Well I should rephrase that =P if the tire is in overheating over the whole tire I would increase pressure, not decrease it. I would also look at how I was driving but still =P
I understand what you said tristian and I practice that. I am not getting why though you would increase pressure to make the tires heat quicker, physics is telling me the oposite. I can understand that it's because you want to counteract the absense of pressure buildup that you would get during a race that would prevent the sidewall form flexing too much, but increasing pressure, in itself wouldn't increase tire temperature. I could see it though if it meant that you could run a corner a bit harder, hmm maybe thats where I am missing the boat? =P
Lower pressures WILL allow the tyre to heat faster.
But with pressures in real life you are concerned with getting the correct 'hot pressure'. On a cold day the air in your tyres will be cooler, but will tend to increase the same amount, thus your hot pressure will be lower than optimum. So you run slightly more cold pressures to compensate.
It's very rare you'd use tyre pressures to control tyre temperatures in real life - that's a function of camber, compound, construction, track temp, track abrasivity and driving style.
Ok, thanks, that's what I wanted to hear =) I understand why you have increase cold pressure for a cold day. But I didn't know that pressures are not used to effect tire temps. I do realize that compounds aswell as driving style and track conditions effect temps but I was always under the impression that you could adjust pressures to adjust temps. Maybe I had been watching too much NASCAR while I grew up =P
Not 100%, no. But bikes don't have camber adjustments in the same way to define how the tyre contacts the track. And the recommended pressures for car tyres don't allow much range for tuning temps - sure you can get a bit of control over them, but that vast majority of that is done via setup.
Same with bike tyres to an extend - if you've got overheating tyres something, other than pressure, is wrong. A bike is, in many ways, more reliant on 'correct' pressures than a car, simply because a car can't fall over at the slightest loss of grip
Is there are graph anyway showing the "peak" grip for different pressures for a given tyre?.
I remember seeing one for heat vs grip, but can't remember seeing one for psi vs grip (ps if anyone remembers the link to the heat vs grip graph please post it).
I also made a kPa vs. grip one, and the grip was best with the lowest pressure, linearly going down as pressure increased. This was without changing camber or anything.
Trying to do get as much lateral grip out of the rears as possible (circles + clutch in + not too fast to get downforce) and then noting the maximum commonly reached lateral reading from the RAF tyre extract graph tool thingymabob.
I'm currently doing loads of data collection / research into tyres using LFS, I can make a thread with all the data when I'm done If anyone would be interested.
Exactly, you can't go too low - that's all i'm really saying, in lfs it seems to work. If your tyres aren't heating up enough within the optimum pressure range you don't go 10psi lower to generate heat because you'll be generating the heat on the sidewalls rather than where you want it and can 'cause tyre failure. First priority is to have the tyres within the correct pressure range, second priority is to have the tyres at the correct temps. You will never be able to drop tyre pressures 15psi to generate heat if you're running at near freezing temperatures and your compound isn't soft enough - you do the best you can by setting the car up for maximum grip but you don't ruin the shape of the tyre 'cause you'll just lose more grip, and yes you will probably want to run the pressures lower, but only within the narrow operating range, you would still run them higher in qual than in a long race though. The best way to get the heat up in a too cold situation is a softer compound but if that isn't there then softer car, increase toe, and through the car around more to generate heat.
Tristan pretty much covered what I also mentioned earlier, the pressure envelope is quite narrow (~5psi), so you can't be going around making setup changes by drastically changing tyre pressures - we're not in 1950 anymore. Within that small recommended envelope maximum Cf is probably generated at the lower end of the pressure, it's just that you really need to be very close to the optimum pressure all the time.
Quoting Mr Paul Van Valkenburgh:
So what I am talking about is that in a short stint you need the pressure higher so that you are at the optimum pressure when you go for your most important lap, but in a race that would mean lap 2-3 would be at optimum pressure and above that it wuold be too high. In all real life aplications I've never seen or heard of people going with a really low pressure for qual, and then raising it for the race, there might be exceptions of course but I haven't heard of them. If you had to use low pressure in qual to generate heat you also have to do it for the race.
We simply do not want the heat that is generated by sidewall flex to be the way we generate heat in tyres - that is why touring cars with the tyres enclosed (enclosed=less cooling from the air) have very low profile tyres, whereas single seaters can have larger sidewalls. We generate heat in the tyre with the car setup and also distribute the heat with car setup, not by running low pressures.
I'm not saying that the LFS tyre physics seem to be completely wrong, just that the tyre pressure performance envelope seems to be a bit off. All the other factors are right to a certain extent imo -> less pressure = better road compliance and more rolling resistance and more grip, but IRL you want to run HOT qual and race pressures very close to eachother or you're simply throwing away performance, in lfs it isn't the same. Another thing I don't know if lfs simulates or not is the large amount of effect download has on the shape of the tyre - on an oval you run much higher pressures because the download at high speeds will push the tyres down and will assume the same optimum shape they would've with lower pressures on a street track at low speeds with less download.
An interesting thing about tyre temps is that LFS perhaps always displays the average reading or "pit reading" - not peaks, or it doesn't simulate peak temps? IRL tyre temps vary greatly while on track from and can go from 150 degrees f to 370 degrees f within seconds during a turn. Valkenburgh had some figures of tyres cooling at 50 degrees fahrenheit per second down high-speed straights from their peak temps after the corner. This is why you see tyres "shine" in corners and then go dull again on straights.
I was getting confused typing.. parts of my post might not make any sense. illepall
An example of tyre pressure trickery that can be used and also illustrated my point of running higher pressure for low runs: In a kart race where you have maybe 2-3 warmup laps before the green flag is thrown the lead kart determines the speed - and in effect also determines how much pressure buildup everyone is able to generate. He can choose to run pressures 1-2 psi higher like in a qual setup for a 15 lap race and then proceed to lap the warmup laps very slow, so those that have put race pressures will be struggling for the first few laps and by the time their tyres come in the leader should be well on his way.
Googling I found that some nascar sim setup guides say it right "run higher pressure for qualifying than you will for the race"
I am one of those who qualifys with 1.4 bar and races with 2.4
What's the main reason why unrealistically low or high tyre pressures actually work in LFS?
I would say what was mentioned before already: no tyre sidewall damage.
until that is simulated there will be no reason not to run low pressures to achieve maximum grip.
to be honest I don't think LFS tyre heat model is (that much) off, it is just the sidewall damage simulation that is lacking, which results in these unrealistic pressures. I am always trying to get optimum tyre temperatures across the surface of the tyre, but with camber changes you cannot achieve that as the pressures are way too low, even when using 1.9-2.0 bars the outside and the middle of the tyre are almost even, whereas the inside is a lot hotter, I guess 2.3-4 would do ok for street cars (TBO class especially), but that would reduce grip significantly and would make you really slow, and would take 5-6 or even more laps to get the tyres to optimum temps.
edit: on the high tyre pressure thing: I only saw that with the fox and on oval setups. the fox has downforce and it is easy to drive, however those high tyre pressures do result in very nervous handling. on the oval it is simple: higher pressures=less rolling resistance, thus higher top speed and that is what's needed for ovals.
I dunno but would too high pressures result in the tyre exploding, due to creating too much pressure inside? then it is another thing left to be simulated so it can be avoided
I remember seeing once in some finnish magazine a test like this (not a serious one). They just took some old tire, attached a big-ass compressor and started pumping. Well, the big-ass compressor could just do about 7 bar pressure and it wasn't enough. Even with some knife action didn't do it so they had to cut it even more to make the tire to fail.
well I am waiting for other replies on this issue, but based on this experiment, max pressure is not that unrealistic (anymore, remember S1?), as it reduces grip considerably.
