Some Hypermiling techniques denounced by AAA

[MazdaMatt]

Absolutely, you are right that correct hypermiling involves looking well ahead and staying safe (you'd think this would just be standard practice!). Check back on page 1 for my comments about purists vs. morons. The AAA is afraid of morons overinflating and driving like most people drive. But... you never know when the guy beside you is going to suddenly swerve over and side-swipe you, or the guy in front is going to spill his coffee on his lap and slam the brakes on. Grip = safety. I will modify my techniques and my car in ways that will improve MPG without EVER reducing safety.

[dcb]

Dude, you ignore all the data in which to make any safety related decisions though! For all you know you are in more danger to a blowout or because of the reduced turn-in response or increased braking distance or increased tire wear that the lower pressure brings. You reek of death!! DO SOMETHING QUICK!!!

[MazdaMatt]

Sorry, that post makes no sense. Reduced tire pressure, even BELOW the mfg specified will result in better braking performance. Instantaneous turn-in response is greater with higher pressures, but with a sacrifice in ultimate turning grip (reduced delay, reduced friction). AND a properly inflated tire will have the entire tread surface in contact with the road, wearing evenly instead of down the middle like an overinflated tire will. All three of these points are tire basics that anybody who uses a race track knows. Why do you raise your tire pressures? It is to reduce the friction with the road! While this gives you reduced fuel consumption, it does not magically give you extra friction when you try to stop and turn, and it does not magically make your rubber less proned to wear.

[dcb]

Oh man, you are posting racing advice in a public forum?!?, ARE YOU TRYING TO KILL PEOPLE!!!!

[PaleMelanesian]

Sorry, but tires wearing down in the middle went out with bias ply tires. Radials will not wear in the middle with higher pressures, even MUCH higher. How does it sound to get over 100,000 miles out of an Accord's OEM tires? See wayne at cleanmpg. Or my own tires, with only 15,000 so far, but they still look new with minimal wear anywhere.
Or this, earlier in this very discussion:

Originally Posted by trikkonceptz

Well I will have my proof on un-evenly worn tires in about 50K miles I guess....

Prior to Hypermiling I had a set of tires on my vibe that didn't even last 12K inflated to 32psi, I replaced them with the exact same tire/brand/size and have had them inflated to 50psi since day one .... 20K miles later, they still look new and the car handles and coast incredibly well.

So already, I have proven AAA wrong, how wrong only time will tell.

Also, from this SAE paper (note that we're all using radials now),
Tread wear vs inflation pressure


Traction vs inflation pressure


Also about traction, how about this article at tirerack?

The tires ... were inflated to the vehicle manufacturer's recommended inflation pressures of 29 psi front and 33 psi rear, while the other car had its tires inflated 30% lower (20 psi in the front and 23 psi in the rear). We chose 30% underinflation because it was the percentage of loss initially established by the US DOT at which passive pressure monitoring systems must warn the driver of low inflation pressure on future cars.
...
The underinflated tires delivered acceptable steady-state cornering force once they stabilized on our test track's skid pad, but the car was uncooperative anytime it was asked to change directions. It proved to be over 2 seconds slower around our test course (2 seconds represents about a 7% loss of handling performance).

[MazdaMatt]

I'm sorry, but your charts just aren't convincing me; quite the opposite. Firstly, your infated pressure vs. predicted wear chart tops out 4 psi below your COLD recommended reading and seems to be trending towards a decline after 40psi. Your tires are probably running 49-51psi hot which is way off the charts (they did not specify cold pressure, so I can only assume that it was tested pressure). Your charts are comparing proper to under-inflation, not proper to over-inflation. You can not infer that the trend continues forever else we'd all use 5,000psi tires, or better yet, steel hoops.
Secondly the shoulder-crown wear index chart does show some trending towards wearing down the middle up to 40psi, which again is 9-11psi short of the hot pressures you are running.
The charts for braking power vs. psi show a flat trend. I can tell you from personal experience that this is not true. Also from the combined and accepted experience of many years of many racers in many types of cars with many types of tires.

Anecdotal evidence: I accidentally did not set my tire pressures after the "tire guy" mounted and balanced them. The mounting put the pressures around 50-55 psi on each tire. At the end of the day, 1" rubber on each side of my tire was still clean! It had not yet touched the road that day. You can't tell me that if i continued to drive like that, the shoulders (which don't touch the road) would wear at the same rate as the crown(which is supporting the whole load of the car).

[PaleMelanesian]

Fine then. Your personal experience trumps mine, and several others', and SAE engineers. Your one day of higher inflation matters more than thousands of miles others have been tracking.

[MazdaMatt]

I don't mean to offend, but it seems that the data you're providing is being bent to your purpose. Even on that page that you linked there is a note at the bottom that says the paper is a dissapointment. I'm an engineer. I could go and submit a paper to SAE showing opposite results, it doens't make me right. I'm just worried that some people in this community are warping their "facts" to justify things that they do. Sure, overinflate your tires, but don't expect better performance out of them. lower RR is due to lower friction. Friction is the stuff that makes you turn and stop.

[PaleMelanesian]

Ok, I mis-spoke. I'm not out.

The data in that study agrees with my experience and that of others. Perhaps your tires were only touching in the middle because they were already worn on the edges from underinflation, and now with higher inflation, they went to "flat", but since the edges were worn, they did not touch. I assure you that my tires are on the ground all the way across the tread.

I have informally tested traction, as well. In my limited, non-scientific testing, it's at least as good now as it was at Honda's recommended 32psi, on both dry and wet roads. It's not as good on loose gravel. Since I've tested that, I can make informed adjustments to suit when I'm on that surface.

[MazdaMatt]

My tires were brand new, that's why they were fresh off the mounting and balancing machine. When i let all the air out, i can clearly see a convex shape in the tread. These are DOT rated tires, not anything special.

I am glad to hear that you have tested the effects in different conditions and adjust accordingly. I think that is what AAA is afraid that people will NOT do if they just hear that its a good idea and bump up their pressures.

I will try to find some published information that supports OR denies what I've been saying and I'll post it up; better to know than to be correct, afterall. Oh yeah, I also don't like that paper because it only tested to 13k and blindly assumed the results at 80k.