Yup, the boxy rear end is a big reason I went with the fit. Its not great for economy, but perfect for actually getting stuff to fit.

 

I do not buy the idea that a notch back sedan is more aerodynamic than a flat back hatch. A chopped off rear is called a Kammback. All of the cars that emphasize efficiency (Prius, both Insights, for example) are not notch back sedans. Their roof slopes more than the Fit, but I still think the Fit's shape is better than a sedan. The Fit has a steeply raked windshield that slopes into a raked hood. Looks pretty aero to me.

I think it is an engine issue.

 

The Fit has to work harder to maintain highway speeds and combined with the short gearing to make it acceptably quick....its not going to get >9000 mpg

 

The fit is a TALL car. It has a VERY flat and tall back end. This creates a vacuum behind the vehicle which causes mass amounts of Drag. The prius and insight's rear roofline cuts down a fair amount before hitting the rear. they also have a lip spoiler to help cut down on Drag. Here are some Coefficient of Drag numbers;

Civic - .28 (hybrid is .27)
Insight (Previous Gen) - .25
Insight (current Gen) - .28
CR-Z - .28
Prius (Previous Gen) .26
Prius (current Gen) - .25

FIT GD - .35
For Comparison Sake, the Civic Hatch (1999 - the rounded smooth bubbly hatch) - .36
The Fit GE is likely (I don't have the number) around a .34 (slightly better than the GD) and maybe a .33. This is a BIG difference, especially when you are talking about an engine with very little torque. Also I've found that just driving behind a minivan or SUV (not tailgating) improves my economy by 3-4mpg. Other vehicles with more torque (whether it be larger engine or electric motor) don't have to work as hard to fight the drag. My last tank was over 45mpg - I was primarily in lines of traffic doing 50-55 until I had to use the A/C and take small trips for the last two days of that tank. ended up with 41.67 for the tank.

The FIT isn't as bad as an element or our ridgeline, but it's definitely not as slippery as a civic or insight. (It's almost 4" taller than both of them).

~SB

 

Also in general, Sedans ARE more aerodynamic than sedans. Compare a few that are offered in both formats.

Geo Metro Sedan - .32, Hatch - .34
Civic Sedan (96-2000) - .32, Hatch, .36
Saturn SL (sedan)- .32, SW(wagon) - .36
Pasaat ('97) sedan - .31, Wagon - .33

of note, some hatches & sedans have similar CoD like the Aveo at .32 for both but in most cases, sedans are more aerodynamic.

~SB

 

I am impressed by the aerodynamic efficiency of my soon to be 5 year old Fit.. 4th and 5Th gear acceleration from 80 MPH on up amazes me.. It is a 1.5 liter station wagon after all.

 

I am not too hot on physics, but I _think_ Cd is a relative number, and is therefore useful in comparing shapes of similar size. You would need to know actual drag to say one vehicle has more drag than another. I _think_. The Fit is taller than the Civic, but also narrower.

In any case, point taken, sedans are better than I thought. Trunk lids have gotten shorter and higher, and I think this helps a lot with the low pressure area you would otherwise get in the notch.

This site (don't know about its reliability) says the Fit has a Cd of .29. This may not be the same as the US version, but I expect eventually the car we get will get the tweaks we see on on other models, like the hybrid.

Network access 18 models of mainstream cars drag coefficient inventory

Meanwhile, I notice that the Fit is within 100 lbs of the Civic in weight, but has considerably less power. I am guessing the engine is running at higher RPMs for similar speeds, and that this is a bigger issue than the aerodynamics.

It appears to me that many of the Fit's rivals (most of whom are in the 40mpg/hwy club) have somewhat larger engines. (The new Accent, for example) They also may have other tweaks like 6 speed transmissions, and again, I think we will see this in the Fit eventually.

I think the Fit will eventually match the others' fuel economy, but NO ONE has copied those magic seats!

 

^^^ This. We have to trade some aero efficiency in exchange for our insanely roomy fits. The fit is not optimized to get superb mileage at 75 mph. It loves 45-62 though. That's why I don't belive the gearing of auto vs MT makes much difference in the real world.

 

Drag isn't really relative outside of the medium being traveled through. in this case, it is AIR.

Drag would be different if you were measuring how something travels through Air vs how it travels through water but that is due to the Medium changing (air vs water). In regards to vehicles, Air is a constant (save for humidity and other similar factors but they are negligible)

On a vehicle, there are two primary places where drag occurs. at the front (when air is being separated by the car) and at the back (where the vacuum created has to suck the air back together that was just separated). a nice smooth front that splits the air without a smooth back lowering the vacuum behind (like the FIT) will have a higher rate of drag than a vehicle that has both a sharp nose & sharper tail. (like the civic sedan)

I think it is a combination of two different things; the fit's small engine and the shape of the car. A 6MT won't be overly effective until the fit's engine size grows a little. The 1.5 is a great little engine but the torque isn't really enough to work well with a 6MT on US roads. The auto shifts out of 5th all of the time on hills but that's ok because it is an auto. If drivers had to manually shift out of 6th and to 5th or down to 4th as often as the automatic transmission does, many would opt for the auto. I could see a 6AT working to improve economy but not in MT form without some kind of increase in Torque. (You made note of other vehicles with larger engines using a 6mt and this to me makes sense... more torque - but they likely also have less drag). I'd love to see what an R18 from the civic would do in the FIT. 140hp and likely better fuel economy. They'd have to relocate the battery and figure a way to shift weight further back though as the fit is already very nose heavy.

~SB

I'd be surprised if the fit has a .29 CoD but it would be nice to hear... that'd be a big drop from the GD's .35

 

If I read the link right, that was for the chinese fit. I'm pretty sure the front end is different, and that might do it.

 

Drag is not relative, but I do not think Cd is a measure of total drag. A large vehicle and a small vehicle can have the same Cd, but the vehicle with the larger frontal area will have more total drag.

 

I wouldn't think that a nose/tail would do all that much but you never know. (well, someone probably does) speaking of Drag, I saw a tractor trailer with the aero extension and sideskirts off the trailer. I heard that it improves Tractor trailer economy by something like 2mpg. that for a truck is HUGE.

~SB

 

Is the British Hybrid any different from the Japanese Hybrid? I doubt the American hybrid would look like the Japanese hybrid because of the bumper requirements in the US. Japanese cars have hardly any bumper compared to cars in the US.