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tires inflation

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#1 SirEvan

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Posted 16 July 2012 - 17:11

This is a dumb question, but my mom brought it up and I didn't have a good answer for her. How much air do you guys put in your tires? Do you inflate to what the tire says (or close to it), or do you go off the vehicle sticker on the inside of your door?

I have never done anything but what the tires state, and in most cases my vehicle sticker matches the tires anyway (except if i put larger tires on). But my mom has a Suburu outback, and while her tires say something like 50 psi, the vehicle sticker on the door says to put in something like 25-30psi...almost half! I look at her tires and they look highly under-inflated (bulging out on the bottom), but she seems to think that she should be going off what the door says and not the tires.

So what would you guys recommend? Door....or tire?


#2 +mulligan2k

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Posted 16 July 2012 - 17:14

door, the tire doesn't know the weight of the car that it could be fitted too

#3 BajiRav

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Posted 16 July 2012 - 17:19

I always go by the vehicle spec.

#4 threetonesun

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Posted 16 July 2012 - 17:19

But my mom has a Suburu outback, and while her tires say something like 50 psi, the vehicle sticker on the door says to put in something like 25-30psi...almost half!


Door... I can't think of any tires besides temporary spares that would be at 50 psi, unless that's possibly the max inflation. :s

#5 Another Canuck

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Posted 16 July 2012 - 17:21

Door.

The spec on the tire is the maximum inflation pressure. Always use the spec listed on the inside of your door.

#6 ccoltmanm

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Posted 16 July 2012 - 17:26

Tire. Highest psi possible. Best mileage possible. Right?

#7 tsupersonic

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Posted 16 July 2012 - 17:31

Tire. Highest psi possible. Best mileage possible. Right?

Nope. You always want to be using the vehicle specs, which are usually on the door.

#8 Another Canuck

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Posted 16 July 2012 - 17:33

Tire. Highest psi possible. Best mileage possible. Right?


You realize you're talking minute fractions of an MPG, right? You'll be lucky if you save $20 a year.

The decreased rolling-resistance of an over-inflated tire is not nearly worth the decrease in handling, comfort and stopping power, and increase in road noise and risk of blowout.

#9 OP SirEvan

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Posted 16 July 2012 - 17:33

Tire. Highest psi possible. Best mileage possible. Right?


Thats what my thinking is. Plus, what if you put larger tires on? I went from 17" run flats on my 335i to 19" lower profile tires. The door says around 50psi, my tires say 51 psi. But what if it was different and the new tires had a max rating of more? then you would be under inflating. I've always been told you don't want to bubble your tires out because it leads to decreased gas milage, as well as earlier failure of the tire, and have always gone with within 5% of the max PSI on the tire.

@mulligan, I could maybe understand that, but when I buy tires I buy for a vehicle, and rim size...so it would stand to reason that those tires were made for that vehicle/rim size, and therefore would know the max weight of the vehicle?

#10 cybertimber2008

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Posted 16 July 2012 - 17:34

Tire. Highest psi possible. Best mileage possible. Right?

Over inflating increases your risk of hydroplaning.

I go with what the tire says, but I fill to ~5psi below the max when my tires are cold.

#11 articuno1au

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Posted 16 July 2012 - 17:36

I do tyre pressures, but I buy tyres designed for my car type.

/shrug

#12 ShareShiz

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Posted 16 July 2012 - 17:38

Tire. Highest psi possible. Best mileage possible. Right?


wrong

.. best to do what the car manufacture says, they don't do loads of testing for ****s and giggles.

#13 Astra.Xtreme

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Posted 16 July 2012 - 17:40

Tire. Highest psi possible. Best mileage possible. Right?


That will decrease the life of the tire pretty badly. Always go by what the car is rated for.

#14 Another Canuck

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Posted 16 July 2012 - 17:41

Thats what my thinking is. Plus, what if you put larger tires on? I went from 17" run flats on my 335i to 19" lower profile tires. The door says around 50psi, my tires say 51 psi. But what if it was different and the new tires had a max rating of more? then you would be under inflating. I've always been told you don't want to bubble your tires out because it leads to decreased gas milage, as well as earlier failure of the tire, and have always gone with within 5% of the max PSI on the tire.

@mulligan, I could maybe understand that, but when I buy tires I buy for a vehicle, and rim size...so it would stand to reason that those tires were made for that vehicle/rim size, and therefore would know the max weight of the vehicle?


I think you're reading the spec wrong. 50psi is absurdly high. It should be somewhere in the 30-40psi range.

The 335i is a relatively light vehicle. You do NOT need 50psi of pressure in your tires.

#15 +Bryan R.

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Posted 16 July 2012 - 17:41

PSI is a universal measurement of the pressure the air is under regardless of the tire. You go by what's on the car.