Tire pressure

[lmp]

Hey,

I know there are a lot of conversations about tire pressure, but I somehow didn't find any, exactly about following.

As I understood from many posts, to get better economy it is good idea to pump tires harder than recommended from manufacturer.

So main question is how about drawbacks from hard tires. Mainly I'm talking about safety issues. For example one issue could be rainy weather. Not only.

Other question is why if it is much better from economy (so ecology too) point of view, why Toyota recommends lower pressure?

And as addition, I'm from Europe so we have different units If I have calculated correctly it is somewhat 2.7 atm (40 psi) people tipically use?

Cheers

[Kcissem]

Originally Posted by lmp

Hey,

I know there are a lot of conversations about tire pressure, but I somehow didn't find any, exactly about following.

As I understood from many posts, to get better economy it is good idea to pump tires harder than recommended from manufacturer.

So main question is how about drawbacks from hard tires. Mainly I'm talking about safety issues. For example one issue could be rainy weather. Not only.

Other question is why if it is much better from economy (so ecology too) point of view, why Toyota recommends lower pressure?

And as addition, I'm from Europe so we have different units If I have calculated correctly it is somewhat 2.7 atm (40 psi) people tipically use?

Cheers

I do believe the only drawback is ride comfort, which is the main reason toyota recommendations are conservative. Higher PSI will benefit you more than hurt you, IMO. I have not raised the PSI myself yet on my 2 week old prius, but plan to on the next fill up. I plan to try 40front/38 rear.

[eestlane]

Hey Lauris, prauks Riga! Don't listen to all of the "high pressure nuts" on this forum. I tried it higth and I tried it low. Fuel economy is improved very little versus the rougher ride, more damage to suspension components due to excessive shock, poorer handling in crosswinds, tires being more susceptible to road hazards (some gravel roads in Latvia, just like in my birthplace Estonia), etc. Toyota engineers ran many tests to recommend the proper tire pressure for this car. After all, the main purpose of the Prius is to get good gas mileage. So why would they throw away some of that good mileage just to get a little bit of a softer ride?

[bac]

Sorry .... gonna have to quote in English measurements of psi.

Anywho ........ I've done a lot of experimenting with tire pressure. I've gone as high as 44/42, and as low as 33/35 (Toyota's). After all of this, I've found 38/36 to be about perfect.

It's really a trade-off between comfort and FE. However, I have found that if my fronts are 40+ psi, the auto gets a bit drifty on the highway at speed (75+). Therefore, safety also plays a role.

My advice is to try out how different tire pressure feels to you .... then make an educated decision based on that feel, and what you've read on this board.

... Brad

[F8L]

Originally Posted by eestlane

Hey Lauris, prauks Riga! Don't listen to all of the "high pressure nuts" on this forum. I tried it higth and I tried it low. Fuel economy is improved very little versus the rougher ride, more damage to suspension components due to excessive shock, poorer handling in crosswinds, tires being more susceptible to road hazards (some gravel roads in Latvia, just like in my birthplace Estonia), etc. Toyota engineers ran many tests to recommend the proper tire pressure for this car. After all, the main purpose of the Prius is to get good gas mileage. So why would they throw away some of that good mileage just to get a little bit of a softer ride?

Care to show us "nuts" your scientific testing of high pressure vs low pressure?

[eestlane]

Dear F8, as a professional test engineer I am quite capable of running various tire pressures and comparing long-term mpg differences, which I did. I found no mpg increase from higher pressures that were worth the negatives I stated. An increase of 2 mpg is not a significant percentage of the overall mileage, and not worth the disadvantages. Also, as an engineer, I somewhat resent the amateurs on this site claiming outrageous pressures (50 psi) as being "safe", when Toyota's professional engineers recommend 35/33 psi. You think they designed a very good car and then arbitrarily assigned the recommended pressure willy-nilly: "Oh, let's see now, what should we recommend as tire pressure? Oh well, lets say 35/33 and see if the customers accept that value"? Think again.

[bob749prius]

Children...Children...You are blowing this out of proportion. As long as you say within the limits posted on the tires itself, safety is not an issue. Both of you are right. It can be argued the same way as to what is the best way to drive a Prius; for enjoyment or for max. MPG. I find this and other posting interesting if not educational. Let the buyer/driver decide. I thank you for your comments and discussion. Bottom line; both of you are right.

[msirach]

There is a retired tire engineer that has some very good data and has answered a lot of questions on another forum. Here is the link to his info.

[msirach]

Here is a link to an article at officer.com on tire pressure. I hope these articles helps clarify what some of us "nuts" are doing. I have the Bridgestones on our Touring and it will glide, coast, roll and propel itself much farther with at least the sidewall rating of 51 psi than at the paltry 30's of the doorsill placard. Super highway mode can be engaged much easier and farther as well.

[hill]

Originally Posted by eestlane

Dear F8, as a professional test engineer I am quite capable of running various tire pressures and comparing long-term mpg differences, which I did. I found no mpg increase from higher pressures that were worth the negatives I stated. An increase of 2 mpg is not a significant percentage of the overall mileage, and not worth the disadvantages. Also, as an engineer, I somewhat resent the amateurs on this site claiming outrageous pressures (50 psi) as being "safe", when Toyota's professional engineers recommend 35/33 psi. You think they designed a very good car and then arbitrarily assigned the recommended pressure willy-nilly: "Oh, let's see now, what should we recommend as tire pressure? Oh well, lets say 35/33 and see if the customers accept that value"? Think again.

You hear that Evan? those of us with 60mpg - 600+ mile per tankfull are not safe. Those of us who've been running 48-50psi and higher are dangerous. toung&cheek done. Now, on to serious-ness.

Example #1 Our Lexus 400h hybrid came with a tag stating 34psi. Most 400h owners ended up with balding tires within 12K miles.

Example #2 My electrical engineer father in law always designed his projects with circuit boards with an empty spot. He said the reason was because his fellow engineers were often "idiots who'd forget critical things, and the bald spot allowed for intigration of the item(s) they'd left out".

In case the point is not glaring, what ever your craft, it doesn't mean "THE-authority" is always authority. Sometimes one has to reverse engineer, so that proven results match what the slide rule says, in stead of the other way around.

That said, no one running 50lbs here on PC is hard driving, diving through gravel hairpins, because we know soft tires on a BMW will respond differently than our Prius. You have to be senseable take all the variables into account. 50lb psi prius drivers drive slower, and more anticipatory.