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Why Tire Pressure Matters

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  • Why Tire Pressure Matters

    I have not been as good about monitoring tire pressure as I should. Maybe one a month or so.

    I read an article about tire pressure recently and it stated that low tire pressure can cause heat build up and create a blowout risk.

    That got me to thinking perhaps I should monitor tire pressure more closely. I have noticed that tire pressure affects handling. And I understand that tire pressure impact tire wear. But I did not understand that low tire pressure could create a blow out risk.

    Are handling, wear and blow out risk the main considerations? How low does tire pressure have to get to create a blowout risk? Are there other considerations?

  • #2
    I adjust my tire pressure frequently for performance considerations, so I tend to check or adjust the tire pressures very frequently, as in virtually every day I ride. Low pressure gauge and tiny air pump is in my fanny pack for the trials bikes at almost all times, and the street bikes I test before leaving the garage. I'm not the normal rider though, every street ride here starts with a very rough gravel road and on competition trials bikes we ride the tires as flat as physically possible.

    ... I'm also very careful with monitoring the tire pressures on my heavy trailers :/ those things blow tires super easy if they are soft for sure. But I have to confess on the car I tend to ignore the tire pressures more then I should mostly because cars are completely



    Going to see if we can do the worlds fastest front fork rebuild right after morning coffee

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    • #3
      Handling is a big first clue to tire pressure, although most people I've met don't notice the changes. The damagingly-low pressures that cause heating/blowouts make their presence known early, if you don't ignore them.

      Me, I pick up the change in handling somewhere about 5-10% low, depending on the vehicle. Motorcycles are VERY noticeable to me at 5%.
      Jeff

      "Remember when being socially distant was a symptom of a potentially debilitating mental disorder, instead of a government mandate? C'mon, it was just a few weeks ago!"

      "Modern Liberalism: The embodiment of an irrational fear of letting other people run their own lives."

      '13 XT250
      '10 ZG-1400 (operational again)

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      • #4
        I am not quite as sensitive but I can tell on the Versys and CB500X. I do not notice on the KLX250S. I notice a bit more on the CB500X than on the Versys. Both steer heavier when tire pressure is low. I probably notice 10% to 15% under inflated on the front tire. I do not notice under inflation on the rear tire as much.

        CB500X has a slow leak on the rear. Three plugs. One is leaking a little.

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        • #5
          Back when I had a hardtail* I dropped my back tire pressure down to 20psi, just for a little "boinginess". It held in turns (at least as well as a hardtail can hold) but I could tell when it dropped below 18psi as it would shift, shuffle, shimmy, and otherwise act shitty when leaned over.

          Another issue folks don't consider with under-inflated tires...when you hit a bump it forces the air up into the "top" portion of the tire, which "balloons out" accordingly. This can rub against your fender, causing additional tread wear and --- if you happen to have a plastic fender, that same friction can melt a hole in it.





          * no rear suspension is definitely NOT a beginning rider modification
          Sent from your mom's phone
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          • #6
            At what tire pressure do you get blowout risk? Is blowout risk due to low tire pressure mostly long periods of time at highway speed?

            @Shadowshack 20 psi would be 44% low for target 36 psi. Was that okay for short trips around town but would have been dangerous at highway speeds?

            I am feeling like being lax about tire pressure up to maybe 30% low is a performance and tire wear issue for short trips around town. Potentially a safety issue for longer trips at highway speeds. Is that about right?

            Are there braking issues related to tire pressure? Braking in turns?

            I suppose performance becomes a safety issue in certain circumstances.

            Getting around the discs to check pressure is difficult and I usually lose some pressure checking. I just ordered a new tire pressure gauge. Maybe that will make it easier to check without losing pressure.

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            • #7
              Closest thing I have experienced to a blow out on a motorcycle was when I sheared off a valve stem, that went flat faster then you could ever want to stop.

              Braking hard on a tube tire can slide the tire on the rim bead and shear off your inner tube valve stem, this is why lots of bikes have rim locks on their tube type tires. The tire is more likely to slide on the rim when the tire pressure is very lower.

              When a tire blows on my heavy trailer due to under inflation, it is heat generated within the rubber, fabric and steel tire plies that give up the ghost, the layers literally separate.

              They make 90 degree valve stems easier to get at, and if you spin your wheels up to warp speed the inertia from the valve stem won't result in air leaking past the valve, that's why they install right angle valve stems on GP race bikes and F1 cars.

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              • #8
                Originally posted by Sorg67 View Post
                At what tire pressure do you get blowout risk? Is blowout risk due to low tire pressure mostly long periods of time at highway speed?
                Not sure, but overinflated can lead to the same blowouts that underinflated can.

                @Shadowshack 20 psi would be 44% low for target 36 psi. Was that okay for short trips around town but would have been dangerous at highway speeds?
                Well...my bike is rated for 29psi on the rear with a solo rider so I was at about 2/3 at 20. That said, I took numerous freeway rides and outings to the mountains. I went 15K on that tire with no rear suspension & lower pressure before restoring the suspension, and the tire lived on about another 3K at normal pressure after that.

                I go by the motorcycle manufacturer rating, a lot of folks swear by the tire manufacturer rating but here's the issue: say there's a tire that fits both a 300 pound Honda Rebel and a 900 pound Victory Vision. The tire says "35psi" yet both bikes will handle differently at that pressure. The Rebel will call for lower pressure, whereas the Vision might be higher.
                Sent from your mom's phone
                "If I wanted a windshield and tunes, I'd drive my car."
                Ride Safe, Chop Safer
                "Unofficial Beginner Bike Chop Shop"
                "Motorcycles are not unsafe. However, they are extremely unforgiving of inattention, incompetence, ignorance, and stupidity."
                Support your FLIBS (Friendly Local Independent Bike Shop)
                sigpic
                3500cc worth of Honda: http://shadow-shack.20m.com

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                • #9
                  What I am hearing is that being manic about tire pressure is more of a performance and tire wear issue. You have to be pretty far off to create a significant safety issue. Fair summary?

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                  • #10
                    Yes modern tires have a fairly wide range of acceptable operating pressures
                    their load carry capability is dependent on the air pressure otherwise, you are only riding on the tire sidewalls,
                    air pressure is how you control the amount of tire deformation for your application. & the rim must suit the tire to allow high or low pressure applications.

                    ... for example if shadow has a tube type rear tire and regularly runs low tire pressure, he should have one or two rim locks on his wheel.

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                    • #11
                      Plus or minus 25% - Safe
                      Plus or minus 10% - Pretty good
                      Plus or minus 5% - Optimal
                      Plus or minus 0% - Racing

                      ?

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                      • #12
                        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.

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                        • #13
                          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.
                          Jeff

                          "Remember when being socially distant was a symptom of a potentially debilitating mental disorder, instead of a government mandate? C'mon, it was just a few weeks ago!"

                          "Modern Liberalism: The embodiment of an irrational fear of letting other people run their own lives."

                          '13 XT250
                          '10 ZG-1400 (operational again)

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                          • #14
                            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.

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                            • #15
                              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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                              Knowledge speaks, wisdom listens.

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