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I was wondering what is the highest safe air pressure?

It depends on the tire and what you mean by safe.

But generaly 100psi is where you should start getting nervous.

By then I'm sure you will get a bunch of distortion on the tire so you wouldn't want to run anywhere near that high since there realy is no benefit to it.

Just a guess, but before it gets hazardous, uneven wear is probably an issue.

:Banane37: Well here is my 2-Cents on tire pressure as if this has not been discussed many times in the past on multiple

Forums. Makes no difference though the question has been asked so here is my response.

My original tires on my HCH II at the Sidewall says,

{44 psi Maximum Tire Pressure}

So I have decided that if the Manufacture says this is the (Maximum) I will go with it and not ever give it another thought. :)

Now that is what I have decided. There are a great many Hypermilers that choose to run their tire pressures at 60 psi to I think 70psi. I have not read in any Forum about even {1-Blow-Out} from them running higher tire pressures. So I think it just comes down to a "Personal-Choice" on what an owner feels comfortable with.

I think one of the differences that owners have commented on with running higher tire pressures is the "Ride-Quality" becomes much Harsher/Firmer with the increased tire pressures. Other than that one thing being mentioned I have not really heard or read any other negative comments revolving around running the higher tire pressures.

Terry (tiger)

I'm going to go with the engineers on this one, and say that max sidewall is the maximum cold pressure that you can run with the intended safety margin. I'm quite sure that you could run 150% of that and be fine most of the time, but that's not what the designers intended.

Harsh ride also means harder on the suspension. So if you have bumpy roads you might think you can handle it, but you should be aware that you may be shortening the life of your suspension. That's a decision you have to make. Also in the snow traction suffers and i believe stopping in the snow suffers.

As far as the intended saftey magin goes. I don't think thats 100% true. no one said the max sidewall pressure had anything to do with saftey. It could be some law or other factors such as load rating or something. Why do most models of tires have the same number? It can't be because all tires have the same failure points.

Next time I talk to one of the engineers I'll ask them to clarify.

The benefits of heightened sidewall pressures are noticeable, however, one must consider what is riding on those tires.

If you have a small runabout that you use to commute solo to and from work on low(er) speed roads, higher sidewall pressures are acceptable. Carting the family around with the possibility of a blowout? Doesn't seem worth the extra MPGs.

Just my $.02. If the tire says XXpsi, stick with it.

Actualy higher pressures are better and will likely reduce the chance of a blowout under higher load.

If you have a lot of weight in your car you chances of a blow out are GREATER at LOWER psi than higher psi.

Or as the engineers say "load capacity increases with PSI" Nothing wrong with being at max sidewall if thats all you feel safe with. Just remember that you are putting your family in danger if the PSI gets TOO LOW.

For those of you that drive a fully loaded car to get air in before a trip and only put in the psi that the factory recomends (such as 32 or 36 or whatever) that that number is the COLD rating so since air expands when it gets hot you are actualy putting in LESS air than the manufacturer recomends and are running on an underinflated tire. VERY DANGEROUS. Check the tire pressure before the car has been moving and before the sun heats up the tires. Thats when they should read at least what the manufacture recomends. When you get to the pump at the gas station I can gaurantee the PSI has gone up and thats not a bad thing.

So remember the rating is COLD rating. So measure your tires when they are COLD or you will definatly be underinflating them if you fill to the manufacturers recomended PSI when they are WARM.

Bahh.. Enough babbling from me. Just trying to clear some misconceptions.

Since this is in regards to an Insight, only two will be in the car. ;)

Actualy higher pressures are better and will likely reduce the chance of a blowout under higher load . . .

I couldn't agree more - I run my Taurus at max sidewall (44 PSI) which expands to roughly 46/48 PSI on the roads. 30's are way too low for the tires we're talking about to be run at.

However, 60 PSI? In the heat of a FL summer, I might be leery to make an extended commute with twisties and some high(er) speeds involved. Recall that I speak from the position of a mid-sized vehicle driven as FE as possible.

Anyone in the hot climates run high PSI (55+) that can comment on any of this?

60 in the summer in florida may be a bit high ;) Your right about that. Figure a 1psi increase per 10F. So if it is 70f when you fill them to 60psi they would be 63PSI when they get all warmed up. It probably won't be a big deal, but after about 45psi the return you get starts to level off. I don't know too many people that run 60 or 70psi. Maybe 2 or three ;) Max sidewall is what I would recomend most of the time unless you are going for every bit of FE.

Here is my two cents:

I jumped to 40psi right away when I noticed that it came from the factory that way. The tires (one or two) were dropping psi to fast for me and I cranked them to 44psi (Max Side Wall). Notice a nice jump in MPG and kept them there.

Later, had a damaged tire replaced and told Goodyear to make sure they put all tires at 44psi. Notice my MPG was better, and when I check the pressure, they were above 50psi.

Pushing my 2,500 pound boat back in the garage takes two people at a running start with the tires at Max SW, 50psi to reach the speed it takes to clear the lip on the floor. If my tire pressure drops below 45psi, it take three people to roll up that inch or so lip. Below 40psi, forget it, I pump the two tires up.

Bottom line, 52psi is the most I push my tires too.

GaryG

This stuff should be so simple, and yet is the subject of raging
and continual debate across every forum I've hung out on. At
least over *here* we agree that MPG is important...
.
I've got a gorgeous picture down at the end of
http://techno-fandom.org/~hobbit/cars/tpms/
which shows exactly what happens to Prius tire run at
Toyota's, uh, "recommended" pressure. Blow up the big
version and take a close look at that sucker; that should
clear up a lot of misconceptions.
.
_H*

Great post and compleately wrong.

If someone wants to feel safe then the best thing for them is ignorance.

We have talked to the engineers. We aren't talking about personal opinion. We are talking facts. It is far more dangerous to be 5psi under inflated vs 20psi over.

As far as car manufacturers knowing what is best. Um. remember the Ford/Firestone fiasco? Humm. I think the lawsuits kind of proved that saftey isn't always the bigest concern for auto manufacturers.

So Terry, It's not about being elitist. Do you call a teach an elitist because he researches and tells the student something that differs from what he thinks is right and doesnt say to the student "if you feel comfortable with that answer I guess we can call it correct." Of course not.

If people don't want to know the facts then they can just go to some fluff site that will pat them on the back and say "good for you." I don't want sound like I'm not happy for guests to visit and for people to join us, but they have to realize that we are very serious about this subject and don't just take for granted what we are told. We check our facts, talk to engineers and manufacturers. Research some more. Discuss. And constantly test to make sure what we believe to be fact is fact.

Did you see the picture in the link hobbit posted? Is that just "guess work" Did he just imagine that? Hey, did you read the part where he said the tires were at factory specs?

Did you know the chance of hydroplaneing goes down with higher PSI? Most people think the opposite. Go read some of the material on proper tire inflation from the major tire manufacturers. It's all documented. I think intellegent people will know that cleanmpg's sole purpose is to educate them. Cleanmpg isn't out to pander to people and make them feel good. There are many self help groups for that.

Again, what we say about PSI is not ambiguous. It is not guess work or what we "feel". It is researched information. Information gathered by talking to engineers, testing, and validating the results.

If we were out to try to get everyone over max sidewall pressure we wouldn't tell them about the negatives. We do. I think you will be hard pressed to find a thread on here discussing the matter that doesn't mention the negatives more than a few times.

I run my Prius II tires (original OEM tires) at 52F/50R and have gone as high as 58 F/56R with no problems except for a harsh ride. I would say anything up to 60 PSI is fine unless your tires are getting very thin and then maybe 50 should be the max. If you want a comfy ride go for the manufacturers recommendation, but your FE will suffer. Wayne has suggested (and I agree) increasing by 5 PSI from where you are, wait a week to adjust, then if it seems ok, try 5 PSI more until the ride becomes too firm or you reach 50 PSI, above that the gains are pretty negligible, I personally wouldn't go over 60 PSI, but it probably wouldn't be unsafe until about 88 PSI or so, I certainly wouln't drive around with my family at 88, but 58 is ok for me.

Dennis

Terry

You made a good point in that post and I'm not one to say it was wrong. Safety is a big concern, and liability must be addressed.

GaryG

I have a 05 Chevy Cobalt Ls when i got new tires put on they put 32psi for the tires. I drove around for a week an thought my car was doing good like mpg,handling,an so on. I tried 40psi wow my mpg went up an it handled way better. Its a little rough but thats fine with me.

I had the tires on my Civic at 50 psi for the trip I made to the marathon. I droped them back down to max side wall the very next day.

The ride gets way to harsh and the car skitters over expansion joints and ripples in the road on cloverleafs and other turns at hwy speeds.

Psyshack,

You would have the Insight ride. In addition to feeling everything on the road, the grated concrete highways can make the car feel as though a wheel has loose lug nuts and is about to fall off.

Has anyone ever found a documented case of a blowout due to overinflation?

I've heard a story from someone online that claimed to work at a tire place.

It is hard to say if a tire blows from high PSI or from other factors. It is possible the tire blew because it hit a nail or something that would have blew even a normaly inflated tire.

I've never heard of a tire blown just sitting there or driving normaly. I've hit my fair share of pot holes and haven't blown any. And with my stiffer aftermarket suspension the tire is taking a bigger beating than it would on a nice soft suspension.

We talk about high PSI a lot and no one has ever said "I tried that but my tire blew." I've only heard anecdotal comments.

How many miles have we driven with high PSI? I've probaly got about 15K miles (I'm a relative newbie to hi PSI) I know wayne has a lot more than that, and I'm sure you and others do as well. Maybe we need to count the number of miles so we can say as fact "xxx miles on high psi without a blow out."

Here is a thought - underinflated off road tires rob even more fuel economy.

My tires are supposed to be inflated to 32 psi.
Max tire pressure on the tire says 35 psi
When I pushed it to 40 psi, I noticed the car wanted to veer off the road in the corners.
Later my tires began to have an odd wobble to them. I later found a blister on one of them that was raised a good 1/4 " and several inches long.
I stay at 35 now.

An important point that I should add is that these were cheap Wal-Mart tires. Even at the proper pressure, they look low . So... if you are going to put your life and others at risk ... don't buy the cheap tires !!

Stay safe !

Yeah. If you are seeing that the tires don't like more than max sidewall pressure then it is a good idea not to go higher than it. I hope people use common sense. And if they see things like you saw they would lower the psi to max sidewall.

I've heard that Pirelli (sp) is working on Active Tire Pressure Management. It's a system that will adjust the air pressure.

My tires are supposed to be inflated to 32 psi.
Max tire pressure on the tire says 35 psi
When I pushed it to 40 psi, I noticed the car wanted to veer off the road in the corners.
Later my tires began to have an odd wobble to them. I later found a blister on one of them that was raised a good 1/4 " and several inches long.
I stay at 35 now.

An important point that I should add is that these were cheap Wal-Mart tires. Even at the proper pressure, they look low . So... if you are going to put your life and others at risk ... don't buy the cheap tires !!

Stay safe !

I was just reading your Post here and notice you do-not have what kind of vehicle you own.

You did the correct thing when you saw the Blister on your tire and then adjusted the tire pressure to a lower level.

Speaking of Wall-Mart and tires. Many of the people I work with have bought their tires at a Super-Wall-Mart here and have not had the 1st problem with them. Also I don't know if many people know this but Wall-Mart has more expensive tires like Michelin if one wants the better tires. Their price even on these Michelin Tires is still very competitive.

tiger

Anyone in the hot climates run high PSI (55+) that can comment on any of this?

i ran at 60 + psi in the summer, all i can say is, if I had the power I'd push for higher but it seems after 60 psi the air compressor (gas station) doesn't want to give air no more! must be a "safety" feature hehe ;)

no problems, although I did notice bumps on the side of my tires, right now I run my 03 prius with 44 psi for all tires (2 front bias) and my previous car I did corner quite hard, I won't be doing that with the prius since hehe... its limits are easily reached.

I've been running 55 to 60psi in my Michelin Harmony tires year round here in South Carolina with no problems. My tires are one size over OEM size and they handle better at the higher pressures than they do when the psi is in the 30's and 40's.

no problems, although I did notice bumps on the side

60 is the highest I've heard -- I try to run 45-50 cold in my Michelin MXV4s.

The bulging you mention may be broken steel belts, maybe from popping a curb or hitting a good sized bump at high pressures.

50/cold works well in the Winter for me, but in the warmer months, I recommend driving on the highway (or similar) to heat-up the tires before adding air -- otherwise as the heat rises, so does the temp.

Also monitor treadwear. If there's too much wear in the middle of the tire, back it off 5-lb.

I'll admit there's a higher risk of tire failure from a road hazard, due to higher pressures, but that seems to be minimal, and not significant enough to outweigh the benefits of better FE.

RH77

At higher pressures the tire doesn't warm up as much on the highway as lower pressure. It is pretty arbitrary when you over inflate so getting them warmed up realy won't make a difference in the amount of air you put in. If it is 50 or 52 it realy doesn't make much of a difference.

2001 Prius purchased new. For the first 10k miles I used Toyota's recommendation (35/33) for the OEM Bridgestone Potenza P92 tires; max sidewall rated at 50 psi. By about then I was observing excessive wear on the tire edges and was reading the (now very old) Prius groups where some people suggested higher pressures. I experimented with higher pressures and made many detailed measurements of tread depth wear. Settled on 42/40 to give even tread wear. I changed those tires at about 33k miles for...

Goodyear Allegra in the stock size 175/65R14. These had a lower load rating than the Potenzas, which is a whole 'nother controversy. Their sidewall max was 44 psi and again, by repeated tread depth measures, settled on 42/40 for even tread wear. They never gave me any problem either (besides a glass cut flat) and I ran them for about 45k miles. Note that in both cases I changed tires with still about 4 mm tread depth because I had read that there is substantially reduced wet traction at the US legal minimum.

Next, the current tires are Nokian i3 185/65R14XL. These are monsters by Prius standards, with way excessive load capacity. That was an intentional choice because I wanted to be able to use much lower pressures for unpaved 'roads' and still have a reasonable amount of load capacity. I am into these tires by only about 17k miles so far, but am tending towards running them (on pavement) at 48/44 psi out of a sidewall max of 51. As always I am hunting for the most even tread wear. Frequent tire rotations with the 'deepest' tire moving to the 'fastest-wearing' position, which happens in Prius to be left front. If you really watch things closely, you can keep all tires equal to with 0.5 mm of tread depth. I depth-check and rotate tires more frequently than anything else, except for underbody inspections at the same time.

Related to this topic: For all three kinds of tires I have run them at or slightly exceeding their max sidewall rating, at least for a while. I have watched all extremely closely, and have seen no indication that pressures around the sidewall max are endangering me. Indeed, this are just about the only way to achieve even tread wear with Prius. I have no indication that this degree of 'overinflation' causes excessive center tread wear, even though 'soft-tire' people talk about that a lot.

No experience with going vastly higher than the sidewall pressures. Supposedly at 80-90 psi there is a possibility of wheel failure. And just to throw another idea out there, someday somebody ought to try a fuel economy run with 4 limited service spares at about 80 psi. Those things have pretty small contact patches, suggesting low rolling resistance. It would look funny though.

DAS

Tochatihu. I wonder if there are any rules in tour de sol about using 4 limited service spares. They are after all oem equipment.

Or for that mater even just using one.

Hahaha, that's right, full OEM. Just saying that I'm curious about this; the real hypermilers are too sensible to drive a car on 4 donuts...

Right?