Adjusting tyre pressures

Discussion in 'Setup Information (Under Construction)' started by Alex Hodgkinson, Mar 5, 2021.

  1. Alex Hodgkinson

    Alex Hodgkinson Sector3 Developer

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    I often get asked about how to adjust tyre pressure, what to aim for regarding tyre temperatures and so on so here are. It's especially important to know the ropes now that we've opened up tyre pressure adjustment in fixed setups.

    The great news is that all you need can be found in the garage menu, in the bottom left corner:

    20210304141124_1.jpg

    Close up:
    upload_2021-3-5_19-41-9.png

    What this is showing us is the inside, middle and outside temperature of each tyre's tread.
    The most important thing you can do here is adjust the tyre pressures to make optimal use of the tread area. Think of a balloon. The more air you put in it, the more it bulges and becomes rounded. A tyre's tread reacts to it's internal pressure in the same way. The higher the pressure inside, the more rounded the tread becomes, when viewed from the front.

    We can see this effect in the garage menu by overinflating a tyre and then looking at the temperatures:

    upload_2021-3-5_19-47-1.png

    The central temperatures of each tyre's tread are much higher than the temperatures of the inside and outside sections. This is because the bulged tyre is running on the small central section, which generates much more heat than the inside and outside which are effectively lifted away from the road surface by the over-inflation.

    Now let's look at what happens if we under-inflate our tyres:

    upload_2021-3-5_19-49-48.png

    This time it's the total opposite of the over-inflation. The tread of the tyre becomes concave when viewed from the front and the weight of the car is carried by the shoulders (inside/outside edges) of the tread.

    Those two examples show what happens if you go to the extremes, but their effects are very important to consider for adjusting within the normal range. What we're looking for is a nice even spread of temperature across the tyre tread. So, if the tyre's inside temperature is 50 *c and the outside is 60*c, we aim for a middle temperature of 55*c. If was 52 we would need to increase the pressure a small amount. whereas if it was 57 we would want to decrease it a touch.

    upload_2021-3-5_20-5-28.png

    Looking at the the example above, we can see that each tyre could really do with slightly different pressure adjustments. That is entirely normal and should be expected in fact.

    I'll finish off with some more points worth considering while adjusting pressures:
    • Default tyre pressures are symmetrical, and tailoring them to match right or left hand circuits is beneficial

    • It typically takes 2-3 laps for a preheated tyre's pressure and temperatures to stabilise

    • Tyres which start off cold can take 6-8 laps for temperatures and pressures to stabilise

    • Default pressures are designed for long runs

    • Tyres which are not preheated will benefit from increased pressures for qualifying runs
     

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  2. RampageRacing

    RampageRacing Well-Known Member

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    This is very timely and valuable information for me. I have been wondering about tire pressures and doing some experimenting by tweaking pressures, running laps and checking results in the garage using the monitor that you showed. I pretty much drive GT3 cars exclusively in R3E along with an occasional GT4. Is there an optimum operating temp for the tires in those classes like in ACC? Also I have a good range of temperatures across each tire but I am having trouble getting the individual tires to reflect the same approximate temperatures all around the car. Is getting a uniform temperature on all the tires a tire pressure issue or is it more an issue with other chassis adjustments such as toe, dampers, etc. For example, I was running the Callaway Corvetter at Mid-Ohio chicane in practice sessions last night. The LF tire was showing a range of 72-80F, the RF tire was at 74-68F and both of the rear tires were running from 58-66 degrees across the tires. This was after 16-20 laps stints. I wanted more heat in the rear tires and to try to match the fronts better. Is this a function of pressure or chassis set-up? The car handles very well and I am within .7 seconds of the fastest Leaderboard time with my race set-up but I want to get faster. I do use asymmetrical settings on the car in regards to tires pressure and camber. Any insight or knowledge imparted would be appreciated. I understand that it makes a difference whether a track is predominantly left or right turns and that will determine which tires work the hardest but is there a way to use air pressures to balance the temperatures?
     
    Last edited: Mar 6, 2021
  3. Nir Tal

    Nir Tal Well-Known Member

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    Thanks for the info Alex.
    In the telemetry app I built, Im doing a simple calc for the optimal tire middle temp, so in a glimpse look i can tell if each tire is over/under inflated.
    Middle - ((Inner + Outer)/2) = ideally should be zero. Plus Value means overInflated, Minus means underInflated.
    I believe adding this value to the TyreInfo section on the garage menu screen could be helpful
     
  4. Maskerader

    Maskerader Well-Known Member

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    I once "broke" my FWD car by adjusting the rear pressure too much, I guess the tyres ballooned too much and the contact patch became tiny. Problem was I only realised it after the race started, this really impressed me but also got me thinking: wouldn't it be nice to be able to adjust your tyre pressure in the pit menu for your next set of tyres? Or this feature won't ever be used, really? Especially since in this game track conditions never change during a race...
     
  5. Michael Andersen

    Michael Andersen New Member

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    Thanks for the update Alex. Much appreciated.
     
  6. Alex Hodgkinson

    Alex Hodgkinson Sector3 Developer

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    You could actually go one better than that and build something which will give you suggested pressure changes.

    You'd make use of the equation below:

    Pressure change = Current pressure-(current pressure * (average(inside+outside temp) / middle temp))

    Temperatures in kelvin

    It won't be 100% accurate as changing the pressures affects both central and edge temperatures, but maybe using half the value the equation above gives would account for that.
     
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  7. Nir Tal

    Nir Tal Well-Known Member

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    Yes, I didnt thought about it :) but actually, i just experienced with it and concluded that middle tire +1degC means around 1kPa to be decrease.
     
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  8. Tomas Machan

    Tomas Machan New Member

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    Nicely clearly written and explained.
     
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  9. graveltrap

    graveltrap New Member

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    When is the tyre data in the garage screen taken, last time across the start finish, when you leave the track and return to the garage or somewhere else?
     
  10. rubenbatista

    rubenbatista Member

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    In the exact moment you click "return to garage".
     
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  11. Nico Kunze

    Nico Kunze Well-Known Member

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    Pretty sure its the moment just before you teleport back to the pits
     
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  12. Pierluigi Vinci

    Pierluigi Vinci New Member

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    no problem to understand optimal pressures, is there any recommended ratio between inner and outer temps? IE for front tyres aim for a difference of 7 or 10 degrees and so on
     
  13. BeefMcQueen

    BeefMcQueen Well-Known Member Beta tester

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    It rather depends on the car class. Aim for a delta of 5 degrees on the Scirocco, GR4, GR5, Fr-J, GRC for example. WTCR, WTCC up to 15 degrees and most of the rest and GT3, GT4, GTE around 10.

    Oli
     
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  14. Pierluigi Vinci

    Pierluigi Vinci New Member

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    Thanks
     
  15. Maskerader

    Maskerader Well-Known Member

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    Interesting. Why it's like that? I would think with driven front wheels you want the best grip on them and therefore not as big of a temp difference. What makes FWD benefit from such settings?
     
    Last edited: Oct 28, 2021
  16. BeefMcQueen

    BeefMcQueen Well-Known Member Beta tester

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    The question maybe is: under which circumstances you want that maximum grip with front driven wheels? straight line acceleration perhaps wouldn't be the strength with such massive camber settings. I guess it's down to how camber changes during cornering. So having the outside tyre contact patch flat on the ground and maximised during hard cornering while applying the throttle at the same time, might outweigh those straight line acceleration/braking flaws. Overall this might be leading to that rather huge Delta of 15 degrees throughout a lap (because you're not just cornering, but also spend quite some time braking and accelerating only using the inner part of the content patch)
    But that's just a guess... That's definitely a topic I, too would appreciate if an expert could shed some light... @Alex Hodgkinson :)

    Oli
     
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  17. Alex Hodgkinson

    Alex Hodgkinson Sector3 Developer

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    There are a few reasons for that:
    • Touring Cars have much higher body roll when cornering compared to GT/Sports cars.

    • As they have a higher centre of gravity and narrower track they also transfer more load onto the outside tyre during cornering. A higher tyre load is something which requires an increase of static camber, as load is directly proportional to optimal camber.

    • Front suspension layout is usually not a double wishbone setup as they typically use MacPherson strut type, like a road car. What that means is camber recovery (how much camber the wheel gains as the wheel travels up in to the wheel arch) is usually quite poor. This means you need to run more static camber.
    Hopefully those are clear enough, although they don't directly address the why 15 degrees delta question. What I've explained is why Touring cars need more static camber than other car types. The 15 degrees delta is simply a result of that requirement.
     
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  18. Vale

    Vale Well-Known Member

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    Are there any other classes where the deltas are greater than 10 degrees front and 7 degrees rear, which I believe is the Gt operating window?
     
  19. joe cronk

    joe cronk New Member

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    Thanks, i appreciate that i have a lot to learn that helped and made sense i need all the help i can get!!