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

[Christ]

There are several ways I can quantify pressure change's effects. I'll figure out what I'm gonna do when I actually do it.

[CapriRacer]

I hope everyone will understand that a lot of posts were directed my way - and rather than answer them individually, I'll put them all in one post:

Originally Posted by natefish

Perhaps the article was accurate in 2005 when it was published. Mr. Storton seems to have a pretty good list of qualifications after his name, I doubt he just made stuff up for fun.

Can you provide the source the makes you think he is wrong?.....

The article was inaccurrate in 2005.

Tire Guides - which is a publication that summarizes the vehicle tire placard information for all vehicles sold in the US - has this listed for a 2005 Ford Crown Victoria - 4 versions:

Crown Victoria Police Special: P225/60R16 97V 35 psi front and rear

Crown Victoria: P225/60R16 97T 32 psi front and rear

Crown Victoria LX: P225/60R16 97T 32 psi front and rear

Crown Victoria Sport: P235/55R17 98H 35 psi front and rear.

I went back in model years, and it says something similar back as far as the 2000 model year.

Bottomline: Sgt. Storton did not present correct information at the time he published his article. And he could have prevented that mistake by simply visiting a Ford dealer.

Originally Posted by orange4boy

...................Oh, I know what I'm looking at. Those are woven steel wire belts that run around the circumference of the tire. The individual wires are angled, yes, but as a whole they run around the circumference of the tire. ...

First, they are not woven. They are parallel individual strands - which is why there are 2 layers, one going one way and one going the other way.

Yes, they are circumferential, but so are the plies.

The point is that the radial plies are going to try to form a circle (in cross section) when subjected to pressure. The belts resist this, but do not prevent it. The net result is that increasing the inflation pressure tends to shift the pressure within the footprint from the shoulders towards the center - in other words, towards the direction of forming a circle in cross section.

Here's something that says this is true:



If the principle is true, then we also ought to see it in the real world - and we do. The problem is that there are other factors which affect tire wear more dramatically, so this tends to get disguised and lost, but it does appear clearly from time to time.

Originally Posted by orange4boy

......I agree there is a difference between some guy's opinion and solid, good information. That's why I found scientific and government studies as well as textbook references that support my positions.

You have yet to do so. ....

Oh, how quickly we forget. Remember this?

Originally Posted by CapriRacer

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!........

Or this?

Originally Posted by CapriRacer

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

Contrary to your assertion, I have been providing documentation.

So now what? Personally, I think the list needs to be reviewed to see if each item is properly documented - and whether there is any contradictory information.

[dcb]

Originally Posted by CapriRacer

...
Crown Victoria Police Special: P225/60R16 97V 35 psi front and rear
...
Bottomline: Sgt. Storton did not present correct information at the time he published his article. And he could have prevented that mistake by simply visiting a Ford dealer.

What are you going on about? because he says 35 psi instead of making a chart you dismiss the whole of the article?


re: grip, look at your own pic

you can clearly see the contact patch getting more rectangular with higher psi. Meaning the load is pretty well balanced across the tread, not round cross sectioned.

Look, guy posted his test results, where are yours?

[CapriRacer]

Originally Posted by dcb

What are you going on about? because he says 35 psi instead of making a chart you dismiss the whole of the article? ........

Sorry, but that was in response to:

Originally Posted by natefish

Perhaps the article was accurate in 2005 when it was published. Mr. Storton seems to have a pretty good list of qualifications after his name, I doubt he just made stuff up for fun.

Can you provide the source the makes you think he is wrong?.....

and that's what I provided. If you would like a point by point rebutal of the article, I can provide it, but that hardly seems necessary.

Originally Posted by dcb

.......re: grip, look at your own pic.........you can clearly see the contact patch getting more rectangular with higher psi. Meaning the load is pretty well balanced across the tread, not round cross sectioned......

The question on the table was if the steel belts in a tire prevent the tread face from arching. So it's not the shape of the footprint, but the pressure distribution - in other words the colors within each footprint - that are important here.

[dcb]

The color distribution across the contact patch seems most uniform at the 45 psi image, to me. You don't have those peaks under the sidewalls.

And it is readily apparent that the whole tire is having to flex much less, which leads us to more efficiency, which is what its about.

[orange4boy]

First "documentation" link yields these little gems:

Fact or Fiction? Tire contact patch and air pressure.

The tire diameters are within 1.6% of each other. The rear is 28.5% wider than the front. Now, don't get excited, we're not going to look at grip or tire force curves here, so we don't need to even try to talk about tire compounds. One point Camp A argues is that the wider tires have better cooling, so a wider tire typically is made of a softer compound and that's the reason it gets more grip. I.e., it's not because they have a bigger contact patch. Fine. But if the contact patch is not really the same size (within a reasonable tolerance of course) than the argument is based on something bogus (even if the wider tires DO have softer or better gripping compound. I've never built a tire or talked with a tire engineer so can't be 100% certain.)

It's a guy who downloaded some tire pressure/load/patch pressure/patch size charts from a tire website. He only compares patch size to load and pressure and does not deal with traction or safety.

But really this page is really addressing the original autospeed article right? I already said that that part of the article (the one about different widths of tire) was not important to this discussion as we want the narrowest tires for better efficiency. And The title of the article is an overstatement.

"documentation" #2 is an news article about the rollover tendency and tire blow out issues of the infamous Ford explorer.

Worldandnation: Rollover fear tied to tire warning

Ford spokesman Mike Vaughn said Sunday that he could not confirm information in the Ford document, which was distributed to reporters by a Little Rock, Ark., lawyer who is suing Ford and Bridgestone/Firestone, but he said tire pressure is not the issue.

"Yes, increasing the tire pressure does increase the ride characteristics," Vaughn said. "Higher pressure will give you a harsher ride. But the issue is this particular tire. The recalled tires are the ones that show the higher failure rate. It is not an issue with the air pressure or with other tires."

So, you were saying...

[orange4boy]

More terribly interesting information:

The chart shows the Minimum inflation pressures at certain loads. Then it gets very interesting.

I point you to note #3

Cold inflation pressures may be increased above those applicable to the tire loads up to the maximum marked on the tire with no increase in load.

[Andrew63]

Originally Posted by SVOboy

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.

To what pressures do NASCAR and F1 teams set their tires?

[orange4boy]

More interesting tire info. Especially if you want to drive on the Autobahn.

Link: Tire Tech Information - Air Pressure/Load Adjustment for High Speed Driving

The European Tyre and Rim Technical Organization (ETRTO) establishes the standards for tires sold in Europe, and recognizes that the tire's deflection must be minimized and controlled in order to surpass high speed driving stresses. In order to accomplish this, the tire inflation pressure recommendations and the tire's rated load capacities are customized when speeds exceed 160 km/h (99 mph) for all tires up to and including a V-speed rating, and when speeds exceed 190 km/h (118 mph) for all tires that are Z-speed rated and above.

The Autobahn's unlimited speed opportunities explain why many German vehicles identify alternate tire inflation pressures to accommodate higher than North American highway speeds and heavier than typical two-passenger loads. In order to accommodate higher speeds, the tire size and inflation pressure recommendations are tuned beyond what is branded on the tire's sidewalls. These increases in recommended tire pressure are usually determined by agreement between the vehicle and tire manufacturers. In the absence of such an agreement, apply the following:

Beginning with the vehicle manufacturer's recommended tire pressure for normal highway conditions, tire inflation pressures are initially increased and then the tire's rated load capacities (branded on the sidewalls) are reduced as speeds climb.

In our example shown below, the vehicle manufacturer's recommended 35 psi for a 225/45R17 91W Standard Load tire installed on a vehicle initially rises in 1.5 psi increments for every 10 km/h (6.2 mph) increase in speed until the inflation pressures max out with an increase of 7.5 psi when the vehicle's top speed has increased 50 km/h (31mph). Then as the vehicle's top speed continues to climb, the rated load capacity of the tire is reduced in 5% increments for every additional 10 km/h until the vehicle's top speed has increased an additional 30 km/h (18.6 mph). In this case the 225/45R17 91W Standard Load size's rated load capacity of 1,477 lbs. is reduced to 1,255 lbs. when applied to a vehicle with a 270 km/h (168 mph) top speed.

For W-Speed Rated Tires
Vehicle
Top Speed Required Tire
Pressure Increase Tire Load Capacity
% of Branded Maximum W-Speed Rated Tire
35 psi O.E. Example
mph km/h psi bar % of value branded on sidewall psi lbs.
118 190 0 0 100% 35.0 1000
124 200 1.5 0.1 100% 36.5 1000
130 210 3.0 0.2 100% 38.0 1000
136 220 4.5 0.3 100% 39.5 1000
143 230 6.0 0.4 100% 41.0 1000
149 240 7.5 0.5 100% 42.5 1000
155 250 7.5 0.5 95% 42.5 950
161 260 7.5 0.5 90% 42.5 900
168 270 7.5 0.5 85% 42.5 850

NOTES: Never exceed the maximum cold inflation pressure branded on the tire's sidewall.

I assume these cars are not stopping at the side of the road on the Autobahn onramp to adjust their tire pressures. It must be considered safe enough to drive with the higher pressures than OEM recommended for the balance of the trip below the insanely dangerous speeds of the Autobahn.

[shovel]

One nice thing about this particular discussion is that the topic at hand CAN be tested with some degree of reliability. You take the same car, same test track, same driver, and 3 sets of tires in 3 widths (if you want to be really thorough)... run the track at low/med/high pressures and observe vehicle behavior at turns.

Not something I have the resources to do in my back yard... but we here on this type of forum ARE the audience of motoring, learning, debunking, and building shows. My mom doesn't care about this topic and also doesn't watch those shows, so her demographic isn't one those type of shows need to worry about - we are.

So.... anyone involved in one of those shows want an idea for a segment? Anyone know any good email addresses of people on such shows?