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 or making a Paypal contribution here: paypal.me/SupportTMC

Tire pressure

Discussion in 'Model S: Driving Dynamics' started by Merrill, Jun 7, 2013.

  1. Merrill

    Merrill Active Member

    Joined:
    Jan 23, 2013
    Messages:
    2,098
    Location:
    Sonoma, California
    Just wondering what everyone that has the 19's is running for tire pressure. It says 45F and 45R, are you going with this?
     
  2. MikeC

    MikeC Active Member

    Joined:
    Jul 9, 2012
    Messages:
    2,411
    Location:
    Los Angeles
    I am. 45 all around.
     
  3. jerry33

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

    Joined:
    Mar 8, 2012
    Messages:
    12,764
    Location:
    Texas
    The 45 psi is the starting point--then you adjust it for temperature and other conditions. Tire pressure recommendations are always based on 65F 18C ambient temperature. If it gets hotter than that you need to increase the pressure to compensate. There are other factors as well.
     
  4. matt.wis

    matt.wis New Member

    Joined:
    Jun 10, 2013
    Messages:
    2
    Location:
    Wisdom
    Tire PSI matters

    I was delivered with PSI of 44-45 on all four tires. That caused some real yaw. 42 is what P85 needed. Hard to believe, but 3 people all agree. If you apply so much torque to the rear tires, you need to be careful on this.

    Matt
     
  5. jerry33

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

    Joined:
    Mar 8, 2012
    Messages:
    12,764
    Location:
    Texas
    The 45 psi is vehicle placard pressure for the 19" tires. I should have made that clear. Adjusting for conditions could be lower or higher depending upon what the conditions are, although adjustments are usually higher).
     
  6. Al Sherman

    Al Sherman It's about THIS car.

    Joined:
    Nov 29, 2012
    Messages:
    1,692
    Location:
    Batesville, IN
    I have the P85 w/21 inch wheels. The placard says 42 all around.
     
  7. mnx

    mnx 2013 P85

    Joined:
    May 6, 2009
    Messages:
    2,281
    Location:
    Ancaster, Canada
    Hey Jerry: Why the reason behind the between between the 19" and 21" inflation pressures? Is it because the 21's are 8.5 wide vs. 8" for the 19's? (I am running 19x8.5 aftermarket wheels, so I'm wondering if 42 or 45 is a more appropriate pressure.)
     
  8. jerry33

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

    Joined:
    Mar 8, 2012
    Messages:
    12,764
    Location:
    Texas
    My opinion is that the pressures were chosen mainly because of the handling differences between the sport tuned P85 suspension and the normal S85 suspension based on test track evaluation. Also lower pressure for the 21" tires creates a slightly larger contact area which helps traction on dry pavement. Conversely the 19" tires likely have the higher pressure to reduce rolling resistance. Tesla stated that the 19" tires get about 5% more range--the higher pressure helps them keep that promise. (Presumably those who don't purchase a P85 are more interested in economy than performance.)

    The difference air volume between the 8" and 8.5" rim width isn't enough to matter--I'd still run 45 on the 19" (it will help the tires survive pot holes). To determine the best handling pressure for dry pavement, use an infrared temperature meter or chalk to get the most even contact pressure. Your local SCCA should be able to help with this.
     
  9. roblab

    roblab Active Member

    Joined:
    Jul 15, 2008
    Messages:
    2,038
    Location:
    Angwin (Napa Valley) CA
    Not wanting to start any arguments here, but with my old EV, I'd run the tires at 50 lb, when the tire said 44. The tire dealer said there was no problem over inflating by 10% "or so", and I wanted range back then.

    Also, I live on mountainous roads. Curves and cornering ate the edges of the tires. Over inflating kept the wear even, which should be some sort of indicator.

    I run 48 in my 19" tires on the S. This also has the added benefit of keeping the tire pressure warning from appearing. At 46, it would appear about once every month for evidently no reason.

    I have no problems with acceleration or steering with the higher pressure. Only better range. With air suspension, I don't experience any unnecessary harshness.
     
  10. ZBB

    ZBB Emperor

    Joined:
    Feb 27, 2013
    Messages:
    1,419
    Location:
    Scottsdale
    Tesla may have made a change... The tire pressure label on my 60 w/19s says 42psi all around...

    VIN is 11,1xx and it was delivered last week...
     
  11. jerry33

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

    Joined:
    Mar 8, 2012
    Messages:
    12,764
    Location:
    Texas
    Overinflation is defined as setting the pressure above the maximum pressure on the sidewall (51 psi on my 19" tires) when the tires are cold. The vehicle placard pressure is a starting point based on a set of assumptions. If your conditions are different than those assumptions, then you need to adjust the pressure to suit.

    The maximum pressure on the sidewall is set so that there will still be a safety factor after the tires are almost worn out, have hit numerous pot-holes, and maybe have been repaired, or in the worst case may not have been built so well at the factory (this last applies to new tires as well as old tires). I don't recommend setting the cold tire pressure above the maximum on the sidewall, just like FlasherZ doesn't recommend combining two 120V lines to make a 240V line. However, if you are going to do this:

    1. Get a good pressure guage such as a model 50406 or model 50404. (one of these has an in-line inflation--use that one)

    2. Replace the hose that goes between the gauge and tire with a longer one that allows you to stand behind or in front of the car.

    3. Get a clip-on chuck.

    4. Stand where you cannot see the tire when adjusting tire pressures. (Note that these are good practices regardless of the pressures you run. Should the tire explode when you are near it, it will just about ruin your whole day.)
     
  12. wycolo

    wycolo Active Member

    Joined:
    May 16, 2012
    Messages:
    2,428
    Location:
    WY
    > 4. Stand where you cannot see the tire when adjusting tire pressures. [jerry33]

    Really?? They're not setting the bead! :confused:
    --
     
  13. jerry33

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

    Joined:
    Mar 8, 2012
    Messages:
    12,764
    Location:
    Texas
    If the tire's sidewall should rupture while your hand is practically touching the tire during it won't be pretty.

    There is a fair amount of energy stored in a tire. Even if you're far enough away, some debris could be shot into your eye, so it's best to stand where the car's fenders give you some protection. Yes, the chances of a tire rupturing while you're inflating are slim--but not zero. In particular, if you've used the slime to repair the tire internal damage is unknown.
     

Share This Page