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Tesla Updated Tire Pressure Guideline to 50 PSI for 21" Tires?

Discussion in 'Model S: Driving Dynamics' started by Gr8pursuit, Apr 28, 2015.

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  1. Gr8pursuit

    Gr8pursuit Member

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    Picked up my car from SC for servicing and saw on invoice that my tires were checked and inflated to 50 PSI.
    Asked the service advisor and was told that Tesla now recommends 50 PSI instead of the original 42 PSI
    for my VIN (P85D w/245/35/21 Continental Sport Contact 5 tires).
    Not sure if it applies just to the D's or tires specifically.
    Can anyone else confirm this??
     
  2. Gr8pursuit

    Gr8pursuit Member

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    Out of curiosity I checked my tires' pressure and they all read 42PSI, which is what I had before I took it into SC.
    Now I going have to call the SC, something is not on the same page.
     
  3. krisg81

    krisg81 Member

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    My car was at the service center (P85D/21's) and one page said 38front/40rear PSI was recommended, but the other page said they were all set to 42PSI. That was just 1.5 weeks ago.

    50 PSI on 21's I assure you is wrong, and would be at risk of a blowout if set to that PSI cold- that's like a rolling brick, and will go up to 55PSI+ when warmed up- that's right at the maximum manufacturer limit and is not worth the tiny bit of range you will gain, and the horrible ride you will have as a result.
     
  4. Kalud

    Kalud Member

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  5. dsm363

    dsm363 Roadster + Sig Model S

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    I emailed my service center and they said it is still 42 psi for P85 21" tires.
     
  6. Blurry_Eyed

    Blurry_Eyed MS Sig #267, MX Sig # 761

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    The tire/alignment shop I take my car to is very reputable and have people there I really respect. They recommend that on my P85+ (21inch wheels, Michelin pilot sports - staggered sizes) I keep all the tires on all four corners of the car inflated to 45psi.
     
  7. linkster

    linkster Member

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    #7 linkster, May 11, 2015
    Last edited: May 11, 2015
    I have run 49 (cold) since Jan '13 on the 21 Conti's. Owners should always follow the manufacturers reccomended tire pressure spec sticker which is located (so I am told :wink:) inside the drivers door jam.
     
  8. jerjozwik

    jerjozwik Member

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    just thought i would chime in here, feb 2016 built p90d with 21. door car says 40psi all around, burbank SC set them to 42.
     
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  9. CSFTN

    CSFTN Member

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    Just had service done. The official position they expressed to me (service, that is) is 'we fill them to what is posted on the B pillar (inside driver's door).' Yes that has varied quite a bit from build week to build week, but they fill it to what's on the B pillar. So, go look at your B pillar.
     
  10. SomeJoe7777

    SomeJoe7777 Marginally-Known Member

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    Tire manufacturer's maximum inflation pressure listed on the tire sidewall is maximum cold tire pressure. The manufacturer is aware that pressure will rise above that due to heat and loading, and that is already taken into account by the maximum cold pressure inflation
    value.

    Safe tire pressure values for any car are within a range. The lowest pressure value in the range that is safe is limited by the tire load rating, vehicle weight, axle weights, and maximum speed. The highest safe pressure value is limited usually by the maximum inflation pressure on the tire sidewall. Note that these pressures are considered "safe" for the tire only. The vehicle's handling requirements may dictate a tighter pressure range.

    Lower pressure values give a better ride feel and quieter tire operation, but lower efficiency, less responsive handling, and possibly uneven tread wear. Higher pressure values improve efficiency and handling, but result in more tire noise and harsher ride.

    Vehicle manufacturers test different combinations of pressures to get the handling and ride characteristics they want, while making sure that the pressure is also safe for any vehicle load and speed. The resulting optimal pressure (according to the vehicle manufacturer) is then posted on the B pillar. This is usually tested only for the OEM tires. If you use different tires, especially ones with a different load rating, size, profile, or manufacturer, the optimal pressure that delivers similar ride characteristics as the OEM tires may deviate from the B pillar pressure.

    I have a spreadsheet that I use to calculate the safe pressure range for any tire and vehicle. For the Tesla OEM 19" tire (Michelin Primacy MXM4) on an 85D, the safe pressure range (for the tire only) is 35.8-51.0 psi for the front tires, and 40.7-51.0 psi for the rear tires. These pressure ranges can carry full vehicle load (vehicle + 902 lbs of cargo and passengers) at 155 MPH. Tesla chose 45 psi as the recommended pressure for a balance of efficiency, handling, and noise, and has verified that the vehicle handles properly with that pressure.

    A similar calculation can be carried out for the OEM 21" tires.
     
    • Informative x 1
  11. AWDtsla

    AWDtsla Active Member

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    Why such a large min pressure variation on a car that should be pretty close to 50/50 weight?
     
  12. dhanson865

    dhanson865 Active Member

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    Except Tesla prints new B pillar stickers so you have to ask is there a new sticker waiting for you?
     
  13. SomeJoe7777

    SomeJoe7777 Marginally-Known Member

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    The Model S is close to 50/50 weight distribution unloaded, but when loaded to maximum GVWR the load distribution is not supposed to exceed the GAWR on each axle. With a full 902 lbs of load within those limits, weight distribution is more towards 45/55 (F/R).
     
  14. AWDtsla

    AWDtsla Active Member

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    But 99.999% of the time I am not even close to GVWR. That may not be enough 9's.

    edit - well ok it's the min pressure so I supposed it doesn't matter.
     
  15. SomeJoe7777

    SomeJoe7777 Marginally-Known Member

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    True, those are min pressures necessary for tire safety. You probably would not use pressures that low in the Model S, because it wouldn't handle very well.
     

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