I know a higher tire pressure than what's recommended in the manual can help to get better milage.... I recently checked mine and inflated them to 35psi. It seems to help just a bit, but I was wondering a couple of things:

What's the maximum safe pressure--is it the 44 that is printed on my tires, or is it in reality more like 40?

From your collective experience, what's the optimum pressure?

(I drive an '04 HCH; half city, half highway) thanks
--A

It depends on what you mean by safe.
If you drive and corner at high speeds with 5 obese passengers in high heat (or would it be low heat?) and rain you have a different threshhold of what is safe.


My tirewalls say max is 44 psi
My doorjamb says 32 PSI
I keep mine at 40 PSI

You have to find your own personal comfort level.

Need fewer troops to support.
Drive a hybrid.
Best tank 71.65 MPG.

Before this car I spent two years learning hypermiling on my 2004 HCH1.

Amy,

The 44 PSI rating on the tire is the maximum safe cold air pressure. I run my 2004 Prius at 42 (front) 40 (rear) to get better MPG (and tire wear) at the sacrifice of a somewhat harder ride (you feel the bumps more). You should hold the front to rear differential that is written on the door jam as it is intended to give the car better handling.

JeffD

You can put a good amount of air in the tire. An under inflated tire is more dangerous than an over inflated one. The blow-out pressure on a tire is somewhere between 100psi and 200psi. After around 55 or so psi there is no gain in FE so its pointless to go higher than that. Just to note you are more likely to blow your tire at 30psi than 50psi when taking a corner or driving on the highway.

Pros of Higher presure.
1) Faster stopping times.
2) Less hydroplaining
3) Better FE
4) Higher load carrying capacity

Cons:
1) possibly uneaven wear on your tires (check them regularly for wear and reduce preasure as needed)
2) longer stopping distance in snow.
3) rougher ride (can cause suspension to wear out quicker)

My hydroponics experiment

You ever notice how hard it is to lip read cartoon characters?
"Crazy is what the sane call Delta Flyer"

Depends on tire make... my car came with Dunlops OEM with a stated MAX of 51 psi.

As for mileage improvement... I think its more psychological than reality. You did something you though would improve mileage and you drove accordingly and tahda... you got better FE. Try it for a month and tell me what improvement you made if any.

I did this experiment. I drove at +5 psi over OEM spec for 1 month and another month at 51psi (MAX). Well at first I thought I was getting better gas mileage at MAX but it turns out that I only gained about 10 miles per tank... which is nothing.

BUT... what did improve (the higher the PSI):

o Stopping.
o Cornering.
o Stopping in the rain.
o Traveling at high speeds (70 - 80 miles per hour) in the rain.

So for those reason I increase psi... to about plus 10 over OEM.

Please note... that the higher you go the firmer the car feels so you will feel bumps more than normal.

livvie;

Interesting observations from you on the real benefits of increasing tire pressure way up.

Makes one wonder if it really makes a major difference or simply changes ones driving habits to work with the increased tire pressure.

Terry

tigerhonaker
2007 HAH
__________________
Click on Pictures to Enlarge:

My tires were inflated to 50 PSI from the dealer and i drove around with them that way for 2 days. When i checked with my gauge i took them down to the reccomended 32 psi. I haven't noticed any difference in comfort or mileage so i feel more comfortable with them at the reccomended pressure.

I guess the better handling and less hydroplaining is psychological as well.

Its a fact that increasing tire PSI helps FE. Just because in your one week of testing you didnt see it doesn't mean anything. What where the weather conditions for both weeks? How was trafic? Theres lots of variables. One could offset the others.

What needs to be done is for people that say it is unsafe to actualy talk to a person who's job it is to engineer and test these tires. And those that say it doesn't help, I'd like to see a test of over a year.

My Mileage was about 34 to 35 before I increased it. It has jumped and has stayed consistantly high.

Note, when ever you change the PSI the tire will wear differently and will take time for it to show the most benifit. There is no doubt you will see a noticable difference going from 35 to 45 even displite that fact.

My hydroponics experiment

You ever notice how hard it is to lip read cartoon characters?
"Crazy is what the sane call Delta Flyer"

Just today i was wondering why I couldn't get quite up to my normal average on the last two tanks, then this post reminded me that I didn't check my tires after the last oil change I had about the time the mileage dropped. Got home tonight and yep, they had reset them to 32. So... while there are always many factors influencing FE, this reminder makes me likely to believe that the pressure does make a difference, expecially considering this is the second time it's happened this way. I will try to drive the same the next tank and see if it goes back up with the tires back at 40.

Amy,

You'll find folks here that run tires at the pressure listed on the sidewall, at 32 psi, and anywhere inbetween. All my tires had a 51 psi max on the sidewall, and I've run them at 45 psi for about 2 years now. Because there are SO many things that can influence your MPG, it's difficult to quantify if, or how much, tire pressure helps. I've found that anything that makes a 0-2 MPG difference is very difficult to detect without some kind of controlled experiment. However, I believe that higher pressure can help. I *feel* like the car rolls better with the higher pressure.

*** Retired after 65,000 outstanding miles ***