference visually doesn't look too great here mainly because the line was probably taken with the FOX, which is pretty lightweight so the tyre pressure had less of an effect.

Wow, more lovely data to digest! (Btw, does the RAF file give you access to the tyre wear data?)

I'm most surprised that the lateral grip doesn't drop at high slip angles - I guess this is what Scawen meant about the grip being too high at high slip? Much more pronounced than I had imagined - it really doesn't drop at all. Weird that it was "better" in the older patch (by which I mean that I believe the more physically realistic one to be the one that falls beyond the peak, rather than having a plateau). [Edit: but the longdit. grip does fall at high slip you say? Scratches head....]

And I'm intrigued about the high pressure effect. Modest drop in grip at high pressure, big drop in slip angle required to get it. This should presumably make the car more driveable too? (Not to mention shorter time constant, thus more crisp anyway...)

I know you meant cooling. I suggested the open wheeler because there is more exposure to ambient air, and the velocity thereof is not shielded by a wheel well. I suggested the setup/track familiarity because if you are real comfortable with it you'll notice that your heating/cooling cycles are noticably modified by a high wind setting.
Aha. Well, I will give it a whirl, but I would have thought that even a high wind will pale into insignificance compared to a race car's average speed around just about any track. The downforce will be affected as it scales with the square of the total air speed on the wing, but the cooling effect (he says confidently :)) should I think just be linear with speed.

Keling

8th August 2009, 05:20

Thinner => softer => better contact　:nod:

AndroidXP

8th August 2009, 07:31

Wow, never noticed that. But I guess it doesn't modify the circumference?Errr, the bumping is a direct result of one section having a smaller radius than the others. Of course if all sections are worn the wheel diameter and with that also the circumference decreases.

Theoretically, if you have a tyre with a radius of 30cm (23.62'' diameter) it needs to rotate at 884.19 RPM to achieve a wheelspeed of 100 km/h. If you wear down this tyre by half a centimetre to 29.5cm radius, the required RPM increase to 899.18, or if you rotate the worn wheel at the same RPM required for a non-worn one, the wheelspeed will be 98.33 km/h.

However, do note that the speedo in LFS works by measuring the speed at the differential / wheels and simply assumes a certain tyre circumference to calculate the actual speed (like real cars do). If you drive a car in 5th gear at 5000 RPM the speedo will always display the same speed regardless of how worn or inflated the tyres are. Now if you had a GPS like system that showed your actual velocity, it would be clear that you're actually moving at a different speed than the speedo displays with worn or differently inflated tyres.

AndRand

8th August 2009, 08:43

10772 - This is how a grip/slip curve looks in LFS in general. Note that these are all lateral grip curves - the longitudinal grip curve looks pretty much like the pre-U lateral curve to the right.
I am a bit surprised. First, I thought grip curve is symmetrical in both directions (3d chart with grip circle would be interesting :scratchch), second, I will try to do the tests - with temperature rise the grip curve should not only move higher but also shoud get less steep, so the transitions are softer, similar to lower pressure effect but with less deformation, thus better control, right?

logitekg25

8th August 2009, 14:45

Errr, the bumping is a direct result of one section having a smaller radius than the others. Of course if all sections are worn the wheel diameter and with that also the circumference decreases.

Theoretically, if you have a tyre with a radius of 30cm (23.62'' diameter) it needs to rotate at 884.19 RPM to achieve a wheelspeed of 100 km/h. If you wear down this tyre by half a centimetre to 29.5cm radius, the required RPM increase to 899.18, or if you rotate the worn wheel at the same RPM required for a non-worn one, the wheelspeed will be 98.33 km/h.

However, do note that the speedo in LFS works by measuring the speed at the differential / wheels and simply assumes a certain tyre circumference to calculate the actual speed (like real cars do). If you drive a car in 5th gear at 5000 RPM the speedo will always display the same speed regardless of how worn or inflated the tyres are. Now if you had a GPS like system that showed your actual velocity, it would be clear that you're actually moving at a different speed than the speedo displays with worn or differently inflated tyres.
so to simulate this could two people hop on a server, and get the xrg, and the xrt (so the xrt can definately keep up and check speed) set a quite low ratio for both, test top speed of the XRG, let the tires cool down, then do a burnout until the tires are about to explode let them cool, do it again, let them cool once more, then test the same speed?

do you know what i mean :really:

AndRand

8th August 2009, 17:59

Theoretically, if you have a tyre with a radius of 30cm (23.62'' diameter) it needs to rotate at 884.19 RPM to achieve a wheelspeed of 100 km/h. If you wear down this tyre by half a centimetre to 29.5cm radius, the required RPM increase to 899.18, or if you rotate the worn wheel at the same RPM required for a non-worn one, the wheelspeed will be 98.33 km/h.
And how can you achieve better laptime by this? :really:

Degats

8th August 2009, 18:12

You're probably better off using an InSim app with frequent MCI(?) packets, as this will accurately report actual velocity.

logitekg25

8th August 2009, 18:43

he diddnt say anything about better laptime ;)

AndroidXP

8th August 2009, 19:00

And how can you achieve better laptime by this? :really:
:confused:

The smaller circumference certainly doesn't help you achieve better laptimes.
However when the tyres are worn down likely following things happened:

1) You drove for a quite long time and are more likely to be "in the zone"
2) The tyres have less heat capacity, cooling down from the usual overheat phase thus enabling you to go faster after having to drive careful
3) Your fuel level is lower than on race start
4) The tyres behave differently somehow (???)

Neilser

8th August 2009, 22:36

Errr, the bumping is a direct result of one section having a smaller radius than the others. Of course if all sections are worn the wheel diameter and with that also the circumference decreases.Er, yup, I know that :) I'm just saying that LFS isn't necessarily going to model both a height change AND a circumference change due to the thinner piece of rubber. My best guess (but it IS just a guess) is that LFS does not model the circumference change.
However, do note that the speedo in LFS works by measuring the speed at the differential / wheels and simply assumes a certain tyre circumference to calculate the actual speed (like real cars do).
A useful reminder - I think I had probably forgotten that LFS uses the axle/diff speed.
However, it wasn't what I was getting at anyway - I didn't say I expected to see a higher top speed come up on the speedo, but that the revs for top speed should be different.
The real top speed (if the limiter doesn't kick in) would be approximately the same with a smaller rolling radius, as it's decided almost entirely by aero drag, with the main thing causing a slight change in speed being the modest change in engine power at the new, higher engine speed.
But in a setup which has max speed sufficiently close to redline revs, I was thinking that the car might actually hit the limiter... But in fact maybe you'd need to use an analyser to see the difference, if it is only a couple of percent or so (2% means only 140 RPM at 7k RPM).
I think I'm going to check this out next time I wear my tyres down a lot :)

Neilser

8th August 2009, 22:45

1) You drove for a quite long time and are more likely to be "in the zone"
2) The tyres have less heat capacity, cooling down from the usual overheat phase thus enabling you to go faster after having to drive careful
3) Your fuel level is lower than on race start
4) The tyres behave differently somehow (???)
FWIW, my money's on number 4, if the "worn tyres are better" hypothesis is correct at all.

AND, I've just realised that your super-cool tyre data-gathering technique could actually help prove what's going on here :)

All one would have to do would be to test a tyre when fresh and then again when worn down almost to the canvas and compare the grip/slip data.
Now this won't necessarily reveal the effect I mentioned earlier - that a tyre may get heated less for a given cornering force (due to less mechanical work being done in the thinner rubber layer, due to less distortion). But it should certainly show up any "magical" extra grip which is appearing at a given slip angle.
(It might even reveal the reduced heating too though, I guess.)

AndRand

9th August 2009, 11:12

But in a setup which has max speed sufficiently close to redline revs, I was thinking that the car might actually hit the limiter... But in fact maybe you'd need to use an analyser to see the difference, if it is only a couple of percent or so (2% means only 140 RPM at 7k RPM).
I think I'm going to check this out next time I wear my tyres down a lot :)
You can always change FinalDriveRatio :tilt: I think it is neglectable... maybe the mass of the tyre changes, which placed at the end of the tyre radius (we are talking about less than 1cm change) can make a slight difference, but... very very slightly

AndroidXP

9th August 2009, 14:34

AND, I've just realised that your super-cool tyre data-gathering technique could actually help prove what's going on here :)Of course doing a RAF extract of the worn tyres could bring some light into that, but... the problem is to acquire worn tyres in the first place. Heating them or changing pressure is something that can be done in a minute, but wearing them down is a far more daunting task.

The easiest way is probably to let the AI drive lots and lots of laps on a balanced and not too difficult track, though if the AI pits for refuelling or crashes (doing a reset) all the wait would've been for naught. Even if it succeeds and wears down the tyres, it could happen that it simply doesn't use the tyres in a way that provides useful data.

bbman

9th August 2009, 15:43

Of course doing a RAF extract of the worn tyres could bring some light into that, but... the problem is to acquire worn tyres in the first place.

If it needn't be a specific setup, why not ask for longrun-tests in any endurance league forum? :shrug:

AndroidXP

9th August 2009, 16:37

Well, I guess if they record their tests in single player mode...?

AndroidXP

9th August 2009, 17:39

Anyway, did a "quick" test with one FZR AI on KY Nat, letting it drive 2hrs on R3 slicks. The maximum tyre wear was reached at about lap 35, in which it did a pitstop to refuel where it also changed the tyres. From looking at the wear of the F9 view, it seemed like it was worn about 30-35% - it was definitely over 30% though, as the AI set its pitstop strategy to change when worn > 30%.

Looking at both left and right rear tyre data (lateral grip vs. slip angle) and comparing lap 6 to lap 35 shows that there's definitely NO change in tyre behaviour by wear (as I suspected, to be honest). The curves looked pretty much 99% identical and the tiny difference can most likely be attributed to a difference in tyre temperature, air pressure and/or car weight.

Neilser

9th August 2009, 17:57

Looking at both left and right rear tyre data (lateral grip vs. slip angle) and comparing lap 6 to lap 35 shows that there's definitely NO change in tyre behaviour by wear (as I suspected, to be honest). The curves looked pretty much 99% identical and the tiny difference can most likely be attributed to a difference in tyre temperature, air pressure and/or car weight.
Hey - nice one :) And the negative result isn't a bad thing - it actually simplifies matters, because I just remembered another thing (which we could call number 5 :)):
The "less heat while cornering" effect I've been mentioning (or at least hypothesising, but like many people I've personally observed that worn tyres run cooler) almost certainly comes with another effect if physical realism is preserved: lower rolling resistance. Perhaps THIS could be the magic ingredient to explain why worn tyres are "quicker"?
(I should have remembered this sooner, ouch.)

How to verify it? Well, I guess it should mean that the real top speed would be higher - that might be the simplest place to look. So if you review the (actual, not speedo) straight-line speed for your AI at low/high tyre wear...

AndroidXP

9th August 2009, 18:18

Bob Smith

9th August 2009, 20:17

Larger tyres generally exhibit lower rolling resistance, so I'm not sure your reduced rolling resistance hypothesis necessarily holds true. Most rolling resistance comes from rubber hysteresis in the sidewalls, which should be unaffected by tread wear.

Neilser

9th August 2009, 21:49

Impossible. Reading the speed would be a piece of cake, but there's no way to do a useful speed comparison on an almost full and empty fuel tank. Also there's no track on LFS where you can reach air-resistance limited top speed. The oval comes close, but not quite - even there it depends on how well you exit the last corner. Besides that, the AI absolutely sucks at the oval (it was actually braking there on the KY Nat run :doh:)Wow, chalk up another dumbness point for the AI :)

OK, scratch the terminal velocity approach - maybe it's possible to get at it a little more indirectly by checking the axle torque and car acceleration at the same speed for both tyre states?
You will also know the mass of the car (which will differ due to fuel loadings) and thus I *think* (hey, it's late ;)) that all the required ingredients will be available to allow us to calculate the power dissipated into the tyres?

The power to the axles (call it axlepower) is proportional to axle torque * axle speed (more precisely, it's 2 * pi * torque * axle-turns-per-second, which will give you a result in Watts if torque is in Nm). If it's the same in both cases (due to the rolling radius being identical, which might be the case) then so much the easier but it's not actually a requirement.

The power soaked up by the rate of change of kinetic energy of the whole vehicle mass (call it accelpower) is easy to calculate from the mass, velocity and acceleration. The kinetic energy is 0.5 * m * v^2, so accelpower will be
m * v * dv/dt or just m * v * a (with kg and m/s and m/s^2 for units, this will also be in Watts).

The power soaked up by the aero drag will be the same for both cases (cos same speed) and thus we don't need to know it (but the RAF file may have enough info to allow it to be calculated directly? I've not yet used a RAF analyser.) The missing piece of power is presumably being used up by the rolling resistance (if I've not forgotten anything), most of which is probably heating up the rubber. (I think??)

So if (axlepower - accelpower) differs between new tyres and worn tyres, we have our smoking gun, provided of course I've not been too hasty and missed something major (!).

Larger tyres generally exhibit lower rolling resistance, so I'm not sure your reduced rolling resistance hypothesis necessarily holds true. Most rolling resistance comes from rubber hysteresis in the sidewalls, which should be unaffected by tread wear.
Goshdarnit Bob, your objection is disgustingly plausible :( Not sure why a larger tyre should have less resistance, but certainly the sidewall argument seems sound.

But, maybe the sidewall distorts more with a thicker tread layer because of the extra effective leverage? (Reaching a bit here :))

OK, recalling that what I'm chasing here is "if and why worn tyres are quicker *in LFS*" (i.e. not in real life), maybe another place to look hard is cornering. (This may be a lost cause! But read on if you want to indulge me...) I've watched a replay where worn tyres *may* have been the secret to carrying a lot of speed through a high-speed complex of corners. If the worn-down tyre is scrubbing less speed off, then a test for this might involve monitoring the axle torque required to maintain steady speed while cornering at a given acceleration. I'll maybe have a go at this...

(I must admit I'm doubting somewhat that worn tyres are actually quicker! But if they do turn out to be quicker, it doesn't have to be physically realistic - it can just be an (accidental) artefact of the way LFS models those rather complex lumps of rubber...)

AndroidXP

9th August 2009, 22:47

I'm really not sure what you're pursuing here as a whole? Seems to be a whole lot of effort for nothing really :)

I think it's pretty clear that the tyre wear itself has no direct physical influence on the car's performance (in LFS). All the factors you're speculating about here are far to small to have any serious impact on laptimes, compared to the uncertainty factor that is human control, or other actually big factors like tyre temperature or fuel weight. If there was an artefact, a physics oddity, then somehow it would have to be big enough that untalented drivers (relatively speaking) benefit from it, too, for it to be "noticed" so widely. And if it were that big, you'd see all world record laps taking 60+ laps beforehand to wear down the tyres to get this then very tangible advantage of having worn tyres, and I'm pretty sure hotlappers do anything to set a WR ;)

Honestly, I think it's more to do with ones mind than having an actual physical reason. You want to believe... no, you know that a worn tyre makes you faster so in the end you are faster. Suddenly in your mind the worn tyre actually made you faster, whereas it was probably just you believing in yourself resulting in better driving. And with that you have the self-reinforcing "evidence" of worn tyres making someone faster, where there can hardly be found any measurable effect of tyre wear itself.

Comparisons of LFS to real life are also somewhat useless. While LFS is quite good and complex in general, if you start going into the details you just notice more and more areas that very much matter for racing are only very roughly approximated if simulated at all. Tyre heat and wear is (officially) a very WIP part of the simulation, with most behaviour being barely more than educated guesses. I could now list all the obvious deficiencies of LFS' tyre model, but really there's no point. Making a fully abstract model of a tyre where in the end the correct behaviour just falls into place is, while noble, not really realistic in terms of being a reachable goal either.

Right now, I think LFS in terms of realism is so close, yet so far.

Bob Smith

10th August 2009, 08:22

Not sure why a larger tyre should have less resistance, but certainly the sidewall argument seems sound.
Perhaps it is due to larger tyres generally being used to support larger weights, so are made stiffer, thus flex less, or that larger radii wheels will be less affected by the small bumps that are present on any non-smooth surface.

bbman

10th August 2009, 09:04

Honestly, I think it's more to do with ones mind than having an actual physical reason. You want to believe... no, you know that a worn tyre makes you faster so in the end you are faster. Suddenly in your mind the worn tyre actually made you faster, whereas it was probably just you believing in yourself resulting in better driving. And with that you have the self-reinforcing "evidence" of worn tyres making someone faster, where there can hardly be found any measurable effect of tyre wear itself.

Nah, the lesser heat capacity definitely makes a difference - if your tyres can cool between the corners you'll be able to push more than with a full tread... For example, the temperature will steadily increase in those long fast corners of KY GP on fresh rubber - a worn tyre can cool down even on those short straights...

AndRand

10th August 2009, 16:41

excuse, one question - why do you think worn tyres can make a run quicker? Because of some lad who took his time to wear them down just before WR attempt?... :really: maybe it made him... lucky :)

Whitmore

10th August 2009, 18:34

Perhaps it is due to larger tyres generally being used to support larger weights, so are made stiffer, thus flex less, or that larger radii wheels will be less affected by the small bumps that are present on any non-smooth surface.

Think about where the tread is in contact with the road (i.e the contact patch). The tread there is flat so it has to flex from its normal curved shape. If we assume the same contact patch, the tread on a larger diameter tyre has to bend through a smaller angle when it reaches the road (becomes part of the contact patch). Bending through a smaller angle results in less rolling resistance.

Bob Smith

10th August 2009, 20:31

Whitmore

10th August 2009, 21:13

Interesting but I've always assumed that the contact patch would get longer, and thus the angle would remain similar. That's also assuming the tyre were just as vertically stiff, so would vertically deform as far. I think that the extra rubber makes the tyre stiffer, leading to less deformation, thus less hysteresis.

The stiffness and the contact patch size depends mainly on the tyre pressure, (unless we are talking run-flat tyres) so it will only get longer if you run your bigger tyre at a lower pressure than your smaller tyre. In order to compare the effect of diameter you need to assume the same pressures. After all, a smaller dia tyre at 50 psi will have a lower rolling resistance than a bigger tyre at 10 psi.