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.
You didn't seriously post the popularmechanics article, did you?
Lets start with the popular(stupid)mechanics link. I'll just quote myself since I already went over this one before.
I debunked that debunk back in my other thread for the airbox mod. If you follow their link to the popularmechanics magazine link, its complete, utter bullshit. Its amazing how little critical thinking ability people have.
Debunking a Mileage Myth: Can You Really "Pump Up" Your Fuel Economy? - Popular Mechanics
I'll outline it for you. In order to test a difference in fuel economy, you need to re-create the conditions identically. They failed to do this.
They took an 800 mile round trip with their Honda Fit from LA to Phoenix, AZ. Going to Phoenix, they had tires at 45psi for that trip and got 42.19mpg.
TWO DAYS LATER, not even the same day, they drove back to LA and used tire pressure at 32psi. They noted 42.14mpg.
What are the flaws here?
First of all, they went in two entirely different directions. They didn't make two round trips, they made two trips. Having driven that route before, I can tell you that there is a significant climb through a windy (as in, many turns) road in the mountains/canyons getting into Arizona. That would have reduced their fuel economy going to Arizona and increased it going back. They also didn't account for wind speed or record it to make sure there was or wasn't any. It is more than likely that there was some kind of wind and either it blew in the same direction for both drives or it changed after two days. In addition, temperature changes would have affected their fuel economy given a two day difference.
They didn't note the time of departure from either location and whether or not they hit any traffic. If you've ever driven out of LA like I have a dozen times, you'll know exactly why I make a point of this. They are also wrong in saying that the vehicle's handling is compromised; quite the contrary, it is improved due to less sidewall flex and roll. Your car becomes more responsive and predictable.
This is why I don't trust for-profit magazines to report anything accurately or correctly. Another thing: they also over-inflated the tires beyond the max sidewall rating by 1psi. Its only 1psi, but still. In all their wisdom, they should have known better.
Popularmechanics: 0
XtremeRevolution: 1
Check your sources before you post them and think more critically. Not everyone who agrees with you is correct. I'm not trying to be rude; in fact, I've learned this the hard way a few too many times.
I won't go through all of the links because:
1. for-profit magazines that get paid to say what they do
2. people who don't know jack and just go based off what the above people wrote
I do however go based off of what people actually experience. One of my biggest sources is the cleanmpg.com forums. I'll get to that later.
I have a friend who works at Firestone, and has for about 8 years now. That doesn't mean he knows a **** thing about tires. In fact, all he really knows how to do is read their brochures and install the tires as specified by his manager. Your point about working in the tire industry is, well, useless to me and useless for an argument's sake.
Tires are not overinflated if they are run at the maximum sidewall. They are run within the tire manufacturer's safe specifications, and that is a cold pressure. They are overinflated if they exceed the maximum sidewall pressure. What GM recommends is a suggestion as a best compromise. If you increase tire pressure, you will gain fuel economy but you will lose ride quality and that's a given.
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.
Spring rate of a car going over bumps remains marginally and insignificantly affected; that's what we have shock absorbers for. I've had my tires at 50psi for about 2 weeks now and there is a very marginal difference in how the car handles. The Cruze Eco LRR tires are stiff enough as it is. Increasing that tire pressure just makes those little bumps and road variations a little easier to feel.
With regard to wear rate, you're confusing bias-ply tires with radial tires. In fact, everyone who has "over-inflated" their tires to maximum sidewall on cleanmpg.com have an entirely different problem; its not that their tires wear unevenly, its that they wear perfectly evenly and last
too long. Too long as in, they're 80k miles into their all-season tires with almost half of their tread life remaining and they have to replace them due to dry rot, not wear. Go to cleanmpg.com, go to the forums section, and search for "tire pressure." You'll get the idea after the 30th page of reading through threads. The reason for this is how our tires are designed. These are
radial tires, not
bias-ply tires. What's the difference? You can google this till you're blue in the face, but I'll sum it up; radial tires have a separated sidewall and tread so that when you inflate them, the tread maintains its uniformity regardless of pressure, up to a point of course, which is usually about 2x that of the maximum sidewall pressure. I'll repeat this, radial tires, when rotated will not wear unevenly regardless of tire pressure, so long as that tire pressure is kept between at least 25psi and the maximum sidewall pressure.
Why do I not trust your sources? Because it has been demonstrated
repeatedly that tires last longer on both ecomodder.com and cleanmpg.com forums when they are inflated to the maximum sidewall pressure compared to the manufacturer suggested pressure. It is in the best interest of every tire maker to keep you from getting 1.5x the life out of your tires than the tires are rated for. If I ran a tire shop, it would be bad for business. Why would I want you to go 60-80k miles on your tires when I could fill them to GM's spec and have you come back in for a new set at 40-50k? Think about that for a second. How many people have actually inflated their tires to max sidewall, rotated them regularly, and come back to you and said "****, these tires didn't last me at all, I guess I should have kept the tire pressure at the manufacturer recommended spec."
Start reading critically. In your first article, the following line can be found: "and could result in uneven tire wear." Key word there is "could," not "will certainly", not "will definitely", but "could." Why did they use "could?" Because they're not sure and because it doesn't apply to all tires. See: bias-ply vs radial.
Since I really do get tired of repeating what I've said over and over and over again, start reading this thread from that page onward, and let me know if you have any questions. You can also find similar information in my "how to get better fuel economy" thread. Both of these can be found in my signature.
http://www.cruzetalk.com/forum/57-how-forum/5479-how-bypass-intake-resonator-8.html
NHTSA tested stopping distance from 60-0. It can be concluded from this that the stopping distance is insignificantly affected (if at all) by tire pressure. You'll see that in
one of 4 conditions, you have a 2.2% deviation, which, while consistent, can be written off as expected error. In either case, if we are to assume that the difference is linear, we will have a 2.2% reduction in stopping distance going from 35-50psi. In layman's terms, it will be insignificant. Increasing from 35 to 50psi is the same increase in tire pressure, but the difference in lost surface contact will be less than when going from 20-35psi.
[SIZE=+1]Table III-8[/SIZE]
Braking Distance (in feet) from NHTSA testing
Stopping Distance from 60 mph
| Surface | 15 psi | 20 psi | 25 psi | 30 psi | 35 psi |
|---|
| Wet Concrete | 148.8 | 147.5 | 145.9 | 144.3 | 146.5 |
| Dry Concrete | 142.0 | 143.0 | 140.5 | 140.4 | 139.8 |
| Wet Asphalt | 158.5 | 158.6 | 162.6 | 161.2 | 158.0 |
| Dry Asphalt | 144.0 | 143.9 | 146.5 | 148.2 | 144.0 |
The above chart proves that the following article is full of BS:
Over-inflating tires is not a gas-saving move | Consumer News | Seattle News, Weather, Sports, Breaking News | KOMO News
Who are you going to trust? NHTSA or komonews.com, an article written by a journalist? Also in the wet, you're going to skid a lot easier if you have to slam the brakes on in a panic stop." Wait, you mean thinner tires don't dig through water and prevent you from hydroplaning? What school of engineering did Herb study at? Oh, right, he's a journalist.
Moving on:
Tire Pressure - Cars.com
Your tires will not bounce on the road. They will stay planted because you have shock absorbers. Increasing your tire pressure does not cause the tire to "bounce around" as if your shocks are blown. Bad information, unless your shocks are on their way out. These are another group of people who claim your stopping distances are affected. See NHTSA testing above. You decrease contact area slightly, but you increase pressure per square inch.
Michelin tire site = biased
Good year tire site = biased
Whenever a tire manufacturer has something to gain from giving you a piece of information, they're biased. I shouldn't have to sit here and argue that in business in the US, its about the money, not about what's best for the American people. I won't count how many times this has been proven. Long gone are the days when a company will act in your best interest and not in the interest of their stock price and profit margin.
Tuffy Auto Service sells tires = biased
Moving on:
Save Money On Gas: Avoid These 12 Gas Saving Myths - Saving Advice
^ No need to repost, they clearly state their information is taken from edmunds.com.
Moving on:
Edmunds Employees Put to the Tire Pressure Test - Edmunds.com
How was this test performed? I'm not seeing any data here with regard to "over-inflation." All I see is "When a tire is overinflated, the contact patch is reduced and the center of the tire tread wears faster than the outer edges." Again radial vs bias-ply. Not the same tire. I am appalled at how many people don't realize tire technology has changed in the past 50 years.
So far, the articles you posted haven't proven anything except that people still have no clue how radial tires work and they think we're still using bias-ply tires, and that they're pulling numbers or "facts" out of thin air, perhaps from someone else's article who was equally ill-informed. Until I find evidence by an agency such as the NHTSA proving that there is a notable difference in stopping distance based on tire pressure, I'm going to keep going back to the test results I posted a few times now.
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!
