Incorrect Information re: Tire Pressure in Efficiency Mods
 

I'd asked the webmaster twice to take down this misleading information from the "65+ efficiency mods" section of the site and nothing has been done...

Increased tire pressure DOES NOT help wet traction, as a matter of fact it harms it. The fact is that you are increasing tire pressure to decrease your contact patch to decrease friction. Decreased friction equals less traction all around and would be particularly noticeable in the wet.

Your information is misleading and since the site also encourages people to maintain as much momentum as possible through turns, this can be dangerous to boot, making people think they have more grip than they really do.

Also, increased pressure will make the center of the tire wear faster, since this area is put in increased contact with the road. The center of most all-weather tires is critical in pumping water out from under the wheels and decreasing the tendency to hydroplane.

Please correct this. The information on this site should be based on science, not counterintuitive and fantastic claims.

I think we do a surprisingly good job of being scientific and accurate here. Part of being scientific is taking comments like yours seriously.

A smaller contact patch would improve contact with the road in standing water or snow, hence the "improved wet traction" claim. Perhaps it's just hydroplaning resistance and not wet traction? Dunno.

At first, I was apprehensive about inflating past the pressure recommended by the automaker. Now I inflate to sidewall max without a worry. I haven't had any issues with irregular wear. Here's a post from a member who carefully measured his tire wear and found they were wearing normally at sidewall max: http://ecomodder.com/forum/showthrea...les-12438.html

Where is your science to back up your argument?

I distinctly remember reading a paper that stated that increased pressure does in fact increase wet traction. I do not have the link handy, but I will look for it.

On some older tire designs center wear may be a problem. I personally have never had a problem with any tires I've used and I run over max sidewall pressure.

Maintaining momentum through turns is a good idea for saving gas. I see no reason to take that tip it down. Obviously taking turns at dangerous speeds is a hazzard. I think you better go post your message on every performance forum on the internet as they're much more likely to be taking turns at dangerous speeds than we are.

Quoted from NHTSA (Tire Pressure Monitoring Final Rule(Part III)), bolding is mine.

Taking the above to its logical conclusion, inflating tires higher than placard makes the contact patch even a bit smaller, which would not increase stopping distances.

24,000 miles rotated once.

This car was totalled and I had it repaired. The alignement has never been checked or adjusted.

I go around corners fast enough to discourage most tailgaters.

Original 8-93 front brake pads have 50% left.

No problem in wet weather, and I might drop the pressure in snow.

Contact patch size is reduced with higher pressures which places more weight per square inch on each square inch of contact patch.

If that is misinformation then show us we are wrong.

The 3 grooves in the attached photo measure .230 average with a variation within .005 inch!

regards
Mech

Tread measured .250 when installed.

regards
Mech

Yeah, while I agree that overinflation is not a good method of fuel savings, you wont win that argument here. Those that believe that running max sidewall is worthwhile outnumber those that believe otherwise.

I'm not clear if you're saying overinflation is the same as running max sidewall pressure. Would be interested to know the reasons why you believe running max sidewall ("overinflation"?) is not a good method of fuel savings.

Overinflation would be over the car's recommended value. It may be a good way of saving fuel, but it does pre-maturely wear tires (but I am sure that someone will say that it doesn't, as I said above this is a very tough argument.) It also causes suspension to wear prematurely as well as drivetrain, but once again someone will dispute that. I also believe (this is something that I know will be questioned, read previous post) that it does provide significant safety hazards under certain driving conditions. Argue away, like it has been in other posts and for the same reason that I told the OP that this may be the biggest waste of his time. I will keep my inflations within reason.

I run my tires higher than MFG recommends at 44PSI instead of 32 (max sidewall is 50PSI) . Last winter I did some tests on my weekly drives home from school. Higher pressures increases my wet and snow traction by a good margin (over 15% better traction). I also tested stopping distance on wet and icy roads. I found that higher PSI was about the same to slightly better stopping distances.

My tire wear is better than when I was at OEM PSI. at 15K miles on these tires and they still look new, wear is very even (better than at OEM).

When I worked at a major auto maker I liked to put this topic up for discussion. The people who did track testing and noise testing came up with the same resign for the OEM specks on tire pressure: ride comfort and noise.

The idea is that it is a balance between noise + comfort + wear + MPG + cornering + users not checking pressure = the OEM recommended pressure.

From what I have personally found and what these people talked about, tire noise increases quickly above about 35 PSI on most tires. Also, most car MFG's have noise limits for their cars at certain speeds. keeping tire pressure lower is a cheaper way of reducing noise so that other components do not need to be as well noise insulated (which is expensive).

When I look at the US DOT, they warn about under inflating tires but do not have any complaints about over inflation (until you pass max side wall).

It comes down to personally choice between ride comfort (both noise and bumps) and increased traction & MPG. I found the sweet spot for my car to be between 42 and 46PSI, any more and the ride gets worse and the MPG does not improve.

autoteach, Weather Spotter -

Good inputs, & I appreciate the civil discussion on this topic (unlike stuff that's been going on in other threads!). As others, I'll choose to do what I want, but like to have good information to base my decisions on. From the information I've read here, I'll continue to inflate over the manufacturer's recommendations; I've not seen strong enough data to change my mind on that. I have no beef with others that would rather not "over-inflate".

Clev pretty much summed it up.

As far as the negatives: Over-inflated tires will cause extra noise and a harsher ride, that much is certain. Most of us hypermilers don't drive fast so that helps reduce those two problems a lot. Having no any real data myself, I would still agree over-inflation probably causes increased wear on suspension and increases the possibility of being damaged by road hazards. Again, we drive slowly (compared to most people), deliberately, and attentively, reducing these problems.

Lastly, over-inflated tires will make it easier to spin your tires on dry pavement. So while it's easier to do a burnout, your 0-60 and 1/4 mile times will increase. Also not really much of a problem for us non-racers and ricers.

Feel free to continue to portray opinions as facts. The manufacturer uses many factors to determine their recommended pressures, and fuel economy and performance often take a backseat to comfort.

Well, I am not sure which portion you are calling opinion that is not fact. I work on plenty of cars (check the username) and I have seen the difference in inflation of 4psi effect wear pattern either way. Or was it my opinion that it saves fuel a misrepresentation of facts or opinions. Is it the suspension and drivetrain wear? The tires are an active part of the vehicles suspension, stiffening that portion causes wear at others, that is not an opinion. And I qualified my safety concerns as opinion.

I am being civil, and what I said to the OP is exactly what is occurring here as well as what has occurred on the numerous threads on this topic. There is about as many people on each side of the fence, and those that have weighed in before and were dismissed, or realized the futility of the situation, are probably going to sit this one out. I dont blame them. I suppose I should have sat it out and just let the OP get the onslaught without the explanation. This topic becomes a hostile environment, and I believe it to be more so those that feel they have been cheated out of fuel economy by the manufacturers rather than those that believe otherwise. I wont reply to this thread again, and not because I want to get the last word in, but because there is no other reply necessary for the OP to see that there is no way that he will ever convince ~50% of this population that the other ~50% of the population is correct (and it goes both ways).

My words of advice, inflate your tires to the pressures that you see fit. If you drive an suv, 32psi should be a minimum despite what the manufacturer says (ford). Live with the consequences of your inflation, be it + or - MPG, handling, tire wear, noise, or component failures. Learn from that, and don't try to share what you have learned from it because those that believe otherwise already know your full of **** ;)

Just the part that stated that exceeding the manufacturers' recommendations causes poor tire wear. That is by no means universal. In fact, I see far more uneven edge wear in "properly" inflated tires than in "overinflated" tires, especially in larger cars.

I really didn't realize this was such a touchy subject, or that argument had been going on elsewhere on the board. I'll keep it civil, but I do have a few responses.

Agreed, my point is that people will take turns faster than they ought to if they believe they have more grip than they really do.

Oh, ok, so taking that to its logical conclusion, having NO rubber on the road would not increase stopping distance, correct? The resource you cited was written during the Firestone fiasco, where the concern was underinflation. It's clearly only comparing underinflated tires to ones inflated to the placard pressure. You're applying a trend across a boundary (the placard pressure) and it's invalid.

I'd really like to hear how you arrived at that figure, because since opening this thread I have searched for a good study with a skidpad or drag strip and different tire pressures and found none.

Had you asked the people who design the suspensions I'm sure you would have gotten a different response. The tires act as a spring, and are designed into the suspension that way. You're also messing with the dynamic geometry of the tire while cornering, and I'm sure there's suspension designers that would not be pleased with that.

But that's one more vote for less traction.

The bottom line is that EM is responsible for what it puts on the site as fact and there is no proof that increasing tire pressure past the placard spec will increase traction. Just take it down already. I don't understand why EM would feel the need to say anything about wet traction anyway, many people here seem to feel it's a question better left to performance driving forums.

How I came up with my better wet and snow traction numbers:
Disclaimer: this was not a very scientific test.

Last winter on some wet and snowy days I went out and from speed tried stopping, I did it both with OEM psi and at 44 PSI. The higher PSI allowed me to press harder on the breaks without skidding, thus allowing me to stop sooner. I also tested start up traction by using my scangauge to see what rpm I started to spin.The OEM psi had me spinning sooner by about 10% than when the tires were at 44psi.

I will give you that this test is not that great, but with it and my driving I noticed a difference. It may not be the same on all cars.

About the suspension people, I did not ask them. The ride quality is based on the shocks and the tires ability to dampen bumps. I will grant that when cornering I am slightly changing the angel of the suspension. On my car I think this is a good thing (my OEM ties wore badly from cornering). Once again I think each car is different, which is why there is so much debate on the effects.

traction is a function of surface area and down force. Higher tire pressure results in a smaller contact patch but more weight per unit of area. Once again it is a balance.

I put up 100,000km on my last set of tires on my civic. They are currently retired in the shed with about 4mm left on them and it is quite even across the tread.
Re: traction. I gave up searching for scientific data on traction at elevated pressures. Stopping distances in the wet too for that matter.
I will say this though: If the wheels bounce under braking or cornering due to being so hard, braking is seriously compromised. I've experienced it and it's not pretty. Thats not to say braking is compromised in all other situations. On the contrary, i "feel" it is better, as is the general consensus here too. But i have yet to find ANY scientific data on that, other than the stuff the NHTSA did, but only up to 32psi if i remember correctly. Which is suspicious and smells like a conspiracy......
I'd love an accelerometer or something to measure it properly but alas, they are a little pricey.
I'd like to also add that inflating to sidewall from new will most likely result in centre wear as it has also happened to me also. Inflate normally for the first 500 miles then sidewall 'em. Well, thats what i did and it worked. My yaris was sidewalled from when i got it and i figure there was maybe 10,000 miles on them. That was at the end of 2008. They have had many more miles put on them and there is no centre wear.
So if the OP could provide data that shows a loss of traction, in the wet, at sidewall that would be great.

ollie

I tend to read owners manuals whenever I'm a passenger in someones car for a longer car ride, I've read alot of owners manuals and they tend to have this pattern that boils down to, If you have snow tires or are driving on the highway you should increase your tire pressure by 4psi to decrees tire wear, this is seems to be consistent among most of the owners manual I've read.
So in that aspect increasing your tire pressure by at least 4psi is fallowing the auto manufacturers recommendations.
There have also been a number of studies, like people have already posted links to, that boil down to say that going up to the designed pressure does help with traction and wear and no reviewed studies that have shown that you should lower your tire pressure.
If you have a study that says lower pressure for modern tires (not bias ply) is better then please tell us about it, if you worked on someone else's car and noticed that the tire wear was uneven then you need to give a detailed history of how many miles they put on those tires at what pressure under what conditions, high wear down the center could be because their tire pressure was to low, not to high, with radial tires the center of the tread has more support due to the how the tire is constructed so it doesn't cup and pull in like the older bias ply tires did when they were under inflated.

Different on wet and dry
 

On the wet:

Greater surface arear (broader tires or low infaltion) will reduce grip, as pressure pr sq inch are reduced.

Grip/traction are also very much down the the rubber compound. Soft rubber = more grip, and wears easy.

Higher inflation (providing good compund) will go through water better beacuse of pressure per sq inch are higher.

On the dry:
More surface arear = more grip - best is slicks. Boarder tire = more grip and traction, but also equals more rolling resistance.

Harder rubber compund = less wear and less grip

Higher pressure = less wear because the tires dosent flex as much, and therefore dosent build up as much heat.

Higher pressuer = more milage due to: lower rolling resistance, less flex, and a smaller contact arear.

Higher pressure migh lead to early wear out on the rubber bruches in the suspension on some cars, if they are not top quality, as the bruches are subjected to stronger forces.

Higher pressure = better cornering, as car dosent sway so much

Higher pressure = longer braking distances due to less contact surface, and on very uneven surfaces could lead to "jumping" which can further prolong brakingdistances as contact with the road are lost in the jumps.

I drive with 2.8 bar instead of the recommended 2 in my tires, and havent seen much negative effects, but if I go to 3 bar, the handling og the car goes bad op uneven surfaces, and braking distances are longer. Car also starts to Jump.

That last point I made was really speaking to well under-inflated tires, not those inflated according to spec. It's a practice often used by people drag racing with street tires. There's probably not much difference between over-inflated tires and normally inflated ones in this area.

There's also no proof that increasing tire pressure beyond placard decreases traction to any significant degree. If you're worried about traction so much, you're going to be running soft tires with poor rolling resistance anyway.

My tires wear substantially at the edges at placard pressure. This is the case on at least six vehicles that I've owned over the last 10 years, from my '99 Metro to my '85 F250. Since airing up the tires on my three vehicles to sidewall pressure on two cars and a truck, the tires are wearing much more evenly. Higher tire pressures have contributed to over $1,600 in fuel savings over the past 2 years, and my tires are lasting longer because I'm not throwing them away with bald shoulders and tread left in the centers. The suspensions on both cars are both still fine after 100,000 miles, so I guess I'm not concerned that I might have to prematurely spend a whole $200 on replacement struts for my Honda.

Please have a look at this article.
Driving Under Pressure (full article) - CleanMPG Forums

100 psi on Crown Vic tires on this Ford pickup:
http://i188.photobucket.com/albums/z...ressurePic.jpg

In years past I ran my tires at max sidewall. They always wore down at the edges of the tread. I now run them at max sidewall + 6-8 lb, which means 50-52 psi. Very even tire wear after 54,000 miles on this set of tires.

Before buying my Civic I drove Volvo 240 wagons for over ten years, about 25,000-30,000 miles a year during the last few years of that period. Mostly highway miles of course but not exclusively by any means. I inflated my tires to 32 and 35 psi which was max sidewall for those tires in those days.

Every time a tire wore out - and they did wear out, driving that many miles - it was always the edges that wore. Plenty tread in the middle, shoulders always worn. But I'd run them at sidewall pressure, which was actually a few psi more than the vehicle placard spec! So what's up?? Worn at the edges supposedly means under-inflation, right?

Exactly. Bought new car (Civic), got it new tires. I've run these tires at about 50-52 psi. since about a week after purchase. Max sidewall is 44. And I'm happy with it. Now I'm not suggesting anyone do that. This set now has 54,000 miles on them. The center tread is only about .001 inch deeper than the edges. So I'd say I've beaten the edge wear issue.

And what's more, I think I can lay to rest the bunkum about over-inflation causing wear at the center of the tread. I'd think that after 54,000 miles at 50+ psi, on tires with a max sidewall rating of 44 psi, the center tread would be gone if there were any truth at all to that concept.

Oh yes, the long running debate about traction and handling etc. I take corners and curves fast enough to scare some of my passengers. The tires haven't let go of the pavement yet. Fortunately my current (very occasional) car pool buddy is a pilot so he's used to feeling some G-force in a turn.

http://www.tirerack.com/images/tires...e_60_25_sm.jpg

Hydroplaning info here: Tire Tech Information - Air Pressure vs. Wet Performance

Be sure to read that part under the last pic about the tests at 'Michelin's Laurens Proving Grounds'.


I like the HydroEdge (44 sidewall max) tires and normally try to keep them at 40 PSI, as a compromise between comfort and MPG+Performance.
Had them on my CRV and loved them. My wife has them on her Corolla and we maintain them at 40 PSI.

If they go down a few PSI over the winter, they will still be pretty safe.
But, if they were at 'factory' pressures and got low.?. Dangerous IMHO.

My compressor gets a lot of use on other people's cars. The guy across the street, my sister-in-law & etc.
When I can easily see their tires are low, it's not a surprise to see the meter reading 15 to 20 PSI.
That's just asking for poor handling and wear..

Speaking of wear, Hypermilers over at CleanMPG Driving Under Pressure (full article) - CleanMPG Forums sometimes use pressures above sidewall.
My guess is almost all of them are using well above factory placard pressures.
But, I don't hear them talking about excessive tire wear.. Some of them do report longer tire life.
Maybe, that long life could be due to hypermiler driving techniques. No jackrabbits or hard braking etc.

One side benny is less brake dust on your alloy wheels!! :thumbup:

http://i46.photobucket.com/albums/f1...pe/medFord.jpg
This baby came from the dealer at 40 PSI. Same Low-rolling resistance tires they give you on the Escape Hybrid.. :)
I keep them at 40 (sidewall 44 max) and the ride is good for an SUV.

Adding my experience to the story,

When I began hypermiling with my Vibe I was careful to make one change at a time and watch the changes to see if it was worth the modification. I can absolutely attest to the MPG increase once I raised the tire pressure from placard to 50 psi cold. Now with my increase I used the nitrogen product in order to keep the pressure stable as the tire temp increased.

I did notice a harsdher ride, but I also witnessed improved traction when cornering, (No squealing tires) and improved wet weather traction, (no hydroplaning). In line with that I saw a nice 3mpg bump in mileage.

Now I also believe that in order to save money manufacturers use the tire as an additional dampner in their suspension design to make cars roll smoother.

I say this because I also have a vehicle that has a very low profile tire. 225/30/20. These tires have to run at higher PSI because sidewall flexing results in breaking of the bead and destroying a rim. In addition I spent some serious coin and bought an adjustable coil over suspension for this vehicle and had it professionally tuned for proper height and dampening.

WOW !! this vehicle rides likes a serious luxury car with nothing felt as far as bumps. In fact if I do not remind myself that i am 2 inches off the ground I will rip my bumper off the car accidentally. That proved to me that a properly engineered suspension can do its job properly despite the tire and independent of it.

Its just too many companies count on soft squooshy tires to act as a suspension instead of the suspension doing the work.

Also and I saw no mention of this in this post. There is no money in replacing tires every 80K miles or more. Dealers make more money off of parts and service than the sale of the car. Ergo, a tire that wears faster means more trips to the dealer for new tires and other related services.

I would also like to add that I have no data on better braking for the simple reason that our driving habits tend to teach us to brake very little and respond to changing road enviroments much sooner than later. I also have the added benefit of owning a vehicle that has ABS and traction control which negates the need to skid all together.

Not trying to argue either way, arguing for science. Found this. Like the idea of the chalk...
Proper Tire Inflation

edit: I know I said I wouldn't reply, and I just didn't see a reason to withhold this information.

Great atricle, I gotta try the chalk test...
 

I keep my Yokohama Avid Touring tires inflated 44 front, 40 back.
Over 44 and ride starts to get too harsh.

At 44 front, 40 rear the front and rear both have the same small amount of sidewall bulge.

I gotta try the chalk test. I expect it could reveal wheel alignment issues too.

Pete

So it sounds like we can resolve some of the mystery by chalking our tires and seeing if we are wearing unevenly ... I hope to try this tonight or tomorrow with my daughters sidewalk chalk ..lol

I think it's received wisdom that over-inflated tyres bulge in the centre of the tread and wear unevenly, from the olden days of cross-ply tyres.

'Overinflation' of a radial tyre will reduce sidewall flex and that is where rolling resistance is reduced. Not due to a smaller contact patch (which may exist due to the circumference of the tyre sitting a little less 'flat' on the road, possibly)

Inflaton pressure is equal on the inside of the tread area and the sidewalls of the tire.

Since there are two sidewalls for each tread area the increased pressure should not really affect the tread wear. That has been my observation over 50,000 miles on my VX and Insight.

When I put the new OEM tires on the Insight I monitored how long it took the nibs to wear off the tread area, and I do not drive around corners slowly.

It was 1000 miles before the nibs were worn off the center of the tread, and I was averaging close to 70 MPG in the Insight, and it was a automatic (CVT).

I will probably never run manufacturers recommended pressures in any car I own again.

I'll bet the Michelins on my VX will last 100,000 miles at 44 PSI and the 10% increase in mileage will easily pay for the $225 total the tires cost me, and I can still go close to 60 MPH on an average Interstate cloverleaf.

My 59 Corvette would do 70 ;), manual steering and 4 wheel manual brakes.

regards
Mech

My first new car (1976 Ford Pinto Stallion) had a set of Firestone Steel Radial 500 RWL tires on it. I ran them at sidewall maximum inflation for about a year. One day I decided to try the owners manual pressure instead. Driving down I-65 at an average speed of 65 to 70 mph (yes, the speed limit was 55 in 1977) the entire tread row of the left front tire peeled off really making a mess out of the left front fender and scratching up the left door and rocker panel as well. The other three tires had broken cords in the sidewalls and would make the car physically wobble going down the road. I learned two important lessons from that experience.

Lesson 1: Firestone would not stand behind their product. I've never bought a Firestone tire since then. :mad:

Lesson 2: While the tires do tend to ride more firmly (harder), they last longer and give better fuel economy. :thumbup:

If you want to talk about a safety hazard, the Firestones on my Pinto should have trained the company (there were lots of lawsuits over that tire) to make a tire that the tread row wouldn't peel off of. The Ford Explorer fiasco was using Firestone tires that the tread peeled off of. Firestone tried to claim they were underinflated. Underinflation is a serious safety issue, but I don't agree that overinflation is a problem.

F150 came with OEM Firestones- best dang tires it ever had. I hunted for exact replacements but there were none to be had :mad: :(

Anyone got hard MPG gain data for me to add to the wiki? Several of you said you saw gains, give me some numbers and how you go them (ABA, tank to tank, other).

The wiki viewers thank you!

Getting away from the controversy over what constitutes ideal tire inflation pressure, and back to the original post's intent:

I think there is merit in considering rewording that recommendation, regardless of where one stands in terms of ideal PSI.

Increases in steering response and wet traction with higher PSI may be generally true, but by no means universally so. Just one example would be two brands of tire in the same size, one with a max sidewall of 44PSI and the other with a max sidewall of 51PSI; is anyone here completely confident in stating that max sidewall is the ideal wet traction pressure for both?* And tire wear is such a wide open issue, with so many variables, that simply increasing inflation pressure beyond manufacturer recommendations is by no means a guarantee of longer tire life.

I'll toss out an alternative wording:




*(Putting this down here to try to keep topics separated.) My own experience is that max sidewall lowers traction, wet or dry, when compared to some value in between max sidewall and doorjamb pressures; exactly where depends on the car, the tire, moon phase, and a bunch of other stuff.

It might be hard to get new data from these guys. If they think like me at all,
they don't want to waste fuel (and tire life) running around on mushy tires.


Haha! I was just thinking about the guy with the "Experimental Test Car" sign on his trunk..

Maybe I need a sign that says, "Warning! Keep Back, Over-Inflated Tires!"
In smaller print it would say "Tires at 40 PSI exceed manufacture's recommendations for achieving a mushy ride".

Getting them to do testing might be hard, getting the data they have should not be bad. They must have data or why are they still doing it? Do they like the rough ride?

I do not need great data (it would be nice) even a "I did this and saw an approximate improvement from xx.x to xx.y" or a "this got me about 1MPG).

The Vehicle My Mule in my garage has good descriptions of how I achieved my mileage. So from that the best I can offer is Tank to tank numbers related to PSI.

Best mileage I got with factory PSI was 32.93mpg
Increased pressure to 44PSI (Sidewall Max) and achieved 36.21mpg (Also improving technique)

Then later on i hit a high of 38.8mpg at 44psi
Jumped up again to 50psi and saw a bump to 41.3mpg, but I also slowed down 5mph on my entire highway trips.

So inconclusive but at least it contributes to the gains.

What car what that with?

I also added your data to the wiki:
Increase tire pressure to max sidewall - EcoModder

Ideally we'd like to have published, peer reviewed and duplicated, studies to go on. Unfortunately, we don't seem to have that.

What we do have are some published studies showing that higher inflation pressures improve rolling resistance - and anecdotal reports to support this - but there doesn't appear to be any published info on the affect inflation pressure has on steering, traction and wear - and the anecdotal reports is mixed.

I think eco30BMW has a point. If a statement is going to be made, it ought to be backed up by data - and if the data is anecdotal, it ought to be consistent. It might be better to rephrase the statement this way:

That strikes me as a balanced way to describe the mod. I've updated it.