Nitrogen experiment

Quote:

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Originally Posted by Matt Vastine

In summary, put an appropriate amount of air in your tires and go ride.

Now give my hat back Mitch.

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And that amount would be? If I say 28psi hot, I'm sure there will be torches and pitchforks before long telling me that's wrong.

Quote:

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Originally Posted by Kasey Lewis

And that amount would be?

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At the risk of sounding repetitive...

Inflate with the recommended pressures, go ride, check air pressures at the wall/ inspect tire wear/ evaluate your "feel" and personal performance, adjust as needed.

am i missing something here?
i mean the real question here is ,optimal operational air pressure, right.
air pressure in our situation is mostly controlled by heat on the tires applied at variable track speeds.
so, if one knows what temp each is raising the tires to ON track, one may set the pressure accordingly at pit..
how does it matter if its meere mortal air pump air of Nitro as long as the pressure is correct at the optimal temp.
how far off am i on this ?
i may be completely wrong for all i know.

Interesting thread. Disclaimer: I'm one of those dreaded engineers, holding strange beliefs in the laws of physics and conservation of mass and energy and other such perversions (you know, the stuff the design of your motorcycle is based on), so take this with a small boulder of salt.

Ideal gas law (which governs most familiar gases at reasonably experienced temps and pressures) says that if you take any volume of an ideal gas (dry air and nitrogen both qualify) at 90F and 24 psig and heat them to 205F in a fixed volume, the pressure will rise to 28.9 psig. As noted, air is 79% N2, so I seriously doubt that the difference is in the molecular weight of N2 vs. air (28.0 vs. 28.97) or other slightly non-ideal characteristics, but most likely has to do with moisture content of the two gas supplies you are using. (Would be very interesting to run your oven heat-up test with a *completely dried* air supply against the bottled N2 and the compressed air source. A bottle of calibration "air" would probably provide that.)

One other variable is the stiffness of the tires. The pressure rise noted above would be for something that does not change volume AT ALL. Seeing as how tires are reinforced rubber, I would expect that different tires expand somewhat under the increasing pressure, thereby somewhat muting the pressure rise by their expansion. (Also, different brands may expand differently.) So, for that same pressure rise from 90F to 205F example from above, if the tire internal volume increases by 10% due to the pressure rise, then the pressure rises to only 27.8 psig instead of the 28.9 psig in the non-expanding tire example from above. (This example results in a 10% volume increase for a ~10% increase in absolute pressures, so seems somewhat reasonable if you guess-timate that those two are linearly related.)

and THEN, there is the variable of how much rubber is left on the tire to hold its volume.......
just too many daing variables
LOL

I'd guess the belts are by far the main contributor to the tire's resistance to expansion rather than the tread rubber, so probably not a significant factor. Another round of tests to prove out that theory though... oh the humanity!