My 2004 toyota prius, I keep at 38psi. But, with the hch 2006, I'm unsure what is the "ideal" pressure to keep it at to help out the mpg. (I'm tempted to crank the pressure for max gas mileage)
Anyone got any thoughts on tire pressure?

I keep mine at about 42-44 (HCH 2004). Works good, no safety issues. I just ignore Honda's spec on the sticker and try not to exceed the tire's rated pressure.

So far I've yet to hear of anyone having a tire pressure related blowout on a 14" or larger tire that can be attributed to tire pressures. I've heard of a few guys on 13's having problems with sky-high pressures, but 13's tend to be pretty flimsy compared to larger 14 and 15" tires. You should be able to run 44psi without any problems. That's what I run in my car, and what many others do as well. It's good for about 3% higher FE in steady-state cruising than 35psi based on my testing.

I keep my HCH at 44 and my FEH at 40. I can tell when they are low, because the mileage goes down dramatically.

I am considering lowering the HCH to 40 for the winter, but haven't made that decision yet.

-Charlie...

Just a note of caution:
as some have stated above, as long as you stay within the upper limit that is printed on the sidewall of the tire, you should be fine. But how does that really work? The pressure is typically cold pressure (someone correct me if I'm wrong), so what can push you over the limit if you inflate the tires to at-the-limit values? Changes in ambient temperature, and vehicle loading can. The closer you inflate your tires to the limit, the less marging of error you have. If you inflate to within a few psi of the limit, and do so on a cold day, with an empty vehicle, my guess is that if it warms up and you load up the car, you could find yourself easily over the limit.
Just food for thoughts...

Forgive me for a silly question, but doesn't overinflating the tires make the speedo and hence mpg guages less accurate?

Don

I tried an experiment because I was not a believer of high psi equals better FE. I noramlly run 36psi all around and was getting around 48mpg. I bumped up the pressure to 51psi all around (max psi) and noticed an increase of 2 mpg on the first tank... but then it went back to my normal average. I do have to say that my worries in the rain were incorrect. I thought a higher psi tire would be worse in the rain but it turns out it actually behaved better in the rain.

What did I get out of this experiment? I noticed that handling got better as more psi were added to the tires. I noticed no increase in FE.


As PSI heads to MAX PSI (with everything else being equal):

Pros:

Handling improved.
Better handling in the rain.

Cons:

Ride quality got worst. Every bump could be felt and heard.

--
FE: remained the same, with a slight edge towards the higher PSI runs. Please keep in mind that I got maybe a few extra miles per TANK not per GALLON. My first tank fluke could have been attributed to my driving style changing to conserve as much fuel as possible.

I'm at 58 PSI in my 2004 HCH, no noticably negative effects. Last 3 tanks have averaged about 51 MPG, a little up from when I was running only 48 PSI.

No. Tire diameter does not increase by that much to skew the results. Changing tire sizes will do that.

I could be wrong but the stated max is cold MAX. Warm max can vary... but yes, you probably don't want to go over cold max.

You could always go with Nitrogen filled tires where the cold and warm psi should remain the same... or near same. If you are worried about over inflated tires.