How tire pressure works

Discussion in 'Car and Track Knowledge Base' started by SunnySunday, May 26, 2019.

  1. SunnySunday

    SunnySunday Well-Known Member

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    So i'm sort of a rookie when it comes to car setups in general, but I just thought we could have a discussion about the newly added feature of adjustable tire pressures.

    In my very limited understanding of tire pressures I thought that this was something you'd only really adjust to accommodate different track temperatures and weather conditions, but since raceroom does not really feature these conditions I have a hard time understanding why this feature is even in the game?

    In my understanding a higher tire pressure would equal a hotter tire due the fact that compressed air increases temperature? So if you have a hard time heating your tires, for example when the weather is cold, you would increase pressure. Lower pressure would then result in a cooler tire. But if you go too low on pressure the tire would deform and cause higher than ideal friction, which might in return overheat your tires. A too high tire pressure would result in less contact patch with the ground, causing the tire to lose surface grip and also result in a too hot tire due to the smaller contact surface getting all the work load, combined with the fact that higher pressure means higher temps. But again, since raceroom does not have different weather options I don't really see the point of this feature. Or does track temperatures differ in morning, day and afternoon settings?
    I am thinking this correctly?
     
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  2. Paul Darke

    Paul Darke Moderator Beta tester

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  3. Winzarten

    Winzarten Well-Known Member

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    Everything here is AFAIK: :)
    It is the other way around. While, increasing pressure will heat up the gas, the increase will stop the moment you stop increasing the pressure. From that point the gas will cool down back to ambient temperature.

    Decreasing pressure in tyre usually increases their temperature, because it makes the tyre softer, increasing the deformation during tyre rotation, producing more heat.
    Increasing pressure makes the tyre stiffer, causing it to deform less, thus producing less heat during rolling.

    The center tyre temp is most affected by pressure changes, so you can change the pressure to tune that, as you would like to see linear progression from tyre inside, which is usually hottest, because of camber, to tyre outside.
     
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  4. yoori

    yoori Well-Known Member

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  5. SunnySunday

    SunnySunday Well-Known Member

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    Yeah ok this makes sense.
     
  6. benoityip

    benoityip Member

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    When I tracked my real car in semi slicks in Tokyo r888, I keep the hot pressure at 34psi around all corners. The psi is measured by a couple of laps after heating up the tyres. My corolla is front heavy, the rear tyre is very difficult to heat up, so I set the cold pressure at the back a few psi more that the front.
    In normal days, I have 24psi front and 28psi rear at cold conditions., And when heated up, all corners recorded around 34psi.

    More info can be found in https://www.toyo.co.uk/page/index/identifier/set-up-advice

    I could not be bother playing around too much with tyre pressure since it is only a very fine tuning to the handling of the car.
     
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  7. Wilko Jones

    Wilko Jones Member

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    So in a nutshell, lower the pressure to bring the temps up. I take it I should be avoiding extremes and lowering the pressure to achieve the desired temperatures, correct?

    So what are the benefits of having a tire at optimal temperatures? I never understood how to get tires up to temperature. I always thought it was something I had to do on track, like; driving harder or going faster.
     
  8. Jona777

    Jona777 Well-Known Member

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    Lower tyre pressure = more surface from the tire on the road/more friction = hotter tires
    Higher tire pressure = less surface from the tire on the road/ less friction = colder tires

    Benefits of having optimal tire pressure = more grip and less wear..
    And indeed avoid extremes..

    Imagine your bicycles' tires to understand this concept.. When tires are deflated you have to step harder on the pedals and your tires will wear of quicker.. when tires are on the ideal pressure, you'll advance more easily and it is more durable..
     
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  9. Joel Willstein

    Joel Willstein Member

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    I was always under the impression that your tire pressures should be about the same at all four wheels after they heat up, which would mean that the car is pretty well balanced around the track. In R3E most of the time you can't adjust the tire temps at all, so all you're left with is springs and shocks. The problem is that you can only make the adjustment for front and backs, not individual corners.

    The problem I've been having at Monza is that the right front tire temp is always about 10 degrees cooler then the left front which is within a few degrees of the rear temps. If tire temps aren't activated, how do I go about raising just the right front temps?
    Thanks,
    Joel
     
  10. JAM_Racing

    JAM_Racing New Member

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    The tire pressure being the same at all four corners has a lot more to do with setup then tire pressure itself, assuming that the pressures aren't all over the map. If you have all the tire pressures the same before going out on the track, but your setup is feels tight (understeer) the fronts will be much hotter, and if it's loose, the rears will be hotter. I find in road course setups that having the tire pressures within 1 lbs. front to rear, and working on the setup of the car till it feels good is more important. Tire pressure adjustments are a "fine tuning" adjustment in relation to springs, shocks, which are a course adjustment, meaning small changes in springs and shock deliver bigger results on track, and maybe too big so be careful. Always adjust one thing at a time and run a few laps. If you change too many things at once, you won't know what actually helped, thus you won't have learned anything about setting up that car, or for that track. Once you get the car to be neutral but slightly on the loose side, then maybe fine tune the setup with tire pressures. Most often my road course setups have the rears 1/2 to 1lbs lower pressure at the rear tires.

    In oval, tire pressures can make a much more drastic change in the car your setups are asymmetrical in nature. Most of the time you'll be leaning on the front right, so expect that tire to be hotter than the rest. I always shoot for tire temps to be as equal front to rear on the left side as I can get them. The right side tires are generally both hotter by at least 10 degrees, with the right front being about 5-10 degrees hotter than the right rear. If you're too tight the right front tire gets too hot, but putting more air in it, even though it might cool the tire a few degrees, increases the spring rate of the front right corner of the car and will just make the car tighter. If the car won't turn, the last thing I would do is add air to the right front. Depending on where in the corner the car is tight, (entering) I would stiffen the right rear and/or soften the right front, depending on how soft it is already. You don't want the whole car rolling over on the right from or you'll never get it to turn.Sometimes stiffening other areas help take the stress off the right front. If exiting, I might soften the left rear or stiffen the left front, but that can depend on how it rotates in the center of the corner. Again, watch your teams. They'll tell you what tires are working too hard, or not hard enough. Then match that with what the adjustment you're thinking about doing to that corner with what the end result will be to the handling.

    Typically in road course setups you want to adjust the fronts and rears together (both fronts get the same adjustments, or both rears). If you have a lot more right turns then left, for example Monza, I might prioritize making the car turn really well to the right, and make sure that it's not underivable in a left hand turn. You spend a lot less time turning left so sacrificing a little time in a couple left handers to be much faster in the right handers would make sense, and you'll gain back the time lost in the left handers and more!! Also, If you're not really sure what's happening with the car, go look at the tire temps. They will tell you what's happening. If you're temps look good, but the car really isn't quite where you want it, maybe you don't really need a car adjustment, maybe you just need to change your driving style a little.

    Just my $0.02 for what it's worth.
     
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    Last edited: Jan 12, 2020
  11. ravey1981

    ravey1981 Well-Known Member Beta tester

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    Since the last big update you can make adjustments on any corner independently.
     
  12. R.Noctua

    R.Noctua Well-Known Member

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    It was sad to know that it was the other way around, not what I thought.:confused:

    It's especially funny that I fought with the Porsche GT3 CUP and its cold tires trying to increase the pressure...
     
  13. Michael_James

    Michael_James New Member

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    Lower tyre pressure causes more friction.