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

[markweatherill]

Originally Posted by thatguitarguy

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.

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

[CapriRacer]

Originally Posted by orange4boy

......

From what I have found so far, max sidewall reduces...
1) risk of rollover
2) blowouts from overheating
3) stopping distances
4) hydroplaning
5) slipping in snow
6) body lean in cornering

................

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.

[CapriRacer]

Originally Posted by markweatherill

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

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

[tasdrouille]

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:

15. Over-Inflation Detection

Table of Contents
ETV commented that, although requiring the TPMS to monitor high pressure is as important as monitoring low pressure, the NPRM did not consider or address this issue. ETV stated that manufacturers specify a safe maximum tire pressure, and that the final rule should address this aspect of vehicle safety. ETV�s comments recommended an intermittently flashing yellow telltale warning when the vehicle�s tires are within five percent of their maximum inflation pressure and an intermittently flashing red telltale when the vehicle�s tires have exceeded the maximum inflation pressure.

We have decided not to adopt a requirement for over-inflation detection for the following reasons. First, the TREAD required a rulemaking to detect a significantly under-inflated tire, not over-inflated tires, so such a requirement is arguably outside the scope of this rulemaking. Furthermore, we are not aware of vehicle safety data reporting over-inflated tires as a significant safety hazard. In addition, available information does not suggest that over-inflation has the same safety implications as under-inflation, which causes heat buildup in a tire, potentially leading to permanent tire damage and sudden failure.

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

The best possible option is still the recommended tyre pressure, specified by
vehicle and tyre manufacturers. It provides the best combination of aspects like
handling performance, comfort, wear, noise, etc. To come to the requested
vehicle-tyre performance level, a lot of knowledge, objective and subjective testing
is required.
However, considering the goals of the “Uitvoeringsnota Klimaatbeleid” [their policy to control climate changes], a
contribution is expected from increasing the tyre pressure of passenger vehicles to
reduce fuel consumption and therefore exhaust gasses. According to this research,
this is not possible without affecting other aspects of the tyre. Nevertheless an
increase of 0.2 bar (advised tyre pressure plus 10% an all tyres) is not significantly
changing the handling behaviour of the vehicles and is therefore seen as
acceptable. Considering the fact that low tyre pressures are worse because they can
negatively affect the behaviour of vehicles and lead to high tyre wear, the increase
of 0.2 bar can help to avoid these pressures.

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

[orange4boy]

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

Please, show me them.

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.

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

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.

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

[CapriRacer]

Originally Posted by orange4boy

From what I have found so far, max sidewall reduces...
1) risk of rollover

Originally Posted by CapriRacer

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

Originally Posted by orange4boy

Please, show me them.

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

[orange4boy]

From NHTSA Passenger van tire inflation study.

Analysis:
Good tire care improves vehicle
handling as well as fuel efficiency
and tire life. Proper tire maintenance
can prevent such events as tread
separations and tire blowouts which
may cause loss of control of a vehicle,
when not handled properly, and result
in a rollover. Low tire pressure can
also increase stopping distances and
the chance of hydroplaning on wet
surfaces.

Two birds with one stone.

[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

"When you increase the tire pressure, you increase the chance for a
rollover." ....... said Sean Kane, of Strategic Safety, an Arlington, Va.,
research firm looking into product liability claims across the country
dealing with Ford Explorers.

[tasdrouille]

"When you increase the tire pressure, you increase the chance for a
rollover." said Sean Kane

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

Table 7. Effect of under-inflation on rollover threshold

This simplified analysis suggests that moderate to severe under-inflation has
negligible effect on rollover threshold. Even extreme under-inflation of 100kPa
only results in a 3% reduction in the rollover threshold.
Under the dynamic situation the effects of under-inflation on rollover
propensity are likely to be more pronounced. This is because manufacturers
go to a great deal of effect to tune the suspension characteristics to match the
recommended tyres at the recommended pressures. Quite subtle dynamic
effects from under-inflated tyres can be magnified by the complex dynamics of
vehicle motion. However, this review could not find any quantitative research
findings on these dynamic effects.

[dcb]

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

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