Much has been written about the various steps people use to try and improve their mileage. Some of the are logical, safe and advisable. Others may save a few dollars in the short run, but might end up costing more in the long run. Finally, there are some that are downright dangerous or might even be illegal (although, O.J. can walk free, I doubt some of the reckless drivers will end up doing time).
I'd like to have a thread that serves to discuss the other side of these techniques.
Let me start out by saying I am not an engineer, nor have I studied physics (since high school, that is), so much of what write about is gathered from 32 years of driving as well as speaking with various mechanics and doing some online reading (translation...I am not an expert).

First point to discuss, tire inflation. I was in Sears Auto Center this weekend and I asked the manager about tire inflation. He mentioned that 'over inflation' had dubious value, since it reduces the tire's useful life and provides less traction (less rubber meeting the road) in case of severe tire maneuvers. Now, I know there are many out there who would argue against this line of reasoning, some with more knowledge than this manager. But the question is, if you improve your mileage by from 35 MPG to 40 MPG (assuming 12,000 miles per year and $3/gallon) you will save 42 gallons or ~$126/year. But if your tires last 3 years instead of 4 (wild, unsubstantiated estimate) and a new set costs $450 (just a guess), you've ended up giving up your fuel saving by increasing the effective cost of your tires. Now, throw in the possibility that your car might not perform as well under an extremely adverse situation and you might ask yourself, is it worth it?
For anyone saying they handle as well, answer this one question...if you were coming down a steep hill at a high speed on a rainy night and were going around a sharp curve and needed to make an evasive maneuver, would you prefer the tires to be inflated at the manufacturer's recommeded pressure or would you want the tires to be over inflated by 5 or 10 PSI? I don't have the answer and hopefully, no one will ever be in that situation, but I think a scenario like that is enough to have people think twice about over inflation. Shouldn't it?

Another situation (although I rarely see it at these forums) is tailgaiting large trucks. Forget the danger factor, which should seem obvious to anyone out there, what about the increased likelihood that a stone will get thrown up and crack or chip your windshield?

I've seen others discuss swithing the gear to neutral (which I believe is illegal, not sure) while driving. What about the safety factor here?

My point here isn't to get up on a soap box and tell others that their techniques are wrong. Rather it is to start a discussion that deals with the other side of the mileage improving decisions.

I don't have the answers, I am not an expert and I am not saying that anyone is doing anything wrong. Some of these things are wrong for me, so I don't do them, but if you are comfortable with them, it's your choice. This thread is for the newer hybrid drivers who are trying to learn.

 

You make some interesting points and, like everything else written, some of them require plenty of thought.

The tire issue is, of course, a major item on your list and yes, 5-10PSI should be avoided for an extra couple MPG. But 2-3PSI shouldn't affect handling and may give a small improvement in gas mileage without increasing risk or tire wear significantly.

As for "coasting', I'm not sure what the difference is between throwing the vehicle into neutral and the engine cutting off on its own as you slow down. Both require braking without engine assistance.

Which brings me to another point. Engine braking. Many people drop down to the B setting (or on other cars, the option to drop a gear for hills or slowing down) to use the engine to save brake wear. I do this myself sometimes - and it doesn't seem to affect MPG).

I wonder what's cheaper to replace though, as set of brake pads (and maybe rotors) or a gearbox out of warranty?

 

Plenty of references, but it appears to violate some state laws (Google), probably for a good reason.

 

Empirical evidence from running my TCH Bridgestone tire pressures at 42psi front / 40psi rear for the past 34,000 miles has led me to believe that Toyota has the recommended pressure set on the low side. I find the handling very good, even in the rain.

I say this as tread depth measurements on my tires have shown very even wear, with no evidence of premature center wear that would be expected if the tires where in fact over inflated. The tires measured 10/32 new, and currently measure 6/32 after 34,000 miles. The centers measure about 1/2 mm thicker than the edges. If anything, I think the higher pressure has extended the tire life as well as improved handling and MPG.

The few times the dealer has lowered the pressure to 32 psi during a service, I noticed the handling was markedly poorer, especially noticeable when cornering.

 

My understanding is that higher pressures are better on wet roads (to squeegee out the water and prevent hydroplaning) however lower pressures are better on dry, gravel, or sand (more surface area). I think manufacturers used to specify lower pressures because they gave a more comfortable ride, but with the push for greater gas mileage and the scandal with the Firestone tires on Ford Explorers (the specified pressure was way too low) I'd doubt that they would still do this.

The difference between switching to neutral (or even manually shutting off the engine) and having it done automatically is one of control. When the TCH shuts the ICE off you still have full braking and steering and power is available instantly (albeit limited to 40HP until the ICE kicks in again). When a conventional car is shut off to coast you loose the power assist in the brakes and steering and restarting for power is more involved. Thus it is potentially dangerous.

The merits of tailgating trucks are so offset by the dangers, it isn't worth discussing. I don't even like to be anywhere near their tails. Have you ever been behind one that has thrown a tire tread? Forget the pebbles!

 

I agree. For years, I have measured my tire wear across the entire tread width, and I have found that the book values supplied by Toyota for my Corolla, Camry, Tundra, TCH over the years have been to low, resulting in uneven "outside in" tire wear. My TCH has Michelins, and I run them a little lower than Nash at 40/38. They have 16,000 on them now (the other 4K is on the Primacy snow tires) with perfectly even tread wear and much less than 50% gone to the markers. Rain is what Western Washington is all about, and the handling is better at this inflation that when set at factory recommended settings.

I would argue against the implication that over-inflation acheives it's improvement in wear from loss of footprint, and therefore loss of traction. Instead, I think the primary mileage improvement comes from reducing the "squirm wave" flexing as the leading edge of the footprint distorts and also the trailing edge as it restores shape. Less distortion cuts down on compound heating, which is a major contributor to wear.

 

I have been following the discussions here for a while and decided to jump in on this one. For those out there that have raced in SCCA or rally competition, most of you would never keep a tire at or below "recommended" air pressure.

The tires run cooler, have a precise "turn in" when cornering and are more stable and predictive when inflated 3 to 9 pounds below maximum. The tires will not scrub off speed in a corner nor roll over on the sidewall under severe lateral load like a tire that is at standard pressure or below. This will place the tread where it will do the most good (flat on the road). The only place for an under inflated tire would be on the drag strip or rock crawling.

The manufactures have to balance ride qualities along with other issues (they do not know what type of replacement tire you will use) when deciding the "recommended" tire pressure on a vehicle. The best bet is to buy the same type of tire over several cars, watch the tire wear and pressure and make your own decision about inflation pressures. By the way, mine are factory Bridgestone’s (until they wear out) inflated to 42 psi.

When these are replaced it will be with Michelin tires at 41 psi. I have put about 550,000 miles on those tires in our family in the last 11 years and I trust them with my life. More importantly, I trust them with my family's lives in all weather conditions.
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David, I agree with everything you say, I've always been a fan of increased tire pressure (and Michelins) ...but have a question, perhaps I am able to answer it myself, but....here goes:

The difference beteen 41 psi and 42 psi is small. How do you know you are getting exactly 41 or 42? I have 4 pressure guages, (5 if I count the one on my air pump) and none read the same. Time for a new guage? But how do I know that new one is correct?

 

I use one gauge at the house. It's made for racers and it's a little pricey but the accuracy is to within .5% and reads to the 1/10 of a pound. You can find them for 55 to 60 dollars online if you want to pay that much for one. It's an Accutire racing tire gauge with an internal bleed off valve.

Yes, I do my own maintenance and I am a little **** about it but we all have our vices... sometimes more than one....

 

I agree with all the tire comments. I have seen increased handling when the tires (Michelin) are inflated to about 40 psi. My one concern is when they get hot, after a very long trip (500+ miles), I have seen them hit about 50 psi.

I don't have the best pressure gauge though.

The net is (as far as I am concerned):

Increased psi = better handling, mpg
Normal psi = better ride

I will take the better handling and mpg over ride (I came from the truck world).

Mike