HaulingAss
Well-known member
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- Oct 3, 2020
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- Western Washington, USA
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- Cybertruck DM, 2010 F-150, 2018 Performance Model 3, 2024 Performance Model 3
Yes, plenty of people think a well inflated tire is more vulnerable to flats than one at 15 psi. Yes, plenty of articles make this claim. But it's based upon the assumption that a tire is similar to a balloon. It's not for reasons I will cover below.
It's not a valid analogy to compare the ease of popping a balloon that is fully inflated because tires have aramid fibers with almost zero stretch to them. Kevlar is just branded aramid. When a tire is inflated those bands and fabrics are loaded in tension. It's what prevents a tire from getting increasingly larger as the pressure is increased.
A balloon's membrane gets progessively thinner and weaker as it's inflated, a tire does not, it becomes stronger due to the fabrics and fibers that are loaded in tension.
Try poking a sharp rock through parallel strands of strong fibers that are loaded in tension, it's more difficult the more tension the fibers are under because they don't want to part. You could think of it like trying to poke a wood splitting wedge between two strings of a guitar into the soundhole. If the strings are tight, they don't want to let the wedge penetrate. If you slacken them off, the wedge will go right through easily. Now imagine weaving six more guitar strings at 90 degrees to the normal strings across the soundhole to simulate the aramid fabrics used to reinforce the tire carcass. The tighter those are strung, to a point, the harder it will be to penetrate them. Sure, if the fibers are loaded to near the breaking point, it will be easy to penetrate as the fibers break. But a properly inflated tire does not load the fibers anywhere near their breaking strength.
A balloon does not have aramid fibers that prevent the balloon from growing in size and becoming thinner and weaker. I think this false analogy is why so many think a well-inflated tire is more likely to "pop".
But probably an equally important reason why under-inflated tires are more vunerable to sidewall damage is due to the bulge that sticks out just above the contact patch. This makes the tire vunerable to cuts in that location if the tire slips off a rock that has a pointed edge simply because it's sticking out excessively and putting itself in harms way.
The hysteresis of rubber materials due to deformation and viscoelasticity is the main reason for the heat build-up and rolling resistance of the rolling tire because the deformation of the rubber as it rolls absorbs energy. That's why under-inflated tires run warmer. And warmer rubber is softer and easier to cut than colder rubber.
It would be better to say that the best tire pressure varies widely depending upon the application (than to say it's subjective). Certainly, it's just an educated guess, and different people will have different guesses. But my observation is that most off-roaders either air down too much, or not at all. My advice is to err on the side of not airing down enough. You can always lower it more if it's not working well enough when challenged. Just be aware that the better performance and improved occupant comfort at lower pressures comes at the expense of making the tire work harder and making it more vulnerable to rock cuts and breaking the bead.
Running lower pressures causes more flexing of the aramid fibers used in the tire carcass, particularly through the sidewalls, and this can cause what is known as flex fatigue, weakening the fibers over time and reducing the cut resistance of the sidewall. The point here is that running higher pressures results in lower temperatures, less flexing and less degradation of the structure of the tire over its useful lifetime. Tires live a hard life, use strategies to reduce the abuse they recieve by repeated flexings and high temperatures, while still having them perform well on whatever surface they are working on.
The Cybertruck starts out relatively heavy and the more load you are hauling, the more conservative one should be when airing down.
As an interesting side note, lowering tire pressures for bumpy surfaces can improve occupant comfort and actually reduce rolling resistance by allowing the tire to roll "through" irregularities rather than up and over them. Of course, the increased flexing of the sidewalls and tread does consume some of the saved energy in the form of heat, but your shock absorbers will run cooler (which is where most of the energy savings come from).
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