Tire Pressure on Fuel Economy

Yes they do. I had to check out tire-loading information from my Prius.
Less than 160km/h 2.4bar/35psi front and 2.3bar/33psi back.
More than 160km/h 2.6bar/38psi front and 2.5bar/36psi back.

That “butt shaking firmness in search of 2 MPG improvement and tire squealing turns” is just your opinion based on nothing.
Increase in shaking is minimum. Tires don’t squeal in turns even at speed limit through tight turns in intersection. And gain is more than 2MPG.

Again I’m not trying to get you change your tire pressures.

Tires can be safely inflated to pressure marked on their sidewall so no “pop”.

 

This is quite true, simply because running my tyres at the recommended pressures shows over the life of the tyres that that pressure is too low. Resulting in premature replacement as the tyres have worn edges. That is the simple fact of "why NOT just the recommendation?".

If you over-inflate tyres, then you may have some credible argument. However, inflating by 3-4 PSI is not even outside the margin of error, and, as indicated by tyre wear, seems to be more in the "correct" region.

Thank you.

No.

Again, this is your right and personal preference.

Thank you again.

Go in peace to love and serve your beliefs.

 

Boy ain't THAT the truth!!!! (Guilty, but based on more hands-on experience than most)

Unfortunately, the Inflation information printed on the door sticker is ONLY valid for the OEM supplied tires. No two tires offer EXACTLY the same: Rolling resistance, wet traction, sidewall stiffness, drive-by noise, or handling at printed pressures. God forbid you remove OEM tires rated for 41 PSI and install some ULRR ones rated for 51 PSI!

THE single biggest reason OEMs choose a tire pressure is COMFORT, followed closely by drive-by noise. Notice, neither are FE, performance or SAFETY related in any way.

A digital one from a reputable vendor costing over $40 (not at the parts counter display) and/or Milton as others suggested.

 

Is that true?
I don't know if I believe that.
OEM tires can vary. The same "Prius" can come with a variety of different supplied OEM tires. BUT...the door jam PSI for whatever Prius remains the same.
When the placard say's "Whatever" PSI...for the tires...I believe that's the recommendation from Toyota for the tires on The Vehicle. Whatever tires you should put on.

I believe the manufacturer is recommending the best PSI for the vehicle.
The ratings that distract people that are on the tire....is from the Tire manufacturer (obviously) and they can have no idea what vehicle the tire is going to end up on-assuming aftermarket personal purchase. So that PSI rating is not necessarily the BEST for the vehicle or even the tire, It's the MAX the tire manufacturer approves for The Tire not the vehicle the tire ends up on.

Therefore, I always go by the PSI recommended by the VEHICLE manufacturer....not the tire manufacturer.

I think some people read the MAX PSI as determined by the TIre Manufacturer and take that as a green light to "Pump It Up" and in my opinion this is a flawed and incorrect approach.

In every new vehicle I have had...coming with whatever set of OEM tires, the max rated PSI on the side of the tire was always and has always been much higher than the recommended PSI by the vehicle manufacturer. I go with...the vehicle manufacturer knows better what's best for the vehicle...the tire manufacturer is just setting a MAX that they believe the tire can be inflated to and operated safely. NOT what is necessarily best for the vehicle.

 

You beat me to it.

Again, my pref.: go slightly higher than what's spec'd. It satisfies many facets of me:

1. Maybe a smidge better mpg.
2. I'm sure there's wiggle room in the psi spec.
3. Tire pressures will be ok a bit longer.
4. A pound or two is not going to rattle my teeth, and the suspension won't notice the difference.

 

Not knowing the logic Toyota uses in selecting tires specifically, but most OEMs spec tires that will all meet their design criteria for the pressure the VEHICLE OEM wants to operate with. Again, for RIDE quality.

Two words: Ford Explorer

Agreed, you should not need to inflate tires to "COLD MAX" unless you are traveling for extended periods at highway speeds, in HOT climates near full load (for the tires).

Two words: Ford Explorer

 

There is actually a mathematical formula to determine the correct pressure for a replacement set of tires compared to the OE set. It involves cold inflation (sidewall and vehicle mfg recommendations) pressure and load capacities of the old and new. But for the life of me I cannot find it at the moment.

 

Yes but, this reminds me of my days in structural engineering offices. A newish engineer would be sizing bracing on a wall: lots of bracing, different load cases, different spans, and would come up with unique sizes for every location, making for a lot of consternation and checking. A more seasoned engineer would go through the same sizing exercise, but then come up with one, maybe two (if it would save big bucks) cases, for the whole wall.

 

Two Words: What? What?

The Ford Explorer case is pretty specific.

Sure...you can pull it out to argue Manufacturers aren't always setting PSI with the best interests of the vehicle or tire in mind. BUT...I think the Ford Explorer...Firestone Tread Separation case...very specific unto itself.

It was just a nightmare alone.

But overall?
The doorjam recommended PSI on most every vehicle is a legitimate and valid recommendation for that vehicle....and not based on trying to cover up intrinsic flaws in designs to the detriment of the vehicle, occupants and/or tires.

Ford Explorer...Yeah...but exception..not the rule.

 

Not at all a specific case, a HUGE wake-up call to consumers who were not doing even BASIC maintenance, like checking TP or fluids. Maintenance lapses can and do KILL.

While the details are sordid, but suffice it to say Firestone disagreed with the TP recommendations of FMC for the SPECIFIC tire being used. They told FMC there would be failures, FMC refused to modify their inflation recommendations; result: People DIED.

THE reason FMC did not want more TP? Ride. The reason they did not want one more ply to handle the lower TP? Cost.

If ANYONE thinks TP recommendations are there for safety, two words: Ford Explorer.

 

I disagree.
Very specific case.

 

But it still proves that Ford does base there tire pressure suggestion on comfort. In this specific case the pressure suggestion was so low that it cased tires to fail. But since their tire pressure suggestions are based on comfort you should get better handling and safety by just raising the pressure.

And why would this be limited to Ford? Customers are still the same ones that prefer comfort over handling and safety. And as long as tire pressure suggestion isn’t so low that it causes tires to fail then there’s no controversy over it.

 

i pumped my new michelins up to 42/40 from 36, and am not seeing a difference in local ev miles. i wonder if it has more effect at highway speeds?

 

Doesn't "prove" that at all.
Again very specific case. Which was primarily a case that included arguable alleged design defects in the vehicle itself. Allegedly Ford lowered the PSI of the tires to reduce the risk of roll-over.- The decision wasn't based on comfort.
With continued problems the debate between how much of the problem was vehicle design, tire inflation, tire defect became a HUGE case. With a ongoing debate and argument.

But bottom line...The Ford Explorer...Roll-Over/Tread Separation case.....is a very singular case. By definition almost the OPPOSITE of what ANY automaker would do as standard operating procedure. Nearly an anti-example of your argument. However....

I would say, that comfort IS part of the decision an automaker makes in choosing recommended PSI, but separate from a tragic and singular case such as The Ford Explorer case, comfort is NOT the ONLY criteria.

My opinion is unchanged. In my opinion, the recommended PSI for the vehicle...is best determined by the manufacturer of the vehicle itself. The singular tragic anomaly of the Ford Explorer case aside, the designers and builders of the vehicle I think much more qualified to determine recommended PSI than the tire manufacturer who is NOT making a recommendation based on the vehicle, but based solely on the TIRE.

The number put on the side of the tire...is a number that represents what it say's...MAX PSI...which means it's the maximum PSI the tire manufacturer believes the tire can be inflated to....but it in no way represents what may or may not be the best PSI for the vehicle the tires are attached to.

Those that do NOT want to believe this?
Well....many use various threads of logic to justify inflation to various inflation levels.
Again...I've decided that I think the best choice.....is to just go with what the manufacturer recommends.
The tragic case of Ford Explorer/Firestone doesn't IMO justify in any way abandoning this logic.

 

OK. I didn’t look into it that much as we don’t even get those vehicles here. So you’re right on that one.

So now you’re agreeing with me that comfort is one factor in determining tire pressure suggestion? And since the comfort factor will only lower the suggested pressure then you must agree that raising the pressure from suggestion gets better handling and safety?

You started this by saying that over 40psi is dangerous so then that must mean that your personal opinion is that it’s safe to increase the pressure by only 2psi from suggested 38psi (front if driving faster than 160km/h).

 

No I THIS is what I said:

Given The Prius is a highly computer controlled vehicle, employing Regenerative Braking, Traction Control, and numerous systems that are directly tied into feedback that the vehicle gets from tire and pavement, it felt dangerous to me to severely alter the feedback created by pumping my tires up to marble floor levels of low rolling resistance firmness.

"Felt" dangerous to me. And I'll stand behind my entire statement. Nowhere do I say over 40 IS dangerous...under 40 isn't.

I don't care if you obviously disagree with my approach.
But don't start "saying" what you think...I think...and misquoting me.

 

Yes that’s what I meant “that comfort is one factor in determining tire pressure suggestion”. And you did agree with that.

Tire pressure suggestion is a compromise. Lowering the pressure will increase comfort. From those you can deduce that increasing the tire pressure from suggested value will make other factors better while lowering the comfort level.
Which part of the text above you disagree?

 

Listen...I think I have very clearly stated the reasons I choose to NOT run my tires above recommended PSI.
All along and at every step, I have said...those that want to...or see benefit...to increased pressure...will not be persuaded by my opinion.

I do not agree with the blanket statement that increasing tire pressure will make "other factors" better.
It certainly "changes" some factors....but "better" is a subjective term.

I have no desire to rehash or restate my neither my personal experience with experimenting with increased tire pressure, nor rehash the reasons I feel it's not the best choice.
For anyone that is interested...they can scroll up....and ignore, agree, disagree, or continue on with whatever approach they like.

 

My 2004 Prius came with unsafe tires (Goodyear Integrity) when inflated to the Toyota specified pressure. The sidewalls were too soft, the tires tracked very poorly (wobbled at highway speed and had poor traction. Raising the pressure to just below their MAX 42(F)/40(R) stiffened the tires enough to make the ride reasonable as well as giving a small improvement in MPG. When they wore out at about 50K miles I bought good tires (all rated at 51 psi MAX) and never looked back.

I'm sorry, but Toyota didn't pick a pressure that worked with their chosen tire for the 2004 Prius. Mistakes do happen.

JeffD