Place your bets on the smart...

[smartzuuk]

I'm aiming for at least 100 mpg US based on repeatable round trips of at least 100 miles.

Here's the plan for the smart, as I see it today:

Current (stock) front tire width is 145mm, rear is 175mm

I've got some steel wheels in trade now, and will be putting the fronts from this set onto the rear.

In Europe, the car is rated for 3.1 L/100 hwy with the 145/175 combo - but with a wider combo (175/195) it is rated at 3.3

So there is roughly a 6.5% penalty based on the extra 50mm per side of the car. My best guess is that I can gain 4% economy by putting the narrower tires onto the rear. (Note: 2000-2002 smart diesel models came with 3.5 inch front wheels instead of 4 inch, and had 135 mm tires as stock... I could acquire those, but not at 'any cost'...)

I'm going to do a wheel skirt mod. Not going to get technical on this one - simply put, I'm going to use Darin's number of 3% as a gain.

Vortex Generators - this one could be interesting. The smart is .36 cd I think, and it's abrupt end at the back seemingly make it a good candidate for the VG mod. I'm going out on a limb and saying another 2% gain there.

These mods collectively add up to a 9% potential improvement. Being that I can already get 93 mpg US on a round trip in cold weather (39-45F) without my Milligan's fuel conditioner - getting repeatable round trips of 100 mpg is very realistic. The question remains at what speed... I'll aim to do it at 50 mph.

I don't need to pulse, glide, or go fishing to do any of this... I'll simply set the cruise and go...

There are a host of other things to play with, but they are all small percentage items IMO.

Thoughts?

I do plan on keeping good records of these mods, and posting the results.

[Matt Timion]

First, good luck!

I'm surprised that the CD of the SMart is so high. Car engineers continue to amaze me when they build "high MPG" cars with horrible drag coefficients.

As for the speed, I think the scangauage is the best critic. Find the "sweet spot" and let it rip.

I have a road trip planned for California in a month. 1 1/2 years ago the same road trip yielded 46 MPG in my 89 Civic LX. I'm hoping to break 50 mpg in my Fit. I plan on going 65MPH the entire way, travel time be damned.

Unless, of course, I get better MPG at 70mph.

[Peakster]

Originally Posted by Matt Timion

I'm surprised that the CD of the SMart is so high. Car engineers continue to amaze me when they build "high MPG" cars with horrible drag coefficients.

Isn't it really difficult to have good Cd with a short car? Long sedans can have nice gradual airflow over the car whereas air has to hit the front and trail off the rear of a short car much more abruptly. I'd be surprised to find any micro-car with a Cd of less than 0.32 or so without having the roof-line super low.

[zpiloto]

Originally Posted by smartzuuk

I'm aiming for at least 100 mpg US based on repeatable round trips of at least 100 miles.

These mods collectively add up to a 9% potential improvement. Being that I can already get 93 mpg US on a round trip in cold weather (39-45F) without my Milligan's fuel conditioner - getting repeatable round trips of 100 mpg is very realistic. The question remains at what speed... I'll aim to do it at 50 mph.

I don't need to pulse, glide, or go fishing to do any of this... I'll simply set the cruise and go...

There are a host of other things to play with, but they are all small percentage items IMO.

Thoughts?

I do plan on keeping good records of these mods, and posting the results.

Good luck. I think the slower the better if traffic will allow. There's a sweet spot as far as MPH go just need to find it with your gearing and the SG. With the cd of .36 I think some where around 40 MPH would smash it.

[smartzuuk]

Well, 40 mph netted the 93 mpg to which I refer... so that is a likely place to start. Thanks!

[MetroMPG]

The only potential fly in the ointment: at 40 mph, the savings from the aero mods listed will be smaller than estimated. e.g. The 3% improvement I measured from wheel skirts was taken @ 95 km/h / 59 mph.

I'm not saying don't do the aero mods. Just that they won't contribute as much if you drive slower than the test speed.

Still, I won't be surprised if you pull it off.

EDIT: also, you should get better fuel economy if you don't use cruise control, and instead allow the vehicle speed to rise/fall with the grade.

[smartzuuk]

The beauty of the smart is that, when coasting in gear, it doesn't use fuel... I'll have to dig up the technical explanation...

...the same is true with cruise downhill - it may still stay 'engaged' (ie: ready to pick it up at the bottom), but the car may not use any fuel if the grade is sufficient... the car will speed up as well, if it's REALLY sufficient...

The drive by wire system in the smart loves cruise - yes, I can get get great mileage manually too... so I will try tests with and without cruise...

I am hoping to do this at 50 mph - so hopefully my wheels skirts will offer similar results. (I have achieved 105 mpg on a non-round trip going 50 mph).

[MetroMPG]

Does the smart transmission truly "freewheel" when you lift off the accelerator? I understand diesels don't engine brake much.

And do you happen to know any smarties around Brockville, ON who would be willing to show me his/her smart? I'd like to see one up close sometime. (Or get a ride, or better yet drive one. )

[smartzuuk]

I'm working on getting you matched up with a smart owner.

There were some discussions about the fuel cutoff here. And somewhere else as well, but finding the thread at CsC is a tricky thing... I need to review further to collect up the pieces of discussion...

[MetroMPG]

Originally Posted by smartzuuk

I'm working on getting you matched up with a smart owner.

Cool, thanks.

--

Ah, so you CAN go into neutral from any gear! I thought that being a sequential shifter, it would be like my last motorcycle where to get to neutral from 6th, for example, I had to shift sequentially down through 5-4-3-2 to get to N. (Although the motorcycle had a clutch, where the smart doesn't).

As for what's better, decelerating in gear with engine braking & fuel cutoff, vs. freewheeling in neutral with the engine idling, sounds like a test or 2 is needed...

Like: reset the SG passing a marker at a fixed constant speed, drive past a second marker and go to neutral. Coast to a stop & record FE info as well as the point at which you stopped.

For the comparison run with engine braking/fuel cut-off, you'd have to practice to figure it out, but with trial & error you could work backwards and calculate the point from the "stop" mark at which you have to release the accelerator to engine-brake in fuel cut-off mode to come to a stop at the same point. Sorry if that's confusing!

The point would be to compare the 2 techniques covering the same distance and using the same initial speed.

Sounds like someone at the smart forum already figured out that when descending a grade, anything less than 7% will yield better FE if you go to neutral due to the engine-braking effect. That suggests coasting in N on level ground will also beat using fuel cut-off mode.