Ye Olde Tire Pressure

[obbop]

Read a thread but question not answered in my particular case.

Accepting input regarding tire air pressure level.

Door sticker calls for 35 psi but that is likely the level that takes into account the comfort level of the ride.

Coot has enough natural padding that I act as my own shock absorber.

New tires:

Bridgestone Dueler H/L Alenza P245/75R/16

Sidewall shouts out that maximum carrying capacity is at 44 psi.

Typical total vehicle weight is around 5,000 pounds, around 500 pounds more than the gross empty weight that doesn't include driver, fuel, tools, a couple sand bags in the bed, etc. Towing a rare event and heavy loads in bed also rare.

To maximize fuel mileage and wet traction (snow tires used in winter) and to obtain maximum tread life, Coot wonders about the trade-off(s) between following manufacturer's 35 psi level, the 44 psi on the tire, or some point in-between.

Not in the mood to set a level, attempt to record results, try another psi then observe results at that level. Too lazy and too subjective.

Just want to pick a psi and stick with it.

Input would make shanty dweller gleefully giddy.

 

[Squishy]

Are the new tires the same size as the old ones? If so, I would shoot for 2-4 PSI above OEM.

 

[CapriRacer]

My standard recomendation is 3 to 5 psi above the placard.

My logic is just what you alluded to - that the pressures are generally set for ride comfort.

However, some of the newer models have larger tires than their predessors, and it's obvious to me that an effort is being made to address some of the issues raised during the Ford / Firestone debacle. So I don't think that my "3 to 5" recommendation is always appropriate.

But given the size you quoted - P245/75R16 - it's clear that this isn't a newer model - so......

"3 to 5"!

 

[obbop]

Critter is a 2004 Silverado pick-em-up-truck

 

[Ramblin Fever]

My advise, set him at 40-42, should be good.

Only thing is, I don't advise you "just to pick a set psi" and go with it, because sometimes you *need* to find what works best for that tire/vehicle combination; and without doing so, can actually cause you to wear your tires out faster.

 

[Papa Bear]

Like R.F., I keep mine a couple of pounds below max.
Good ride, good mileage and good tire wear.

 

[obbop]

Appreciate the input.

Will output air until 40 psi is attained and will observe/feel effects then adjust up or down until what appears to be an optimal level is reached.

The higher than 35 psi should allow a little better mpg. Will watch tread for weird wear patterns.

Hoping the dude that did the alignment performed the chore properly.

 

[Papa Bear]

Hope he wasn't cross-eyed ??!!

 

[oilnoob425]

Quote:

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My logic is just what you alluded to - that the pressures are generally set for ride comfort.

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Why everybody keep saying that?? is this statement actually a true fact and written in stone somwhere? if so i'd like a link.
I for one always thought that manufacturer set it's psi for optimal balance. And it's a good idea to acctualy follow factory engeneer's reccomendation than taking adwise from some car forum. I'm i wrong? If so prove it with good links please. Thanks.

 

[CapriRacer]

[quote....... is this statement actually a true fact and written in stone somwhere? if so i'd like a link.
I for one always thought that manufacturer set it's psi for optimal balance. And it's a good idea to follow the factory engineer's reccomendation than taking adwise from some car forum. I'm i wrong? If so prove it with good links please. Thanks.

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Let address it this way:

You'll never get anyone to admit that anything is done in such a way that safety is compromised - and clearly this is the case with inflation pressures.

Also, each vehicle manufacturer has its own methodology in determining inflation pressures and they are not going to publish this. So the only thing we have to go by is our experiences in dealing with the engineers that actual do this type of work.

I spent 5 years as a technical liaison between a major tire manufacturer and a major vehicle manufacturer. The company I interacted with certainly considered ride an extremely important issue and sometimes even lowered the pressure recommendation in order to get a better ride.

My collegues - who called on other vehicle manufacturers -reported similar types of things.

I am sure there are exceptions, but I think there is general agreement that this is the case - that tire pressures are generally biased towards ride comfort.

However, I want to point out that the load carrying capacity of tires and pressures as specified by vehicle manufacturers is more than adequate, so this isn't a case of being "safe" or "unsafe". It's more a "degree rather than kind" sort of thing.

Frankly, I am in agreement with you that trying to second-guess the vehicle designer is generally not a good idea. Certainly I've "taken to task" folks who have made pressure recommendations that are based on what I consider to be "faulty" logic. But by the same token, there are trade-offs in vehicle design.

I hope that clarifies things.

 

[obbop]

Something to consider.......

Vehicle manufacturer has no idea what brand/type of tire may be mounted upon the vehicle in the future.

The engineers do know what tire will be installed at the factory. Surely that affects psi recommendation.

The tire manufacturer hopefully has done what needs doing to determine the max psi placed on the tire sidewall.

The characteristics of the factory-installed tire are likely different to a certain extent than the replacement tires.

OEM tire was the Goodyear Wrangler S/T. A lousy tire!!!! Horrid wet road traction. Almost dangerous in cootish opinion. The S/T gave a smooth ride and were quiet when rolling down the road but rain clouds caused increases in blood pressure, gastric acid output and other mind/body reactions that could conceivably lead to a shortened life span or perhaps, over time, mental trauma leading to pre traumatic stress stuff (PTSS).

Now, with the four round Bridgestone rubbery rollers, wet road traction is much improved. The sidewall screams out to fill to no more than 44 psi.

Who knows what the sidewall flex etc. is with the new tires compared to the old. And, the "hardness" of the rubber and additives is different between the tires.

Thus, the label slathered upon the truck is likely now just a general recommendation.

Above advice included a compromise setting, somewhere between the label psi and what is on the sidewall.

Makes sense to me. If at the higher psi negative results are detected it's a simple matter to reduce psi by a few pounds then note any positive or negative differences.

For general purposes, when new tires are not the same as the ones installed at the factory, the psi label on the truck could conceivably be considered a baseline advising to not go under the suggested psi.

If catatrophic tire failure due to Coot pumping new tires up to 40 psi results in mass mayhem on the road, with semi's jack-knifing, school busses rolling over and landing in the river, dozens of cars caroming across the lanes, mass destruction due to Coot's tire's psi resulting in multitudinous wrecks let it be a lesson to all present.

/worst-case-scenario fan
//mass destruction actually unlikely
///film at eleven

 

[CapriRacer]

Quote:

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........The engineers do know what tire will be installed at the factory. Surely that affects psi recommendation........

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If by that you mean brand - well, no! Tire manufacturers are told by the vehicle manufacturer what characteristics the tire is supposed to have and the tire manufacturers ......ah......I guess the best words is "comply".

But this has very little to do with pressure and a lot to do with wet traction, dry traction, snow traction, rolling resistance, ride - stuff like that.

Quote:

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.......The tire manufacturer hopefully has done what needs doing to determine the max psi placed on the tire sidewall.........

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Actually this is set by tire standards organizations. To give you an idea of how this works consider an 1/4" SAE grade 5 coarse thread bolt. All bolts that fit that description have to meet a variety of characteristics, including thread dimensions, tensile strength, etc.

The same is true for tires excpet there are several standarding organizations and they don't quite agree on the formulae. The results are pretty close - and for practical purposes interchangeable. But the important point is that if you design a tire to meet the load / pressure characteristics, then the maximum allowable pressure becomes a moot point.

Quote:

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.........The characteristics of the factory-installed tire are likely different to a certain extent than the replacement tires.......

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True, but it is not true about the load / pressure relationship - witn the provision that tires derive from different standards.

Quote:

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......Thus, the label slathered upon the truck is likely now just a general recommendation........

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Yes, but not in the sense you meant this.

I know this is terribly confusing because this isn't quite "black and white". I'm hoping that the "bolt analogy" helps explain the situation.

 

[obbop]

Analogies are nifty!!!!!

 

[Dominic]

1. Never go over the cold inflation pressure for long-term use. AutoX is one thing, 4000mi highway driving through death valley is another.

2. I always over-inflate a little bit. If I want to be sure of the tire pressure I go up to cold max and run the tire through water and measure the tread contact patch. Then I lower the pressure and do it again until I get the maximum pressure for maximum width. Then I lower it 2psi to compensate for COLD/HOT cycle for highway driving. For my subaru this means 40F/38R, and the door sticker is 32F/30R go figure

for the record I tend to not run tires with a cold psi rating less than 51.