Just a bit of info I don't see covered enough or at all.

On your tire, valve stem, always keep a valve cap on the stem.

At high speeds, the pressures of the air in the tire can easily blow the valve stem out, causing almost instant deflation.

If you happen to be doing any speed higher than say...75mph...that is almost assured death.

On z-rated tires, at 150 mph or more, if you have a sudden deflation, we'll see you in the obits.

That cheap little plastic cap is the difference between life, and death.

 

Where did you hear this? I have never, ever heard anything like this. I'm not condoning removing the caps, don't see any point in it...but why would tire pressures increase simply from high speeds? Higher temperatures do cause air to expand, say 5-10 psi and is not necessarily caused by high speed, but rather sustained movement across high friction surface such as asphalt, but this is hardly enough to "blow out" the valve core. They are screwed in tightly and can withstand pressures of at least 80 psi. Car and truck tires are inflated to higher pressures and they use the same valve stems as motorcycles. I constantly see cars missing valve stem caps.On the other hand, those "tire flys" or any other aftermarket valve stem cap that weighs more than the plastic one can actually rip the valve stem out of the rim at sustained high speeds due to centrifugal force, but blowing the valve core out? I just can't see it ever happening.

 

That is so crazy sounding it may be true. I guess if the valve fails, the cap will slow the deflation, but a spinning tire would push the stem IN not out. I thought the cap just kept dirt out of the valve so when you filled it, dirt didn't stop the valve from sealing.


What ever the case, this is one of those things that should be filed under 'just do it'.

 

I have heard something or other about this thing before, but at really - really top speeds, filed it under the stranger things have happened category. But I always make sure I have the dust cap covers, (thats wot we call them) stop crap building up around the valve, it also acts as a kind of slow release system if the valve should fail (from having to much crap around them of course) true or no, it makes sense to have them on. maybe the Mythbusters should take that one on.

 

The loss of pressure due to valve core failure can be caused when the centrifugal force acting on the valve pin (what you push to let air out) exceeds the spring tension of the valve core. Most standard valve core springs are more than capable of extreme speeds because the tension required to counteract the escaping air upon filling is greater than the centrifugal force that could be reasonably generated. There are certain circumstances when this would be possible, but none that anyone here would have to worry about. The simple fix for people that have salt flat cars is to turn the valve sideways so that the centrifugal force no longer acts on the valve pin or to simply seal the valve and utilize a pressure regulating check valve.

In the event that the valve core failed, and centrifugal force did indeed depress the valve pin, the result would be a slow leak the same as pushing the pin in to let air out of the tire. It doesn't just blow the tire out when you need to let a couple pounds of air out by hand. That valve is made so that the air cannot force it's way out but rather is set up to be a slow release valve that has a controlled airflow even under full open condition or failure.

The ideal gas law can assist with temperature expansion of air and although it is complex, it is better than not knowing what your expansion rate is. So for general air, you gain 1 psi for about every 5 degrees Kelvin or roughly 10 degrees Farenheit. So let's start at 50 degrees and assume that you have run your tires clear up to 250 degrees. That would be a little less than a 20 psi increase which is well within the failure limits of a conventional valve core. Note also that bike tires hold considerably less heat than auto tires. An extreme heat condition would come not from racing a motorcycle, but from driving a heavily loaded vehicle at high speeds with the wheels out of alignment thereby creating a high friction setting at low (comparatively) cooling speeds.

So let's assume that the valve core failed and the little plastic piece was now holdingthe air pressure in the tire. At best, it would slow the leak, but not by much. In a catastrophic failure of the valve, the pressure would easily overcome a plastic valve cap and blow it off the valve. There are metal ones with better threads that can actually hold pressure, but the plastic ones unfortunately are destined to a life of keeping dust and moisture out, nothing more.

Anyway, keep your valve caps on. And if you really believe that you will someday be at the mercy of your valve cap, get some metal ones or some better valves or something.

 

Thank you Professor Ty.

 

Back when I raced the valve cap had to be metal to pass tech inspection, I never knew why maybe that's it.....