Questions about tire pressure and caster

Discussion in 'FM4 Tuning' started by Speedster911, Sep 5, 2014.

  1. Speedster911

    Speedster911

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    Hi,

    Just a few quickies:

    * What's the unit used for tire pressure in FM4? Is it Psi? I.e. if I'm setting front and rear to 2.4, is that 24 lbs and/or psi? Please enlighten me. I'm from SEA and here we typically keep our values at either 28 lbs front and rear or 30 on all fours, depending on roads. They're not the best.

    * Reducing caster allows faster wheel to wheel lock, allows the front wheels to turn more/faster, correct?

    * How can you get some of the R2 and R3 race cars to hit higher top speeds? I've tried reducing aero, increasing tire pressure, lowering ride height, stiffening up dampers and playing around with the gear rations in a way that the final drive value is tuned for speed, and the 5th and 6th gears are made shorter for better acceleration. More top-end power.. faster redlining in top gears and hence better top speed.

    Thoughts? Thanks for reading.
     
  2. Imari

    Imari

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    The unit is bar, if I remember correctly. 2.4 psi wouldn't be enough to hold the weight of the car off the ground. 1 bar = about 14.5 psi from memory. Google will give you the exact number if it matters.

    Caster controls how the wheels gain and lose camber when you turn the steering wheel. A high caster car will gain a lot of negative camber on the outside wheel and positive camber on the inside wheel as you turn the steering wheel. A car with zero caster will have camber that does not vary at all with steering angle.

    Steering ratio is what would affect how many turns of your gaming wheel would result in full lock in game. I don't think Forza allows adjustment of this, from memory.

    Sorry if much of that is vague, I may be a little drunk. Hope it helps.
     
  3. Speedster911

    Speedster911

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    4,251
    As for the tire pressure stuff, yes I will need to Google that. By default, the game has it set to 2.1 F/R for all cars. Increasing that definitely improves steering response and allows the wheels to turn faster and a little more. Not too sure about that, but a good feeling it does.

    As for the caster, that's the exact explanation given in the tuning menu. I've always felt keeping caster very low or at zero with negative camber, allows the car to turn better - not just initial turn in but also better performance as you hit the apex.

    Wish Forza had a S2-like setting for steering lock.
     
  4. Imari

    Imari

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    Location:
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    It may be one of those things where real life characteristics aren't necessarily replicated perfectly in game.

    On of the downsides of high values of caster is that it increases the steering weight. Whether that is also replicated in game I'm not sure, but if it is and you're using an FFB wheel then that may be why you feel it's not turning as well. It happened to me in iRacing a few seasons ago: the optimal setup was to run very high caster which resulted in extremely high FFB. The actual fastest way to drive for me was then either to turn the FFB down (giving up steering feel) or run less caster (giving up cornering grip).
     
  5. Speedster911

    Speedster911

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    @Imari I believe the game does attempt to simulate that. As I mentioned, keeping caster very low lets you go lock to lock faster. The front wheels generally turn faster. If you switch to cockpit view you can see and feel the steering wheel moving more freely, so it does get light.

    Unfortunately, I do not use a wheel so I can't truly put this to the test.
     
  6. Frizbe

    Frizbe Premium

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    So if your tire pressure is 2.1 by default then it is in bar. The default on all the Forzas I've played is 30 and 2.1 bar=30.87 psi since 14.7 psi=1 bar. They say optimal tie pressure is 32-35 psi after 3 laps when you look at your telemetry in game(press the up button) so you'd be looking for 2.2-2.4.

    Can't say I have ever played with caster personaly so not sure there but from the other posts I think I might start messing with it later today.
     
  7. Speedster911

    Speedster911

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    4,251
    Hey, appreciate the feedback. Thanks for putting the tire pressure numbers in perspective. Makes a lot more sense now.

    On the really low profile tires, I keep tire pressure relatively high. On the higher profile/smaller rim tyres, I can keep it low, as it not only adds grip but introduces a certain level of sluggishness which I actually prefer for some cars and tracks.

    You really should try playing with caster, it makes a lot of difference on certain tracks coupled with specific tuning parameters.