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Thread: What is "COLD" tire pressure?

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  1. #1
    Dale Rudolph
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    What is "COLD" tire pressure?

    There are a couple of new treads here about tires so I thought I would ask something that I should have asked long ago.
    It is recommended that you check your tire pressure when they are cold.
    What is considered cold ?
    Is it considered cold on a 80 degree day if the bike has been in the garage all
    day and has not been ridden ?
    On a day where the temperature has not gone over 40 degrees in the previous 24 hours considered too cold to check tires ?

  2. #2
    Benchwrenching PGlaves's Avatar
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    A given amount of air in a tire will produce a different pressure reading at different temperatures. So a "recommended" pressure has two values: a pressure reading in pounds per square inch (p.s.i.) or in Bar, or some other standard; and, a temperature.

    BMW specifies recommended "cold" pressures at 20 degrees Celsius, which translates to 68 degrees Fahrenheit. BMW actually specifies pressures in Bar (1Bar = 14.56 p.s.i.) such as 2 Bar, or 2.1 Bar, or 2.2 Bar etc. Those specifications in Bar are converted to p.s.i. in U.S. publications.

    BMW specifies pressures to the nearest .1 Bar = 1.46 p.s.i so are actually less fussy that many riders tend to be.

    So the short answer is that to be precise, "cold pressure" ought to be at 68 degrees. When checking add a pound if it is a bit warmer and subtract a pound if it is a bit colder. You will likely wind up within 1/10th Bar.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://www.bigbend.net/users/glaves

  3. #3
    Dale Rudolph
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    Thanks Paul

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    Registered User 39520's Avatar
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    I agree with Paul about 68 degrees, and you can do temp corrections for cold days.

    While the BMW tire pressures for your bike are a good place to start for sure, I would not take them as gospel. However, they certainly are what you want to use until you get qualified alternative information.

    I had a funny tire wear on an RT - I spoke to the tire factory rep at a rally and he said that his engineers recommended +4 lbs over BMW recommendations for my particular tires. Tire wear problem cleared up on the ride home and I never saw it again.

    OTOH, I showed up for a track day on an F800ST. The service manager from my local BMW dealer, who is also a track instructor, told me to take about 8 lbs off the book values. What a difference it made. it's possible to do because the sidewalls on recent tires are very strong. On the street I went back to book for tread life and fuel economy.

    For guys on airheads, tire technology has changed a lot, a whole lot, over the years. The pressures BMW recommended for tires made 25 years ago may, or may not, be correct for tires today.

    I know this muddies up the water. It's a good idea to talk to tire reps. It's a good idea to talk to high mileage riders, or track riders, whomever more resembles your style of riding.

    Ub
    05 K75s
    86 R65, bought new.

  5. #5
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    BMW uses the typical condition for "cold" in Germany which is commonly called "Raumtemperatur" (room temperature) and is 20?? Celsius.
    As far as the pressure is concerned, I would stick with the tire manufacturer's recommendation rather than BMW. It may be more relevant to the specific tire you have. I had exactly the same experience concerning an unusual wear pattern on a rear tire (Metzeler) and the tire rep explained to me why and told me to increase the tire pressure.
    As far as the track is concerned, the instructors like you to run on a slightly lower pressure because it increases the contact patch and helps warming up the tire faster and keeps it there.

  6. #6
    Registered User lkchris's Avatar
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    Quote Originally Posted by 39520 View Post
    For guys on airheads, tire technology has changed a lot, a whole lot, over the years. The pressures BMW recommended for tires made 25 years ago may, or may not, be correct for tires today.

    This gets repeated often and I pretty certain it's incorrect.

    Only bias ply tires are available for Airheads, i.e. no new radial tech

    Airheads still wear the same size tires they always did, so no 55-ratio tires, for example.

    You will NEVER find a tire manufacturer website that provides conflicting pressure information from that originally given by BMW.

    BMW has NEVER issued "update" bulletins or pressure stickers.

    Nobody ever describes the "new technology" and what specifically about it means pressure changes are necessary. This time once again.
    Kent Christensen
    21482
    '12 R1200RT, '02 R1100S, '84 R80G/S

  7. #7
    Registered User WalterK75's Avatar
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    I've always assumed that "cold" meant the temperature of the tires before I start riding for the day. That is, ambient temperature. I set the pressure as recommended or maybe one half to one psi more.
    That which the Fascists hate above all else, is intelligence.
    Miguel de Unamuno

  8. #8
    Registered User dwyandell's Avatar
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    It's good to be clear about what 'cold' tire pressure means, but in my observation, a REALLY RELIABLE way to get the wrong pressure in your tires is to use an inaccurate tire gauge. I don't care how much the thing cost--gauges can be all over the place and even 'good ones' can be WAY off. Beware.

    I'm sure most of us have a dozen pressure gauges stashed in various tank bags, tool boxes, etc. Take a few minutes some afternoon to collect them all into a pile and compare how much variation there is among the gauges you own . . .if you do this, you probably wont ever worry about ambient temperature again.

    If there's a really simple and short way to calibrate gauges, I dont know what it is. The slightly longer way is to compare a few of the better quality gauges you own on a large tire that won't lose much pressure with each measurement (a truck or large car tire) . .. if several better quality and newer gauges more or less agree, then that's likely about the right number. Compare each to that 'reference' reading, and mark each with a permanent marker as to how many pounds high or low it reads. Throw any away that dont give reproducible results. Some digital gauges, and the better mechanical dial gauges, can be calibrated (look for a small screw on the back) but most of them can't.
    Dave in Vermont
    '84 R80ST
    '81 R100 hack

  9. #9
    Polarbear Polarbear's Avatar
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    Cold and weight at max!

    Tire sidewalls say cold max air pressure 41lbs at max weight, say 778lbs....e.g....I always run max air for fully ladden bike on trips where i am usually near gross weight on the bike. Maybe less air if the bike is not so, by only a few lbs. of air. You adjust as required. Elevation, maybe some change too, so do the math. ? Randy

  10. #10
    Bill Lumberg 175781's Avatar
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    This. Cold means the tires haven't been heated by driving or exposure to a flamethrower. In the summer, I check and adjust pressure in cold (not driven that day) tires. When the temperature drops or rises significantly, be it bike or truck, I know my next check will show tires over or under pressure for that operating environment. My February tires would be grossly overpressured at 95 degrees. My July pressures would leave me running on sludge-rubber placed in a 20 degree environment. Not that 20 degrees celsius is bad.
    Quote Originally Posted by walterK75 View Post
    I've always assumed that "cold" meant the temperature of the tires before I start riding for the day. That is, ambient temperature. I set the pressure as recommended or maybe one half to one psi more.
    R75/6, 2004 R1150RTA.

  11. #11
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    Quote Originally Posted by PGlaves View Post
    A given amount of air in a tire will produce a different pressure reading at different temperatures. So a "recommended" pressure has two values: a pressure reading in pounds per square inch (p.s.i.) or in Bar, or some other standard; and, a temperature.

    BMW specifies recommended "cold" pressures at 20 degrees Celsius, which translates to 68 degrees Fahrenheit. BMW actually specifies pressures in Bar (1Bar = 14.56 p.s.i.) such as 2 Bar, or 2.1 Bar, or 2.2 Bar etc. Those specifications in Bar are converted to p.s.i. in U.S. publications.

    BMW specifies pressures to the nearest .1 Bar = 1.46 p.s.i so are actually less fussy that many riders tend to be.

    So the short answer is that to be precise, "cold pressure" ought to be at 68 degrees. When checking add a pound if it is a bit warmer and subtract a pound if it is a bit colder. You will likely wind up within 1/10th Bar.
    Owner's Manual of my '12 GSA says 68 degrees. I run 36F/38R. Don't ask me what kind of oil I use or how often I change it!

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