Maximum PSI ?

I didn't know that.
In this case, I rest my case, and I admit was mea culpa. to insist on something I thought was right.

 

Just curious. Have anyone seen any tire inflation recommendation given by tire manufacture? The label on the side of the tire is the maximum cold inflation pressure the manufacture indicates to be safe for that tire model. It is not the recommended inflation pressure. I have never seen or read any tire pressure recommendations given by tire manufactures.

 

The label might be for OEM tires. Yes, Toyota uses different brands from the factory, but how different are the tires? Are they all the same sidewall pressure rating? close in load rating?

When the gen 2 Prius was new, people here following Toyota's tire pressure setting were reporting excessive wear of the outside tread, a sign of underinflation.

They don't because they don't know how heavy the car the tire is on is going to be.
On the other side, the car manufacturer's recommended value assumes the owner will always use a tire of the exact same specifications as what was installed at the factory.

Take two tires that are exactly the same in size and ratings except for the sidewall pressure. The car maker uses the 44psi tire, and recommends 34psi. If replacement tires are rated 51psi, they'll need to be inflated to 39psi in order to support the same weight as the OEM tires at recommended pressures.

 

Sounds plausible, but not sure about that. Tricky stuff like that, and the automobile manufacturer doesn't tell you about it? Think I'd stick with recommended tire pressure.

 

Few months back, had an article about the tires used on RVs come up in my phone feed. Do any highway traveling, and you've seen them, perhaps not competing up with the cars, but keeping up with the trucks on the interstates.

The common tire model installed by the manufacturer was one designed for local delivery trucks like UPS's brown ones. The max speed rating is 60mph. How many RV manufacturers inform owners to keep it under 60?

 

That still says nothing about tire manufacture recommendation. The sidewall number is still a max pressure safe to operate that model of tire. I don't think the tire manufacture is "recommending" to inflate the tire to that number.

 

I've seen a bit different wording on different tires. One of my past tires just gave the required pressure for use at its maximum load rating. It wasn't worded as a maximum safe pressure.

I noted the same on a few of our past cars. Well, including the spouse's present daily driver too, which I bought for her just over 3 decades ago. Also excessive tendency to hydroplane, at lower speeds than some other cars. All of these issues were eventually fixed by bumping the pressure significantly above the door placard suggestions.

Ford Explorers of that era suffered a rash of fatal rollovers, with several hundred killed in the U.S. alone. While defective Firestone tires drew the initial blame, the investigation ended up with a laundry list of errors by the tire maker, vehicle maker, and drivers. One of the very significant errors: a too-low recommended inflation pressure by the vehicle maker.

These issues ended my faith in those recommended pressures. They haven't regained my faith.

And it didn't help that, after seeing several comments here long ago that numerous European models have multiple choice pressure recommendations, based on usage. And when we later rented cars in a couple different places in Europe, I actually saw that on the cars we rented. Someday I'll have to dig up my own pictures of those labels.

If European cars can have a spread of recommendations on the same care, why don't we see the same in the U.S.?

 

Humm, that sound like the sidewall psi is actually the "minimum" pressure required at its maximum load rated for that tire. Of course, when I buy tires, it never comes with an owner's manual, so I don't know for sure what it really means. But, looking at 4 different tires Bridgestone, Yokohama, Goodyear, and Michelin, all say "MAX" on the sidewall psi.

 

The maximum pressure on the tire sidewall is the maximum safe cold tire pressure. Never exceed this pressure when the tire is cold. There will be zero benefits in handling, durability, and fuel economy. However, you will see dangerously poor handling, dangerously harsh ride, significantly increased wear on suspension, significantly increased risk of road-hazard damage, significantly increased tire wear, and a tire that can explode and be very dangerous.

While tires usually take 100+ psi before they explode and seriously hurt or kill someone, still don't this. You can watch YouTube videos of how tires explode like a bomb when they are overinflated.

The load rating saturates well before the maximum cold tire pressure. See the table here:

https://www.toyotires.com/tires-101/tire-load-and-inflation-tables

When I first bought my 2020 Prius Prime XLE, I was putting 40 - 44 psi. The handling and ride was rather poor and the car felt very unsafe. I started using the recommended pressure after a while, and the car became a different car, handling and riding much, much better. I didn't notice any change in the fuel economy at all. I am getting ~ 65 mpg in gasoline mixed driving and ~ 38 miles in EV city driving.

 

Not only that, but tire manufacturers cannot provide recommended tire pressure without knowing what vehicle the tire is used on. They can only provide max tire pressure which will always be the same no matter what vehicle the tire is installed.

 

As long as you do not exceed the max pressure, you should be OK.

 

I left a 'don't' out of the first line of my response. Tire manufacturers don't make a recommendation for a pressure for a car, because the tire can go onto numerous car models; each with different needs from a tire.

What you quoted was an example for the second line. that the car manufacturer's recommended pressure may not apply to all the possible replacement tires the owner could put on the car.

It seems the car manufacturers all American drivers want soft, couch like rides from their cars, or they are trying to mask the harshness of suspension designed for performance or for trucks.

I find the ride with pressures under 40psi spongy, even wallowly, depending on the car. Ride quality is like seat comfort, user dependent.

Kept the 2005 Prius tires around sidewall ratings, and was getting 58mpg in mixed driving.

 

Well you haven't looked very hard, it seems.

 

Not exactly. The tire makers provide pressure recommendations based on the weight load that the tire will be carrying.
What exact vehicle really isn't important.

 

Can you point me to any documentation or web site where I can find such recommendation? No, I have never looked for them. As I said, I never had any tire I purchased that came with owner's manual. If I have to go online and look for it, certainly the tire manufactures are not pushing very hard to educate consumers about their recommendation.

 

Moreover, keep in mind that the four-wheel alignment is done at the factory-recommended tire pressures. If you change the tire pressure, the alignment will change significantly, which will in turn alter the handling drastically, usually in a bad way.

From my experience going over the factory-recommended tire pressure had no noticeable effect on mpg.

 

It is the industry (TRA (US), ETRTO (Europe), and JATMA (Japan)) that makes the load vs. pressure tables, not the tire manufacturers. It makes no difference if you have Michelin or Toyo as long as they have the same dimensions and of the same industry spec (such as P-metric or ISO-metric).

You can find the load vs. pressure tables and charts here. Note that P-metric (starting with a P prefix) and ISO-metric (no P prefix) have different load vs. pressure ratings; therefore, make sure that if your car came with ISO-metric tires, do not switch to P-metric tires and vice versa. For example Toyo Nanoenergy A41 is ISO-metric, whereas Toyo Nanoenergy A29 is P-metric, and they are not interchangeable.

https://www.toyotires.com/tires-101/tire-load-and-inflation-tables

 

Not to mention that the selection/recommendation of tire class and specification is done by the auto manufacture, not the owner. The vehicle owner can select from a variety of tires, but the range of tires available for the owner to choose from is usually provided by those who are far more knowledgeable of the product and it's end use.

 

How will recommend the auto manufacturer a tire that is produced many years after car manufacturer date?
I think the process is like this: tire producers (Michelin, Bridgestone, Dunlop, Goodyear, etc) go to Toyota, Ford, etc car manufacturers and present their stuff. If the car producers will be convinced to choose one, here we go.

 

Toyota (and others) often have more than one tire put on a specific model. Maybe due to supply limits (from any one tire manufacturer), or who knows.