I'm no physics professor, but I do have a lot of first hand experience with racing tires, both on karts and cars.

Now, I don't know what temps you start out with, but when you turn into a corner in say a Formula BMW in LFS the car responds immediately. This does not happen in real life with new cold slick tires. It takes about half a second for the fronts to start responding in such a light car with such relatively large footprints. It's important to note that this only happens with brand new, cold slick tires. This phenomenon is almost imperceptible with street tires because a, the car is much heavier, and b, the tire surface area is less because of the tread. Once the slick tire has a lap worn into it, this first-corner scramble for grip will never happen again no matter how cold the tire is.

This brings me to wear. A common misconception is that rubber leaving the tire takes away grip. Not so, at least these days. Grip is lost (or gained) purely via heat, in the form of the molecular composition of the tire. Cold tires are baked specifically so that they will gain grip as the temperature changes, we all know this. What most people don't realize is that the tire's composition will never return to factory. You can't stick a pizza in the oven for 3 minutes and just let it cool down. It won't be the same. As soon as a tire is overcooked, it's done. One really slidey lap on a hot day will usually ruin a tire set for life in heavier classes. Heat those sticker bad boys up once with a blanket, bring them back down slow, and you won't leave the pits without grip, or at least enough of it.

The second part to that is that extended running at even optimal temps will cause the tire to die or fall off. Cook a pizza too long and it gets really hard. Same thing with tires. It's got nothing to do these days with rubber coming off. The tires bake themslves to oblivion well before they delaminate.

You can see this easily. Go to an IndyCar race, or even an SCCA event with Formula cars, and just look at the tires coming off the cars. The quick cars will have a nice even river pattern on them, very fine, like wood. The slow cars will either have a very big, messy pattern or worse, an uneven one. The big pattern means bad (overcooked) tire, the uneven pattern means bad car. If the fast cars with the nice, sexy patterns make a really long stint, look at the tires again when they come off. They'll be ugly, and if you're like me, they'll make you want to puke, because no one who drives seriously likes to see a tire treated that way.

As far as surface goes, the smoothest surface (think concrete indoor kart track) generates the most heat, but offers the least grip. It also chews the tire less - the rubber will last longer, but it will lose grip quicker due to heat. The rougher surface (think Bahrain with their stupid acid wash) offers the most grip, but less heat (less friction, less heat). It also chews tires a lot, but the composition lasts longer due to less heat. The differences don't make as much of a difference as they could, since pretty much all naturally mantained tracks keep the rubber for a good while.

That's my experience with tires, anyway. I always say to people, the most interesting thing about tires is that they get to 200, maybe 300 degrees. My oven does that every day. Tires are just a frozen pizza.

Quote from MadCat360 :

Now, I don't know what temps you start out with, but when you turn into a corner in say a Formula BMW in LFS the car responds immediately. This does not happen in real life with new cold slick tires. It takes about half a second for the fronts to start responding in such a light car with such relatively large footprints. It's important to note that this only happens with brand new, cold slick tires.
*snip*

Interesting insight there

The FBM's tyres in LFS effectively come at a pre-warmed 65 degrees - not up to racing temps, but certainly not cold. It's probably best to think of them as lightly scrubbed and is probably the best way of treating fresh tyres in the absence of warm-up laps in LFS.
It would be interesting to have the option of brand new tyres when changed on a pit stop though.

Quote from Degats :

The FBM's tyres in LFS effectively come at a pre-warmed 65 degrees - not up to racing temps, but certainly not cold.

Well, that solves that.

Quote from Degats :

Interesting insight there

There's more to it, as well. It's a problem at all speeds, in the karting series I'm competing in this year, the end of the pit straight at Infineon Upper is bent 90 degrees, and it's quite narrow. In the morning, when it's about 55 or 60 degrees and we leave with brand new slick tires, sometimes it's hard to take that turn at walking pace. You can drift that corner at 3 MPH with cold tires. Karts have this problem in the extreme since they're so light and the tires are so huge compared to the size of the car.

When we exit the pits and get down to turn 2 (exit is just at the exit of 1), we have to take turn 2 at about 10 or 15 MPH, normally taken at 50 MPH, which is sometimes hard to do since the braking zone is downhill and very bumpy, and we only have 1 very cold brake disc to work with very cold rear tires. Even at 15 MPH, we almost don't make it around the corner, but we have to go that fast because any slower and the tires would just not heat up at all. Once we get out of the turn 2 and 3 complex (right left right right) the tire's are pretty good and you can take a pretty normal warmup lap.

The other problem is that you have a very cold set of rear tires, so as you're heating the fronts, they're gaining grip (this is over the course of half a second on turn in), they bite, and then the cold rears start to come around. If you're not ready for them (you've been understeering) you'll spin, even at 15 MPH. And it's worse on banked turns. This also means you can't weave on the straight. Normally we don't weave, it wears your steering rack out more than it heats the tires, but at these temps it's tempting. Problem is, the rears are so cold that a pendulum-inducing weave will make you spin.

So all you can do is bite the bullet and hope you make the first turn. I've seen some really cold days where almost everyone, even experienced racers, spin in turn 1.

Quote from yeager :

Slightly off topic, but only just. I've got this book some of you may find an interesting read.

http://insideracingtechnology.com/booktiredescrptn.htm

That's a good book indeed. I had lunch with the author once at a convention

Quote from ColeusRattus :

In which racing series? I personally can't recall a fastest first lap unless the driver messed up all the other laps after that.

Watch an Indy 500 qualifying run. Speed fades for most drivers. Whether it's due to wear or temperature change or a combination I can't tell you.

Well, that's a phenonemon limited to oval racing then.

One thing I've always noticed in all driving simulations (LFS included) is that the tires are always slipping. Take a UF1 with the default config up to 60 mph and quickly bounce the throttle open and shut. In LFS the engine speed rapidly jumps up and down a little bit as the ever-present amout of wheel spin reacts to the different amounts of torque.

Quote from Rotareneg :

One thing I've always noticed in all driving simulations (LFS included) is that the tires are always slipping. Take a UF1 with the default config up to 60 mph and quickly bounce the throttle open and shut. In LFS the engine speed rapidly jumps up and down a little bit as the ever-present amout of wheel spin reacts to the different amounts of torque.

I haven't noticed it, are you sure it wasn't a hot clutch or something?

Quote from Rotareneg :

One thing I've always noticed in all driving simulations (LFS included) is that the tires are always slipping. Take a UF1 with the default config up to 60 mph and quickly bounce the throttle open and shut. In LFS the engine speed rapidly jumps up and down a little bit as the ever-present amout of wheel spin reacts to the different amounts of torque.

Yes and this is technically correct behaviour. It shows however that the speedo needle updating isn't slightly latent even for small changes like it is in real life. Before LFS took speed display from the axle speed, it was not like that, but now that it does (that was changed a couple years ago) you can see this phenomenon. In the very first patch it was released, there was basically zero buffer on the speedo - it literally read exactly what the wheels were doing at any point in time and it looked strange. It needed to be limited in rate of travel in terms of max degrees per second, and have some latency. There is likely not enough latency on tiny changes yet - it seems this nuance isn't noted by most developers.

You'll find that wheels under power are not actually revolving at a speed that matches the actual road speed; there is a small discrepancy there because of the way tires actually work. Real tires are, in fact, in a constant state of slip when you're in motion, it's just a matter of how much.

Quote from S14 DRIFT :

I haven't noticed it, are you sure it wasn't a hot clutch or something?

Not the clutch slipping. The attached replay shows the effect.

Quote from Ball Bearing Turbo :

Yes and this is technically correct behaviour. It shows however that the speedo needle updating isn't slightly latent even for small changes like it is in real life. Before LFS took speed display from the axle speed, it was not like that, but now that it does (that was changed a couple years ago) you can see this phenomenon. In the very first patch it was released, there was basically zero buffer on the speedo - it literally read exactly what the wheels were doing at any point in time and it looked strange. It needed to be limited in rate of travel in terms of max degrees per second, and have some latency. There is likely not enough latency on tiny changes yet - it seems this nuance isn't noted by most developers.

You'll find that wheels under power are not actually revolving at a speed that matches the actual road speed; there is a small discrepancy there because of the way tires actually work. Real tires are, in fact, in a constant state of slip when you're in motion, it's just a matter of how much.

I'm not looking at the speedometer, I'm looking at the tachometer.

And in real life tires do not slide constantly when driving straight on pavement. The rubber in the contact patch does not move relative to the road surface except where it deforms to conform to the road surface at the front edge and then begins to return to it's normal curve at the rear. Even when turning the contact patch will remain static to the surface with just more scrubbing at the edges, at least until the point where the turn or acceleration (or both) causes the contact patch to start sliding and/or become so deformed that no point is static any more.

I would watch the video, but it seems to not be Z patch.

edit: and I think you're talking about the difference between being on the throttle and off the throttle. Do it in a real car and the exact same thing happens.

Fixed the replay (was running Z13 beta, switched to regular Z.) With an automatic you get that, but with my manual tranny car it sure doesn't happen.

Quote from Rotareneg :

I'm not looking at the speedometer, I'm looking at the tachometer.

Heh, well then that makes even more sense because the phenomenon is the same and given gear reduction shows less of an error percentage wise. Same principle to gauge needle acceration applies anyway of course.

Quote :

And in real life tires do not slide constantly when driving straight on pavement. The rubber in the contact patch does not move relative to the road surface except where it deforms to conform to the road surface at the front edge and then begins to return to it's normal curve at the rear.

When under power or braking there is a slip ratio relative to the surface. Just because you don't perceive it, doesn't mean it's not there. Read up on tires.

Quote :

Even when turning the contact patch will remain static to the surface with just more scrubbing at the edges, at least until the point where the turn or acceleration (or both) causes the contact patch to start sliding and/or become so deformed that no point is static any more.

No, there is no transition from static friction to dynamic friction on a tire in motion. As long as there is a torque on the tire (longitudinal accel) there is a slip ratio occuring.

I did do a bit of reading up before posting, as far as I can see, the idea of tires constantly sliding are related to the Pacejka tire model, not real life.

Any computational tyre model, be it empirical like Pacejka, or otherwise, relies on slip ratios and angles to produce force. All tyre models work like this because, oddly enough, this is how tyres work too.

Best Motoring (Japanese equivalent of Top Gear, but better) did a test a while ago testing what would happen to the tyres, brakes, engine water and engine oil temperatures when you ran them on a track for extended periods of time. The cars were all driven by experienced racing drivers. There were 2 heats each lasting 20 minutes with a 30 minute break period between the heats. The air temperature was 32.1 degrees Celsius, the track was 43 degrees Celsius and the humidity was 50.6%. The tyres fitted were those recommended by the manufacturer, they were inflated to 0.2 psi less than the manufacturer recommended. Below are the tyre temperatures which were measured from the outside shoulders of the front and rear tyres.

After heat 1 (20 minutes):


After heat 2 (20 minutes more action after a 30 minute break):


Below are some of the laptimes for the Evo VIII taken during the second heat:


What this shows us is that even as the tyre temperature increases the drop-off in performance is not very severe (just over a second, in fact) and it seems the tyres have quickly reached a plateau and they don't degrade after that. What's more interesting, though, is the condition of the left front tyre at the end of the second head. I've attached an image of it to this post.

So, in summary. Yes, it's possible to get temperatures well over 100 degrees centigrade with standard road cars and standard road tyres. The drop-off in performance with temperature does not seem severe (at least not as severe as LFS shows).

As has been said before, though, the tyres are obviously very difficult to model accurately.

Quote from ColeusRattus :

Well, that's a phenonemon limited to oval racing then.

Well no, add to that the V8Supercar serries... they posted some clear graphs of lap time degradation over a stint. Their normal control tyre can expect to see a second a lap difference from start of the stint till the end. They also have a sprint tyre they can run with much softer compound that has much more dramatic degradation of lap times over a stint of the same length.

Interesting post amp88, the evo tyre looks like it has suffered quite abit from overheating on the shoulder and a little on the edges of the tread blocks. It is suprising it didn't effect his lap times more.

My understanding though is that road tyres should be more stable in their chemical makeup than a race compound and therefore I'd expect it to have less performance drop off than a slick or true race compound. Did they have times from both stints?

Excellent find amp88.

Quote from Glenn67 :

My understanding though is that road tyres should be more stable in their chemical makeup than a race compound and therefore I'd expect it to have less performance drop off than a slick or true race compound.

I've attached another image from the book "Speed Secrets" by Ross Bentley. It shows how the grip changes with temperature on a "typical" road tyre versus a "typical" racing tyre. Clearly there's some ambiguity here because we don't know what the tyres really are (is the racing tyre an F1 tyre or a champ car tyre or a V8 Supercar Dunlop control tyre), but the graph is supposed to give a good idea of the grip curves relative to temperature.

Quote from Glenn67 :

Did they have times from both stints?

Times from the first heat:

:jawdrop:

Wow, great data there Amp. That should make it clear for those who say "LFS tire model is totally correct" that it quite isn't so. It's not like I'm suddenly asking for perfectly simulated tire physics, just a little 'tweak' (yes, yes, it's not that simple) to get rid of this :soapbox: syndrome would be a great move towards realism.

Again more interesting data...

You can see that the times from both stints degraded over the length of the stint and also that the second stint was slower than the first in general. This correlates to the aging of rubber exposed to heat as much if not more than from mechanical damage One would suspect that with the much higher tyre temps on the front in the first stint that was when it suffered chunking of the tyres. Do you have data from any of the other cars or more commentry of when the tyre sustained the physical damage?

Did you catch the coverage of V8Supercars which showed the graphs I refer to? Think it was Oran Park round (memory fails )

The graph you show only indicates temp and shows what I'd expect from different compounds, it would be interesting to see a graph that measured traction verses age of tyre.

Quote from Glenn67 :

Again more interesting data...

You can see that the times from both stints degraded over the length of the stint and also that the second stint was slower than the first in general. This correlates to the aging of rubber exposed to heat as much if not more than from mechanical damage One would suspect that with the much higher tyre temps on the front in the first stint that was when it suffered chunking of the tyres. Do you have data from any of the other cars or more commentry of when the tyre sustained the physical damage?

I've attached a shot of the tyre after the first heat. It's not looking too healthy, but it's nowhere near as bad as at the end of the second heat. There's no mention of the driver going aggressively over kerbs or anything, so we can only assume the damage was done through high temperatures in the second heat. It could be a side effect of the tyres being put through a second intensive heat cycle so quickly after the first one. There is some data for all of the other cars through each of the races. The only thing stopping me from reporting it all is laziness

Quote from Glenn67 :

Did you catch the coverage of V8Supercars which showed the graphs I refer to? Think it was Oran Park round (memory fails )

It was actually Winton

Attached it too.

Quote from amp88 :

It was actually Winton

Attached it too.

That's it I knew I could rely on you! I wouldn't suggest that graph as being highly scientific but it does serve to illustrate that tyres do "go off" some worse than others depending on compound and tyre design.

Looking at the tyre from first and second stint it does look like there is a correlation to tyre wear/damage vs lap time also. This is were LFS is odd when towards an end of stint when tyres are cooling more you can work them harder and get the fastest lap times were in real life it is more likely that graining wear and damage to a tyre would result in worse lap times in this phase even though temps are less.

It is interesting that the graph you posted for temp vs traction does show a signicifacnt leveling out in the overheated region and that they don't bother graphing above 127degC which would indicate it's hard to get a tyre that hot - possibly due to tyre failure?

I'll add I'm very skepitcal about that temperature vs force graph.

Why? The road and race tyres have the same shape curve, which I find unlikely, given what I've previously read, and most of all, both tyres give zero grip at 120°F, or 49°C, which a road tyre is unlikely to reach without spirited driving. I'd not notice cars everywhere driving like they were on ice, so at least that part of the curves are complete rubbish.

yeah I was thinking that that graph also wasn't exactly scientific but to serve only as a guide to how different tyres behave. Cold tyres certainly have more grip than zero