Dealer had my tires set to 28 PSI - My 2005

<div class='quotetop'>QUOTE(macreative\";p=\"51662)</div>

Today's tire air pressure reading is a poor indication how the dealer set it two months ago.

There are two reasons.

First, you are always going to lose some air as time goes by. Some air molecules always manage to seep through the rubber and the seal between the tire and the wheel.

Second, air pressure rises with temperature. It is quite hot in Lancaster, CA, in the Mojave desert, in mid September. It is now at least twenty to thirty degrees cooler than that in the Los Angeles basin. As the temperature cools off, the air molecules are less active and get closer to each other so the pressure in the tires drops.

 

The poll is missing a common pressure... 44/42

 

I check the pressure of the tyres on my Prius every week (when I fuel up ). Usually keep it in the low 30s, but my tyres are different than the US version. I think I'll try to put a bit more pressure in them to see if I notice any difference.

 

Tires in Europe

<div class='quotetop'>QUOTE(Batavier\";p=\"51754)</div>

I use that 42/40 pressure. It works fine even in European tires. My tires are Michelin Pilot Primacy 195/55 R16.
I use same pressure in Bridgestone Blizzak WS 50 winter tires.


-Heikki

 

i use 38/36 which i guess is half way. i cant compare the ride as being stiff or rough since i came to the Prius from a ford pu with HD susp.

but right now, i am tracking gas mileage in my sisters car so i am putting gas in it. when filling her tank the other day (she has a medium ford station wagon type thing) besides the leg workouts from stopping the car (power brakes???) i noticed the ride as being a lot like a boat. in my mind, not desirable to me at all. body sway and rock was scary to me. i couldnt imagine what would have happened if i would have had to make an emergency manuver in that beast.

but is the car all that bad really?? probably not. i am quite frankly amazed at the vast differences in the way the Prius drives as compared to normal cars.

i realized that it took a few days to get used to the steering and brakes of my Prius, but i had not realized how many other things i have unconsciously gotten used to.

this experience had led me to believe that if my next car is not a Prius that i will have to learn to drive all over again.

 

<div class='quotetop'>QUOTE(DaveinOlyWA\";p=\"52042)</div>

My first car was a Fiat Spyder. Not power brakes or steering. I went from that to a Maxda 626 with power everything. A month or so later, I had to move the Fiat and was surprised at how hard it was to steer and brake! Still miss my Spyder though.

 

Tom and Ray (Click & Clack) of Car Talk fame have been my most trusted reference over the years. They have repeatedly stated that one shouldn't increase tire pressure more than 3 PSI over the car manufacturers recommended pressures. It's a safety issue.

Thus I choose 38 and 36 for my tire pressures - best mileage while still staying safe.

 

Within a week of getting my Prius, I had Michelin Harmony all-season tires put on. The dealer set the tires at 30psi F/R.

Over the past 6 weeks I have played with different settings up to the tire's 44psi max, with no F/R delta, and in different 3psi delta's F/R. The Dunlop Graspic DS2 should be in next week then I can start the science experiment all over again.

First of all, I noticed the ride quality really deteriorated especially at the tire max of 44psi. Pavement breaks and expansion joints became very harsh. On the Trans Canada, minor road imperfections really became apparent.

Second of all, I was worried about the lower psi causing dangerous heating of the tire. I took the car on a couple of two hour trips at 110km/h and temps still around 10-15 C. Even with the tires at 30psi F/R, the sidewalls stayed cool. Of course, if the temps had been 35-40 C, I might have had much different results.

Third, I was surprised at the difference in fuel economy. That is, there was VERY little difference according to the MFD and my infrequent refueling.

Eg: on a given stretch of Trans Canada at 110 km/h, the car would use 4.7 litres per 100km with tires at 44psi F/R. With the tires at 30 psi F/R, the car would use 4.8 to 4.9 litres per 100km.

So that works out to 60.1 MPG, Imperial gallon (4.54 litres per Imperial gallon), with the tires at 44psi. At 30 psi, 58.9 down to 57.7 MPG.

BTW the conversion factor is: MPG Imperial = 282.48 / litres per 100km. Sorry, don't know offhand the conversion to U.S. gallon (3.78 litres per U.S. gallon though).

So at the worst I've sacrificed 2.4 MPG on the highway. There was no difference in city speeds up to 60 km/h.

Fourth, handling issues. Honestly, the Michelin Harmony changed the car's handling - in a positive manner - much more than the tire pressure itself did. That and the fact my camber was WAY off, according to the dealer.

Although the car felt a bit nervous at 110 km/h with the tires at 44psi, at 30psi the car felt solid and in control. Given the much improved ride at 30psi, I probably won't add in the future. Though if I was going on a long trip at highway speeds in very hot summer, then I might add up to the factory recommendation 33psi.

 

<div class='quotetop'>QUOTE(jayman\";p=\"52781)</div>

Quite true. And you may actually find yourself choosing to pump the PSI during the winter because of that. It increases your awareness of the snow & ice, allowing for a more accurate feel of the driving conditions.

 

I set mine to 44/42 very early on in my ownership of my '03. I've gotten 32k out of the tires, which are known to be an issue over premature wear on the classics. I will have to put new rubber on the car before I head up to Colorado next month. They're getting just too borderline to be trustworthy in the event that I get into bad weather on the drive. As for driveability, I've had no issues with the car whatsoever regarding poor weather handling, or noise beyond the damage done to one tire driving the car to the dealer for an alignment after running over a none too small dead animal. That tire has always been noisy, and would continue to be so, regardless of the tire pressure.

 

What pressure (range) do you use for winter tires?

 

The winter tires I'm ordering apparently have a maximum cold inflation of 51psi. You can bet I would never run them at that either.

I would start with the factory recommended pressure and see what results you get. Then add air if you want to.

Don't expect the same dry handling from dedicated winter tires. Tires with soft squishy treads feel sloppy and squirmy on hard pavement, especially above freezing.

That said, I've driven on Bridgestone Blizzak WS50's and Dunlop Graspic DS1's, and swear by them. I wouldn't trade the winter snow and ice traction for anything.

 

there are pluses and minuses to all settings really and the "best" setting really depends on what you are looking for.

the lower the pressure, the smoother and softer the ride.
that is a given.

the higher the pressure, the better your mpg will be.

as far as 44/42 being dangerous, nope... not even close. your tires can easily hold 60 psi with no danger.

pressures are set with the max amount of safety and comfort in mind. keep in mind what tires go through on a regular basis all the time anyway. just tooling down the freeway and hitting small changes in elevation can put a strain on the tire that is 10 times greater than the strain exerted by air pressure.

so yes 44 psi will give you handling issues AS COMPARED TO lower tire pressures... but is it enough to cause noticable differences in handling. under certain circumstances, yes... that has been shown with most types of radials. but for most every day driving needs, you will never notice the difference.

personally, (and i base this on my brother who was a tire expert having worked in the industry for most of his life) in the winter if rain and snow will be prevalent, lower pressures will make a difference. but depending on the tire, too low a pressure will introduce body sway which will make things worse and dramatically increase wear.

keep in mind that tires deflate over time and he recommends that tires be 2-5 psi higher than normal

 

The 44/42 setting came from the classics. It was found that the tires would wear MUCH better than the factory settings, without any notable detriment to the ride quality of the car. The tires on the classics ended up being underrated for the car.

 

In other words when it came to the tires on the classic, Toyota's testing 'in all areas of the grid' was flawed. Not sure what the Toyota guy meant about the tire pressure effect on the plastics (maybe rattling??). But ride vesus tire pressure is going to be a function of the specfic brand/model of tire, and less so the car itself.