Incorrect Information re: Tire Pressure in Efficiency Mods

[gasstingy]

My first new car (1976 Ford Pinto Stallion) had a set of Firestone Steel Radial 500 RWL tires on it. I ran them at sidewall maximum inflation for about a year. One day I decided to try the owners manual pressure instead. Driving down I-65 at an average speed of 65 to 70 mph (yes, the speed limit was 55 in 1977) the entire tread row of the left front tire peeled off really making a mess out of the left front fender and scratching up the left door and rocker panel as well. The other three tires had broken cords in the sidewalls and would make the car physically wobble going down the road. I learned two important lessons from that experience.

Lesson 1: Firestone would not stand behind their product. I've never bought a Firestone tire since then.

Lesson 2: While the tires do tend to ride more firmly (harder), they last longer and give better fuel economy.

If you want to talk about a safety hazard, the Firestones on my Pinto should have trained the company (there were lots of lawsuits over that tire) to make a tire that the tread row wouldn't peel off of. The Ford Explorer fiasco was using Firestone tires that the tread peeled off of. Firestone tried to claim they were underinflated. Underinflation is a serious safety issue, but I don't agree that overinflation is a problem.

[Frank Lee]

F150 came with OEM Firestones- best dang tires it ever had. I hunted for exact replacements but there were none to be had

[Weather Spotter]

Anyone got hard MPG gain data for me to add to the wiki? Several of you said you saw gains, give me some numbers and how you go them (ABA, tank to tank, other).

The wiki viewers thank you!

[wdb]

Getting away from the controversy over what constitutes ideal tire inflation pressure, and back to the original post's intent:

Originally Posted by eco30BMW

I'd asked the webmaster twice to take down this misleading information from the "65+ efficiency mods" section of the site and nothing has been done...

I think there is merit in considering rewording that recommendation, regardless of where one stands in terms of ideal PSI.

Increases in steering response and wet traction with higher PSI may be generally true, but by no means universally so. Just one example would be two brands of tire in the same size, one with a max sidewall of 44PSI and the other with a max sidewall of 51PSI; is anyone here completely confident in stating that max sidewall is the ideal wet traction pressure for both?* And tire wear is such a wide open issue, with so many variables, that simply increasing inflation pressure beyond manufacturer recommendations is by no means a guarantee of longer tire life.

I'll toss out an alternative wording:

Increase tire pressure (but do not exceed max sidewall!)

Tire pressures above manufacturer's (doorjamb) recommendations reduce rolling resistance which decreases the amount of power your car needs to move. They also tend to improve steering response and increase wet traction, up to a point. Higher pressures may also decrease tire wear.

*(Putting this down here to try to keep topics separated.) My own experience is that max sidewall lowers traction, wet or dry, when compared to some value in between max sidewall and doorjamb pressures; exactly where depends on the car, the tire, moon phase, and a bunch of other stuff.

[Xringer]

Originally Posted by Weather Spotter

Anyone got hard MPG gain data for me to add to the wiki? Several of you said you saw gains, give me some numbers and how you go them (ABA, tank to tank, other).

The wiki viewers thank you!

It might be hard to get new data from these guys. If they think like me at all,
they don't want to waste fuel (and tire life) running around on mushy tires.


Haha! I was just thinking about the guy with the "Experimental Test Car" sign on his trunk..

Maybe I need a sign that says, "Warning! Keep Back, Over-Inflated Tires!"
In smaller print it would say "Tires at 40 PSI exceed manufacture's recommendations for achieving a mushy ride".

[Weather Spotter]

Getting them to do testing might be hard, getting the data they have should not be bad. They must have data or why are they still doing it? Do they like the rough ride?

I do not need great data (it would be nice) even a "I did this and saw an approximate improvement from xx.x to xx.y" or a "this got me about 1MPG).

[trikkonceptz]

The Vehicle My Mule in my garage has good descriptions of how I achieved my mileage. So from that the best I can offer is Tank to tank numbers related to PSI.

Best mileage I got with factory PSI was 32.93mpg
Increased pressure to 44PSI (Sidewall Max) and achieved 36.21mpg (Also improving technique)

Then later on i hit a high of 38.8mpg at 44psi
Jumped up again to 50psi and saw a bump to 41.3mpg, but I also slowed down 5mph on my entire highway trips.

So inconclusive but at least it contributes to the gains.

[Weather Spotter]

What car what that with?

I also added your data to the wiki:
Increase tire pressure to max sidewall - EcoModder

[CapriRacer]

Ideally we'd like to have published, peer reviewed and duplicated, studies to go on. Unfortunately, we don't seem to have that.

What we do have are some published studies showing that higher inflation pressures improve rolling resistance - and anecdotal reports to support this - but there doesn't appear to be any published info on the affect inflation pressure has on steering, traction and wear - and the anecdotal reports is mixed.

I think eco30BMW has a point. If a statement is going to be made, it ought to be backed up by data - and if the data is anecdotal, it ought to be consistent. It might be better to rephrase the statement this way:

Increase tire pressure (but do not exceed max sidewall!)

..........There are mixed anecdotal reports about improvements in other properties. Some folks report improvements and some report degradations.

[MetroMPG]

That strikes me as a balanced way to describe the mod. I've updated it.