So I've just had a couple of my best commute-only tanks. On my lousy 6-mile commute with 13 stop signs/lights, driving normally but at the speed limit, getting over 50 MPG.
After this last fill-up, I decide to check my tire PSI, and lo-and-behold, they are all at 30-32 PSI. Probably the result of the dealer resetting them when I had my recall service done about a month ago.
I normally inflate the tires to 36-38 PSI. But at 30-32, I got equivalent or better mileage. Hmmm.
Which got me to thinking (always a dangerous thing). I wonder if there is a point of diminishing returns regarding PSI, especially for us "mediocre-milers" who get around 48-50 MPG.
I know that there is a huge difference in MPG if your PSI slips down under 30; I'm not questioning that.
But I'm wondering how much value you get by inflating them much over the recommended 32 PSI. Perhaps at 32, you have already achieved a fairly optimal amount of low rolling resistance, and the benefit of going to higher PSI is not that significant for those of us who are not hypermilers.
I had a similar experience when I had the recall done. I have noticed an increase in mpg since the recall was done and finished out the tank with about 50 mpg. Then I increased the tire pressure to 40psi and noticed and additional 2-3 mpg increase on the first full tank after the recall. It's been very hot here, 90-100 deg, so maybe the added heat increased the psi even more for enhanced FE.
This has come up in at least 3 different threads, but I'll post it here too. In my testing, 97 Civic HX, 195/55-15 tires and mileage calculated with a ScanGauge the results were:
46psi: 59.7 mpg
35psi: 57.6 mpg
That was 1.3 miles, 3 runs in each direction for each tire pressure setting, 48mph constant speed. Results were pretty consistent from run to run. Like you said, it doesn't appear to be a dramatic difference, especially if you're not going for hypermileage. It's a definite measurable difference, but not a huge one.
As pressures drop lower, I imagine the difference is more extreme however. Normally I can move my car back and forth in the garage with one hand when it's in neutral with the parking brake off. The other day I couldn't get the car to budge an inch, even pushing as hard as I could with both hands. I look around and the passenger side tire is flat - I'd run over a screw the previous day aparently.
I've considered doing another set of runs when it cools off and compare 45psi to 35psi to 25psi. I've got a digital pyrometer being shipped to me, so I can even take tire temperature readings. My two main reasons for not having done the test already are that I don't want to potentially damage the tires from running them underinflated, and also the data doesn't help me personally. Sure, it's interesting to know, but I check my pressures every few weeks anyway and they never even get below 40, in my case.
___Although you will not get me to do it lower your pressures back to 34 #’s for a day or two and see the real world difference. You would be surprised at how much better you are performing behind the wheel as well as your HCH’s efficiency due to being setup a wee bit better today then last year given all those extra miles.
The mention of diminishing returns raises another issue in my mind. The conventional wisdom is that under-inflated tires will show relatively more wear at the edges, while over-inflated tires will show more wear at the center of the treads. Tires are designed so that an optimal tread surface area is obtained across the tread at the recommended psi. Has anyone noticed premature wear patterns of any kind as a result of increasing the psi in their tires?
I generally find that tyres are more likely to wear on the edges first due to tracking problems etc. I have also heard that power steering can have this effect on some models - not sure why.
I purchased my car used and the tyres are now almost due for change because of edge wear. Since owning the car I have over inflated them to 48 psi cold in the hope of squeezing a little more mileage out of them.