What is the Difference Between Overinflated and Underinflated Tires?

General Discussion
1

Oh boy will this subject open a can of worms… What is the Difference Between Overinflated and Underinflated Tires?

inflate
inflate1016×867 108 KB

First off, properly inflated tires offers the best performance and safety for you. And in general driving a few pounds one way for another makes little difference, but some carry it to extremes… For instance the recommended tire pressure on my Toyota Corolla is 35 PSI on the Front and 33 PSI on the Rear, but the Maximum pressure listed on the tires is 51 PSI…

There are some who push the maximum pressure limits thinking it will generate less heat (less flexing) and greater gas economy…

And on the other side of this discussion are those who drop the pressure down 10 pounds or more to drive in snow because their father, grandfather, or old “Gus” at the local garage recommended it…

Over inflation reduces the traction and surface contact with the road, which cause instability and loss of vehicle control, especially on slippery surfaces. The car will respond poorly to steering inputs and may not react as the driver intends.

The effect of over-inflated tires stresses sidewalls and can cause a harsh and bumpy ride. It also puts stress on suspension and wheels, leading to increased wear and tear, possibly even premature failure of components.

They are also susceptible to blowouts or sudden failure. Finally, overinflated tires will wear out sooner due to the uneven contact with the road and likely will have to be replaced before its normal lifespan.

On the other hand, under-inflated tires occur when there is insufficient air pressure which has an adverse effects on performance, fuel economy and safety.

With an increased contact patch on the road surface, the vehicle’s ability to grip the surface will be comprised. The driver may find it difficult to steer the vehicle, and this could lead to instability and unexpected handling.

An underinflated tire will generate more heat than usual which will cause increased wear and tear as well as the risk of a blowout. An Under-inflated tire’s fuel consumption will be higher due to the increased rolling resistance which results in poor performance. The vehicle might find it difficult to achieve top speed with tires that are underinflated.

The difference between overinflated and underinflated tires is quite obvious. Overinflated tires and underinflated tires can both cause negative driving effects, so it is best to maintain the correct tire pressure rating as stated by the manufacturer.

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Then why start it when it’s been covered 100’s of times already?

5 Likes
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The amount of PSI in the tire… :rofl:

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Why cover it again? Well it’s just like a well-traveled road, it has been covered (repaved…) over and over again, yet it still isn’t fixed… You saw the various and contentious and contradictory opinions about the “proper” tire pressure depending on driving conditions and vehicles used and it still is unsettled and some members are still following old, unsound advice… That’s why…

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Over inflated tires do not damage the car’s suspension parts. I worked on a project to use 50 psi tires on a Buick LeSabre becauase we could measure a 1 mpg improvement. We changed the suspension to make it ride like it had 35 psi tires. The loads were comparable with the 50 psi vs 35 psi tires..

Overinflated tires have a lower rolling resistance that improves the mpg.

Everything in moderation, however. If it recommends 35 and the sidewall max is 51, don’t run 51 psi.

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I never said over inflated tires would “damage” a car’s suspension parts. I wrote, “It also puts stress on suspension and wheels, leading to increased wear and tear.” Just driving a car will cause “wear and Tear” on the suspension parts. When the tires do absorb some of the road’s humps and bumps, the increased rebounding of the suspension increases the wear and tear… But what do I know, you’ve heard plenty of my wife '85 Toyota that we donated last summer; but in over 230,000 miles, I never had to replace a ball joint or a tie rod… But hey, maybe "85 was just a good year for Toyota.

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I bothered to run the calculations myself, for my 2010 Honda. The same can be done for anyones’ ride here:

Tire Pressure - 2010 Honda Accord EX - All-In-One 02 With Annotations
Tire Pressure - 2010 Honda Accord EX - All-In-One 02 With Annotations1920×1113 394 KB

As you can see, Honda, at least, did their homework. The cold spec pressures satisfy, front and rear, at least 110% of gross axle and thus vehicle load. That’s 5 adults, full trunk, full gas, and the dog. - a situation which occurs quite rarely in my case.

There is no practical reason for me to maintain cold presures of more than 1psi over the specified 32 with the OE size and standard load tires installed. If I go XL, according to the inflation table, I can optionally inflate to 33 or 34psi cold for equivalent load capacity.

Car will handle and ride fine, in either case.

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For a Toyota 2005 Corolla:

Tire Pressure - 2005 Toyota Corolla LE - All-In-One with Annotations
Tire Pressure - 2005 Toyota Corolla LE - All-In-One with Annotations1920×1078 447 KB

Woahhh - that’s some margins! Ideally, I could run pressures in two alternative ways:

29psi all around,

or:

30psi up front and 28psi in back, and still statisfy at last 115% of gross(the most I could ever carry) load.

Toyota probably specified 30psi all around for that generation because it’s easy to remember in North America, and aims more toward fuel economy standards, given it’s a Corolla.

I’d probably run handling pressures, such as the 29psi all around, or slightly lower in back, like I’ve seen on many cars abroad, but the idea of running different front and rear cold pressures might not be understood in certain markets.

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Ummm, that’s a 2004 (pro date 06/04) Toyota, not a 2025… :smiley:

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The model year begins in July.

They often start mfg for that model year before it begins.

All the maintenance records from shops, DMV documents, the title, all said 2005 on them.

I uploaded the images I did, however, to illustrate other points.

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Damage, wear and tear, same difference. Neither adds any appreciable load or stress.. I have seen the data my test people took.

A consideration Chris ignores… It isn’t just about load carrying capability. Higher pressures make the steering and cornering action of the tires to be quicker because the tires is a bit stiffer. Lower pressures make the handling lazy.

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Just one ? Shouldn’t cosideration be plural ?

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You posted 2025 NOT 2005…

That was my point, not trying to be an ■■■ about it, just pointing out your oops, nothing more, noting less…

And model years start whenever the manufactures decide to start it, I have seen a pro date of 01/94 and it was a 95 year model, they never made a 94 Neon, but they started manufacturing them in January 1994 and called it a 1995… lol

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I am quite sure that the cold pressures that my example Honda and Toyota arrived at did take into consideration the dynamic forces you stated.

I did experiment with pressures 5-10 psi higher than those vehicle specs, and found the handling on both cars to be a bit too skittish, too responsive. Those cars have conventional power steering on them, and they felt almost like they had electric steering at 35-40psi! Too light, no weight buildup when turning the wheel into a turn, etc.

Like I said, engineering, testing, calculating, and what the intended vehicle use is, determine the ideal cold tire pressures for a vehicle, not ones personal preference, or other misc. factors.

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And it will never be settled.

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Fixed it, thanks. You, among others here, know I have… issues… with numbers..!

That practically echoes the point I was trying to make. But you insisted on calling mine a 2004 instead of 2005 model year.

(Y’can’t win on CarTalk Community..)

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Having worked in vehicle development for GM, I can assure you that cold tire pressures are partially determined by the preferences of the engineer tuning the ride and marketing’s buyoff of that ride. That would constitute personal preferences and other misc. factors. Other makes do the same.

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Logically, the way a vehicle rides will feel smoother/softer at lower tire pressures - even if that is not one of the goals of arriving at specified pressures.

19

Those tire inflation illustrations are highly exaggerated to help the novice understand different tire inflation conditions. They also seem to inspire lectures containing faulty information.

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Do you care to provide us examples of such?