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Thread: Why Tire Pressure Matters

  1. #11
    Flirting With The Redline 2000 Posts! Sorg67's Avatar
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  2. #12
    Flirting With The Redline 8000 Posts! Trials's Avatar
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    Air pressure must be appropriate for the load regardless of application, it's not a fixed specification. The tire pressure stamped on the tire is the maximum load that can be carried with acceptable tire deformation and the air pressure that is required to carry that maximum load.
    ... that's why the same tire used on 2 different bikes will be riding on different tire pressures.

    The thing you are trying to avoid is heat generated within the tire casing itself that will cause delamination of the tires rubber and cord layers. It is the flex and deformation of the tire that creates that internal heat, like taking a piece of plastic and bending it back and forth until it starts to get hot and shape deform. If the tire has more air in it, the tire does not flex and conform to the road surface as well, now you have less heat generated and less traction available.

  3. #13
    RiderCoach 8000 Posts! WoodstockJeff's Avatar
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    In the age of flat-tread bias-ply tires, you could run a chalk line across the tread, roll the vehicle forward, and see if the chalk was cleaned off evenly. Chalk left on the edges meant over inflation, in the center meant under inflation. Even wear meant the tire was properly inflated for the current load.

    That doesn't work for motorcycle tires, and even most car tires have a rounded profile today.

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  4. #14
    RiderCoach 4000 Posts! AZridered's Avatar
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    There's no particular pressure deficit that increases risk of tire failure. The issue is heat build-up. A tire could be 50% underinflated and never be a failure risk if the rider only travels at low speeds. Steering and braking are another matter. If a tire's inflation is too low for the conditions in which it is being used, the risk of overheating and carcass damage increases.

    I did some work with a major tire company some years ago and they had a 'rule of thumb' recommendation of 10% pressure rise from cold to warm. Basically, choose your favorite cold pressure and then ride the bike in normal fashion for at least 30 minutes (road use). After the time has passed, find a safe place to stop and check your tire pressures. They should have increased by about 10%. Much less than 10%? You could have started with a lower pressure and that could improve traction for cornering and braking. Much more than 10% means that you probably started out with your pressures a bit low for the type of riding that you just did. Higher pressures could improve traction and ease steering.

    Sometimes a tire manufacturer will publish more detailed inflation pressure information than is found on the standard pressure charts. For instance, the regular fitment chart for the front tire that I use lists 36 psi as the standard 'cold' pressure to use on my bike. Searching through the web site I was able to find these notes:

    Suggested hot tire pressures: Hot 34-36 psi
    Suggested cold tire pressures: Cold 30-32 psi

    I noticed a definite ride improvement when I dropped the tire pressure enough to have it peak at 36 psi when hot. The 'cold' pressure that I'm now using is 32 psi. Of course, that will change by a few psi by this winter.

  5. #15
    RiderCoach 5000 Posts! NORTY's Avatar
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    What I’ve recently discovered is that some motorcycles come with tire pressure monitoring systems AND temperature monitoring systems, in real time.
    This may cause riders to “obsess” over this add’l data.
    There comes a time when “too much can saturate.”
    But, the opposite can be said of the rider that neglects their motorcycle.
    Years ago, drivers wouldn’t address tire inflation/condition unless they were made aware of it by vehicle characteristics or by other people.
    With “on dash” alarms now, we have become sensitive to 1-2 lbs gain/loss.
    Sure, we all can feel 1 or 2 lbs on our motorcycles, but it may be more difficult on a atreet car/truck.

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  6. #16
    Flirting With The Redline 8000 Posts! Trials's Avatar
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    I read that MV Agusta set the standard rear tire pressure at 41.1 psi as opposed to the 33.8 psi for my bike,
    something about tire flex on low speed corners at 140 pounds in full gear I haven't found that to be a huge problem yet, I think I'll stick with 33 on the money. ymmv.

    or maybe the problem is they are taking the low speed corners too slow

  7. #17
    Flirting With The Redline 10,000 Posts! Shadow Shack's Avatar
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    Quote Originally Posted by WoodstockJeff View Post
    and even most car tires have a rounded profile today.
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