Why do low tire pressures improve lap times?

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

  1. davehenrie

    davehenrie Registered

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    The general consensus with most of the setups I've been sent is first, drop the tire pressure to it's lowest possible setting. Shouldn't there be some sort of constraint or physics based penalty if you do this? A drastically under-inflated tire should begin overheating almost immediately .... shouldn't it? Same for over-inflated. Tire temps should rapidly increase (at least on the center section), and in both cases the grip level should be reduced. But I don't really see this. Perhaps it occurs during a long sesssion, but it's not happening for most cars that I'm aware of.
    Should the best physics of any sim be that easy to defeat?
     
  2. Postipate

    Postipate Registered

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    I have been thinking this same thing! Could this be realistic?
     
  3. F1 2004

    F1 2004 Registered

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    The tire model is still not complete.
     
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  4. Lazza

    Lazza Registered

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    F1 teams run basically as low as permissible, with Pirelli mandating a minimum pressure for safety (structural integrity) and teams doing what they can to get on that or even below it where possible. For outright grip it's hard to beat sheer rubber on the road (the old load vs area tradeoff doesn't quite work with rubber). But you'd think there has to be a limit, and not sure most mods allow you to go low enough to find it if it does exist.

    Second point - why are people sending you setups and telling you to change the pressures? Why aren't they sending you a setup with low pressures already? o_O
     
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  5. MarcG

    MarcG Registered

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  6. patchedupdemon

    patchedupdemon Registered

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    Op,do low pressures work out faster over a race distance,or just a few qualifying laps
     
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  7. davehenrie

    davehenrie Registered

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    @Lazza, sorry about being unclear, the setups they send DO have low tire pressures.
    @Marc, exactly, we should be seeing tire failures of some sort, or at least a drastic drop in grip
    @Patched, It has been so long since I've driven a full session, I can't really say. Somebody with enough time and concentration, might want to check out some of the recent releases. But, you would think we would be seeing posts from leagues if their events were getting repeated tire failures/traction loss.
     
  8. MarcG

    MarcG Registered

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    Whether proper Tire Failures (aside from "flats" when 100% worn) are even in the game I'm not sure, we don't get blow-outs and I've rarely (if ever) seen punctures. Someone with more knowledge in this area may be able to shed more light on this, perhaps it's something for the Wish List section if nothing exists currently.
     
  9. Comante

    Comante Registered

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    Minimum pressure allowed does not mean that the tire is at zero pressure, the tradeoff should be in handling, but a lot depend on tire construction. If tire sides are really stiff, low pressure has not the same chewingum effect that it has on common road tires. Considering that tire damages or rim damages due to impacts with the tarmac are not modeled, there are less reasons to increase tire pressure for safety reasons. I hope someday road impact will be able to damage tires/rims/suspensions , but I don't think this is gonna happen.
     
  10. rocketjockeyr6

    rocketjockeyr6 Registered

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    Agreed that tyre failures would be a welcome addition to the game.
    In terms of performance, there are many factors, especially the weight of the vehicle, which of course is in conjunction with downflorce.
    As Comante noted, the biggest factor is the tyre construction. Most race cars have bias-ply tyres, while road cars have steel-belted radials. They drastically differ in almost every aspect, other than that theyre primarily made of rubber, and inflate with air. :D (or nitrogen :rolleyes:)
    Of course, there is a point where performance will drop, but depending on the car and the tyres on it, that pressure can be pretty low.
    A riding lawnmower tyre, and a Go-Kart tyre are actually very similar in construction. While Ive put 60psi into the mower tyre to make the customer happy, the kart owner requested 6psi.
    As Comante noted, the sidewalls are the biggest factor in bias-ply tyres, as that is literally what supports the weight of the vehicle, while radials have the steel belt for support. Look at F1's old Bridgestone's vs todays Pirelli's. The Pirelli's have much softer sidewalls, which allows for better traction but allows for "standing waves" to happen in the tyre itself, which compromises the tyres integrity, hence the mandated minimum pressure.
    In the case of the V8 Supercars, the tyres are still bias-ply, but the sidewalls are much, much shorter, therefore stiffer, which gives more natural support, allowing a lower tyre pressure. Now, if you were to put those tyres on an F1 car, due to its weight, you could run tyre pressures even lower. If V8 Super's are running less than 17psi, you could safely assume that F1's could run somewhere like 10, 12 pounds.

    Its kind of funny, as I started playing around with APEX GT, I found that I got a bit more cold tyre stability by increasing a pound or two.

    Also, do remember that these are COLD tyre values. Most tyres inflated with air will increase about 5psi once up to nominal temp, and the basic formula is up 1 psi per 10 degrees Fahrenheit. I.e. 15psi cold(say 100*F) will end up at 25psi with an average temp of 200*F.
    This is another reason why I cant let go of TrackMap, tyre temps and pressures are all too important not to monitor. :cool:

    By the way, what are these tyre pressures you run? And which mod?

    Cheers
    rocket
     
  11. TJones

    TJones Registered

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    Racecars use also radials nowadays. Karts use bias-ply still AFAIK.
     
  12. SPASKIS

    SPASKIS Registered

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    In my own experience lower pressures fit better for long distances. I always try to keep mid temp in between outer and inner values. (I hardly ever prepare a setup for qualy since we always use parc ferme but I would expect a little bit higher pressures for optimum performance. Please correct me if you have experience. I am basing the statement on my own difficulty for properly warming tires in one lap.)

    For front tires this usually requires values very close to the lower limit. IMO the heating of front tires is excessive so in order to compensate for the pressure increase a low pressure value is required.

    Rear tires usually ask for a little bit higher values since they usually run at very low temperature compared to front tires in most of the mods I have used. I only race tintops. I cannot comment on OW.

    However, this finally depends on the mod itself. I have seen some exceptions to this. In any case, I really doubt that the available pressure range has been taken from any official site. The fact that lower values fit best could be simply as a consequence of using same source of reference tire. I understand that many modders have simply adapted the size of the tire to fit their goal, maintaining most parameters that will be very difficult to figure out properly.

    It has been stated by several car modders that rF2 tire model is difficult to configure in order to replicate a real tire. The possibility of using rF1 tire model has been asked (and granted) by some modding teams for being easier to adjust.
     
  13. aguy0523

    aguy0523 Registered

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    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     
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  14. filippu

    filippu Registered

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    "still not complete" ? :eek: You're telling that after almost 6 years, it's still not right ?

    Yes F1 teams run as low as possible. Doesn't mean that they are indeed low. There were a lot of complaints because the mandated pressures were ridiculously high for race tires.
     
  15. patchedupdemon

    patchedupdemon Registered

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    It's not that bad,after 10 years of iracing,their tyre model still is made up of 6-8 longitudinal bagels that do not allow crossectional/ localised conditions,so when you lock a tyre,the top of the tyre gets heated and wore just like the bit touching the ground,the whole tyre is a contact patch.
    Rf2 tyre is way more in depth,sure it can be improved though
     
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  16. ceecee

    ceecee Registered

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    Last edited: Sep 4, 2017
  17. stonec

    stonec Member

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    The problem with low pressures being always the quickest started after CPM tire model came out, which is the latest "version" of rF2 tire model. Older non-CPM tires have more sensible optimal pressures. With CPM, most F1 mods I've driven are at their quickest with rear pressures around 80-85 kPa.
     
  18. Ronnie

    Ronnie Registered

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    Like some people already said it is the matter of not having tire model and tire building process nailed down yet (and will never have it nailed). Because we could have the best tire model in the industry but if the building, compilation process is borked along the way it will act weirdly. Perfect example is McLaren that we have.

    But back to the pressures. Pressures do affect handling and when CPM came and has been advancing, when you had your tires done properly you could feel even 5 kpa difference in pressures front to rear. Over long distances you usually want higher pressures due to more controlled environment when racing them for longer period of time. For qualy you usually want to go with the lowest possible. Michael Schumacher was known for having even lowest possible for the races but it is very risky to have. Mostly because when you have ultra low pressures you run at risk of having a roll over. When tire is under inflated it rolls over it's shoulder and it is not made to deal with abrasive surfaces like tarmac at high loads and speeds making it very likely to just shred itself and go boom. That's what happened to Pirellis couple of years ago at Silverstone and Spa when it was the first time they sort of mandated certain camber values (no team could go higher than -4 degs while RBR was going even further than that because it was working for them while Pirelli was risking a blow up). In RL you run the lowest possible that is still safe. When it rains you put higher pressures. But in sim that we have right now you can get away with such low pressures because there is no risk of damaging them. If there was then I guarantee you that there would be more variety in pressures. However performance wise it all depends on tire construction, compound, weather and car characteristics what pressures work best and not every time the best is the lowest.
     
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  19. Emery

    Emery Registered

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    rF2 tire model doesn't allow for the tire carcass separating from the rim, so the biggest natural penalty for running absurdly low tire pressures is non-existent. Overheating due to too low tire pressure is available; take a look at the stock car tire for a good example.
     
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  20. jjcook

    jjcook Registered

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    i have had a flat tire in rf2 , however its rare and i think caused by damage not wear - the graphic on the tire display turns to a white icon but you also wont notice any handling differences - if you lose a wheel its a different icon - ie: missing wheel icon and that does impact handling ....completely worn out tires do seem to just keep going , once you notice they are worn they dont really get bad enough to completely disappear like a blow out would cause- ie: no red wear dots left , you can keep going - the brakes on the other hand - break very well and you can no longer drive the car -

    you also need mechanical failures turned on for anything to break - modders can adjust how easily things break in their mods
     

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