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Thread: What's the problem with tire pressure?

  1. #16
    Enjoy The Ride saddleman's Avatar
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    Quote Originally Posted by dockeithdc View Post
    A wise old tire Guru once told me that the proper tire pressure is always changing with weight, temp, driving style ect. His recommendation is to start with the recommended tire pressure checked cold. Ride and when you stop immediately check the tire pressure. The optimal pressure change will be 1-2lbs. If more you are under inflated, less you are over inflated.

    Having the tire pressure monitor on the bike makes this very simple. I have michelin PR 2 on my 08 RT and I have found that my optimal pressure using this technique is 38 front and 42 rear.
    I just changed a set of PR2 tires on a 2012 RT that had just over 15,000 miles on them with 37 psi on the front & 42 psi on the rear & they could have gone another 1000 miles before they were at the wear bars.
    Dave
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  2. #17
    It is what it is. Bud's Avatar
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    Sidewall tire pressure is the maximum per the tire mfg.

    It is not always the recommended or optimum tire pressure.

    Paul and others have it right. It pays to listen to the voices of experience.

    Your mileage WILL vary.
    I used to post here, but now I don't.

  3. #18
    Registered User lkchris's Avatar
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    It's always interesting to see reference to "newer, higher pressure tires."

    Correct me if I'm wrong, but in most cases this is the difference between radial and bias-ply tires.

    In most cases, the tire specified for your bike is one or the other but never both. If that's the case, there simply aren't "newer, higher pressure tires" applicable to your bike.

    (One exception may be Conti's new radials directed towards Airheads and maybe old Ks, but haven't studied that. They have just been introduced this summer.)

    And, the numbers on the sidewall are completely meaningless except that they indicate the maximum pressure safe to use in this tire. This has NOTHING to do with BMW's or the tire manufacturer's recommended pressure for your particular bike and load conditions.

    Except for the following, that is ... A recent presentation at our dealer by a Metzeler tire rep featured the notion that if your goal is to maximize tire mileage, i.e. tread life, then you should indeed run your tires at the maximum pressure indicated on the sidewall. It's printed a little less strongly in Metzeler brochures, too. This of course, is NEVER the basis for BMW's pressure recommendations for your bike and most obviously may involve some handling and/or comfort and/or performance compromises. I'm not doing it, as my goal is fun associated with riding and for sure not carefully saving every penny and diminishing the fun. I mean, if it's about only tread life, just never ride.

    If you've a current model BMW, recommended tires by brand are listed at BMW's website. These charts don't go very far back as regards discontinued models IIRC. There is, not completely coincidentally, sometimes not sizes for older bikes in the latest/greatest tire models, and the older bike guys then use the older models anyway. The notion that perhaps tires (brands) not on the recommended list somehow require completely different pressures is a bit of stretch in logic, too, I think. Look for that brand to publish something instead.

    Bottom line, I think, is that BMW's recommendations are simply fine and are good for a long time. If a tire manufacturer will publish in writing or on its web page that they indeed have different recommendations for you, then pay attention. There's not a lot of data provided by various internet contributors to back up their claims when it comes to varying from BMW specifications, and they should direct you to data rather than their opinions and unscientific observations. I know for sure that I've never seen specifically published by a tire manufacturer that pressures recommended by BMW in, say, the 1990s or 80s or 70s have been superceded by "new technology." I'd love to be directed to it.

    You can also rationalize that somehow BMW's specifications don't apply specifically to you because you must weigh something different than their average rider or something like that, but I'd instead conclude their figures can be recognized as covering normal variations. BMW's figures are quite fine and it's not really about demonstrating that you know more than they do, is it? When it comes to "voice of experience," nobody tops BMW.
    Kent Christensen
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  4. #19
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    Quote Originally Posted by MANICMECHANIC View Post
    To go just a bit further with Paul's analysis, consider what your owner's manual specifies, with the OEM tires. Is that tire still the tire you put on, and under what conditions do you ride it? I remember when car tires would routinely be set to 30-32psi, now with the newer ones, 40+psi is not uncommon, per the sidewall info. My shop has had to deal with tire warranty issues because people put newer higher-pressure tires on their heavyweight bikes, but the owners ran them at the old pressures and destroyed the tires. Your bike is pretty much a constant, its technology doesn't change much, but tires are constantly changing. Become better informed.

    Per your comment on warranties-which matters (the most?) the door jamb sticker or the sidewall number? FWIW. do vehicle mfg's(dealers do not) these days change that sticker when various tires are placed on vehicle as brands change some. Now back to MC tires...I'm not sure I "get" that info from tire mfg's saying max performance comes @ max pressure on sidewall? Somethings missing here...
    "If I had my life to live over, I'd dare to make more mistakes next time...I'd relax,I'd limber up... I would take fewer things seriously...take more chances... take more trips...climb more mountains...swim more rivers...eat more ice cream." Jorge Luis Borges at age 85.

  5. #20
    Small road corner junkie pffog's Avatar
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    Remember nothing is free, yes higher pressure lowers rolling resistance and heat, and makes tires wear longer, BUT also reduce traction due to less heat in the tire and smaller footprint on the pavement.

    Pick your poison!
    2010 F800GS Full Ohlins package, '04 R1100S Replika
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  6. #21
    Registered User chewbacca's Avatar
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    Just something to think about, do motorcycle racing teams or car racing teams call the vehicle manufacturer for a recommended tire pressure? Racing guys, even when a tire rep is supporting the team adjust pressure to meet conditions. When you look up most bike tires they usually have a statement to the effect of what the bike manufacturer recommends. Avon used to have specific recommendations. I don't recall Michelin, Metzler or Dunlop having them but that changed from time to time. As previously stated that sidewall pressure is a max loaded pressure. There is an old timers rule of thumb and I'll probably screw it up. Set the pressure cold. Go ride for maybe half an hour. Check the pressure. If it goes up about 10% your good. More than 10%, add some air and try again. Less than that, let some air out.

    IMO, to get good, consistent readings you have to measure cold. Also, don't use the TPS readings for anything else than to determine you have leak.
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  7. #22
    Benchwrenching PGlaves's Avatar
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    There is a lot more to tire technology that just radial vs bias technology. You also have belted vs non belted in both bias and radial types. There was nylon cord, then polyester cord, then kevlar and steel. And if anybody thinks the rubber compounding and optimal operating temperature for a K112/RB2 combination is the same as for bias ply ME880s, .....

    You can still buy tires that are almost identical to what you could buy in 1975. But most riders don't because there are significantly better tires available today. They are better because they are different, and don't necessarily need the same pressure as the tires of 1975. Some might wish it weren't so, but it is.

    I remember Reg Pridmore telling me in 1986 (RATS, Laguna Seca at the MOA Rally) that the stock tires on his K75 fleet were better track tires than the ones he had on his superbike R90S when he won the championship. I'm confident that was true back then, and moreso now.
    Paul Glaves - "Big Bend", Texas U.S.A
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  8. #23
    Registered User lkchris's Avatar
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    Quote Originally Posted by chewbacca View Post
    Just something to think about, do motorcycle racing teams or car racing teams call the vehicle manufacturer for a recommended tire pressure?
    Of course not because there's no such thing as bone stock motorcycle or car racing and these teams aren't using highway tires. Silly question, proves nothing.
    Kent Christensen
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    '12 R1200RT, '02 R1100S, '84 R80G/S

  9. #24
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    Cool! finally, we have another thread, in addition to the infamous "Oil Thread" that needs to be elaborated upon.

  10. #25
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    Quote Originally Posted by chewbacca View Post
    Just something to think about, do motorcycle racing teams or car racing teams call the vehicle manufacturer for a recommended tire pressure? Racing guys, even when a tire rep is supporting the team adjust pressure to meet conditions. When you look up most bike tires they usually have a statement to the effect of what the bike manufacturer recommends. Avon used to have specific recommendations. I don't recall Michelin, Metzler or Dunlop having them but that changed from time to time. As previously stated that sidewall pressure is a max loaded pressure. There is an old timers rule of thumb and I'll probably screw it up. Set the pressure cold. Go ride for maybe half an hour. Check the pressure. If it goes up about 10% your good. More than 10%, add some air and try again. Less than that, let some air out.

    IMO, to get good, consistent readings you have to measure cold. Also, don't use the TPS readings for anything else than to determine you have leak.
    Changes in tire pressure are directly related to the amount of water in the "air" in the tire. Just a small amount of water,(and it can be from the lubrication used to mount the tire) will greatly affect the tire pressure in a m/c tire due to the small volume. I think you should rethink that old timers rule. Nitrogen will help to mitigate the change in tire pressure.

  11. #26
    Small road corner junkie pffog's Avatar
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    Quote Originally Posted by Gonzo49 View Post
    Changes in tire pressure are directly related to the amount of water in the "air" in the tire. Just a small amount of water,(and it can be from the lubrication used to mount the tire) will greatly affect the tire pressure in a m/c tire due to the small volume. I think you should rethink that old timers rule. Nitrogen will help to mitigate the change in tire pressure.
    WRONG!!!!!!!

    PV=nRT or simpler Gay-Lussac's Law P1/T1 = P2/T2
    2010 F800GS Full Ohlins package, '04 R1100S Replika
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  12. #27
    Old man in the mountains osbornk's Avatar
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    Quote Originally Posted by Gonzo49 View Post
    Changes in tire pressure are directly related to the amount of water in the "air" in the tire. Just a small amount of water,(and it can be from the lubrication used to mount the tire) will greatly affect the tire pressure in a m/c tire due to the small volume. I think you should rethink that old timers rule. Nitrogen will help to mitigate the change in tire pressure.
    I have 78% nitrogen in my tires. Seems to work fine.
    'You can say what you want about the South, but I almost never hear of anyone wanting to retire to the North.

  13. #28
    Benchwrenching PGlaves's Avatar
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    Yes, moisture in a tire can theoretically add to pressure fluctuations. If the interior tire temperatures reach the point that water droplets are vaporized - something in excess of 212F - the steam can increase pressures more than simple heating of air. At the extreme, triple digit ambient temperatures and sustained Interstate speeds my rear tire gets to somewhere between 150 and 160F. No steam.

    If concerned, put a drier on your compressor.
    Paul Glaves - "Big Bend", Texas U.S.A
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  14. #29
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    Quote Originally Posted by chewbacca View Post
    Just something to think about, do motorcycle racing teams or car racing teams call the vehicle manufacturer for a recommended tire pressure? Racing guys, even when a tire rep is supporting the team adjust pressure to meet conditions. When you look up most bike tires they usually have a statement to the effect of what the bike manufacturer recommends. Avon used to have specific recommendations. I don't recall Michelin, Metzler or Dunlop having them but that changed from time to time. As previously stated that sidewall pressure is a max loaded pressure. There is an old timers rule of thumb and I'll probably screw it up. Set the pressure cold. Go ride for maybe half an hour. Check the pressure. If it goes up about 10% your good. More than 10%, add some air and try again. Less than that, let some air out.

    IMO, to get good, consistent readings you have to measure cold. Also, don't use the TPS readings for anything else than to determine you have leak.
    Not that I'm taking potshots at the "theory" above but obviously much is missing with the process as "go take a ride" for a rider in the desert, in the summer would far different than the result for "go take a ride" in the winter on say, the US/CA border.
    As for Osbornk & his N source, I just googled the subject & the geologist whatever website says while N hasn't changed appreciably, oxygen levels have changed. Now , do we have a "tire pressure expert" to step forward & debate the effects of more or less oxygen in a MC tire?
    "If I had my life to live over, I'd dare to make more mistakes next time...I'd relax,I'd limber up... I would take fewer things seriously...take more chances... take more trips...climb more mountains...swim more rivers...eat more ice cream." Jorge Luis Borges at age 85.

  15. #30
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    I am going for a ride. Will check back later!

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