hyper inflation: let's cut to the chase

[ShadeTreeMech]

I found a report by the NHTSA that in pat concerns tire pressures related to braking distance. While the maximum pressure is 35 psi, there is generally a trend for higher pressures to DECREASE braking distance.

Happy reading.

Is there any manufaturers of passenger vehicles that recommends higher than 35 psi? What about vehicle manufactured for overseas markets? Since many of those cars are extremely similar, we maybe could learn a thing or 2

[Clev]

Originally Posted by ShadeTreeMech

There is simply a lack of evidence that 50 psi in a 50 psi rated tire is a bad thing.

I have only anecdotal evidence, but that evidence is available to review in the Garage. I have over 39,000 hypermiles between my two cars--with some 44 psi tires pumped to 51 psi and some 51 psi tires pumped up to 51 psi. I've now replaced four of those tires, and all four had perfectly even wear. This is in mountain and freeway driving, in the dry, rain and snow, and from 20 degrees F to 105 degrees F. I've had zero tire failures.

I recently picked up a pair of used 44 psi tires for the Clunker because of finances. They have a lot of tread left, but one was patched because of a nail. Those I keep at 40-42 psi to be safe.

[ShadeTreeMech]

Found another interesting site. Did a search for ford mondeo (contour in the US) tyre inflation pressures and got this page. It lists seperate tire pressures according to whether it is loaded or not. Go figure, the pressures often go well over 35 psi!

Nearly all these cars are available in the US in very similar form, yet why the more informative chart for the UK? Is there the assumption americans are too thick to understand a simple chart?

[CapriRacer]

Originally Posted by orange4boy

That Tire and Rim Association paper lists the MINIMUM pressures for each load. MINIMUM. .......

Sorry, but if you'll read it again you'll see that it says the load limit for various inflation pressures. I think that means for a given inflation pressure, that's the maximum load carrying capacity.

Originally Posted by ShadeTreeMech

......Is there any manufaturers of passenger vehicles that recommends higher than 35 psi? What about vehicle manufactured for overseas markets? Since many of those cars are extremely similar, we maybe could learn a thing or 2

I have found only found 2 situations where the inflation pressure for a passenger car is specified by a vehicle manufacturer over 35 psi (36 in metric units).

1) Extra Load tires

2) European cars, particularly German cars, where they have dual inflation pressure specs and the one over 35 psi is for max load / high speed (I think you found one of those). Obviously they are considering the Autobahn. When these cars come to the US, sometimes the pressure spec changes, sometimes not.

[orange4boy]

Sorry, but if you'll read it again you'll see that it says the load limit for various inflation pressures. I think that means for a given inflation pressure, that's the maximum load carrying capacity.

Two ways of saying the exactly the same thing. Maximum load for a given pressure has exactly the same practical meaning as minimum pressure for a given load. The chart then has the note that the tire engineer can increase the pressure up to max psi without increasing the load and this difference is what the engineer has to work with when determining recommended pressure. ie, NVH vs performance, which usually means leaning towards soft and squishy so john Q public does not feel or hear the road.

Please note they call it recommended pressure not required pressure, or some such, because there is no safety issue in going above the recommended pressure. If there was you can bet the NSHTA would have long ago had a placard with that in big bold letters. In fact it could well be that higher than recommended pressure is safer as it gives more crisp steering response and better cornering traction. We already know for a fact that higher pressure means better hydroplaning resistance.

[CapriRacer]

Originally Posted by orange4boy

Two ways of saying the exactly the same thing.........

While this may be similar, it's not exactly the same thing. I'll explain that below.

Originally Posted by orangeoy4

.......The chart then has the note that the tire engineer can increase the pressure up to max psi without increasing the load and this difference is what the engineer has to work with when determining recommended pressure. ie, NVH vs performance......

It's the vehicle engineer, not the tire engineer that selects the tire size and the inflation pressure.

The vehicle engineer uses the table, knowing the load that the tire must endure, to select a tire size and inflation pressure combination that not only will carry the load - and knowing that over specifying that combination, a lesson emphasized by the recent Ford /Firestone controversy a few year back - but also have some over-capacity. How he does this depends on the design standards for each vehicle manufacturer. Notice that almost without exception, the pressure specified on the vehicle tire placard is not above 35 psi - and this would include the over capacity (in the form of over-specifying the pressure).

On the other hand, the tire engineer is designing the tire to the table without regard to over specifying by the vehicle engineer. I had a college professor cal this "Over-design / Under-utilize".

The tire engineer generally picks the 35 psi load - for passenger car tires - and uses 35 psi as the test condition.

NVH - for a tire engineer's perspective - is about tread generated noise, since most ride vibration are about "roundness" (a manufacturing issue), and ride quality is more or less controlled by the inflation pressure (which requires a vehicle for testing).

Originally Posted by orange4 boy

....Please note they call it recommended pressure not required pressure.......

I'm going to call what is written on the vehicle tire placard a specification - which it is - much like oil viscosity and bolt torque are specified.

Originally Posted by orange4 boy

......If there was you can bet the NSHTA would have long ago had a placard with that in big bold letters. ......

That's kind of a weak arguement because look how long it took for NHTSA to deal with the issue of inflation pressure BELOW the placard. There weren't any bold letters for that and that was a known quantity for decades. Besides, there isn't a lot of information about what happens in the real world when tires are inflated above the vehicle tire placard - mostly because actual usage inflation pressure information is rarely available from accidents statistics - which is what NHTSA is using to drive what they look at.

[bgd73]

Originally Posted by VegasDude

Don't forget about Nitrogen. They use it in airplanes. That means you really need it.

Hey..that goes along with an old sube. if it works in an airplane...

the air stuff is simple, max it till its uncomfortbale, you maxxed the tire then for your location.
Yesterday, I puffed back up to 40psi...frosty morning today, now the green leafed
60s of spring approaching mid day. That is as complicated as a tire gets.

the night before the big canuckian sink hole, my tires pounced 3 of my 4 tires to 20psi...and they are the best treads I have ever encountered (nokian 1). My car does this with micronical resonance.. it is hardly a mystery. If the car was squishy failing wiggling (ya know OEM).. the treads would go along for the ride. But no. I am crazy about squeaks creaks rattles moans and groans and a false impression that a car is tough. I welded till it was...by my own standard...and that has expenses. It needs tough everything now.

The chinese stuff is not true, even my dad goes for those on his rig. I am in rally crazy mig welder realm, so I seek tires from people who give a *hit about making them. CXhinese does have its benefits... remember, they are forced to pass world standards. they cannot get away with much anymore...unless we speak of electronics..but that is another subject.

[Thymeclock]

Originally Posted by orange4boy

That Tire and Rim Association paper lists the MINIMUM pressures for each load. MINIMUM. Then in a note on the very next page it states this:

In other words up to max sidewall is perfectly safe. Black and White from the Tire and Rim Association.

It's safe to over-inflate, as long as you don't take it to extremes.

Typically my tires are rated at either 28 or 32 PSI and I inflate to about 35. With any more than that the ride becomes too harsh for our bumpy roads.

There are two drawbacks to over-inflation: one is the ride, which will be harder, the more the tires are over-inflated. (If you don't live in pothole land, this may not bother you.) The other is that the car may not handle properly. About 15 years ago I bought a used '89 Celica. The car was very well maintained, but after owning it a few days I noticed the handling was weird; mechanical checks showed nothing wrong. Within the first month I checked the tire pressures and found they were inflated to around 45 PSI. I reduced the pressure to about 35 and then the car handled perfectly. (And I kept the car happily for the next 16 years.)

[puddleglum]

I know that everyones mind is already made up on this issue already, but I'm going to add my personal experience as well. I have read a lot of claims that running tires at max. pressure or a little higher will not increase tire wear and may reduce it. My experience is just the opposite. I have never had a tire wear the outside edges off from running too soft. I have however had 2 sets of tires wear out in the center on my '93 villager at only 35psi. My work van was wearing the centers out running at recommended tire pressure. I am currently running them 10psi low and getting more even wear. My son put oversize tires on his Ranger and experienced severe center rib wear after only 10k miles at 35psi. I have also seen lots of other cars around with noticeable center rib wear. My Rondo is wearing the inside edges off the tires but that is because of excessive negative camber in the design. I have been running the tires at 40-45psi to help compensate but the ride is terrible, the fuel savings is minimal and I am worried the higher pressure may even be adding to the problem because of less sidewall deflection. I'm sure cars with small, narrow tires will benefit from running a little higher pressure, but many cars today have much larger and wider tires than they need to IMO. I just don't think that it's right to be making blanket statements like "max rated tire pressure is always best" or "will never increase tire wear". There are always exceptions.

[Thymeclock]

I am currently running them 10psi low and getting more even wear.

Over-inflation may be debatable but under-inflation (by 10 pounds?!) is NOT a good idea. You will not find anyone advocating it.