Just picked up a beater 92 Civic hatch to deal with that I live approximately an hour from civilization, regardless of if I go north, east, south or west. My first run of sixty-six miles produced calculations of forty-four mpg. I was expecting down around thirty-four, so that was a pleasant surprise.
I noticed a slight miss on the first run. The plugs look real good (new), as do the wires. The cap showed signs of contamination, though it didn't look too old. I may swap it out and I will check the timing. Either could give me a slight boost.
I note that most go by manufacturers directions for tire inflation. However, manufacturers don't know what tire you're running, so should state their specs as approximations. For example, I switched my Astro to 6 ply tires that can hold up to around sixty pounds. I run them at around forty-five, to reflect the load they are carrying. Subsequently, they are wearing better, and some of the slop in the old steering has reduced.
Most tires I see have more wear on the outside than the center, suggesting too little air for the load they are carrying.
On a side note, I drive two other rigs that make the Honda mileage look even better. I have an Astro cargo van does about seventeen to twenty mpg. I also have a Grumman step van (the Twinkie mobile), which does from seven to ten mpg. Gads I like that Honda.
I agree with your tire inflation observations and choices. I discovered around 10 years ago that extra inflation benefits me. Over time I've experienced and learned more of its benefits...and still no disadvantages in sight.
Manufacturers calculate inflation recommendation using the following variables:
- maximum load the vehicle is rated to carry at the maximum speed they expect to be legal
- tire size
- minimum inflation required for those variables
As long as you're not overloading, speeding, or using different size (low profile, narrower, upsized wheels, etc) tires the recommended inflation is safe, but in my experience it's rarely enough to be optimal. Changing to higher load range tires (they don't actually use the ply system anymore, since tubeless radials don't use more plies the way bias ply tires did) doesn't require additional pressure but it certainly allows higher pressure than the previous tires.
I do usually limit myself to the maximum pressure rating of the tire for legal compliance, and I back it off if traction is adversely affected (only ever happens on the rear of my pickup with the bed empty and 80psi Load Range E tires).