Tire pressure PSA, something I just learned

Discussion in 'Equipment' started by AZQKR, Aug 30, 2018.

  1. AZQKR

    AZQKR Long timer

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    So, with the above, it's safe to say BMW uses 68 degrees as their reference when recommending tire pressures, now we know the "why".

    Thanks for the explanation, it's been an enlightening/educational thread for myself and I'm sure others.

    Game, set, match :D
    #81
  2. Retired and lovin it

    Retired and lovin it Been here awhile

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    Reason BMW has said 68 degrees is that a base line reference should be used that is consistent just my opinion, to many variables and you have problems. Don't attack me for simplifying please.
    #82
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  3. AZQKR

    AZQKR Long timer

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    It's worth complimenting your well elucidated response. Simplifying and standardizing brings uniformity across many platforms. :thumb
    #83
  4. Bungholio

    Bungholio Long timer

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    Because they're German and have a penchant for overcomplicating and overengineering, it's just their nature.

    Sent from my Nexus 7 using Tapatalk
    #84
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  5. Pch123

    Pch123 Bar Crossings

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    Your reasoning is almost as fool proof as your ground sheet argument.
    :clap:clap
    #85
  6. AZQKR

    AZQKR Long timer

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    "Because 68 degrees F is the base standard temperature for pressure measure." according to another member who linked to that information. Though I agree, they do have a history of a penchant for over engineering.
    #86
  7. AZQKR

    AZQKR Long timer

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    There was no argument about ground sheet placement from this side. There was difference of opinion based on first hand experience. :bow
    #87
  8. RRF

    RRF Adventurer

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    Isn’t hot temp what’s important? The temp of the tire in use? So if a tire’s optimal hot temp is say, 100 degrees, you want a temp rise of 32 degrees at ambient temp of 68. If it’s 88 degrees ambient you only need a rise of 12 degrees so adding the 2 lbs pressure means tire will flex less, create less heat, and reach the same hot temp.
    #88
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  9. CharlesLathe

    CharlesLathe Been here awhile

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    Okay, I looked at the page the OP gave us a link to, and especially to the graph, and I gave it a shot. Yesterday, the temperature in the afternoon was about 90°. I checked my rear tire pressure and it was about 2psi higher than it should have been. I put a little air in it to bring it to right at 2psi above the recommended pressure per my owner's manual. Just now, this morning, with air temperature about 70°, I checked it again and it is two pounds lower than what I read yesterday, or right at recommended tire pressure.

    As the graph shows, the pressure goes up and down with ambient temperature. Therefore, I only need to follow the 1psi for every 10° variation when filling the tire. The pressure will adjust up and down during the day as the temperature changes so that the next time the temperature is 68°, the pressure will be at the recommended pressure. And when it is 88° the pressure will be 2psi higher than recommended.

    Since the tire sites and my owner's manual don't mention doing this, I'm not convinced it's something I need to worry about, but if someone has a tire gauge that measures in 1/2psi increments, and takes the gauge to work to calibrate it, this would seem to be something of interest. As for myself, now that I've read about it, I'll probably take the OPs advice and do what he says. Or not.
    #89
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  10. Coma

    Coma Long timer Supporter

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    Another thought, several have talked around the tires operating temperature. Just like other things a tire operates best at a certain temperature. Weight, rubber compounds tire casing all go into what pressure is right for what bike. I check my tire pressures once a week.
    #90
  11. flei

    flei cycletherapist

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    #91
  12. AZQKR

    AZQKR Long timer

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    No need to adjust the tires while riding as long as the correct pressure is set in the morning on cold tires [ unridden ]
    #92
  13. Coma

    Coma Long timer Supporter

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    FWIW you can set the tire pressure using the TPME on the GS. You can ride it to wake them up for a sort distance or weak them up with a TPMS wake up tool. A late model Chevy tool works great.
    #93
  14. flei

    flei cycletherapist

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    Apparently, the sarcasm intended in my post didn't come across....
    #94
  15. AZQKR

    AZQKR Long timer

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    Lacking an emoji, that's understandable :ricky
    #95
  16. AZQKR

    AZQKR Long timer

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    I can't set pressures through my tpms system on the GT. I can read what the pressures they are reading however. And it's my understanding the tpms can be off a few #'s on some bikes over actual pressures. I'll continue to use my guage that's known to be accurate and then check it to the tpms readings.
    #96
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  17. Coma

    Coma Long timer Supporter

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    On my GS the read vs measured are very close. I can watch the TPMS display update as I change tire pressure. Depending on the day my OCD will let me just measure with a pencil gauge weekly. :D
    #97
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  18. JTerryM

    JTerryM -/\~

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    Read all 5 pages of this and I've yet to see evidence that BMW (or Porsche or any other maker) state recommended pressure at anything other than ambient. My manuals do not.
    #98
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  19. AZQKR

    AZQKR Long timer

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    The evidence is provided by calls to the motherland by others, but as I haven't called myself [ which still wouldn't satisfy you anyway ], I don't need to call, others confirmed this who've been riding Beemers for decades.

    Ride as you like, I'll ride on tires that have the correct pressures based on the +1/-1 for every 10 degrees above and below 68.

    Theoretically, one could set the tire recommended tire pressures at -20 degrees F, and ride into 110 degree temps before the end of the day, where the tires would be 13#'s over pressured. If set at 42 rear, that would mean the pressure would be 55#'s, well over the max pressure of the tire.

    People who live in climates that range from 115-35 degrees see air pressures well below what the recommended pressure of the tire is listed for. Every winter, tire pressures set in the heat of the summer are underinflated and need more air in the colder temps. Saw this every summer and winter back east for decades. Obviously, ambient temperatures changes affect tire pressures.
    #99
  20. JTerryM

    JTerryM -/\~

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    Yeah, I get the physics and arithmetic.

    Put it this way, if I lived at -20 degrees and rode to work every day at -20*, then once a month rode down into the valley where it's 115*, I wouldn't set my pressures based on an arbitrary value I'll pass through on my way down (68*) just so that I'm not too overinflated when I get there, yet underinflated every other day. I'd set it for current conditions and not bother with adjustments unless they were extreme - like winter/summer, sea level/mountain top, etc.
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