I have both and get the same mileage. Took the HHR to Maine (2500 miles) in July and got 30mpg. Took my 2007 Vette to New Mexico (1500 miles) last week and got the same 30mpg on the way down. I was running late on the way home and hit 120-130 mph a few times through Wyoming and South Dakota so the Vette mileage was down to 27.5.
Lot more room in the HHR so if the wife goes with me it is always the HHR.

 

I have almost the same, an '06 HHR and an '08 Vette. And I noticed the same mileage.

For example, in May I drove the Vette to Indiana, drove around town and stayed a few weeks, drove up to the Detroit area and back to Indiana. Stayed about another week then drove back to AZ. For the ENTIRE trip I averaged 28.9 MPG (city and Hwy). And I had some "fun" along the way (I raced 2 Ford products of friends/relatives....beat both).

Six weeks later I drove the same trip and essentially the same routes and averaged 30.4 MPG (city and hwy), in the HHR.

Each trip was almost the exact same mileage........5000 and, on the interstates I drove 5 over the posted (in most instances ).

Amazing isn't it.

 

The highway mileage of the HHR isn't all that great.I suspect that gearing and the blocky shape are the biggest factors.My tach reads 3000 r.p.m. at approximately 72 m.p.h. which to me seems about 15-20% too high for best mileage.I used to get the same highway mileage (@ 31 m.p.g.) from my '93 Cavalier v-6 wagon as I do from my HHR.However,I don't have any complaints about my average mileage-at present it's hovering around 30 m.p.g.( due to drop with the onset of colder weather)

 

Best mileage on mine happens between 55 and 65..... Probably the speed range GM was targeting with this car. It would drop off some at 72 mph.

 

Actually greybeard, IIRC, ALL government mandated HIGHWAY mileage tests are at 65 MPH (computer and dyno controlled). Results, after, certification, is reflected on the window sticker as the "Hwy Mileage". City mileage tests are ALL done to the SAME computer controlled dyno driven city (stop and go) driving schedule/course. And also reflect on that sticker.

Oh, there is a "human" in the drivers seat controlling the speeds, braking and turning of the vehicle. The computer display provides the course schedule, which the driver must follow.

You will, of course, experience better hwy mileage at constant lessor speeds.

 

My HHR runs at 2500 rpm at 70 mph, mine is a 2.4L auto. My 87 Fiero GT also runs about the same. I also get about the same mileage with the Fiero, but have hit 35-38 mpg driving 55-60 with the HHR.

 

Automatics are geared higher than 5 speeds,hence the differing r.p.m. at a given road speed.

 

I am dissapointed in my HHR SS MPG.

I wont lie i have a lead foot and a love for boost.

crusing at 85mph is bad on gas lol

 

Yes! Yes it is.

 

Had to add my 2 cents as I have essentially the same vehicles as hoganj and Snoopy. My 08 HHR Panel 2.2 and my 2011 LT1 w/ls3 gets pretty much the same gas mileage at 65 mph. I was quite surprised myself.