I noticed my gas milage deteriorating over the past several months and I have been racking my brain trying to figure out why. I thought, well it is summertime...its 100 degrees down here... we are using the a/c more...the gas companies have figured out a way to for the fuel to burn faster in our cars...I'll try a different brand of gas...I need to clean my air filter...I need to reset the computer settings...I'd check the tire pressure but I just had the tires rotated at a Honda dealer 1500 miles ago; surely they would have set it right...right?

My tires were at 29 to 33 p.s.i. I looked on the tires and saw the max at 41 p.s.i. I set them to 39 and noticed an immediate improvement. I finished my last tank at 27 m.p.g. even after a few stints over 6000 rpms.

I still have never been able to get more than 15.5 gallons in my tank and I have a theory about the phantom 1.6 gallons that supposedly still exist in my tank. Maybe the tank extends up from the fill cylinder a couple of inches making the volume of the tank 17.1 gallons, but we never get to use it because the pressure pushes gas up the cylinder and stops the pump before it can reach its full potential. Just a theory. I can't figure it out. I ran out of gas once and the car only took 15.5 gallons.

Anyway, I figured out my mpg problem and I now carry around my own pressure gauge.

 

Just by increasing the psi to 39 you increased your mpg. I need to try it.

 

u will blow up ur tires soon...coz the pressure will rise as u r driving and will be very high at high speed


watch out watch out

 

The harder the tire pressure, the easier the tires roll and the less friction, which equals better gas mileage. *However*, the big trade off is usually in ride quality and uneven tire wear. The ride will be extremely harsh and the centers of the tires will wear out faster than the edges. Additionally, as tires warm up with use, the pressure rises automatically. Like samkws pointed out, if you start at 39 psi, after a few minutes of driving the pressure will rise past the 41 psi, and you do increase your risk for a blowout substantially.

My suggestion: back off the pressure to 34-35 psi. It's still 4-5 psi greater than the stock recommendation, but your ride should be smoother, tire wear will be better and the safety factor will be better. You should still see a slight improvement in MPG too.

 

I will back it down to 35 and see how the mpg holds up. Thanks for the advice. By the way pianoman41 what is your favorite brand of piano? I have a music store and we love Kawai.

 

we used to have a kawai too...but sold it after i came to canada...

 

Wouldn't the tire manufacturer have already taken that into account when specifying the max allowable air pressure for a particular tire, assuming of course they performed testing on said tire beforehand...

 

I believe you are partially correct--the PSI listed on the side of the tire says "maximum cold pressure." I'm sure manufacturers take heat into account, but it still seems like a safe thing to keep the PSI below the maximum specified number. If not for blowout reasons, then at least to improve tread life and ride quality.

 

Kawai's are very nice. I'm partial to the Baldwin's myself, although the Steinway M series are probably the best all-around piano.

 

Optimum fuel economy in an internal combustione engine is obtained when the ambient air temperature is between 68-70 degrees Fahrenheit. Of course your mileage will drop in summer heat and with more A/C use, plus it is likely that the reformulated gas in your area is adjusted to lower ozone in the summer, and that lowers its thermal efficiency. We have reform'd gas here, and I drive out in the County to get the real gas - it has more HP and BTU output per unit of volume - another nice thing the EPA sticks down your throat. They make us use a fuel which clogs injectors and produces less MPG, so you have to burn more of it, it costs more, and pollutes as much.

I would also run a quality FI cleaner through your system if you have not done so regularly - Regane or Technron.

 

With 39 PSI your tires will wear out in the center more because your tire will be in a "U" shape...you will have less tire contact on the sides, less contact meaning less friction meaning increase in MPG

 

.

 

No argument from me on that point...

Of course, stated max pressures on sidewalls don't really mean a whole lot when auto manufacturers (gee, Ford comes to mind ) are telling you to run lower than typical tire air pressure in your tires...