Is it bad to inflate the tires to 46 psi? The ride obviously isn't going to be quite as smooth, but is it dangerous? Will it burn down the tires faster? Right now I have mine at 40 psi, and I've been contemplating going a little higher yet for MPGs. Any thoughts?

 

At 40 psi, you'll get a harder ride and wear the center of the tires, but you may get better mpg. My tires are at 34 psi and I get 30+ for the average mpg. It is all about your driving technique. No jack rabbit starts or stomp on the brakes. I do a lot of coasting up to red lights. I try to get the car into lockup (~40 mph) and 2000 rpm does wonders for good mileage. At 70 mph I'm at ~2500 rpm.

 

The tires I have, for get exctly what ones, but they say the max safe psi is 54. I did not want to go that high. I have noticed a whole lot of ride differance, probly used to a HD pickup, but it does get a LOT better milage. Even with a preload and foot to the floor off redlights I can still get around 30 mpg if I try, I usely dont though.

 

I keep mpg records for my 2.4L auto HHR and graphed it for 75,000+ miles.

The blue line is tank to tank variability calculated via excel while the red line is the running mean. Currently mpg is sitting on 30.6 mpg.

 

Any tires will likely have a much higher Max PSI, but one should go by the vehicle specs, on the Drivers B- pillar, at the bottom...

 

Traditional gasoline engines are most efficient at turning fuel into power at full throttle, because at low throttle part of the the power is being used to suck air past the throttle blades. Diesels and direct injection gasoline engines don't have to suffer that loss. However, you still have to get that power all the way through the drivetrain to the ground, and the more torque you put on the drivetrain, the greater the loss to friction and deforming of parts, and on an automatic, the torque converter is sucking up even more power. End result is that there is a definite sweet spot for acceleration, as well as cruise.

The best technique I've found for me is brief WOT at low RPM with short shifting to keep the RPM's low. Get to speed as quickly as possible while keeping the RPM's below 2000, then coast clutch disengaged as often as is practical, followed by very brief WOT in 5th to get back to 5MPH over the speed limit, coasting back to the limit, lather rinse repeat. Doing this in my 2.2 2008 on 50MPH speed limit roads can net 42+ MPG over 20 mile trips. Air conditioner or window down will hurt a couple MPG, as will ANY miscalculations requiring hard brake application for intersections. If you can coast to a near stop at red lights, you didn't waste any gas, if you used the brakes, you were on the throttle too long before you started coasting. Any traffic around you will get REALLY ticked if use this technique too obviously, so I only get to use it to the max late at night. Do it often enough even subtly will gain lots of MPG though, I get typical tank averages of 34 to 35MPG this way. I've never seen a tank average less than 32.

 

Wow, very thorough! If anything, it looks like the mean is gradually increasing with age/miles...

 

The first tank I had in mine I got 29 mpg, but the last couple I have only got around 24. Average speed shows at 52 mph. I'm using 93 octane in mine.

My mom has a 2007 with a 2.2 and averages about 32 mpg. She does alot of highway driving like I do, and her average speed is about the same as mine is, but she is in Nevada and uses 87 octane. Both of our cars are automatics.

I thought these engines were supposed to get roughly the same fuel economy. Anything I can do to get mine up, or is it simply this ethanol laden gasoline they sell all over the Nashville TN area?

 

I average, about 420 miles/tank of gas during the summer, and about 350/tank during the winter (because I remote start a lot). From what some of my customers say, 420 miles is outrageous. I just do the normal, under 2k acceleration away from signs and lights and it was a night and day difference. Once my 100k maint. is done, it should get better.

 

Good mileage is optimized by driving technique, A heavy foot = poor gas mileage. I rarely take my HHR past 3000 rpm (70 mph = 2500 rpm) and around town at 40 mph = 1600 rpm. Getting the transmission to get into lockup is key, Easy take off, and coast up to red lights. No standing on the brakes or street light to street light drag racing. The 2.2L and 2.4L engines are rated at the same mpg.