What? Put more air pressure in front tires??
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This is a discussion on What? Put more air pressure in front tires?? within the Suspension & Wheels forums, part of the Tech & Modifying & General Repairs category; I have heard quite a few people say that it is best to put more air pressure in the front ...

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    Registered User Lightsped's Avatar
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    Question What? Put more air pressure in front tires??

    I have heard quite a few people say that it is best to put more air pressure in the front tires as compared to the rear tires. According to many people, this reduces understeer.

    IMHO, it would seem more logical to put more air pressure in the rear tires to "round" the tires footprint out more, which would reduce grip, which would increase understeer.

    Seems like "rounding" the front tires footprint out, would reduce grip, which would create MORE understeer.

    Please, someone clear this up for me.

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    Moderator Penguinking's Avatar
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    nope. because the weight distribution on the wrx is about 60/40 ft/rear, then the front tires need a 'lil more air then the back. plus when ur braking alot of the weight transfers to the front tires
    Silver 911
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    Lightsped:

    A little knowlege is a dangerous thing.

    The Rex has a 60 / 40 fore and aft weight bias.

    Da wheels in da front wanna be harda dan da wheels in da back.

    32 psi front - 28 psi back.

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    Moderator schischwein's Avatar
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    Just an additional note to the above: the increased air pressure in front is not to the point that the tyre footprint is round(obviously extreme over inflation). There are some who over inflate in this way the rears to achieve oversteer. This is a dangerous way to do so and there are many better ways to achieve oversteer.

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    Registered User Trypsin's Avatar
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    i have mine set at 37f 32r and it really helps out, the tires are rated to 44 psi i think, any pressure up to there should not round the tires, they are radials, its a bit of a harsh ride though.

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    Moderator Penguinking's Avatar
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    i run mine pretty darn high - something like 38ft/36r
    Silver 911
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    Registered User MadDog's Avatar
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    If we're talking about the stock rim/tires, there's a few things to remember.

    First off, the RE92's that come on the WRX have a max cold inflation of 40PSI. Try not to go over that. The second thing everyone pointed out already; the car's front end is heavier. The third is that a tire handles differently at the limit depending on the tire pressure as well. If you run say 40psi all around, the tires will most likely break away completely differently than what you're used to, and that's not a good thing.

    I'm on S03 PP's, and I run 41F/39R. S03's have a max cold inflation of 50PSI, so there's no worries there. I find it helps with the overall grip of the tire, but still keeps them predictible. The unfortunate side effect is that it makes the ride a little harsh, but I can live with it.

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    Moderating on the run! Big Sky WRX's Avatar
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    Re: What? Put more air pressure in front tires??

    Originally posted by Lightsped
    I have heard quite a few people say that it is best to put more air pressure in the front tires as compared to the rear tires. According to many people, this reduces understeer.

    IMHO, it would seem more logical to put more air pressure in the rear tires to "round" the tires footprint out more, which would reduce grip, which would increase understeer.

    Seems like "rounding" the front tires footprint out, would reduce grip, which would create MORE understeer.

    Please, someone clear this up for me.
    To a point increasing pressure in the front vs rear will help to reduce understeer. Every tire will have an optimum pressure producing the most grip . These are the pressures you should run, anything less or more your compromising grip. As schischwein pointed out there are better ways to deal w/ under/oversteer- sway bars, camber adj, springs etc. The only people really forced to use tire pressure in addressing handling characteristics are those in stock autox classes- they are limited in what suspension mods can be done.

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    Registered User Dick Nogs's Avatar
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    i run 44 front, 41 rear (that's at temperature, not cold).

    I don't know but I feel like the tires are too squirmy at lower pressures. think I ought to decrease the pressure ?

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    Moderating on the run! Big Sky WRX's Avatar
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    What are your cold pressures? What tires?

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    Registered User Dick Nogs's Avatar
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    cold pressures are probably on the order of 41f/38r

    They are Yokohama AVS ES100s in 225/45R17

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    Moderating on the run! Big Sky WRX's Avatar
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    That might be a smidge high, that's real close to what I run in autox, street I'm running 36f/33r- that's w/ a very stiffwalled T1S though.

    If your ride is not uncomfortable at those pressures, then I'd stick with them as your well below the maximum pressures for that tire. If your ride leaves a little to be desired comfort wise you could probably come down a couple of pounds f/r- don't let it become squirmy however as you mentioned.

    The only way to find the "ultimate" tire pressure (most adhesion) is w/ a 200' skid pad (or track) and a pyrometer. Essentially taking three measurement across the face of the tread of each tire and adjusting pressures from there. It's aslo a good way to see if camber adjustments are where they need to be. Someday I will actually do that- pyrometers aren't really that expensive.

    For autox, I look at roll over on the tread (some use white shoe polish for this)- essentially if the tread is scrubbed to far onto the sidewall - I adjust pressure up, not far enough onto the sidewall- pressure down. Not the most scientific, but until I get a pyrometer it will have to do.

    Big Sky

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    Moderator Penguinking's Avatar
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    pyrometer...hmm....so how much do one of those things run ya? i saw a guy at the track that had one of those hand held thingys that has a laser on it and u just point it at whatever and it tells u what temp its at - looked pretty cool, not quite sure how accurate it is though....


    -Robert
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    Moderating on the run! Big Sky WRX's Avatar
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    There are some good infared pyrometers out there, they run in the ~$150ish range. They're pretty accurate and fast. Most normal pyrometers also run in the $150ish range, with some in the $300-400 range that store 10 seperate (12 temp each/3 per tire) runs and dispaly all 12 temps at once- probably a little over kill (at least for me).

    The nice thing about an IR (if has a adequate range) can measure other components as well (the regular pyrometers can also w/ different probes).

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    34 front, 33 rear with 225/45-17 S03s. Works good on the street.

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