This article is often mentioned for those inquiring about increasing tire pressures. It took this article for me to decide increasing my tire pressures above vehicle manufacturer spec but below tire maximum sidewall pressure (cold fill) was A-OK.

- Shannon (Geeky, Wild Texan)

I noticed no difference in FE but much better handling at higher PSI.

Off the topic, Scott, but you wouldn't happen to have a Galaxy Gray HCH2, would you? I was up in Dutchess on Monday and saw one heading south on Rte. 9, somewhere between Poughkeepsie and Fishkill. Wappinger's Falls, maybe?

Would-be hypermiler

Sidewall max for me (44 PSI), I usually go a bit over, but it leaks back down
by the time I am ready to check pressure again.

Government studies (www.nhtsa.gov) show that up to 35 PSI, pretty much everything but the ride gets better, FE, wet and dry handling/traction (this one is counterintuitive), reduced hydroplaning, tire wear, risk of blowout due to underinflation. Most of the differences were small however, so radical changes in PSI aren't going to make that big of a difference, but it sure is a decent argument for inflating to at least 35 or a bit higher, regardless of what manufacturer recommendations are (my sticker says 30, ick).

And when you get below 30 PSI, risk of catastrophic blowout begins to increase. By the time you hit the low to mid-20's you are in serious danger.

Above 35 PSI we can extrapolate that diminishing returns probably occur, and perhaps at some point the curve may inflect for a slight loss for some items, but people using very high tire pressures report nothing significant.

More useful tidbits are that a 10 degree change in temperature equals about 1 PSI increase. Tire engineers have admitted off the record that blowout pressures are two to three times the sidewall stamp, so a few PSI over is no big deal. Underinflation is a far greater danger.

Escaping the myth of reduced traction at high PSI was hard for me. I saw the numerical data, knew it was true, but I was still nervous driving around at 44-48 PSI.
It took someone cutting me off, forcing me to do a panic stop, and later realizing how nicely the car stopped for it to fully sink in.

The two things most noticeable to me when I increased PSI were:
o - hydroplaning was dramatically reduced.
o - the little bumps on freeways are a lot more noticeable.

I don't fear rain like I used to, but I fear concrete highways. :-)

Kurt,


Brilliant post. I had no idea at all.

I've read several threads talking about increasing psi to increase FE, but I was always concerned that I was sacrificing safety.

I currently run 40psi on my HCH-II. The rides a little firmer, but big deal.

I think I'll try 44psi and see what happens.

Once again....brilliant!

Again, you will not see a gain in FE at higher PSI, handling and braking will improve (especially in the rain). I suggest you try running a month at recommended psi and a month at max psi to prove the FE point.

I had the dealer put it at 40psi.

44 fronts, 42 rears (compensate for engine weight)...seems to work nicely on my 06 civic hybrid.

My 06 came from the dealer with 46 in the fronts and 47 in the rears. It's been 2-1/2 months now and the tires are holding the pressure. When I test drove the car, I thought there was a little too much road noise. Now I know it's from the higher pressures.

Mark

I upped the air pressure to 45 on all four and immediately noticed that I actually would glide 1-2 mph faster in certain EV mode spots during my commute. Normally going down the mountain I would be at 56mph and today the car was at 57-58mph. This should definitely help to ensure that I stay at at least the EPA estimate. I did also notice a slight increase in noise and bumpier ride. I'll take that in exchange for being able to glide a little further/faster.

James


Best MPG tank: 57.7 calculated
Best Trip: 73.8mpg displayed(Palmdale"LACR" to LAX)