tire pressure myth?

jaxtell671 · 08-31-2006, 04:51 PM

i was taking care of one of my friends cars the other day and i noticed her tire pressure was a little low. i filled the tires to the max psi pressure of 44psi listed on the side of her tires. when i told her the air was low she said that she only filled it to around 35 because she had heard that filling it to the max psi rating would cause increased tread wear. is she right or is that just some bull that she heard somewhere?

G-man422 · 08-31-2006, 04:53 PM

If you overfill it(or its too low), you get uneven tread wear, but not More tread wear. Usually you dont fill it to max psi though, because it makes fo a rougher ride (sometimes) and air has to have some room to expand, and compress.

TheSilentChamber · 08-31-2006, 05:29 PM

Yeah, dont fill it to the max psi unless your putting the max load on them, in which case you should switch to a higher load rated tire.

Moppie · 08-31-2006, 06:06 PM

Wow.

Did you actualy read what it said on the tyre wall?
Unless its a very large truck, or they are extremely low profile tyres then 44psi is WAY to much.
In fact its dangerously to much, and I hope your friend is good at controlling skids.

Most cars only need between 28 and 38psi, with 32-34psi being a good amount to put in if your not sure.

GreyGoose006 · 08-31-2006, 06:27 PM

no... there are such things as tires that run at 44psi. michelin's harmony tires say to run at 44psi. i believe the majority of minivans, and light weight wuss-UVs run at 44 psi. it cuts down on rolling resistance.

i have a friend who has a suburban that he put 90 (yes 90) psi industrial tires on.

tires should be inflated to what it says on the sidewall, which is recomended pressure, not max pressure (it may say max, but it isnt)

Igovert500 · 08-31-2006, 06:56 PM

For every day driving, I've always filled my cars to the recommended tire pressure on the plaque in the driver's door jam (I think every car has one) which is generally in the range of what Moppie said.

Keep in mind when tires warm up the air inside expands and can raise the tire pressure something like 5psi. So if you are inflating them to the max psi rating, when they are cold, that is VERY bad.

bluevp00 · 08-31-2006, 09:00 PM

Overfilling the tire will cause tire wear in the middle of the tire (it bulges out in the middle when theres too much air in it). But filling within the limits of what it says on the tire should be alright. Myself, I go by what it says in the owners manual (if you're using OEM size tires), the people who made the car usually know best PSI to use.

UncleBob · 08-31-2006, 09:50 PM

Quote:

Originally Posted by GreyGoose006

no... there are such things as tires that run at 44psi. michelin's harmony tires say to run at 44psi. i believe the majority of minivans, and light weight wuss-UVs run at 44 psi. it cuts down on rolling resistance.

i have a friend who has a suburban that he put 90 (yes 90) psi industrial tires on.

tires should be inflated to what it says on the sidewall, which is recomended pressure, not max pressure (it may say max, but it isnt)

the only pressure listed on the side wall, is the maximum pressure. You are incorrect. You should never fill it up to the pressure listed on the tire UNLESS you are loading the vehicle enough to require that amount of pressure.

Over inflating the tires will not only cause a rough ride, it will cause the tire to wear severely in the center of the tread.

The vehicle manufacturers recommended pressure is the best information to follow....regardless of the tire in question (assuming its within the weight rating designed for the vehicle). Believe it or not, the vehicle manufacturer has a pretty good idea what they are doing. The tire manufacture doesn't know what vehicle you're putting the tire onto.

Simply put, you will have a better ride, better handling, better traction and longer tire longevity, if you follow the vehicle recommendations. You may get one or two mpg better with severe overinflation, but at the cost of tire wear, you're not saving yourself any money. And if you get in an accident due to it....

Moppie · 09-01-2006, 12:31 AM

Quote:

Originally Posted by GreyGoose006

tires should be inflated to what it says on the sidewall, which is recomended pressure, not max pressure (it may say max, but it isnt)

Wow.

Ok, go find a bottle of turpentine and drink as much of it as you can.
It might say Poison on the side, but it isn't.

G-man422 · 09-01-2006, 06:44 AM

My michellins have a 44psi max, but i usually fill them to about 38-40psi.

curtis73 · 09-01-2006, 12:54 PM

Every car I know of has a sticker inside the driver's door that lists the recommended inflation pressure. That is based on the floatation of the tire, the weight of the vehicle, and several other factors. For the most part, 99% of your driving will be done with a couple passengers. Every once in a while you'll make a run to Home Depot and get 10 bags of mulch, but there is no need to put more air in for 10 miles.

The number on the sidewall is NOT a recommended inflation, its max. There is no way michelin can recommend a pressure for a tire that might be used on a light truck or a Camry in the same size.

Weight suspension in a tire is a function of pressure and interior volume... Period. That's why CAR manufacturers put those stickers in the door jamb. Auto manufacturers choose a size of tire that will be satisfactory under its max pressure to suspend the weight of the car. It doesn't matter if Toyota puts a Michelin tire or a Firestone tire as original equipment on a Camry, the sticker still says 32 psi. They know it takes about 32 psi to suspend a 3000-lb car. That's also why a 1-ton truck gets tires that hold 80 psi.

Read up on everything tire tech at www.tirerack.com in their tire tech section. I could type up something here, but you know me... It would be 30 pages long.

jaxtell671 · 09-01-2006, 01:42 PM

thanks for all the advice, yeah i did notice that it ran a bit stiffer but i didn't really mind that. but from now on i think i'll just fill it to around 40.

curtis73 · 09-01-2006, 01:54 PM

Although I don't really recommend this for other people's cars (just my own

), you can try different inflation pressures and then lay a good trail of rubber. Pressures too high will create darker black streaks in the center. Pressures too low will create darker streaks near the edges of the tread.

The other way is to just buy a $1.99 tread depth gauge and monitor tread depth on the edges and center of the tread.

GreyGoose006 · 09-01-2006, 10:58 PM

the thing is, the sidewalls on my tires say reccomended...
lets assume that the number printed really is the max, the manufacturers would tell you about 10 psi less to be on the safe side. there is going to be a margin of safety on any tire.

as for the door jamb, its a great idea... that is if you havent switched the brand or size or performance rating of the tire you were using when the car was bought. say you upgrade to wider tires, and get a summer compound, since you live in florida (for example). the whole thing about the door jamb is now not true. even if you keep the tire size and load rating the same, but switch brands, you need to adjust the pressure. the pressure on the sidewall is GENERALLY accepted as a good place to start when filling your tires. i wouldnt suggest going over it, but you are perfectly safe while you are at the pressure listed.

oh, and by the way, yes, michelin harmony tires do recommend using 44 psi. my dad has them on his '05 Oddesy and my mom has them on her '92 Accord. BOTH say 44 psi.

UncleBob · 09-02-2006, 12:28 AM

Quote:

Originally Posted by GreyGoose006

the thing is, the sidewalls on my tires say reccomended...
lets assume that the number printed really is the max

you seem to be rather insistant that you understand this better than everyone, when a awful lot of people say otherwise.

If you'd like some credentials....I work at a tire store. We're not making this stuff up.

I'd suggest you read your sidewalls again. I think you have misread what it says.

Quote:

as for the door jamb, its a great idea... that is if you havent switched the brand or size or performance rating of the tire you were using when the car was bought. say you upgrade to wider tires, and get a summer compound, since you live in florida (for example). the whole thing about the door jamb is now not true.

Here is the large part of the confusion, and its a very common misconception.

The PSI of the tire is MOSTLY ruled by the WEIGHT the tire is supporting.

In other words. No matter what tire you used to have, do have, was stock, isn't stock, width, weight rating ect ect: assuming the weight of the vehicle, and its weight relation (level of CG, weight distribution, etc) it will be the SAME recommended PSI no matter what tire is involved.

Here is a simple analogy. You take a party balloon and blow it up. Now you hold it to the floor with your hand and smoosh it so that it flattens out. The obvious result will be, the more pressure (weight) you apply to the balloon, the more it will smoosh. A tire is the exact same thing. The more weight you add, the more the tire will be squished. The way you compensate for this is by adding PSI so that you have a happy median between too squished, and not squished enough (where it would only ride on the center of the tread area)

Now if you have a very stiff tire, it can support more weight BECAUSE it can support more PSI. If you run a semi-truck tire at 2psi will will eventually overheat the sidewalls just like any other tire, although granted, it will take away, because the structure doesn't have enough support to support a significant load.

The number you see on the stickers on door jams is just that: Its the manufacturers calculated psi necessary for the WEIGHT of the vehicle, and its various likely additional loads. A 1 ton truck, for example, will have some grey area. Because when the truck is empty, vs having a full load to its maximum weight capacty in the back, the required PSI for these two extremes will be quite different. This is where, if you wish to be savy about your tires, that you need to take some guesses at the proper level of inflation. But if you maxed out those 90psi capable tires and never have a load in the back, you will wear them out very fast.

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