# How much more pressure do car tires experience when driving vs. being parked?
**URL:** https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994
**Category:** Factual Questions
**Created:** [May 13, 2023, 5:30pm UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994 "2023-05-13T17:30:16Z")
**Posts on this page:** 16
**Page:** 1
### Author:  [@Jackknifed\_Juggernaut](https://boards.straightdope.com/u/Jackknifed_Juggernaut)
#### Post date: [May 13, 2023, 5:30pm UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/1 "2023-05-13T17:30:16Z")
I recently had some body work done on my car, so the body shop had my car for 2 weeks. I also recently put new tires on it (about a month before that).
When I finally picked up my car and drove around locally for a few miles at neighborhood speeds. Later in the evening, I drove on the highway and shortly got a flat tire.
While I think it would be too much of a stretch to blame the body shop, I wonder if there was a nail or something from the body shop that was already wedged in the tire, but perhaps it the pressure that the tire experienced on the local roads wasn’t enough to make the tire go flat. And once I got on the highway, it was high enough to have the air leak out.
Hence, my questIon.
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### Author:  [@Mikkel](https://boards.straightdope.com/u/Mikkel)
#### Post date: [May 13, 2023, 5:42pm UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/2 "2023-05-13T17:42:38Z")
Probably the nail, stone or whatever moved and made the hole bigger.
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### Author:  [@Kent\_Clark](https://boards.straightdope.com/u/Kent_Clark)
#### Post date: [May 13, 2023, 9:37pm UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/3 "2023-05-13T21:37:36Z")
First, are you ssure it was a nail or something? I had new tires installed once, and it turned out the dealer had a batch of defective valve stems. At some point all four tires went flat (two within 72 hours) and none of them showed any sign of a nail or road damage.
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### Author:  [@TriPolar](https://boards.straightdope.com/u/TriPolar)
#### Post date: [May 13, 2023, 10:17pm UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/4 "2023-05-13T22:17:45Z")
You could have punctured the tire on the highway. The right type of hole only takes a minute to go flat. The small additional pressure from highway driving might dislodge a nail and speed up the process, but so could regular operation on the side streets. Hitting bumps in the road temporarily increases tire pressure much more than the small amount in highway driving.
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### Author:  [@DSeid](https://boards.straightdope.com/u/DSeid)
#### Post date: [May 14, 2023, 2:58am UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/5 "2023-05-14T02:58:55Z")
There certainly are alternative, perhaps more likely, explanations but there is a factual question being asked.
Standard passenger vehicle hits a routine bump in the road at say 55 mph, what is the transient increase in tire pressure assuming tire is filled to recommended pressure ahead of time?
I do not have the answer myself but it seems tractable.
ETA driving flat highway is just the heat increase, maybe 4 to 5 psi.
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### Author:  [@GaryM](https://boards.straightdope.com/u/GaryM)
#### Post date: [May 14, 2023, 3:55am UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/6 "2023-05-14T03:55:27Z")
My Forester increases tire pressure by 2-3 psi after highway driving 20 miles or so. My F150 is about the same.
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### Author:  [@pulykamell](https://boards.straightdope.com/u/pulykamell)
#### Post date: [May 14, 2023, 3:56am UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/7 "2023-05-14T03:56:47Z")
Same here with our Hyundai Ioniq. About 2-3 psi change.
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### Author:  [@Snipe70e](https://boards.straightdope.com/u/Snipe70e)
#### Post date: [May 14, 2023, 4:53am UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/8 "2023-05-14T04:53:51Z")
As the tire warms up the pressure will increase just a few pounds.
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### Author:  [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)
#### Post date: [May 14, 2023, 11:34am UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/9 "2023-05-14T11:34:07Z")
> [@DSeid](#):
>
> Standard passenger vehicle hits a routine bump in the road at say 55 mph, what is the transient increase in tire pressure assuming tire is filled to recommended pressure ahead of time?
Not much. It takes a really big bump to change the enclosed volume of the tire by a significant amount. The thing that causes most of the increase in contact force when hitting a bump is the change in the area of the contact patch. I’m not in a position to do the math right now, but I’d wager that moving the wheel’s axis of rotation a quarter inch closer to the pavement might cause the contact patch area to increase by 30% or so. I’ll post some calculation results later this week.
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### Author:  [@pullin](https://boards.straightdope.com/u/pullin)
#### Post date: [May 14, 2023, 12:58pm UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/10 "2023-05-14T12:58:48Z")
> [@GaryM](#):
>
> My Forester increases tire pressure by 2-3 psi after highway driving 20 miles or so. My F150 is about the same.
Curious if that’s load-dependent. My truck shows 7-8 psi difference after a few hours of highway towing. I haven’t checked it unloaded, as I rarely travel in it that way. Now I’m curious and will pay attention next time I head to my Dad’s house (often go empty 1 way on that trip).
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### Author:  [@GaryM](https://boards.straightdope.com/u/GaryM)
#### Post date: [May 14, 2023, 2:24pm UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/11 "2023-05-14T14:24:15Z")
If you have a non contact thermometer, try taking the tire temp before and after the trip. Both empty and loaded. I never tried that, but after a hi-way trip the tires feel significantly warmer to the touch.
Maybe it’s a job for Mythbusters?
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### Author:  [@Kent\_Clark](https://boards.straightdope.com/u/Kent_Clark)
#### Post date: [May 15, 2023, 3:54pm UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/12 "2023-05-15T15:54:41Z")
> [@TriPolar](#):
>
> Hitting bumps in the road temporarily increases tire pressure much more than the small amount in highway driving.
I wonder if it really does? The assumption here seems to be that the air in the tire compresses in direct proportion to the deformation of the tire when it hits the bump. But the tire is somewhat malleable. Perhaps the non-bumped portion of the tire expands somewhat during the bump, thereby reducing the change in psi.
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### Author:  [@TriPolar](https://boards.straightdope.com/u/TriPolar)
#### Post date: [May 15, 2023, 4:05pm UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/13 "2023-05-15T16:05:28Z")
That’s exactly what I’m finding trying to determine what increase in pressure occurs. It can be enough to cause the bead to separate from the wheel momentarily allowing a lot of air to escape, but at the same time the tire is being deformed by the bump so the air can start escaping from that alone. I haven’t found anything that settles the matter. I suspect that bumps can create pressure waves within the tire of very high pressure but very brief and rapidly dissipating.
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### Author:  [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)
#### Post date: [May 16, 2023, 12:39am UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/14 "2023-05-16T00:39:17Z")
> [@TriPolar](#):
>
> Hitting bumps in the road temporarily increases tire pressure much more than the small amount in highway driving.
I did some math and some simple 2-D CAD work on this, and now I’m pretty sure bumps don’t meaningfully increase tire pressure.
I used my own car as a model. The tire is a 225/55-R17, and with a curb weight of ~3700 lbs, the per-tire load is 925 pounds.
With the tire filled to 35 psi, it needs a contact patch area of 26.4 in^2 to bear that 925-lb load. Based on the geometry of that tire - most importantly, the tread width and tread diameter - the tread has to deform just 0.084 inches away from its circular profile to create a contact patch that’s 2.98 inches from front to rear and 8.86 inches wide (that’s the 225mm in the tire spec).
Viewed from the side, the projected area of the whole tire’s sidewall is 334.6 in^2. This is the area of a circle the same diameter as the tread OD (26.74"), minus the area of a circle the same diameter as the tire bead (17"), and minus the area of the **[circular segment](https://en.wikipedia.org/wiki/Circular_segment)** whose chord is the front-to-rear length of the contact patch (2.98").
Now suppose instead of 925 pounds, I want the tire to bear twice as much load, 1850 pounds. Assuming no change in tire pressure, I need twice as much contact patch area to make this happen. The width of the contact patch can’t change, so the contact patch needs to become longer from front to rear. To make this happen, the tread has to deform 0.337" from its circular profile. This changes the projected area of the sidewall from 334.6 in^2 to 333.4 in^2. If you assume the tire volume is proportional to sidewall projected area, then the tire volume has decreased by just 0.36%, with a commensurately tiny increase in tire pressure. However, that assumption is suspect, because when the pavement deforms the tread away from its circular profile, the sidewalls bulge outward visibly: the width of the enclosed tire volume increases a bit, offsetting the decrease in height and therefore mitigating the volume decrease (and pressure increase) to something less than 0.36%.
Suppose instead of twice the usual static load, I want the tire to bear _four times_ the norm. Instead of 0.084 inches, the tread is displaced 1.41 inches from its usual circular profile. The sidewall projected area is reduced from 334.6 in^2 to 323.5 in^2. Assuming no sidewall bulge at all, and also assuming **[adiabatic compression](https://www.omnicalculator.com/physics/thermodynamic-processes)**, the tire pressure goes from 35 psi to 36.2 psi. This is less than the temperature increase that occurs during normal driving due to viscoelastic heat production. It’s also not enough of a difference to dramatically affect leakage rates, unless that tire distortion during bumps also increases the size of the leak path (which can happen).
> [@pullin](#):
>
> Curious if that’s load-dependent. My truck shows 7-8 psi difference after a few hours of highway towing. I haven’t checked it unloaded, as I rarely travel in it that way. Now I’m curious and will pay attention next time I head to my Dad’s house (often go empty 1 way on that trip).
It’s dependent on how fast and how much the sidewalls and tread flex. These are a function of inflation pressure, load, and road speed. Taken to its logical extreme, a tire that carries zero load will not heat up at all. For a non-zero load, if the sidewalls are flexing too fast/too much, they can generate enough heat to compromise structural integrity of the tire carcass. You get around this by reducing the load, reducing the speed, or increasing the inflation pressure (or moving to a cooler climate). The problem in the late '90s with the Ford Explorer and its Firestone Wilderness AT tire failures was attributed in part to Ford specifying too low an inflation pressure in the Explorer’s owner manual:
> **[Firestone and Ford tire controversy | Operating temperature](https://en.wikipedia.org/wiki/Firestone_and_Ford_tire_controversy#Operating_temperature)**
>
> A tire's operating temperature will increase with higher vehicle load, speed, air temperature, and with lower tire inflation pressure. The combination of inflation pressure, speed, and vehicle load could increase the tire temperature as much as 122 degrees F above the ambient air temperature. Higher operating temperatures will increase the rate of oxidative aging. Tires that were used in southern climates were less ductile and stiffer than tires that operated in northern climates. Tir Higher vehi...
> [@TriPolar](#):
>
> That’s exactly what I’m finding trying to determine what increase in pressure occurs. It can be enough to cause the bead to separate from the wheel momentarily allowing a lot of air to escape, but at the same time the tire is being deformed by the bump so the air can start escaping from that alone.
A tire bead can be unseated from its installed position on the rim if you drive into a curb or other object at a “bad” angle (here “bad” means somewhere between straight on, which will just smash your rim, and almost-parallel so that the curb merely redirects your car’s path of travel instead of peeling the tire out of its seat on the rim). Unseating the bead results in instant 100% deflation, and you’ll need to call AAA for help. But I’ve never heard of an ordinary vertical bump that was small enough to not bend the rim, but somehow large enough to cause a transient leak path to form.
> [@TriPolar](#):
>
> I suspect that bumps can create pressure waves within the tire of very high pressure but very brief and rapidly dissipating.
Relative to the tire, the bump is moving at a small fraction of the speed of sound. Any “pressure wave” coming off of it will manifest as a bulk dislocation of air that quickly equalizes pressure throughout the rest of the tire volume.
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### Author:  [@Isilder](https://boards.straightdope.com/u/Isilder)
#### Post date: [May 16, 2023, 10:43am UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/15 "2023-05-16T10:43:55Z")
There might be a pressure wave from the impacts … The tyre moving up suddenly compresses the air next to it… much more significant than any change in contact patch size… but hard to calculate or measure… maybe the noise volume can be used as a measure ? But the noise can be outside the tyre as well as in …
But certainly a screw or nail could be thrown out of the tyre by highway speeds and the higher pressure waves that hit it. Its plausible but not the common experience.
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### Author:  [@TriPolar](https://boards.straightdope.com/u/TriPolar)
#### Post date: [May 16, 2023, 3:21pm UTC](https://boards.straightdope.com/t/how-much-more-pressure-do-car-tires-experience-when-driving-vs-being-parked/983994/16 "2023-05-16T15:21:27Z")
> [@Isilder](#):
>
> There might be a pressure wave from the impacts
I mentioned pressure waves but didn’t intend that to mean they would likely push a nail out of a tire. A pressure wave could greatly increase pressure at one location inside the tire very briefly but maybe not even close to the tire. @Machine_Elf description of that effect sounds pretty good to me.
> [@Machine\_Elf](#):
>
> Relative to the tire, the bump is moving at a small fraction of the speed of sound. Any “pressure wave” coming off of it will manifest as a bulk dislocation of air that quickly equalizes pressure throughout the rest of the tire volume.
I think leaking around the bead does occur with poor seals. A shock to the tire doesn’t have to result in total deflation, the bead will close up again, usually not well and leaking more over time. But again, that happens when the tire is deformed from impact with an object, not from any momentary increase in pressure if there is any, and your calculations make that sound unlikely.