Why do low tire pressures improve lap times?

Discussion in 'General Discussion' started by davehenrie, Sep 4, 2017.

  1. SPASKIS

    SPASKIS Registered

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    If under lateral acceleration contact patch area is distorted due to tire construction or contact pressure is very uneven within it for sure available grip will be reduced.

    The geometrical effect is in principle being considered by the simulations and contact patch and its loads are also determined. There should be no need to account for those. That's why I asked if someone with experience in tire tool has done tests with extremely low pressures.
    For rF1 or other sims not simulating tires, such load sensitivity has a reason to be there. Not for rF2 tire model.
     
  2. Raintyre

    Raintyre Registered

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    Tgm file includes 'RubberPressureSensivityPower', which reduces grip depending on load. It is a relevant parameter which we need to set properly. Should we need this load sensivity multiplier? The fact is we have needed it so far.

    In the other hand, I did many tire tool tests on varied pressures, on both quasi static and real time section. Right or wrong, i dont care at all. It is not important what is happening on a 16 colors screen. The important thing is that every sim race driver who uses rf2 vehicles to simulate racing setups will find after half an hour that the optimum pressures required to be fast have nothing to do with reality. Rf1 provided much more realistic optimum pressure ranges, then it had much more simulation value on this subject. Many of us prefer less theory and hyprrsophistication but better overall result instead.
     
    Last edited: Sep 14, 2017
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  3. SPASKIS

    SPASKIS Registered

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    I completely agree on this. It makes no sense to complicate a model if you have no procedure or the data required to adjust all the involved parameters.
     
  4. Raintyre

    Raintyre Registered

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    Sorry to sound impatient, just a bit tired after so many years of beta models.
     
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  5. Lgel

    Lgel Registered

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    This is my feeling, and as usual I can be wrong, I am not a tire engineer, but I have real life experience of simulating complex systems.

    The failure of the actual tire model (even if it is "nice to drive") is made clear by the fact that you can't use tire temps (spread around the tire) to setup your suspension as in real life cars.

    There is a recent interview of an F1 engineer on YT saying provocatively "there is no such a thing as mechanical grip, they are tire temps..."

    At the moment RF2 tires demand in incredible amount of knowledge and time of testing, to obtain fantasy tires on many important values due to model not working adequately or critical parameters unavailable from real world or impossible to validate.

    After such a long time in development it is not clear if it will work one day, so a simpler proven approach may be good for RF2 (at least as an option).

    But even if far from real tires, they drive nicely and allow interesting endurance racing when well done.

    Cheers.
     
  6. patchedupdemon

    patchedupdemon Registered

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    I'm new to rf2,could you explain what you can't use temps for setup purposes,is a little lost why you would use temps for setting up suspension
     
  7. SPASKIS

    SPASKIS Registered

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    Tire temps are very important but having the tire in contact with the track permanently is the other big factor for mechanical grip.
    If an F1 engineer said that he is probably working for Sauber. Top teams have incredible suspensions. I would never hire someone who said that. There are good and bad engineers.
     
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  8. Lgel

    Lgel Registered

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    @patchedupdemon
    It is not a question of being new to RF2, it is a question of real life automotive engineering (Google is you friend here if you want to learn basics there are widely available). For instance camber affects a lot distribution of tire temps across thread. Tire temps are the most telling facts about how your tire is working, and suspension goal (apart from comfort of driver) in a race car is to allow tires to work adequately.

    An understeering car (whether by setup or driving style) will overheat front tires and wear them too fast.

    May be this link may help you:
    http://www.rfactor-league.com/TuneToWin/Suspension.swf

    Cheers.
     
    Last edited: Sep 15, 2017
  9. Lgel

    Lgel Registered

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    The result of having tires in contact with the track is read through tire temps.
    Cheers.
     
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  10. SPASKIS

    SPASKIS Registered

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    Temperature is the result of many things.
    Maintaining the tires on track do not assure that you have optimum temperatures in the tires. They are for sure related, but both aspects need to be worked at the same time due to their interdependence. You need to optimize both of them.
     
  11. Lgel

    Lgel Registered

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    As I said I am probably wrong, but for me:
    - tires only obtain grip through friction with the track.
    - friction generates heat.
    - carcass deformation also generates heat.
    - tires have a range of temps where their grip is optimum.
    - tires have a threshold of temp above which they rapidly degrade or even fail.

    You are right, you must not only maintain tire on the ground (a flying wheel has no grip), but assure an optimum contact patch with the track. This optimum contact patch is an equilibrium between contradictory requirements, for instance rear camber diminishes contact patch in straight line, so reduces traction after corner exit, but increases contact patch on the loaded rear tire while cornering, camber helps maintain tire heated in straight line, and hence allow for a rapid rise in temps when cornering in top OW cars.

    Cheers.
     
    Last edited: Sep 15, 2017
  12. Will Mazeo

    Will Mazeo Registered

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    So much this. More advanced tools to extract as much as possible from rF1 tire model would've been a much better way to go in rF2, and would probably use less CPU, maybe the freeze bug would not happen?
    That's probably what Niels did I guess, the tools he was working on that were never made public (or so I heard)
     
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  13. patchedupdemon

    patchedupdemon Registered

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    I didn't understand what you were saying,I can get a good temp spread acroosbte tyres with amber and pressure adjustments,are you implying they are wrong or that you can't acheive a good spread
     
  14. patchedupdemon

    patchedupdemon Registered

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    Niels said he didn't use the rf2 tyre model because it was so hard to work with,he said the model is brilliantly capable,but working with it was just so different,and time consuming and not user friendly
     
  15. patchedupdemon

    patchedupdemon Registered

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    That's the first I've heard about camber being used for straight line heat,everything I've read states camber is for for getting the biggest contact patch while cornering
     
  16. SPASKIS

    SPASKIS Registered

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    Tires obtain grip through temperature.
    Temperature is obtained by friction and deformation hysteresis.
    Convergence should have much more effect in tire heating in straights since it increases friction.
    Camber shouldn't be a determinant heating factor in straights where actually tires cool but it could reduce tire cooling through ground conductance if contact patch area is reduced. This should be more noticeable for high pressures IMO. It certainly will affect temperature distribution throughout the tread.
     
  17. Lgel

    Lgel Registered

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    [QUOTE="SPASKIS, post: 913310, member: 25148"Camber shouldn't be a determinant heating factor in straights where actually tires cool but it could reduce tire cooling through ground conductance if contact patch area is reduced.[/QUOTE]

    Effectively, this setting of high camber was used and described by engineers in F1 (I don't remember the exact season, with Pirelli tires), effectively by reducing the contact patch they were reducing the global cooling of the tire in straights.

    Cheers.
     
    Last edited: Sep 15, 2017
  18. Lgel

    Lgel Registered

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    On many ISI cars you had to run very low camber values (unrealistic) to obtain a correct use of outer part of the loaded tire when cornering (this had no observable effect on grip level).
    It has improved on latest S397 cars, Nissan GT500 for instance.

    Correct distribution of heat across thread is not a static goal, but varies with what the car is doing, braking, cornering, or going straight, and is different with load (loaded or unloaded tire).

    Cheers.
     
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  19. rocketjockeyr6

    rocketjockeyr6 Registered

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    Hmm... I play with TrackMap on, and I can see a difference in how the tyre heats with camber/pressure changes on most mods Ive ever driven. These include various F1(pretty much all based on ISI F1 2012), most GT(ER,APEX,Simtek,Blancpain), and really every ISI/397 car to date. Im not saying they're perfect, but a good amount are pretty damn good IMO.
    EnduRacers GTE mod is one I have the most experience with; our league had a 10 race 1Hr Endurance Cup with it. In that time I noticed that; while trying to preserve my tyres, they cool faster if you come off the racing line in the straights. Under-inflated tyres overheated in a shorter timespan, and indeed, did wear the outsides most. Over-inflated fronts gave good turn in response but understeered in fast corners. At Sebring, I ran with the brake ducts 100% open, thinking it would help cool the tyres as it was a 90+*F day(AccuWeather app). It did in fact reduce average tyre temps, however; I suffered a RF brake failure about 45 into the race. My conclusion was that the rotor was weakened by the constant severe temperature change, as it would have in real life. I cant be sure, but I like to believe it. :D
    Also, the majority of the F1 mods Ive driven get very visible flat spots from lock up, and shake the ever lovin fluff outta the wheel. And the GT mods that you cant see you can still feel in the wheel. Steering hard on that side(left turn for RF, etc.) helps clean it up, but also really take the piss out of that tyre. Driving with wet tyres on a drying line, get hot pretty quick, and cool just as quick when you dip into the wet spots.
    Just my observations.

    Cheers guys.
    rocket
     
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  20. SPASKIS

    SPASKIS Registered

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    The feeling of the tire model is sensational. Its biggest problem is that in most old mods is that tires would be destroyed if temperature raised too high. This happened majorly with front wheel tires that were easily overheated. Contrarily, rear tires could be easily maintained in the 70s and it was actually difficult to make them work in their optimal range. It was very typical to be able not to change them while pitting to change front tires.

    This is certainly due to thermal model not being correctly adjusted to the right parameters. Certainly proving that the validation of the thermal model has not been done. I dare to say that temperature data from real logs has not been crossed with game telemetry.

    What can we expect from 3rd party modders? It's easy to imagine:

    Amateur modders with no single data from real cars have directly used original ISI tires adapting them to the size with a known awesome tool developed by a 3rd party modder.

    Professional modders with access to some data from real teams have broken their heads to get those values by fiddling with all those numbers. Some of them have done a remarkable job here with a great overall result considering the poor thermal model that IMO is implemented in rF2.

    This is what I have tried to prove with all the posts in this and other threads on the past and the numerous controlled tests documented in many times and to which in any case a developer has cared to reply and have an interesting technical debate about it.

    I would really love to contribute in this providing my professional experience in validating professional simulation tools for thermal analysis in the industry I work for. Some will think that my goal is to be right. However my only goal is to have the best tire model implemented in rfactor 2.

    For sure that most of us (rF2 inconditionals) have got used to it and have learnt to care for the tires keeping them in the right temperatures. We all know that tires don't like being too hot. However, many other simracers which I don't like to call them casual but that they just want to drive not caring so much tires which is what they expect and believe realistic when they race online with other friends. Many of these are playing Assetto Corsa at the moment.

    I clearly see that someone in S397 has realized about this and now we have a McLaren with tires that can last for hours when driven carefully (the old way) and only when pushing really hard they seem to show a significant wear.

    IMO if a correct thermal model has been implemented nothing of this would have happened and much more people would be playing rF2 at the moment. For sure the lack of stability of a 5 year old game is the other critical aspect that is responsible of the critical situation where IMO rF2 stays at the moment. The sales coming from the implementation of DX11 have not translated in an increase of online activity.
    In a few weeks the new UI and features associated is another big opportunity to change this negative trend.

    If things are done correctly simracers will come. They are not stupid. Give them a robust platform easy to deal with, free of historical bugs with the best physics in the market. They'll come in thousands like flies to the honey.
     

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