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      12-20-2013, 01:47 PM   #1
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Calibrating Tire Pressure Gauges

OK, so we all know how important it is to have proper tire pressure. But how do you guys actually keep it at a true proper pressure?
What I'm getting it is - how do you know that when your gauge reads 32 psi (or whatever), you actually have 32 psi in your tires?

I'm aware that you can calibrate against a shop's pressure gauge, but I have to once again point out that you don't know how accurate and consistent their tools are either. How do you know if their gauges haven't drifted? And how do you know that the monkey filling your tires is actually doing it to exactly your specified pressure setting?

So I'm looking for ideas or further insight into objective ways to quantify "proper tire pressure." In other words, since we know proper pressure is a good thing, there should be other measurable methods to quantify how good.

What I do is log the gas mileage for every single tank, via odometer reading and filling exactly to the top-off stop (no overfilling). Not 100% consistent, but I figure that the error should be well within +/- 1 gal. I am ignoring any "grip" or performance metrics since a)it doesn't matter most of the time in the real world and b)it would be illegal, difficult, or both to make objective performance measurements of grip on the streets (unless you have a climate controlled, laboratory clean skidpad in your backyard ). I also check my tire wear across each circumferential groove on each tire when I top off with air, and note any anomalies in wear. I usually check air every other week or so, depending on temperature swings, so unusual tire pressures should roughly correspond to exactly a tank or two of good/bad gas mileage.

In my mind, proper tire pressure will yield (in the real world) optimal/near-optimal fuel economy and balanced tread wear across the entire width of the tire. On my previous car, I consistently ran my pressure about 4-5 psi higher than the mfg recommendation, with the result that the tires wore out approx 1/32-2/32 earlier in the centers and no appreciable benefit in fuel economy. I backed off to 2-3 psi higher than recommended and the wear seems to be holding even for the last 6k miles, with the same fuel economy as before. On my 128i, I've only have it for barely 2k miles, but the wear is still even and my lifetime fuel mileage is approximately 23 mpg (mixed urban/highway driving, with plenty of right foot). This seems to fall in line with expectations for our 1's. Therefore, my conclusion would be that my tire pressure settings are good (all else being equal).

So guys - does this methodology even sound plausible/valid? Is there any other method of running an accurate tire pressure gauge?
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      12-25-2013, 08:51 AM   #2
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That sounds great! I had a joy reading this actually. Thanks for the information and your ingenuity. Fantastic!
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      12-25-2013, 03:08 PM   #3
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Nice work.

I'm going to assume all measurements are cold temps. So 34-45 psi front and 37-38 psi rear? When you can't get a cold temp reading in the summer what do you inflate to
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      01-05-2014, 12:50 PM   #4
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My measurements are (almost always, can't promise that) cold, usually after an overnight sit. That is, ambient temperature. Since it's parked in a garage, that doesn't change too much winter/summer. Something like 80F (est) in the summer and 60F (est) in the winter - my garage is part of a much larger building, so it doesn't swing as much as house garages.

Anyone else see any flaws?
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