Posted: 7/15/2002 12:28:26 PM EDT
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Just got new tires on my ghetto mobile. The sidewall indicates 44 PSI and I thought they looked low. I checked it an they were 35 psi. I asked the guy about it and he said that 44 is the maximum PSI but 35 is recommended. Is this BS? |
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Go buy what the car maker says. Nothing else matters. Tire pressure affects breaking and heat disipitation around brakes. Some tire makers increase the pressure rating because it prolongs the life of the tire. All in all follow what the car maker says. Sgtar15 PS When the hell did you get back in here?? |
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Nope, I just went through this the other night with three different autos Depending on the tire, there is a MAX. PSI, then there is listed, the manufacturer's recommended PSI for normal operating pressure. Keep in mind that the PSI is measured when the tire is cold. Edited to add: Here is a good explanation of the effects of tire pressure and tire wear [url]www.goodyeartires.com/kyt/maintaningATire/index.html#1 [/url] |
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44 psi is the recommended pressure. If you put that amt in on an average temp day you're good. Around here (missouri) tire press varies a bit from summer to winter. What they list is what you should keep it CLOSE TO (or if it says max that's the max). There's no way you can keep it at exactly that. If you overpressure you get middle tread wear, if underinflated you get outer tread wear. Use your judgement, and temp does make a difference so check it every 3-4 months even if it looks ok. |
| I've always put 35 lbs in every care I've ever had. And checking the tire presure when the tires are cold means that they haven't been driven on or been in direct sunlight for a few hours. I usually check my tire presure at night or in the morning BEFORE I drive. |
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The vehicle manufacturer tire pressure recommendation sticker on the door or door pillar is a good starting point for what to use for a TP in your vehicle. However, that is with the stock tires and wheels, and is provided by the vehicle manufacturer so that you achieve what they feel is the optimal balance betw. ride quality, handling, performance, and load capacity. However, if you change the wheels and tires (to wider, lower profile, etc.), then the factory sticker is about worthless. IMO and preference, I run TP to attain even wear across the width of the tread. If you run 30 to 35 in a 44 max tire, you may get more wear at the tread edges than at the center, and the tire wears out faster at the edges. When a tire does that, handling gets funky on worn pavement. On 44 max TP tires, I run betw. 40 and 44 PSI, measured cold, as in before driving for the day. The tires wear evenly across. I once got 87,000 miles out of a set of Michelins on a '79 Volvo 245 wagon by keeping the TP at near max and rotating from front to back every 5K to 7K. Also, you may have 40 psi in your rubber in July, but if you live in a northern clime and check the TP in December, it will be much lower not due to leaks, but due to the temperature effects on the air pressure at a near-constant volume. Air is a gas and expands and contracts with temperature. As a gas expands in a constant volume, the pressure increases. Drop the temp and the gas contracts. Winter temps = lower pressures. I've forced myself to check the TP on the first day of each season for certain, and often more frequently. Noah |
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Personally I use pressures that give the handling I want. 32-35 psi as a baseline on passenger car tires and 45 psi on light trucks. If the vehicle pushes raise the front pressure 2-6 psi till it runs neutral thru a turn. If it's loose (damned unusual on American products) raise the rear pressure the same until you get a neutral feel. And don't exceed the pressure that exceeds your shock absorber damping. Sorta vague for anybody but us old speedracer guys but it works. |
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Quoted: Quoted: Are your new tires a one-to-one size replacement for your old tires? For example, if your car had 205/60 R16, did replace with the exact same dimensions? Don't know. I'm not the original owner. If it's a car tire, 44 PSI is almost certainly the [b]maximum[/b] pressure, which is not related to the recommended pressure. Maximum means the pressure beyond which the tire is unsafe and may explode or something. Of course, the listed maximum pressure is probably quite a bit lower then the actual maximum. It's the lawyers, ya know. The best pressure is usually 32-35 on car tires (which also includes most SUVs and light trucks). You can tell by looking at the tread wear. If the center is wearing more then the edges, you need more pressure. If both edges are wearing more then the center, you need less pressure. If one edge is wearing more then the rest, then you need an alignment. |
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Quoted: Go buy what the car maker says. Nothing else matters. Tire pressure affects breaking and heat disipitation around brakes. Some tire makers increase the pressure rating because it prolongs the life of the tire. All in all follow what the car maker says. Does Ford/Firestone ring a bell? Ford was recommending ridiculously low tire pressures to make the ride better and it was a contributing factor to the incidents of tire failure. Clearly Ford had more money & power so they didn't suffer near as bad as Firestone did. |
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I've been trying to find out some info on my tires as well for a while and everyones advice is different,and I'm talking about tire manufactures and tire shops. I went from P225/75R 15" tires with suggested TP of 29PSI to 30x9.50" 15" LT tires with a max of 50PSI.Of course the info on the door is for the old tires at 29PSI,so I have know idea what the pressure needs to be.The installers put 32PSI on the right side and 36PSI on the left side and when I asked them they did not know,so hopefully someone can give you a definite answer. |
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What kind of 'ghetto mobile' is it? Okay... my turn to add to the confusion... if you go by the sticker on the door frame, that is what the manufacturer recommends when using the original type/size tire they installed. Example: My 83 F150 Stock tires listed are P235/75R15 w/ a 41 PSI recomendation. Now, if anyone knows P rated tires, most of the info on the sidewall says Max load is XXXXlbs @ 35 PSI. I haven't seen a P rated tire that's over 35 PSI. Now my LT235/75R15 say XXXX lbs load at 50 PSI. As stated on other posts, you'll have to find a happy medium. I don't carry a load that often, so filling them to 40-45PSI would cause undo center tread wear. On my Sable, it says run 35 PSI from the factory. I run a little higher, 37 or so. No problems w/ tire wear or what. The ride, who cares....... On my old 'boat' (aka 75 Mercury 4 door car), the tires are 14" rimmed. This car weighs as much as a two wheel drive full sized truck. The tire pressure on this is about 3-5PSI over what was recommended by the factory. Granted, the original tires were bias ply and that's what it says on the sticker (now I run Radial). If I recall, I'm running 36 or 37 PSI on them. |
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If it says 44, use 35-37. I have been in the auto field for 20 yr and can tell you that almost anything under 30 I consider underinflated. You should hear people whine that they need tires around 25-30,000, low air, lack of rotate and align. Another thing to look at is the "supposed" change of tire pressure advice from FDord to up the pressure in thier Explorer tires from 26 to 30......ever drive a small truck with large sidewalls and low air? It handles like a major bucket of slush, hey lets put 4 more in the tires, and maybe we can stop wearing the edges of the treads and the treads peeling off might slow down a bit. |
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I've been in the auto business for a few decades, done a lot of front end work, and also raced cars, so I felt like I needed to put my $.02 in here. First, the tire pressure listed on the sidewall as the max pressure is the maximum pressure cold at the [i]tires[/i] maximum [i]loaded[/i] capacity. In other words, if your vehicle is almost always empty, and you drive "normally", you would not want to run that high of a pressure because you suffer premature tread wear. If you tend to carry weight around you would want to increase the pressure closer to the maximum to prevent tire [i]damage[/i]. Same thing if you have a tendency to drive hard and fast around corners because that is increasing the load on the tire on the side of the vehicle on the outside of the turn. Another reason to slightly increase TP over the manufacturers recommendation is if you only drive a very short distance. The rec TP is based on the vehicle being driven a certain length of time (how they arrive at the average I have no idea) and the air in the tire heating up causing the pressure to increase to the desired level. If you drive short distances with little stop and go your tires will not heat up and you will suffer inner and outer edge wear from them being underinflated, which in turn leads to excessive heat build up in the [i]tire material itself[/i] due to excessive flexing of the sidewall, which leads to tire damage and potential blow outs (see reference to Ford/Firestone in above post). If you are someone who does lots of freeway driving everyday - without excessive speed - or have a long commute, then the makers rec is ok. If you drive at high speed a 2-4 psi increase helps prevent damage. Ok, last thing. How do you tell if your tire pressure is set well for your particular vehicle and tire/wheel combination? I will tell you. The tire makers and vehicle manufacturers use, or at least used to use, this same procedure, albeit spending more money doing it. Get a large piece of poster board - not card board as you want something that doesn't crush. It's best if the length of the board is the same as the circumference of your tire. Drive your vehicle in a pattern similar to your normal driving habit. Then wet down your driveway or what ever you have access to. DON'T make a puddle, just make it wet. Drive each tire, one at a time, in turn over the wet patch and then directly all the way across the poster board. Look at the pattern the tread leaves. If it is "light" in the middle then your tires are underinflated. If it's "light" on the egdes they are overinflated. It isn't an exact science as it can take some experience to read subtle differences, and black paint on the tire makes it easier to read than water. But if you really want to go to the effort it does work. And if it's heavy on one edge and light on the other, or smears, you might have an alignment problem. |
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Take some chalk. Swipe a line across the tire from the inside out. Drive so the tire rotates a few times. See if the chalk is not wearing onto the road. You can then tell if you have overinflated or underinflated. Just a simplier method of what Pthfndr was saying to do with the board and water. |
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Okay, with my father being in the tire business all his life,(30+ years) both selling passenger and truck tires and recapping truck and off the road tires, here's what he's told me: Depends on the size of the vehicle, what conditions your driving on, at what kind of load you're carrying. He's advised me that my cargo van with all my tools in it, I should run the tire pressure around 40-42 psi. For my wifes Honda Civic, around 32 psi. Forget the car manufacturer's recommendation. They don't cover the warranty on the tires, the tire dealer does. If your driving a pick up or SUV I'm betting he'd say around 35 psi. Unless you plan on carrying a heavy load. I'll be talking to him tomorrow so I'll confirm this. |
| I once owned a car that rode on same size tires front and back but required different amount of air for front and back. I heard this was for handling purpose. Also if you do a lot of high speed driving, they recommend you put more air in than whats recommended by them. If you want the best in handling, safety and fuel economy, I would go with the car manufacturer's spec. On my SUV, putting max psi imprinted on the sidewall can really screw up the handling and lowers fuel economy. It gets really scary when going through the curve and also makes the car too bouncy. Drive through oil change place near my house always fill up to the max and I always end up taking some air out to stabilize the car. |
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I've been around cars for a long time and done my share of circle track racing. PSI on sidewall is MAX safe pressure for tire, COLD. Vehicle manufacturer's data tag is MINIMUM safe pressure. Add air toward max as load, speed or outdoor & road surface temperature increases. A tire's worst enemy from is HEAT. Wear patterns are secondary. Interestingly there is not a great margin between NORMAL operating temperature and DISASTEROUS temperature. Do not eat up that slim margin by underinflation. Too much is nearly always better than too little! Vehicle data tag should produce acceptable wear pattern and ride. That data is good for ANY wheel and same load range tire. Contact patch is ONLY affected by vehicle wieght at each tire and the pressure required to support that wieght. Interestingly, actual contact patch does not grow with reduced pressure but just changes shape. Modern radial tires change wear patterns far less than bias ply for a given change in pressure. Low inflation causes more flexing in the tire as it rolls, building HEAT. At some temperature the bonds that hold the thing together fail - KABOOM. That was part of Firestone fiasco. A poorly bonded tread that failed at lower than advertised temperature. Ford had chosen the low end of the inflation range from Firestone's load chart (more heat)and the two points intersected. Add poor drivers and high CG vehicle and things got ugly! In as much as 2/3 of all tires on the road are underinflated it is easy to see that all the precious little safety margin with the firerocks on Fords got used up. A normal tire loses 1 PSI per month and / or 1 PSI per 10 degrees F change. Worse if it leaks. Check often! If you are particular, once every week or two. Get in the habit of doing it before you leave home. That walk around is like an aircraft pilots preflight - finds pets, toys, dents, leaks, low tires and the like. Also learn to lay your hand on each tire after a good drive AS SOON AS YOU STOP to gauge temperature. Quite warm is OK but too hot to touch or a difference from wheel to wheel is a warning. Sharp turns or hard breaking can skew this a bit so just be aware of it. Modern tires cool rapidly so the nuances are lost in only a couple minitues. Note that with small trailers without brakes, in particular boat trailers, that heat check on wheel bearings can save you a breakdown. Edited to clear up misconception. HIGH inflation pressures NEVER hurt fuel economy, only LOW can do that. |
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What is the aspect ratio of the tires, what is your car and how much does it weigh? Low profile tires need more air. My 215/40-17's took 44psi, but my 205/55-15's only took 34. Same overall diameter on the same car, except one was a 15 inch and the other was a 17" rim/tire combo. If its a low profile (ie.thin sidewall) tire, you will need that full 44psi of air. Let us know what you're riding on before some idiot here inadvertently kills you or something! |
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Quoted: Personally I use pressures that give the handling I want. 32-35 psi as a baseline on passenger car tires and 45 psi on light trucks. If the vehicle pushes raise the front pressure 2-6 psi till it runs neutral thru a turn. If it's loose (damned unusual on American products) raise the rear pressure the same until you get a neutral feel. And don't exceed the pressure that exceeds your shock absorber damping. Sorta vague for anybody but us old speedracer guys but it works. I have to go with what Arock says, I have been driving for a quarter of a century and have racked up many hundreds of thousands of miles so I have a learned a little bit over the years. |
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I always use between 28 and 32. In fact, the only recall I heard about with my truck was a recall to replace the tire pressure sticker located in the glove box. I lost the sticker, but I guess it doesn't matter since I've already been through 4 or 5 sets by now. |
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Something I've learned from my car about tires is, you will get better efficiency at higher pressures. My manuf. recommended pressure is 38psi front and 35 rear. I run 50psi in the front and 46psi rear. Efficiency is increased as rolling resistance is decreased. The drawbacks are that handling suffers a little bit, and braking distance does increase. My car is little, light, and nible, so I don't feel any change. I'd recommend running your tires AT LEAST at what is inside your door, if not a few lbs more. Shouldn't cause any problems running them a little high. |
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I have a '98 VW Jetta TDI that I just replaced the rear tires on last weekend. I rotate regularly and check tire pressures pretty regularly. These were the factory installed Goodyear's and believe it or not, there is 91k on these tires. I rotated the other pair off the car aprox 10k ago due to several puncture/plugs in one tire and one tire was run "low" which caused a blister in the sidewall. I keep a eye on the fronts to see how their wearing and adjust accordingly. I run this car at 40 PSI. Sleepy717 |
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SA, talked to my dad today. Said without knowing what the weight of your vehicle is, it's hard to say, but generally for a SUV you should be good around 35 psi. Also, DON'T go by the car manufacturer's recommendation. He pointed out that the whole Firestone/Ford issue was due to the fact that Ford was recommending a lower tire pressure than what Firestone was recommending. Said forget the crap you read in the papers. Finally, don't over inflate. If you do you'll wear out the center of the tire faster than the outside edges. Hope that helps. |
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Quoted: Finally, don't over inflate. If you do you'll wear out the center of the tire faster than the outside edges. Accelerated treadwear is just the tip of the iceberg for over-inflated tires. First there's the bone-jarring ride from such hard tires and associated vibration through the steering column. Second, cornering ability is also out the window. Third and most significant is loss of traction. Eliminating all that contact patch means increased braking distances and really poor wet weather performance. |
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I have the same setup, goodyears rated at 44psi max. I run them at 40 because tires gain 3 or four pounds as they heat up, I don't mind the stiff ride and I get better gas mileage. The Tires on the WRX are rated at 44 max, car recommends 32 front and 29 rear, but I run them at 35 f/r as they handle and ride better at that pressure. Try some different pressures and see which feels/works best for you. |
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Always set tire pressures when tires are COLD. If the pressure's right plan on a ten percent increase in pressure when the tire is at operating temperature. Higher initial pressure results in less temp gain and therefore less pressure rise. Lower initial pressure give more heat rise due to excessive sidewall flexing and therefore a larger pressure increase. Low pressure can lead to tread separation by overheating the tire. Think summer day, 75 mph and vacation overload. |