# Explain tyre pressures, please **URL:** \ **Category:** Factual Questions\ **Created:** [October 19, 2007, 9:37pm UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329 "2007-10-19T21:37:05Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![GorillaMan](https://avatars.discourse-cdn.com/v4/letter/g/50afbb/32.png) [@GorillaMan](https://boards.straightdope.com/u/GorillaMan)\ **Post date:** [October 19, 2007, 9:37pm UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/1 "2007-10-19T21:37:05Z")
My car’s manual has various recommended tyre pressures for different situations. How closely is it necessary to try to follow them, and what are the consequences for not doing so? The recommended pressures for a heavy load (3+ people) are about 4psi higher than for a light load. Using the lower pressure for a heavy load results in…what? Lower fuel economy? Greater wear? Instability? And how bad is it to use the higher pressure the whole time - does it just give a firmer ride, or are there potential problems? And then there’s the separate ratings for 100mph-plus, which are several psi higher again. Why the higher pressure, and what if the lower ones are used? (And no, I’d never _dream_ of exceeding the speed limit, but I could probably drive to Germany quicker than I could get to Scotland 😉 ) ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [October 19, 2007, 9:45pm UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/2 "2007-10-19T21:45:29Z")
Both too high and two low tire pressures can result in uneven tread wear and poor tread contact with the road, leading to a loss of control. Too low can also result in over-flexing of the sidewalls, which can lead to failure in this part of the tire, sometimes catastrophic. ---
**Author:** ![Khampelf](https://avatars.discourse-cdn.com/v4/letter/k/8e7dd6/32.png) [@Khampelf](https://boards.straightdope.com/u/Khampelf)\ **Post date:** [October 19, 2007, 9:48pm UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/3 "2007-10-19T21:48:15Z")
The Car talk guys just did this one. In general it’s better to keep the pressure too high than too low. Low pressure stresses the weakest part of the tire, where the tread meets the sidewall. High pressure is evenly distrubuted, and the safety factor is very high. Low pressure increases rolling resistance and leads to, yes, lower gas milage, greater wear, and, I suppose, instability if very low. ---
**Author:** ![Rhythmdvl](https://avatars.discourse-cdn.com/v4/letter/r/85f322/32.png) [@Rhythmdvl](https://boards.straightdope.com/u/Rhythmdvl)\ **Post date:** [October 19, 2007, 9:51pm UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/4 "2007-10-19T21:51:16Z")
Can I piggyback on this question (or is it a hijack?) The “correct” tire (tyre) pressure can be found on the inside of the door jamb (no need to look for the owner’s manual). I don’t get how the manufacturer can set pressures for tires that it has no information on. That is, if I buy brand X, made of Y materials with Z characteristics, how does the _manufacturer_ know how pressure will affect the tires’ performance? Oh, and what gives for different pressures for front and rear wheels?! ---
**Author:** ![Tenebras](https://avatars.discourse-cdn.com/v4/letter/t/977dab/32.png) [@Tenebras](https://boards.straightdope.com/u/Tenebras)\ **Post date:** [October 19, 2007, 9:56pm UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/5 "2007-10-19T21:56:46Z")
The consequences are always death. The only thing certain in this life is that if you improperly inflate your tires you, your loved ones, and indeed everyone you know will die horribly in a fiery wreck. The consequences will be so dire that the living will envy the dead, since at least the dead don’t have to deal with the horrific images broadcast twenty four hours a day over satellite news. To say nothing of the smell. If you insist on driving with improperly inflated tyres, you have several things to look forward to prior to your unfortunate demise. If you drive with insufficiently inflated tires they will tend to wear out faster because they run hotter. This is because the weight of your car causes the tire to bulge. As the wheel turns this bulge is always located near where the tire meets the road, so it is moving around the tire. The constant flexing of the rubber causes heat and thus rubber degredation. Also your fuel economy will suffer. Underinflated tires are more squishy and require more energy to keep moving. While the tires are slightly squishy, you also experience degraded handling and traction. The former because the base your car is sitting on is less firm and the latter because tires are designed with a given pressure in mind and will tend to cup if underinflated. Driving on overinflated tires is also contraindicated as it will make the tires balloon, decreasing traction and making the ride appear stiffer. Interesting article [here](http://www.edmunds.com/ownership/safety/articles/100811/article.html) about driving two BMWs back to back, one with the proper pressure and the other without. Tenebras ---
**Author:** ![GorillaMan](https://avatars.discourse-cdn.com/v4/letter/g/50afbb/32.png) [@GorillaMan](https://boards.straightdope.com/u/GorillaMan)\ **Post date:** [October 19, 2007, 9:57pm UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/6 "2007-10-19T21:57:53Z")
[QUOTE=Rhythmdvl] The “correct” tire (tyre) pressure can be found on the inside of the door jamb (no need to look for the owner’s manual). I don’t get how the manufacturer can set pressures for tires that it has no information on. [/quote] My car does have Ford’s original tyres, and these correspond to those listed in the tables in the manual. > [@](#): > > Oh, and what gives for different pressures for front and rear wheels?! I presume that the front tyres are far more heavily loaded under braking, therefore the need for higher pressure? Edit: [QUOTE=Rhythmdvl] The “correct” tire (tyre) pressure can be found on the inside of the door jamb [/QUOTE] It’s not there in mine ---
**Author:** ![Tenebras](https://avatars.discourse-cdn.com/v4/letter/t/977dab/32.png) [@Tenebras](https://boards.straightdope.com/u/Tenebras)\ **Post date:** [October 19, 2007, 10:05pm UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/7 "2007-10-19T22:05:06Z")
Tires are relatively standardized. If you buy the factory size tires it doesn’t really matter which manufacturer you get them from. If you go and put super hawt 17" rims and low profile tires on your mom’s station wagon, then you should inflate them not to the standards specified on the vehicle but to those in the literature you got from the tire people. But if you just buy the same size tire it shouldn’t make any difference whether you bought them from Firestone or Goodyear. As for why different pressures front and rear, the goal is to have a tire with enough air in it to not significantly deform under the load you place upon it. Imagine, if you will, a pick-up truck. The front axle is directly below a powerful diesel engine and is also supporting most of the weight of the passenger cab. The rear axle is beneath the bed of the truck and, for the most part, is only supporting a cooler full of ice cold beer, your dog, and some kids in lawn chairs riding in the back. The front tires need more air to maintain their shape than the rear tires do, because they are under greater stress. Tenebras ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [October 19, 2007, 10:12pm UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/8 "2007-10-19T22:12:43Z")
[QUOTE=Rhythmdvl] Can I piggyback on this question (or is it a hijack?) The “correct” tire (tyre) pressure can be found on the inside of the door jamb (no need to look for the owner’s manual). [/quote] Not always. Sometimes it’s on the inside of the glove compartment lid, and I’m sure there are even other places they hide. > [@](#): > > I don’t get how the manufacturer can set pressures for tires that it has no information on. That is, if I buy brand X, made of Y materials with Z characteristics, how does the _manufacturer_ know how pressure will affect the tires’ performance? Because they know the only two variables that actually matter: what size tire will fit the car’s wheels best and how much the car weighs. ---
**Author:** ![mangeorge](https://avatars.discourse-cdn.com/v4/letter/m/d78d45/32.png) [@mangeorge](https://boards.straightdope.com/u/mangeorge)\ **Post date:** [October 20, 2007, 12:24am UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/9 "2007-10-20T00:24:52Z")
[QUOTE=Rhythmdvl] Can I piggyback on this question (or is it a hijack?) The “correct” tire (tyre) pressure can be found on the inside of the door jamb (no need to look for the owner’s manual). I don’t get how the manufacturer can set pressures for tires that it has no information on. That is, if I buy brand X, made of Y materials with Z characteristics, how does the _manufacturer_ know how pressure will affect the tires’ performance? Oh, and what gives for different pressures for front and rear wheels?! [/QUOTE] It’s “tire”. How would you spell the verb? As in “I tire quickly”. Pay no mind to those Brits, who seem to think they invented the language. 😉 ---
**Author:** ![Shagnasty](https://avatars.discourse-cdn.com/v4/letter/s/9dc877/32.png) [@Shagnasty](https://boards.straightdope.com/u/Shagnasty)\ **Post date:** [October 20, 2007, 12:31am UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/10 "2007-10-20T00:31:21Z")
The one good use for low tire pressure is additional traction in the short-term. If you are hopelessly stuck in mud miles from civilization, letting air out of your tires until aren’t round anymore can help get you out of the jam. Off-road vehicles in general often use underinflated tire when they get to the difficult terrain. ---
**Author:** ![GorillaMan](https://avatars.discourse-cdn.com/v4/letter/g/50afbb/32.png) [@GorillaMan](https://boards.straightdope.com/u/GorillaMan)\ **Post date:** [October 20, 2007, 12:57am UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/11 "2007-10-20T00:57:38Z")
[QUOTE=mangeorge] It’s “tire”. How would you spell the verb? As in “I tire quickly”. Pay no mind to those Brits, who seem to think they invented the language. 😉 [/QUOTE] Well I started the thread, and I say tyre. So nurrrrr. 😛 ---
**Author:** ![mangeorge](https://avatars.discourse-cdn.com/v4/letter/m/d78d45/32.png) [@mangeorge](https://boards.straightdope.com/u/mangeorge)\ **Post date:** [October 20, 2007, 1:04am UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/12 "2007-10-20T01:04:17Z")
[QUOTE=GorillaMan] Well I started the thread, and I say tyre. So nurrrrr. 😛 [/QUOTE] Well I guess that’s right. And, you get to say “nurrrrr”. 😛 ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [October 20, 2007, 1:07am UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/13 "2007-10-20T01:07:01Z")
Manufacturer’s tire and pressure specifications are typically listed on a door jamb (check all of them, front and rear), the rear edge of a door, the inside of the glove box or its lid, or the owner’s manual. Heaven forbid they all put them in the same spot. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [October 20, 2007, 1:09am UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/14 "2007-10-20T01:09:15Z")
Tyre pressure was brought to bear by Alexander the Great and Nebuchadrezzar II, among others … ---
**Author:** ![mangeorge](https://avatars.discourse-cdn.com/v4/letter/m/d78d45/32.png) [@mangeorge](https://boards.straightdope.com/u/mangeorge)\ **Post date:** [October 20, 2007, 1:11am UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/15 "2007-10-20T01:11:36Z")
Anyway, I don’t have to even think about my tire pressure, 'cause my PU has tire pressure monitors. I don’t need to check my oil, either. ---
**Author:** ![GorillaMan](https://avatars.discourse-cdn.com/v4/letter/g/50afbb/32.png) [@GorillaMan](https://boards.straightdope.com/u/GorillaMan)\ **Post date:** [October 20, 2007, 1:19am UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/16 "2007-10-20T01:19:13Z")
[QUOTE=GorillaMan] My car’s manual has various recommended tyre pressures [/QUOTE] [QUOTE=Rhythmdvl] The “correct” tire (tyre) pressure can be found on the inside of the door jamb (no need to look for the owner’s manual). [/QUOTE] [QUOTE=Gary T] Manufacturer’s tire and pressure specifications are typically listed on a door jamb (check all of them, front and rear), the rear edge of a door, the inside of the glove box or its lid, or the owner’s manual. [/QUOTE] My head hurts. Was I looking in the right place to start with, then? (Which was stored inside the glove box, anyway!) **Mangeorge** , if you’re relying on monitors, you might want to look at **Tenebras** ’s link. ---
**Author:** ![mangeorge](https://avatars.discourse-cdn.com/v4/letter/m/d78d45/32.png) [@mangeorge](https://boards.straightdope.com/u/mangeorge)\ **Post date:** [October 20, 2007, 1:37am UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/17 "2007-10-20T01:37:33Z")
[QUOTE=GorillaMan] My head hurts. Was I looking in the right place to start with, then? (Which was stored inside the glove box, anyway!) **Mangeorge** , if you’re relying on monitors, you might want to look at **Tenebras** ’s link. [/QUOTE] There is no way I can read all that. Anyway, my post was just a little dry Yankee humor. My auto tech (mechanic) checks my pressure at every service. There I go again. :smack: I use one similar to [this](http://www.autogeek.net/acstditigu.html) one. It’s way to cool to _not_ use. I reccommend it, if you don’t have one. ---
**Author:** ![GorillaMan](https://avatars.discourse-cdn.com/v4/letter/g/50afbb/32.png) [@GorillaMan](https://boards.straightdope.com/u/GorillaMan)\ **Post date:** [October 20, 2007, 1:46am UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/18 "2007-10-20T01:46:26Z")
[QUOTE=mangeorge] I use one similar to [this](http://www.autogeek.net/acstditigu.html) one. It’s way to cool to _not_ use. I reccommend it, if you don’t have one. [/QUOTE] I do have a similar one. Maybe I should point out that I didn’t start this thread because I’d never checked tyre pressures before, but that for some reason I started to wonder why the different ratings, and how crucial the accuracy is. It was probably the 100mph+ rating which really got me thinking, because the pressures listed were significantly higher. (If I’m honest, I’m normally into that territory on the M6 Toll (I know some Brits sympathise), but in a steady two figures for the rest of any motorway journey.) ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [October 20, 2007, 2:04am UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/19 "2007-10-20T02:04:38Z")
[QUOTE=GorillaMan] Was I looking in the right place to start with, then? [/QUOTE] If you found the pressure recommendations, you must have been. 🙂 ---
**Author:** ![mangeorge](https://avatars.discourse-cdn.com/v4/letter/m/d78d45/32.png) [@mangeorge](https://boards.straightdope.com/u/mangeorge)\ **Post date:** [October 20, 2007, 2:27am UTC](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329/20 "2007-10-20T02:27:15Z")
I’m sure that tire pressure monitors are required by the NTSA since the mid 2000’s, and I think that pressure charts are standardized to the driver’s side front door jamb. But I’m not sure. I think the service guy at Honda told me that. [Next page](https://boards.straightdope.com/t/explain-tyre-pressures-please/423329.md?page=2)