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Old 12-06-2017, 03:13 PM
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Does tire pressure affect tire circumference?

With this vid I would say, not significantly

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Old 12-06-2017, 04:21 PM   #2
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Not much unless you air way down to pressure's unsafe to run on the road. but it sure will affect ride, handling and tire life.

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Old 12-06-2017, 05:17 PM   #3
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Although that video does not do a very good job of controlling for other factors (even determining the tape light is straight up and down would be challenging with this method), I would still agree that "not significantly" is a good answer.
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Old 12-06-2017, 06:03 PM   #4
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And yet:

Indirect (TPMS) Systems
use the vehicle's anti-lock braking system's wheel speed sensors to compare the rotational speed of one tire versus the others. If a tire is low on pressure, it will roll at a different number of revolutions per mile than the other three and alert the vehicle's on-board computer. Indirect systems (except for the TPMS on several 2009+ Audi models and 2010+ Volkswagen models) are unable to generate accurate readings in cases where all four tires are losing pressure at the same rate, such as the effects of time and temperature.
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Old 12-07-2017, 07:43 AM
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Using a Tire Size and Conversion Calculator, here are some numbers. Imagine if the rim and the contact patch dropped an inch(less sidewall). In my thought it would reduce the effective circumference. I adjusted the second tire to get a ~1" sidewall difference.

315/75R17 - 315/67R17

Current New Difference
Sidewall Height: 9.3'' 8.31'' -0.99''
Section Width: 12.4'' 12.4'' 0''
Tire Height: 35.6'' 33.62'' -1.98''
Tire Circum: 111.84'' 105.62'' -6.22''
Rev. / Mile: 566.52 599.89 33.37

If your speedometer reads 65mph, you are going about 61.4 mph

So going by this, first guess was a miss. Kinda. If the axle was locked there would be a speed difference. But when open, each individual tire would still be going the same speed as all the others. I am guessing that the wheel "speed" sensors are actually determining speed vs rotation.

It also looks mathematically exponential

If your speedometer reads 5mph, you are going about 4.7 mph
10/9.4, 20/18.9, 30/28.3, 40/38.7, 50/42.7, 60/56.7

I would guess that even if someone forgot to air down a tire for rock crawling and locked axle, it would not be enough to mess up readings. Plus I would bet the class of tires makes a difference. My E load KO2s barely showed any drop when I had a flat and the tire pressure was 12psi.

So anyway, this is just stuff I think of when I am having my bouts fighting insomnia.
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Old 01-01-2018, 12:19 AM   #6
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If your running your tires at average pressures, it shouldn't affect it much. Tire pressure, however does make a difference in surface area hitting the trail when taking it off-road. Don't get too crazy though.

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