TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker and becoming a Supporting Member. For more info: Support TMC

Why 45 psi?

Discussion in 'Model S' started by Deans, Jan 16, 2017.

  1. Deans

    Deans Member

    Joined:
    Dec 29, 2016
    Messages:
    208
    Location:
    Colorado
    Why does Tesla recommend a tire pressure of 45 psi for my 60D MS?

    The curb weight is roughly 4600 lbs. With full load, that brings the total weight to 5600 lbs, or 1400 lbs/tire.
    The stock Goodyear tires having a load inflation chart as follows:

    30 psi - 1411 lbs
    31 psi - 1458 lbs
    32 psi - 1492 lbs
    33 psi - 1527 lbs
    34 psi - 1561 lbs
    35 psi - 1598 lbs
    36 psi - 1653 lbs

    This is as high as the chart goes! The maximum load for each tire is reached at 36 psi (1653 lbs).
    The tires can accept pressures up to 51 psi. But what is the advantage? Inflating the tires to 45 psi will help fuel efficiency and range, slightly. But I would think that savings would be more than offset by the shortened tire life due to over inflation. Furthermore, ride quality suffers quite a bit at high PSI and so does handling.

    What am I missing? I've been inflating to 45psi, per the door jam. But the ride is rough. I would like to know why I need 45psi? If it's only to maximize range, and not for safety, that I'd like to lower it!

    It seems like the proper inflation would be in the same range as other cars (32 psi - 35 psi). And that's assuming the car is loaded up with 5 passengers and luggage.

    I'm not an expert and I'm not recommending anyone lower their air pressure. I would just like to understand what I'm missing. Thanks.
     
    • Informative x 3
    • Like x 1
  2. GSP

    GSP Member

    Joined:
    Dec 28, 2007
    Messages:
    2,227
    Deans,

    I would guess that Tesla recommends 45 psi to get better rated range.

    Modern tires can be run at the max sidewall pressure without wearing faster in the center. I have been using 45-50 psi for both my Model S and my Chevy Volts. No problem with tire wear on either Volt. For the first 30,000 miles the wear has been even. I just got the S.

    I like running high pressure with the sporty ride and handling. I like stretching my range also, espically in the Volt. Back in the day when I used to autocross everyone pumped up tire pressures for the event.

    However, high pressure is not for everyone. If you like a softer ride I would try 35 psi. I think you are correct that there would be no problem other than slightly less range.

    GSP
     
    • Helpful x 1
    • Informative x 1
    • Like x 1
  3. msnow

    msnow Active Member

    Joined:
    Jul 14, 2015
    Messages:
    4,950
    Location:
    SoCal
    Mine are Michelin Primacy's and I leave it at the engineering and manufacturer recommended setting of 45/46 psi.
     
  4. JRMW

    JRMW Member

    Joined:
    Nov 13, 2016
    Messages:
    255
    Location:
    Minneapolis
    Discount Tire inflated my tires to 39psi when they installed my winter tires.

    the left half of my display converted from my odometer (what I have set there) to a picture of my car and car tires with red exclamation points stating that the tires were underinflated. I also got tire underinflation chimes.

    the tire under-inflation display wouldn't go away until I inflated my tires over 41psi if I remember correctly.

    not sure if you can disable that somewhere...
     
    • Informative x 1
  5. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

    Joined:
    Mar 8, 2012
    Messages:
    13,238
    Location:
    Texas
    All tire pressure recommendations are based on a set of assumptions. The basic four are:

    1. The ambient temperature is 18C (65F). If it's higher than that you need to adjust the pressure upwards.

    2. Speed. The GY chart (and all other charts from the tire manufacturers (as far as I know) are based on a 65 mph sustained speed. If you run faster than that, then you need to up the pressures.

    3. Load. For cars the load that the pressure recommendations are set at are for what the engineer thinks is going to be normal for that car--not necessarily the GVW.

    4. A daily pressure check at the start of each driving day. (Don't shoot the messenger.) If you don't check every day, then you need to adjust the pressures upwards so that you never go below.

    In addition there are factors particular to each car, such as handling and weight transfer (to name a couple--there are more).

    Another list:

    1. Higher pressure reduces heat in the tire which causes tire failures and shortens tire life.

    2. Higher pressure reduces the chances of having uneven wear.

    3. Higher pressure provides better transient response in an emergency situation.

    4. Higher pressure reduces the chance of hydroplaning.

    5. Higher pressure is required when the temperature is above 65F (18C) or below 65F and inflated indoors.

    6. Higher pressure is required so that the pressure does not fall below the minimum if you don't check pressures each day before you drive.

    7. Higher pressure is required if you carry more load than the car was designed to normally carry (note that this might be less than the GVW--it could be only one or two passengers).

    8. Higher pressure provides better traction in most, but not all, on-road winter conditions.

    9. Lower pressure increase ride comfort, which is highly subjective and probably depends a lot on the amount of "natural padding" present :)

    10. Lower pressure reduces vehicle damage during off pavement usage.

    Note that track use--where you adjust the pressures to get the most contact area is a whole 'nuther subject, and basically not applicable to normal driving (unless you like buying tires frequently).
     
    • Informative x 9
    • Helpful x 2
    • Like x 1
  6. kort677

    kort677 Active Member

    Joined:
    Sep 17, 2015
    Messages:
    3,655
    Location:
    florida.
    as noted by others and the sticker in the door the correct pressure for your 19" tires is 45psi, discount tire didn't do a proper installation.
     
    • Like x 1
  7. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

    Joined:
    Mar 8, 2012
    Messages:
    13,238
    Location:
    Texas
    There is a lot of misinformation out there. Much of it is a hold-over from 40-50 years ago when most North American cars had bias-ply tires.
     
    • Like x 2
  8. kort677

    kort677 Active Member

    Joined:
    Sep 17, 2015
    Messages:
    3,655
    Location:
    florida.
    the door sticker is misinformation? could it be the russians hacking?
     
    • Funny x 3
  9. BerTX

    BerTX Active Member

    Joined:
    May 2, 2014
    Messages:
    1,698
    Location:
    Texas/Washington
    The Eagle Touring tires may need to run at a higher pressure to reduce flexing, increasing the adhesion and life of the foam insert in each tire. I wouldn't recommend running much under the recommended pressure.

    The OP just says "Goodyear", and may not have these tires. I think the recommended pressure was raised when the foam lined tires were being phased in. It didn't hurt the other tires, and the Eagle Touring tires needed the higher pressure.

    Just observing and speculating, here.
     
  10. NikeWings

    NikeWings Active Member

    Joined:
    Apr 7, 2016
    Messages:
    1,846
    Location:
    Los Angeles
    I have ContiSilenys and my door jamb says 42 psi as does my SvC paperwork when they auto check my tire pressure upon any visit. Should I be boosting them to 45psi?
     
  11. msnow

    msnow Active Member

    Joined:
    Jul 14, 2015
    Messages:
    4,950
    Location:
    SoCal
    No whatever the door jamb says. Are yours 19" or 21"?
     
  12. NikeWings

    NikeWings Active Member

    Joined:
    Apr 7, 2016
    Messages:
    1,846
    Location:
    Los Angeles
    21s so why 42 when you guys are talking 45? If I have a sticker of 42, does that apply for any tire?
    Never thought much about tire pressure before but I guess I should start now. Thx.
     
  13. msnow

    msnow Active Member

    Joined:
    Jul 14, 2015
    Messages:
    4,950
    Location:
    SoCal
    #14 msnow, Jan 16, 2017
    Last edited: Jan 16, 2017
    Yours are a "thinner" lower profile tire so basically less air is required. No, the sticker is for your own rim/tire setup. Periodically I switch the right scroll wheel to display "Car Status" which is the PSI pressure of all four of the tires. When they lose a pound or so I use a nice digital pressure guage that I found on Amazon.com and this to fine tune it.
    Tesla — Tire Repair Kit
     
    • Helpful x 2
  14. NikeWings

    NikeWings Active Member

    Joined:
    Apr 7, 2016
    Messages:
    1,846
    Location:
    Los Angeles
    OK, I'll monitor. Could you check that Amazon link please when you get a chance. Nothing popped up for me.
    I got the tire repair kit as swag...they said I'd need it being a Boston driver. :eek: But my blowouts so far have been out the sides and I didn't even try the kit. Used roadside and they've been outstanding. Thank you.
     
  15. pers1

    pers1 Member

    Joined:
    Feb 26, 2016
    Messages:
    45
    Location:
    Asker, Norway
    IMG_0170.jpg from Tesla IMG_0171.jpg

    In Norway I use +10% tire pressure for my winter tires as recommende by Nokian tires.
     
    • Informative x 1
  16. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

    Joined:
    Mar 8, 2012
    Messages:
    13,238
    Location:
    Texas
    No. The vehicle placard pressure is not misinformation. I was referring to the 39 psi that the tire store set the pressures to. I consider that pressure to be the minimum that I never want to go below except in unusual (for me) circumstances. The vehicle placard pressure is a starting point only and should be adjusted to reflect actual driving conditions (almost always this means and upward adjustment for on-road driving).
     
    • Like x 1
  17. GSP

    GSP Member

    Joined:
    Dec 28, 2007
    Messages:
    2,227
    For what it's worth, the door jamb placard on my March 2015 build Model S with 19" Michelins calls for 50 psi. It looks like Tesla recommended 50 for a while, then went back to 45 psi. When Tesla did the annual service on my car, they went to the trouble to reduce my tire pressure from 50 to 45. I will set them back to 50.

    GSP
     
  18. JRMW

    JRMW Member

    Joined:
    Nov 13, 2016
    Messages:
    255
    Location:
    Minneapolis
    I know. My point was that the car had a constant low pressure warning that I could not shut off.

    My goal was to inform anybody who was thinking about lowering their tire pressure that alarms would go off.
     
    • Like x 1
  19. kort677

    kort677 Active Member

    Joined:
    Sep 17, 2015
    Messages:
    3,655
    Location:
    florida.
    isn't the point of the alarms to alert you to low pressure in the tires?
    AFAIK the easiest way to shut those alarms off is to inflate your tires to the correct psi.
     
    • Disagree x 1

Share This Page