Good answers to tire pressure questions

[davidbrady]

Good plan Pete, keeping 'em rolling is key! I'm envisioning a bus treadmill! ROTFL :-)

The author does a good job of illustrating how setting tire pressure is a compromise. Manufacturers know that the tire pressure will build from friction heat while driving, and pressure will also increase or decrease due to ambient temperatures and altitudes. So what do they recommend? The recommend a compromise setting that kinda works across the usual ambient and altitude swings that a driver is likely to see during a days travels, but they correct it by insisting that driver's check and adjust their pressures every day when the tires are in a "cold" condition.

What the manufacturers really want is a consistent tire sidewall deflection. The author points this out with its reference to tire cross section. Tire engineers don't care about internal tire pressure, they care about tire sidewall deflection. Too little deflection can be corrected by decreasing the tire's internal pressure, to much by increasing the pressure. It's the tire's deflection that controls all the properties that the tire engineer is looking for from slip angles, to grip, to tire temperature, to promoting the swirl of chemical release, to ride quality, to longevity, to puncture resistance, to scuff resistance - the list goes on. An incorrect deflection will swing the balance of these properties. We could do away with tire pressure gauges if we could measure deflection accurately.

The author also implies that a tire inflated to the proper deflection (pressure) in a cold condition will be slightly overinflated when hot, but he says that this is okay and that the tire is constructed to handle these pressure increases. In other words, it's non-ideal. In an ideal world, if the tire has the proper deflection in a cold condition, then as the tire heats up pressure could in theory be bled off to restore the optimal sidewall deflection. I'm imagining an active tire inflation control system that adds and bleeds air during a days travels all the while maintaining the perfect sidewall deflection!