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Tire PSI for Max MPGs?

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max mpgs psi tire
56K views 168 replies 39 participants last post by  Gravity 
#1 ·
my dealer uses Nitrogen so it doesnt change from cold/hot when i go in for an oil change im going to have them pump up the tires. But how high should i go? they are at 35ish on all 4. I heard someone go to 51psi??? Im afraid to go that high. I was thinking around 45psi. Not worried about ride quality, i had a 09 colbalt SS and the ride quality SUCKED.. i dont think it can get worse
 
#2 · (Edited)
I'm sitting at 48psi (cold air) will reach 49-50 warm. I'm sure "xtreme" will chime in and tell you that that's perfectly fine.

you should look at his threads he's started concerning mpg and resignator delete they both mention tire pressure.

But I dought the dealer will let you pump them up that high


Sent from iPhone 4
 
#3 · (Edited)
Take a guess as to what would happen if you inflated your tires to 51psi cold (max sidewall for Cruze Eco's tires).

Answer: nothing.

Take a guess as to what would happen if you inflated your tires to 51psi cold and you had a pressure related failure?

Answer: you would defy the laws of physics. Tire failure would make headline news like it did with the Ford Explorer fiasco. Pigs would fly, and I'd eat manure.

The simple fact is that tire manufacturers specify a max sidewall cold pressure with about a 200% wiggle room for liability reasons. You will not wear your tires unevenly (this is an old truth applicable only to bias-ply tires, NOT radial tires). The NHTSA proved that you do not lose a notable amount of stopping distance (about 2.2% or 3 feet in dry asphalt, no change in wet asphalt, no change in wet or dry concrete). You will gain a good amount of fuel economy, and the only compromise will be ride quality. Tires do not fail due to too high of a pressure; they fail due to too low of a pressure or the tires are old and dry rotted and should have been replaced long ago.

I have materials to back all of this up.
 
#4 · (Edited)
I'd like to see some materials because 75% of that is BS. Overinflated tires will absolutely wear in the center more than properly inflated tires, changes in stopping distance are determined by the weight of the car and the width of the tire (what percentage is lost to the contact area due to over inflation), if you have a light car with wide tires it won't be as dramatic as a heavy car with narrower tires. The odds of a sidewall failure or loss of the tire bead with a sharp impact increase dramatically once you go above 40 PSI on most car tires. Fuel economy May go up a few points and yes it will ride harsher. It also changes the spring rate of the car and makes the vehicle more prone to unloading the suspension which can also be dangerous in certain situations. I've been in the tire business for years and would really like to know the basis of your theories. Generally it is safe to go up or down 5 PSI on your tires and not see adverse effects and the only time you should deviate from that is if you put a higher load on the tire (more weight).

For the OP, best advice is stick with the manufacturer recommendations

Edit: and yes underinflation is most definetly the worse of the two and more likely to cause a tire failure because the tire can't maintain it's shape, but that doesn't mean there are not risks with overinflation.
 
#6 ·
Uh Oh now there is a war!!! However filling up to SideWall max is not Overinflating :D hehe. but i have min at 48 cold they get up to about 53 hot and driving cause i live in SoCal and its pretty hot at the moment!
 
#9 · (Edited)
I've fought this battle before, and right you are! Filling up to sidewall maximum is not over-inflating. 48psi cold is an excellent pressure for the Cruze Eco's stock tires. Mine are at 50psi at 78 degrees F.

I have traditionally run my tires at 5 PSI above the door placard and have never had problems with uneven wear due to overinflation. Radials are resistant to tread buldges from over/under inflation, but not immune. Also, my dealer put nitrogen in and I still noticed a +- 2 PSI change in tire pressure, so I'm definitely not sold on nitrogen unless it's free.

Higher pressure in tires will reduce rolling resistance, but not in the way most people expect. Basically, the sidewall on the part of the tire pressed against the ground bulges. Higher PSI reduces this bulge. As a result less rotational energy is turned into flexing the sidewall. The side effect of this is that your ride becomes stiffer and smaller bumps in the road are transmitted to the suspension by the tire. This is useful for improving low speed MPGs because the rolling resistance is a larger component of the overall drag friction on the car. At high speeds, the rolling resistance is overwhelmed by the drag friction of the car through the air. Rolling resistance goes up as a linear multipler of speed while the air resistance goes up as the square of the speed.
Correct, they are not immune. They still need to be rotated. Due to camber changes during cornering, your front tires will naturally wear out the edges a lot more than the centers. A car that has never had its tires rotated will inevitably have the shoulders on the front edges worn out MUCH more than the rest of the tire. The rear of the car is not exposed to this and as such will wear the insides more quickly regardless of pressure. At max sidewall pressure with the tires on my Cruze Eco, 100% of the tread is in contact with the road. Here's some more info:

Tires Explained, Biased Ply VS Radial Tires - What makes each so **** great?

The fronts will wear the shoulders, the rears will wear the centers. So long as tires are rotated, they will ear evenly regardless of pressure. The only time you will ever see a tire that's worn more in the center than on the edges is when it has not been rotated.

I'll invite everyone here to do a search for "tire pressure" on the cleanmpg.com forums as I did, and spend the countless hours as I did to read about all of the people who are significantly exceeding their treadwear rating and wearing down their tires 100% evenly while running max sidewall pressures and higher. One guy (and I don't recommend this because its a bit extreme) ran 100k miles on OEM Accord tires, running somewhere around 60-80psi. However, even if one would argue that he's an exception, everyone else who runs max sidewall pressure will tell you over and over again that their tires are wearing evenly and always have.

You hit the nail on the head with everything you said. I'd give you a beer if you were nearby.
 
#7 ·
I have traditionally run my tires at 5 PSI above the door placard and have never had problems with uneven wear due to overinflation. Radials are resistant to tread buldges from over/under inflation, but not immune. Also, my dealer put nitrogen in and I still noticed a +- 2 PSI change in tire pressure, so I'm definitely not sold on nitrogen unless it's free.

Higher pressure in tires will reduce rolling resistance, but not in the way most people expect. Basically, the sidewall on the part of the tire pressed against the ground bulges. Higher PSI reduces this bulge. As a result less rotational energy is turned into flexing the sidewall. The side effect of this is that your ride becomes stiffer and smaller bumps in the road are transmitted to the suspension by the tire. This is useful for improving low speed MPGs because the rolling resistance is a larger component of the overall drag friction on the car. At high speeds, the rolling resistance is overwhelmed by the drag friction of the car through the air. Rolling resistance goes up as a linear multipler of speed while the air resistance goes up as the square of the speed.
 
#11 ·
How long? Not sure, man. Last time I took a typing test, I benchmarked 131 words per minute with 92% accuracy. It doesn't take me very long to make page-long posts.

Who said I wanted rock-hard tires? That was merely a possible consequence of increasing tire pressure to maximum sidewall. These things are always very subjective. BTW, The Cruze Eco tires are LRR tires.
 
#12 ·
Just to throw this out there for curiosity what would happen to the Eco's mileage if you went with Non-LLR but inflated the pressure?
 
#13 ·
The sidewalls wouldn't be quite as stiff, so you'd gain some rolling resistance off the bat. Many standard all-seasons also aren't rated beyond 44psi, so you wouldn't be able to get to the same pressures anyway. Off the top of my head, I think you'd realistically see around 1-2mpg difference between max sidewall all-seasons and max sidewall LRR tires.
 
#14 · (Edited)
Alright then, I won't go against clean MPG forums since they are obviously more in the know than (the obviously biased) tire engineers. I fail to see how popular mechanics makes a profit off tire pressure (maybe I am wrong) but I also notice you didn't bother with what Michelin, Goodyear, the tire rack Etc had to say about it, just that they are biased. Of course they are biased, they make and sell tires and it is in their best interest to keep you safe so you buy their product and don't sue them.The fact people do it and have no issues doesn't change anything. Millions of people skydive with no issues and a few auger in and turn into pancakes. Anytime it has been scientifically tested the gain in MPG with overinflated tires is minimal compared to proper inflation. The big change is if you go down in PSI. With wear yes a bias ply will wear worse, but radial tires are not immune to ballooning and you can lose 25% or more of your tread life with too high a PSI. Bottom line the BEST tire pressure to run is the recommended tire pressure that the engineers (not clean MPG forums) figured out was best for your particular car, and if you change that without understanding what you are ACTUALLY doing, you do it at your own risk, chances are you will be just fine except for buying tires sooner, but it doesn't change the fact you are using the tire as it was not intended to be used.
 
#19 ·
Popular mechanics is not making a profit; they're just stupid, and I demonstrated why. They performed an uncontrolled experiment and didn't account for all variables. Their testing is invalid, and as a result, they're misleading people.

I don't want to be rude, but we don't live in a perfect world. We live in a world where if your clutch on your Cruze Eco fails, GM will do anything in its power to not replace it and call it a wear item. See the general section of this forum. We live in a world where Toyota has been hiding their random acceleration and sticky pedal problems since 2002, leading up to I think 11 current and open federal investigations. Money is king and you and I both know that. Any company that manufactures and sell tires will recommend want you to come back for another set, and the guys at cleanmpg.com forums have demonstrated time and time again, with no discrepancies, that your tire life is significantly extended by running maximum sidewall pressure and that the radial tires wear evenly.

Show me a single test that's actually been done by an organization that indicates you wear tires SOONER using "over-inflated" tires than with the manufacturer recommendation. You won't find it because its not true. Nobody actually tests this crap, they just tell it to you to keep you from doing it for obvious reasons. Plenty of people here know that's the honest truth and I'm surprised you still think tire manufacturers act in your best interest.

The best tire pressure to run is that which meets your needs, not that which your car's manufacturer recommended. The Cruze Eco tires are designed to run up to 51psi safely. There is absolutely NO basis in telling people that they cannot do so.

Don't bring engineers into this unless you can bring an actual engineer into this. Don't speak on their behalf as if you know exactly why they made their decisions. I can guarantee you they didn't tell us to run 35PSI on our Eco tires to maximize tire wear over higher pressures. I and everyone else here know as a fact, they did it as a best compromise for ride quality. I will admit that running tires at 50psi like I do leads to a notable increase in road variations transmitted into the vehicle. The tires simply don't absorb smaller impacts anymore.

I don 't think a lot people understand how much force you are talking about, think about it this way. Imagine 35 pounds of weight and on your hand. Now imagine 50 pounds of weight on your hand (or do it if you choose) Imagine the difference there. That is what your tire is doing in every square inch. Say (for giggles) the tire is 8 inches wide and 48 inches around.

8X48= 384 square inches
384X35PSI=13,440 pounds of pressure in that tire
384X50PSI+19,200 pounds of pressure in that tire

Starting to get it? and that is just the tread size, that same pressure is on the sidewall at the same PSI so the numbers are actually even higher than that. There is A LOT of potential energy in an inflated tire
I don't think you understand that tire manufacturers are bound by the NHTSA to post VALID numbers on the tire sidewall. Regardless of your calculations, the tire manufacture rates that tire for that specific pressure SAFELY and with at least a 200% safety margin. 51psi max on the Eco tires is a cold pressure. They know that if you inflate at 51psi at 68 degrees F, and you drive down a Las Vegas highway in the summer with 110 blazing heat that the pressure will expand, and they've accounted for that and much more for liability reasons.

What PSI do truck tires run? Just because there's potential energy, doesn't mean there's potential disaster. The real fact is that increasing pressure reduces rolling resistance, which in fact reduces heat created and reduces the variation in pressure. Reduction in heat reduces to less likelihood for a blowout and helps prolong dry rot.

I generally inflate to 110% of recommended inflation pressure. Any more than that I find the ride quality suffers too much.


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That's 100% fine. You tried it and you noticed the difference. It works for you, and neither I nor anyone else can tell you its not right. You value your ride quality, and that's great. You've found the pressure that works best for you.

I'm recommending everyone do the same as you did, and I'm telling them its safe to go to the max sidewall rating if they don't have ride quality in mind.

40-42 psi since day one and that's all I have to say about that!!!
:eusa_clap:
 
#16 · (Edited)
I don 't think a lot people understand how much force you are talking about, think about it this way. Imagine 35 pounds of weight and on your hand. Now imagine 50 pounds of weight on your hand (or do it if you choose) Imagine the difference there. That is what your tire is doing in every square inch. Say (for giggles) the tire is 8 inches wide and 48 inches around.

8X48= 384 square inches
384X35PSI=13,440 pounds of pressure in that tire
384X50PSI+19,200 pounds of pressure in that tire

Starting to get it? and that is just the tread size, that same pressure is on the sidewall at the same PSI so the numbers are actually even higher than that. There is A LOT of potential energy in an inflated tire
 
#21 ·
I'd be careful about running tires at the car manufactor's recommended tire pressure, especially if it's below 30 PSI. Remember the Ford Explorer/Firestone tire fiasco back in 2000. Firestone at one point came out and publicly said that running their tires on the Ford Explorer at the door placard pressure was so severly underinflating the tires that four adults in the vehicle would exceed the tire's safety buffer. Ford wanted you to run the tires low to reduce the chance of a rollover because the overall design of the vehicle was unstable. Overview of The Crisis: Firestone Tire Recall-Ford Explorer
 
#22 ·
I'd be careful about running tires at the car manufactor's recommended tire pressure, especially if it's below 30 PSI. Remember the Ford Explorer/Firestone tire fiasco back in 2000. Firestone at one point came out and publicly said that running their tires on the Ford Explorer at the door placard pressure was so severly underinflating the tires that four adults in the vehicle would exceed the tire's safety buffer. Ford wanted you to run the tires low to reduce the chance of a rollover because the overall design of the vehicle was unstable. Overview of The Crisis: Firestone Tire Recall-Ford Explorer
I actually said this same thing in my long "rant" back on page 1, lol.

It is not safe to go down 5psi from what is recommended. Did we not learn a thing from the Ford/Firestone recall? The culprit was tire failure due to too low of a pressure. What did they recommend? Somewhere between 26-28psi initially. Ford released an official statement recommending an increase to 32psi, which is a 6psi difference, but enough to reduce heat generated by a great deal of rolling resistance.
But nonetheless, I agree completely. What's on the door placard is a suggested pressure.
 
#25 ·
The largest cause of rolling resistance is sidewall flex. Higher PSI = less sidewall flex.
 
#28 ·
Pure nitrogen has all the water vapor removed. Water vapor supposedly causes corrosion on the wheels. Also, pure nitrogen has been reported to not change pressure as much as a result of temperature, but I'm not sure how that works, since temperature changes are what drive pressure changes in a gas and the temperature inside the tire is driven by external factors such a solar radiation (2-4 lbs PSI from sun to shade) and the friction generated by sidewall flexing.
 
#29 ·
Wow...some major misinformation in this thread. I agree that a higher tire PSI will increase MPG to a degree but will decrease the treadlife due to overinflation, depending on how high you go on PSI. You can go about 5-8 PSI over the manufacturers recommended PSI and have minimal impact on tire treadlife. I have REAL LIFE experience as an ASE Master Tech working for GM and Toyota. I have probably replaced hundreds of tires that have had severley worn center tread due to overinflation. Each vehicle is different (vehicle weight, tire size, load distribution, etc) so the max PSI that will start to negatively impact treadlife on our Cruzes could be 42 PSI or higher. Real world results will obviously tell us. I would recommend measuring the tread depth on your tires every 3,500 miles to determine if they are wearing uneven. Check the tread depth with a tire tread depth gauge (available at most auto supply stores) on the edge of the tread and in the center of the tread. They should be close to the same measurement across the entire width of the tire.
 
#30 · (Edited)
Here we go again. Another person telling me there's misinformation. Did you actually read the entire thread, or did you read the first couple of posts and skip past the second two pages? If you did (which I'm guessing you did) go back and read everything.

I have real life experience as a car driver. I've driven nearly 500,000 miles over several cars and have never had a single case of uneven tire wear. What exactly does your ASE master tech certification have to do with this? Did you go to college to learn to design tires? I had a ASE Certified Master Technician service the wheel hubs on my Bonneville GXP at a Cadillac dealership and throw the old wheel hubs on my rims, leaving several gashes that the dealership refused to take responsibility for, so excuse me if your title means nothing to me. I've had more bad experiences than good ones with ASE Certified Master Technicians.

Over-inflation is not the only cause of center tire wear as I'm sure you can acknowledge. Other factors come into play such as whether or not people rotate their tires.

Could be 42psi or higher? It's painfully obvious there's no straight answer here.

Now, real world testing will tell us, I agree with that. The truth is that people have done real world tests - search the cleanmpg forums for "tire pressure and you'll get more information than you have time to read. A particular thread on that forums has infinitely more people who get MORE life out of their tires than others who did not inflate their tires to maximum sidewall with perfectly even wear. Some will claim theirs wore unevenly, but most claim theirs didn't. What can we conclude from that? That tire pressure is not necessarily the deciding factor in tire wear.

However, I will be measuring the tread depth of my tires periodically miles and I recommend that everyone else do the same.

I fully expect rear tires to wear unevenly if they are never rotated, which it seems over 75% of people fail to do. I also fully expect the front tires to wear unevenly on the shoulders if they are never rotated. 3,000 miles is way too soon to be testing this theory if people only rotate their tires every 10,000 miles. Otherwise, there would be no point to rotating your tires!

The rear tires will wear unevenly due to the tread design; its not 100% flat from the factory for a reason. The front tires will wear unevenly with additional wear on the edges due to wear during turning and changes in camber during those turns. If you never rotate your tires, you'll have shoulders worn unevenly on the front and centers worn unevenly on the rear, whether your tires are at 30psi or at 50psi.

I'm not suggesting that everyone inflate their tires to max sidewall. People are free to do what they want to and it is entirely up to them to determine what tire pressure works for them. I'm simply clarifying some real misconceptions people have from stories long ago told by old people who used bias ply tires and think that radial tires function in the same way.

I will personally be testing and reporting the tread depth of my tires and the mileage at which they were rotated every 3,000 miles. I'm running out today to pick up a tire gauge.
 
This post has been deleted
#43 ·
GM recommends changing every 7,500 miles. To make it easier to remember, I change my oil and rotate tires every 5,000 miles.
 
#44 · (Edited)
With the way oil is going longer i would recomend tire rotation every oil chang and check tire pressure regularly

h3llion
 
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#47 ·
I find it interesting that Goodyear gives contradictory answers about tire pressure at Goodyear: U.S. Government Sales - Police Tires. Questions 2 and 3 both hedge their answers - 2 stating that inflating past the door placard "could" have negative impacts on the ride and wear and question 3 stating that higher pressures "may" improve fuel economy. Sounds to me like the tire companies (at least Goodyear) know the answer but their lawyers won't let them say it publicly for fear of lawsuits by the car manufacturers and consumers.
 
#50 ·
Haha got to love onstar

h3llion
 
#51 ·
Just filled up and got my best MPG ever...524 miles on a tank. 38.45MPG 60/40 City/Hwy split.
The DIC shows my driving (hot) tire pressure to be 34-36psi.
On this new tank, I am going to run the pressure up to about 40 and see if I can break 40MPG.....we'll see!
 
#53 · (Edited)
I don't think the police cars come outfitted with the light bars and such, but even if they come fully assembled at 4158Lb curb weight I'd bet there is at least 500 pounds more weight when you figure in an officer(s) with his equipment, weapons, ammo, bullet proof vest(s), radio, computer, fuel...blah blah blah. Their RS-A tires also have a different load range then standard RS-A's.

So anyway if cleanmpgforums.com AND officer.com are in agreement than I guess it is truly a conspiracy of lies coming from the tire engineers. I stand corrected.

I think we can both sit here and pull info off the web that supports our ideas, **** i can probably find one that says you can make your car float with enough air pressure so there is no point to arguing anymore.
 
#54 ·
If I recall, it was you posting links such as that popularmechanics link. Even the manufacturers themselves beat around the answer, saying "may, could, can, etc" because they know what the truth is but their lawyers won't let them say it for liability reasons.

I do think there would be 500 pounds more you can figure in, but not a whole lot more, and if there is, its in the trunk, not in the engine bay. They do use the same Goodyear Eagle RS-As we can buy. The fact is simple: they run maximum sidewall pressure on the front and rear, even though the front of the car weighs about the same. Even if you argued 500 pounds of difference, you'd be arguing about just slightly over 10% for the sake of telling me that max tire pressure isn't a good idea.

Cleanmpg.com forums, officer.com, and you can add ecomodder.com to your list as well. Conspiracy of lies? Nah, its not a conspiracy. Its a matter of liability, money, and comfort. If they told everyone to run max sidewall pressure and some idiot with 10 year old tires ran max sidewall and had the tire explode for absolutely no consequence of the pressure but rather due to dry rot, there would be lawsuits. Why would they tell you to get 1.5-2x the life out of your tires when they could instead sell you a new set? How many people do you think would buy a Cruze if GM filled up tire pressures on them 8psi over what they're previously recommend and everyone complained about the stiff ride?

The difference is I'm pulling information from qualified sources that have no potential gain. Places like NHTSA and Officer.com. If you want to argue, count me out. If you want to have a debate, don't bring biased sources like tire manufacturers, severely unqualified sources like random journalists, and idiotic tests like the one popularmechanics did to back up your point, at least for debate purposes.

For recommendation purposes, I continue to leave it to each car owner to make their own decisions.
 
#55 ·
Qualified sources huh, alright then. Maybe NHTSA if they spread their testing out over more vehicles and more conditions, but I fail to see how any of the other places you mentioned are more qualified than you or me or anyone that can post in an online forum. You have no idea who is behind the keyboard. And I agree if you want to run your tires at 50PSI have at it, but I will guarantee you will be replacing them sooner.
 
#56 · (Edited)
Yeah, I consider a police Sergeant on a forum that can only be registered by actual policemen to be more qualified than some random journalist for a news reporter who just re-phrases what someone else said. I do consider NHTSA to be more qualified than any sources that have been provided here. Their primary concern is safety, and they demonstrated that tire pressure has, for all intents and purposes, no real effect on traction.

You're right, I have no idea who is behind a keyboard, which is why I've tried to find sources that remove some of that ambiguity. Again, Officer.com and NHTSA, not NBC news or popularmechanics, a for-profit magazine.

I'll be replacing them sooner? Perhaps you didn't read the tidbit where I stated I'll be measuring tire depth. I actually bought a tire depth gauge and decided it was inadequate for my purposes so I went on amazon and dropped another $26 on a real one:

Amazon.com: Central Tools 3S401 Digital Tire Tread Depth Gage: Automotive

I'll be rotating every 3500 and will measure the tread depth for your convenience. So far, the reports on cleanmpg forums are in favor of inflating tires to max sidewall to reduce rolling resistance and consequently reduce wear.

I'll be here to eat my words and stand corrected throughout my reporting process on my tread depth should they wear unevenly and give me less mileage than what others are getting on their Cruze Eco. Will you do the same? For as strongly as you're arguing a point with no non-biased or reasonably qualified sources, I sure hope so. I hope you're as ready to be proven wrong as I am.

I invite you to purchase the same tire depth gauge and report your own measurements.
 
#57 ·
Wow, $26 for a tread depth gauge, that is some serious dedication. I'm probably not going to have my ECO tires very much longer But I will do a little demonstration for you if I have time Friday or Saturday, and show you exactly what I mean. I'd say I'll be eagerly awaiting your results but probably by sometime in the next couple of days I will have lost interest.
 
#58 · (Edited)
I wouldn't have bought it if I didn't believe it would be necessary to provide valid results, and I think the answer to this question is pretty important. I want to have zero room for error here and a reliable tire depth gauge is pretty important. I need to measure more than just 1/32".

My results will be continually reported for the next 2 years at least. I'll create a new thread for this once the tire gauge is delivered.

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