QuickRick

Guys and girls,

I wonder just how aerodynamic an HHR is, I suspect it is "brick-like" because the MPG mileage is heavily affected by speed.

I don't notice as big of a MPG drop at higher speeds in my other cars.

Has anyone got the cd rating for our cars?

Thanks,

QuickRick

hyperv6

For the HHR the CD is listed as .354

That is on the standard HHR the SS may be a little better because of the front bumper. It could pick up 1 or 2 counts less of drag .32 or.33

For they type of vehicle this is that is not bad as in the 80's the Fiero was .32 with the aero nose and the Vette was also in the near same area aero wise.

The aero is good on the HHR but with the high profile it has a large frontal area.

Clevelandhhrss

The short answer is absolutely not.
The HHR is actually quite slippery.
Which cars did you previously own???
I would need to drive 85 miles per hour on cruise or faster to get less than 20 mpg.

The long answer is .354 or .35

Better than most, better than almost any old cas (10+ years).

fastsuv

The drag coefficient is somewhat misleading as the actual drag is the drag coefficient multiplied by the frontal area. So a Fiero with the same drag coefficient as the HHR would actually have less total drag because it would have less frontal area.

Steve

hyperv6

If the HHR with less frontal area would have less drag as it would be smaller too.

The Fiero has a lot of other factors like tire width, the air coming over the rear vertical rear window and tail, under pan air flow for engine cooling, rain gutters, ETC. If it had the standard nose it was like .38 and even created lift at speeds over 90 MPH. I only used the Fiero as I have some experience.

The Fiero numbers are based on what they were doing in 1984-88. They were just starting to apply better air tech into the cars.

The HHR uses many new things that clean up the car even more like the improved air flow over the mirrors, flush windows in the front. Note even the gaps in the windshield frame and around some windows like the quarter glass help promote better air flow. Look at some of the new GM cars and the window gaps they have added for air flow. My 04 GP has large gaps front and back.
Today most cars are .30 and some are even in the high .29's.

If the HHR was shorter the feontal area would be near what a normal car would be and the drag count would drop even more.

The Aero things they have done to the new Volt are amazing. They have picked up many miles with some of the aero work they have done. It is amazing how many electric miles are picked up with each count. There are several storys on the web on this and they are good reads.

The opening and closing grille is something that is new too.

catdaddy137

do the glass also

QuickRick

Guys,

My other two cars are an Acura TL and a Corvette Z06. If I drive the same route to my Mom's on Route 95 in each car I notice things.

I can stay with traffic in the TL and on 3 trips going 75-85 mph (the speed you'll mostly drive or else, my MPG is mostly the same at 25-29 (it has gotten 30.5). For the power, weight and size this is pretty good for a 3.2L V6. If I drive a little slower, say 70-80 mph it doesn't change the MPG much if at all.

The same scenario on the 2.4L HHR nets good mileage, I'm not unhappy. I see a larger disparity between 70-80 and 75-85 MPH. I'd estimate 4 MPG difference between the 2 speed sets.**

The Z06 is just crazy efficient! I drove it back from Florida and got 25-27 MPG. Think, this is 505HP and 7 Liters. The car weighs 100 pounds less than the HHR and can get to a top speed of 198. The magic here is that 5th gear is overdrive and 6th is deeper OD still at .50 to 1.
At 70 MPH it tachs 1650-1700 mph in 6th gear. It has so much torque that you can skip gears or lug the engine way down in rpm and it doesn't care.

QuickRick
**p.s. still this HHR gets twice the mileage of the truck it replaced and it is so darn cute!

Clevelandhhrss

Both of those cars have a very very low cd, + exactly what you said about the corvette. That's all she wrote.

SandyBeach

I'm not an engineer but logic would tell you lower mpgs on the HHR at higher speeds is due to the lack of a 5th gear on the automatic tranny and the rear axle ratio compared to your other vehicles. Watch the rpms go up as you pass 60 mph. The faster you go, the more gas you'll burn.

c2vette

On the subject of Aero and CD, I had an GM Electric S10 that had a CD of .29 which is about a 30% improvement over the stock S10. Always thought it would be fun to try similar mods on a regular S10 to see what MPG you could get out of it. Front air dam similar to HHR SS, flush grill, gasket between bed and cab, full length underbody flat panels from air dam back, rigid bed cover (back half only worked better than full length), I would also add full moon wheel covers. If you could do it without impeding airflow through the IC, radiator, engine compartment, etc it might be interesting to try some underbody panels on the HHR. My wife's BMW has pretty much a full pan under the front half, so it could be done I would think.