They are probably talking about truck drivers experiencing less fatigue due to a smoother ride.

 

mine is a MT

 

Those airtabs might work on the same idea as the rear spoilers that were on station wagons back in the 60's & 70's. Those old spoilers picked a bit of the boundary layer flowing along the car top & high sides & redirected the air into the vacuum behind a vehicle that had a blunt rearend. This raised the air pressure at the back of the vehicle which the engine didn't have to fight as strongly to maintain speed.

These old spoilers should work better to kill vacuums at the back of vehicles than the cosmetic spoilers on todays cars do.

 

I'm very interested in how your experiment works out, I put my guess at around 1 mpg over the long run, which may be difficult to measure given the single tank mileage variances that most people experience and the gradually improving mileage that many Fit owners report as break-in up to around 20,000 miles.

I believe that the base Fit is already much more aerodynamic than the vehicles that these devices are targeted for.

But while driving home last night thinking about your suggestion and realized that the Sport spoiler might be the biggest difference between the base and sport Fit fuel economies. Racing people know that spoilers/wings add drag and limit speed, but the tradeoff is worth the handling increase provided by reducing body lift that makes cars squirrelly at speed. I ceratinly don't drive my Fit at speeds where this would be a benefit, so the spoiler is probably only a detriment to mileage.

I will guess that the factory spoiler has as much, if not more, negative effect than the vortex generators have to the positive. Hmmm, now I need to decide whether I want to pull the spoiler off...

Eric

 

I would say that the lower lip on the front of the sport model does more to help gas mpg than the rear spoiler does harm. Lips good spoilers bad(Road and Track article some years ago).

 

The vortex generators might also reduce rear lift, since the air going over the top is supposed to be deflected downwards by less. Of course I have no way to measure that.

I did some coast-down testing that shows they do have some benefit in reducing drag, enough to be measurable even by me. I'll write it up this weekend I guess. Still doesn't tell me how much it will affect fuel economy. But coasting from 100 to 80km/h took 3.8% longer with the airtabs; that's a bit slower than my average highway speed, and it was on a rough tar-and-chip surface (the only straight, mostly flat, and free of traffic stretch of road I know of around here).

Yes, but if most of the difference is in the front part of the vehicle, so that should make airflow off the back relatively more important. Rolling resistance could also be relatively less, with only the four tires. So I hope for at least 4%, possibly more. Knowing they do at least some good is enough for me, so they're staying on the car.

 

I thought about that too, and knew that the "ground effects" on the sport woudn't make fuel economy worse, but wasn't sure about the actual benefit. It's kind of a shame that putting together an objective list of mods and their effect would be so difficult to get really quantifiable results. Testing in the real world has too many variables that influence the results. But if we could...First pick a baseline like: Base Fit, 60 mph, level ground, 70 deg. 40 humidity, tires 32 psi.... then list each change and it's results.

tires to 45 psi = +2 mpg (all these results are just made up)
Tires to 20 psi = -2 mpg
Sport front lip = +1 mpg
Sport rear spoiler = -1 mpg
voltage stabilizer = 0 mpg
vortex generators = +1 mpg
speed to 70mph = -4 mpg
speed to 55 = +1 mpg
fog lights on = -.5 mpg
A/C on = -1.5 mpg
etc. etc.

Then we could pick and choose what to include on our own cars. Obviously, YMMV, but the specific numbers would be unimportant, just whether it makes a difference, and relatively how much.

Eric

 

I find it difficult to believe that these tab thingies would have any effect due to boundary layer dynamics.

 

I am putting my guess at more than 1mpg. Maybe a lot more. I can actually feel the difference in acceleration at speed. First two visits to the gas station show numbers way too good to believe, so I think I'll wait to burn a few more tanks of gas before saying any more about it.

 

I drive (in Calif) 580E -> 132 and it's always windy on the south stretch. My Fit is a b!tch in the wind, it's actually kinda scary. I've been thinking to try an alignment.

 

Did I miss it, or has no one mentioned synthetic oil?

I have a co-worker who drives a Toyota Echo that swears by it. He commutes ~100 miles/day and says he regularly averages 45-50 mpg.

My Fit lifetime average is 37.5 mpg, but recently when I hit ~20k+ miles on the odometer, by average has been climbing every tank.

It is now averaging 39.3 mpg every tank (last 10 tanks). On my next oil change I plan to get synthetic oil to see if that makes a difference.

My driving mix has been the same (40% city - 60% highway) and I've been using the a/c alot. I almost always keep the engine out of VTEC (<3400 rpms) so my highway driving is limited to 69 mph.

I remember reading somewhere that ~25k miles or so Honda engines hit their stride in gas mileage.

 

This is a great thread! I want to know the results for the airtabs AND the synthetic oil. I am all for MPGs! Thanks guys for testing these things out. I cant wait to hear the results.

 

I don't think just using synthetic oil will make a difference. I always use Mobile 1, but for different reasons. Using a lower viscosity oil definately will improve mileage and the synthetics come in some really freakish weights like 0w-40 that would PROBABLY be perfectly safe (I am making no claims here), but Honda would definately void the warranty if you develope engine problems using it...

 

Honda CANNOT void your warranty just because you use synthetic oil. No auto manufacturer can do that. Many cars come with synthetic oil already in the engine and/or trans. Using the WRONG grade of oil may be an issue, but not the use of synthetics which are better than mineral oils.

 

yea... like i said... using a ligher weight oil will improve mileage, but could get you into trouble with Honda...
I use synthetic, but i use the weight that Honda recommends... and all is well. but I seriously doubt i gain any MPG from using synthetic.

 

Hey sfenders,

I see you did end up sticking them all over your car in the name of science, for what it is worth you did a much better job aesthetically than that CRV I put up . If they do return a good increase in gas miliage are you going to have them painted to match your Fit?

 

Now that I have some idea how well they work, I don't care so much how they look. So I stuck another two on the sides. I've got to take this thing to a drag strip, a 1/4-mile time would be a good test of how much difference they make.

I might paint them, eventually. I photoshopped it, seems like they'd look okay matching the body. A lot more subtle. Or something...

 

haha, Sweet

 

They MAY make a TINY difference... buy you definately won't see it in 1/4 mile times. In a 1/4 mile, you spend so little time at a speed high enough for drag to be an issue that any difference would be so small as to not be measureable... probably more than offset by the additional 3lbs of plastic stuck to the car.
1/4 mile is all about acceleration... and that depends 99.9% on power:weight ratios and traction (and driver coordination).
Drag co comes into play for sustained cruising... like an endurance race.

 

Hmm, yeah, it wouldn't make as much difference as I thought. But my quick estimations tell me final speed should be ~5mph higher, even if the time isn't affected much since most of the gain comes in the last few seconds. If it finishes at over 85mph, I'm claiming victory. Otherwise I will admit to a serious case of the placebo effect.