"Inflation pressure does not affect grip": Autospeed article.
 

Except in aquaplaning where higher inflation reduces it.

Something I suspected but didn't have the info to back it up.

AutoSpeed - Tyres, Grip and All That.

ADDED: I'm putting all my links here for easy access:

According to these tests Higher inflation pressure reduced stopping distance and increased coefficient of friction...Scroll down for stopping distances.

FEA chapter III. tire pressure survey and test results

From NHTSA Passenger van tire inflation study.

http://www.maic.qld.gov.au/forms-pub...port-final.pdf

Found some interesting pages from a racing tire book. I have not had time to read the whole thing.

From excerpt#1

http://insideracingtechnology.com/Re...s/vertload.gif

Tire Technology, excerpt from The Racing & High-Performance Tire

From excerpt #2

http://insideracingtechnology.com/Re...bhvrcpslip.gif

Tire Technology, excerpt no. 2 from The Racing & High-Performance Tire

Tire Technology, excerpt no. 3 from The Racing & High-Performance Tire

SAE paper digested for us by Barry.

Barry's Tire Tech

Peak traction goes up and sliding down a tiny bit. ABS would like this. Also they found cornering response and cornering traction improves. The only downside was bruise resistance and puncture blow out got worse with higher pressure (not surprising.)

http://www.barrystiretech.com/sae800...tiongraphs.jpg


This is not advice. I'm just sharing waht I have found.

My personal opinion is that tire inflation to max sidewall is generally better for the following reasons:

1) Lower heat build up. Reduced risk of accident or rollover resulting from loss of control from heat related tire failure.
2) Reduced wear
3) Slightly increased peak traction, slightly reduced sliding traction. Slightly reduced stopping distances (may have to do with increased traction)
4) Reduction in hydroplaning (onset of hydroplaning happens at a higher speed)
5) Reduces slipping in snow* (depending on conditions, sometimes lower pressure is better)
6) Increases tire responsiveness in cornering.
7) Reduces body lean in cornering, improves steering feedback (subjective)
8) Reduces fuel consumption
9) Reduces steering effort

Downsides to max sidewall:

1) Slightly harsher ride quality.
2) May increase rollover tendency in already rollover prone SUVs
3) Harder on suspension components in rough road conditions
4) Increases risk of tire bruising or failure from impact with certain objects.

Heat, Now I get it (wide).
Thank you!

Cool link/info!

In fact, according to these tests Higher inflation pressure reduced stopping distance and increased coefficient of friction...Scroll down for stopping distances.

FEA chapter III. tire pressure survey and test results

Unfortunately, higher pressures were not tested.

(Poor Cara. Sorry Christ)

FEA chapter III. tire pressure survey and test results

Orange4boy, thanks for a new weapon in the EcoModder arsenal :)

tire company in cahoots with oil company to keep making wasteful rollers?

I would run at 90 psi If they would wear evenly. screw ride comfort built into tires, thats what the suspension is for.

I wonder why the tire companies consistently disagree with this...

Edit: Something to note, this article seems to have no empirical testing, which I think is important in this kind of situation. Issues related to tires and fuel economy can often have the books cooked via mental exercises, which, while seemingly sound, are crucially lacking various pieces of the puzzle. Colour me skeptical.

1) Unfortunately, had they done a little research, they would have found this:

Fact or Fiction? Tire contact patch and air pressure.

That directly contradicts Item #1 - and has data to back it up. So it isn't a myth!

2) In item #2, they go with the classic friction formula F = µN. Unfortunately, that does not apply to tires.

Tires get a lot of their grip by penetrating the macro texture of the pavement. When pushed to an extreme, the rubber is torn off the tire - with subsequent increases in force. As a result, it is possible to get more than 1g forces.

If you read up about drag racing, you''ll find reports of well in excess of 1 g acceleration. You'll also find some skid pad testing over 1 g of regular production cars - albeit high performance cars like Corvettes.

So, the whole article seems built on an incorrect series of assumptions.

You know, that is the exact reason why the standard for TPMS makes no provision for an upper pressure warning. It was determined it does not constitute a significant safety hazard.

Possibly not relevant to on-road discussions, but with regards to off-highway driving on extremely rough surfaces anyone who says inflation pressure doesn't affect grip can stop talking immediately if not sooner.

Lol, I think the jist here is on-road use. Letting the air out of your tires is a hokey way of approximating tank tracks, which of course is NOT a good choice for on-road, but which would be able to handle the extremes of offroad better than any tire.

But wouldn't a tire with higher pressure push more into the road surface, due to there being more pressure per unit area between the tire and the road?

And anyway, if it were dangerous and grip was compromised at higher pressures, wouldn't there be a load of test data to prove it?
Instead all we get is people telling us it's dangerous.

ollie

"Except in aquaplaning", is a huge caveat. When you are sliding on ice, snow, or slush, you are actually hydroplaning. You can slide very easily on rough ice, while maintaining perfectly good traction on very smooth dry glass. The difference here is a microscopic layer of water between the solid ice and the tire. The pressure caused by the weight of the vehicle will "squeeze" or "melt" this layer of water from the ice, so that it will nearly always be present in those conditions.

It is why an ice skate will glide over the ice instead of digging into it.

A vehicle with more weight or downforce will push more into the road surface. With weight and downforce being a constant, higher tire pressure only reduces the size of the contact patch.

Therein lies the argument of traction. Higher pressure = smaller contact patch, and vice versa.

Not quite. I don't have ABS. I can stop faster than similarly equipped vans with ABS, too.

At least in this case, ABS was an exercise in "Make it look good, and sell it for more."

But there it's a different mechanism at work. You're generally driving on something that's fairly loose - think dirt spinning out from under the tire - so a larger contact patch reduces the force on each unit area of the dirt.

I thought it felt like my tires had better grip, my snow tires are rated for 51psi and I try to keep them at that, 3rd winter on this set and the tread wear is dead even.

Oh, for sure, off road is a different animal. There you often want to increase contact patch so you don't sink or so the tire can cover medium size bumps and not get stuck between two peaks of a rock, for instance.

On ice, you want a cold tire. The minute you spin and heat up the tire you lose most of your traction.

With chains, lower pressure so the car does not vibrate excessively.

I think most people think of aqua planing as on a hard surface with liquid water. To slide on ice there does not have to be a liquid layer, but there often is.

There are a lot of "it depends" when it comes to tire traction and pressure. The best would be a variable pressure system. I think the Porsche 959 had this.

Variable pressure = something more to go wrong, waste fuel, and weigh more.

I'm always skeptical which is why I will keep looking for better and better info on this. Please post better info if you have it. My later post has actual data although they didn't test above max sidewall.

True, It does contradict item 1, but not the statement that inflation pressure does not affect grip. Obviously this is a general overstatement. Inflation pressure does not affect grip (very much). Let's find more info. I'm not completely satisfied by the AutoSpeed article or the one you posted.

True but... I'd rather have variable tire pressure than A/C or Bluetooth, or an automatic, or an ICE, or 8 way electric adjust seats, or cruise control...

OK, I thought about it for longer than an nanosecond... it's a silly idea. Need lower pressure, Get out and let some air out.

There's no "I'd rather have" in the marketing scheme of the publicly traded auto manufacturers... only "Here's what you need, here's how much more you're going to pay for it."

I know. *sigh* I'm just living in my little dream world here...Ya gotta have dreams.

There's why your market share is down another couple of percentage points this year :-)

You know, I just realized something: 1) US automakers' market share is down to about 50%; 2) By definition, half the population has below-average intelligence. You suppose there's a connection :-)

Have a similar theory about political affiliation but I'm too smart to elaborate.

...ah, a member of the Astute Party?

Did someone just take high school physics? Yes the contact patch affects grip, because the rubber and the road aren't two perfectly smooth surfaces. The rubber conforms to the bumps in the pavement, and the more bumps the more grip.

If bigger contact patch = same grip, why do lawyers love staggered tire sizes?

http://www.modified.com/projectcars/...t_2/index.html

Perhaps someone should take high school physics. More bumps do not equal more grip. If this were so, drag racers, NASCAR racers, IRL racers, Formula 1 racers, etc., would want bumpy race surfaces. The very opposite is true. They put smooth grippy tires on smooth track surfaces. The reason street tires are not smooth like race tires, is that they have to be able to displace water.

Pretty sure the "bumps" are teensy, at which point the rubber displaces around them, causing "traction". Ice is smooth, nope we don't want that.

All of these thing depend upon the rubber formulation, temperature, speed, application, road surface. Here I am talking about passenger tires on asphalt / concrete in normal driving conditions.

My intention is to find and present specific information regarding the relationship between traction and inflation pressure. Whenever this is discussed some people express extreme reserve at inflating to max sidewall and hysteria at inflating somewhat past max sidewall claiming all kinds of calamity and no proof of it. I think these people are misinformed. The AutoSpeed article is interesting, if incomplete, but generally sound, and gave me somewhere to start learning more. The study I posted shows a small reduction in braking distance between low and max sidewall.

My personal opinion on this, at this time, is that up to a point, and generally speaking, higher inflation pressure gives better FE (undisputed) and gives better or the same traction (unknown but suspected) up to and a bit above max sidewall to a point I don't know what that point is but I have a hunch it's somewhere around the point at which 90% of the reduction rolling resistance from slightly higher inflation has been achieved. This is not an extreme pressure. If I had tires that were sold as low RR, I might even just leave them at max sidewall but really, I would only run lower pressures if ride were my priority. Otherwise all other safety/traction,handling issues are better at max sidewall.

One of the biggest and most common dangers is actually underinflation which can lead to blowouts from temperature build up. Higher inflation pressures (not extreme pressures) reduce the possibility of blow out by reducing heat build up.

It is not my intention to give advise, just present information I have found and my opinion on it. My opinion is based on what I have read and some of it is extrapolated from that information. I am willing to change my opinion if I find credible evidence.


From what I have found so far, max sidewall reduces...
1) risk of rollover
2) failure from overheating*
3) stopping distances
4) hydroplaning
5) slipping in snow* (depending on conditions, sometimes lower is better)
6) body lean in cornering

* edited to increase clarity

The only disadvantage to max sidewall I can think of is ride quality.

My understanding of radial tyres is that the tread does *not* deform or bulge depending on tyre pressure.

I think this is exactly why there are debates about the subject - there is contradictory data:

Let's take item #1: There are studies that say that increased inflation pressure INCREASES the risk of rollover.

Item #2: Blowout mean rapid air loss - and overheating leads to belt separations - which usually do NOT result in air loss. Theses are 2 separate issues.

To be fair, increased inflation pressure reduces the operating temperature, so the risk of a belt separation is reduces, but what happen as you continue to add inflation pressure? Obviously at some pount the tire explodes. Which brings me to the "blowout" issue.

We also know that increased inflation pressure also increases the risk of an impact failure. So where is the crossover point between impact failure and belt separation?

Item #3) In the study posted:

FEA chapter III. tire pressure survey and test results

the inflation pressure is limited to a maximum of 35 psi. What happens beyond that? Does the data peak then drop off? This study doesn't say, so we need to be careful to make the distinction that we don't know what happens above 35 psi.

Item #5) Slipping in snow. Lots of folks have been debating this issue for years - and it always boils down to whether or not the surface is pure snow - or snow where is it possible to penetrate to the pavement. The former has lots of anecdotal evidence that lower is better, but the latter also has lots of anecdotal evidence - hence the debate.

But the biggest problem is that passenger car tires (with a couple of exceptions) are designed to operate in the 26 to 35 psi range. It makes no sense for the tire manufacturers or the vehicle manufacturers to test outside that regime. So there isn't going to be a lot of data to be found for pressures above that.

I think you'll find that radial tires may be more resistant to tread arching, but they are not immune.

DEPARTMENT OF TRANSPORTATION
National Highway Traffic Safety Administration
49 CFR Parts 571 and 585
[Docket No. NHTSA 2005-20586]
RIN 2127-AJ23
Federal Motor Vehicle Safety Standards; Tire Pressure Monitoring Systems;
Controls and Displays

Final rule here

From the rule in the response to public comments section:

Surely if inflation above placard pressure was dangerous the NHTSA would have addressed it no?

I also like to point to the following study comissionned by the Dutch Ministry of
Housing, Spatial Planning and the Environment :The influence of tyre pressure on the comfort

If a government is suggesting people go with higher inflation pressures, they must be damn sure it does not pose a risk.

Please, show me them.

Semantic issue. I should have said tire failure instead of blowout. Edited.

I agree, but whatever happens there will very probably not be a drastic change within 10 psi.

I accept your challenge – with one provision. That you show data to support your original statement.

From NHTSA Passenger van tire inflation study.

Two birds with one stone.

Headline: Rollover fear tied to tire warning

A Ford document shows the company urged low tire pressures to keep Explorers stable.

Worldandnation: Rollover fear tied to tire warning

It should be appropriate to also mention that might only be true for the vehicle being discussed, if we take this guy's word for it. Honestly, there's not much meat to that claim yet.

Here's an interesting paper with a lot of info:

THE ROLE OF TYRE PRESSURE IN VEHICLE SAFETY, INJURY and ENVIRONMENT

nooo... it isn't cuz Explorers are topheavy and should require special licensing as well as propery linflated tires, noooo. LOL!