The FIT has great aerodynamics... Maybe too aerodynamic.
 

Okay...

So many of you may have seen my post on doing my 1st road trip with only 31mpg.

Here's the other thing. I see a many of you have posted about the effects the wind has on the car. I got the same feelings and then my inner "nerd" kicked in. I have a BS degree in Aeronautical Science from Embry-Riddle Aeronautical University (Daytona Beach, FL). The fit has super slick aerodynamics. If you look at the car from the side, it looks like the leading edge of a wing. So where am I going with this u ask? The FIT is about the same weight as a Cessna 152. It rotates/lifts off the ground at around 60kts which is almost 70mph. When my car hit about 70mph to my planned speed of 75mph, the car literally lifting off the pavement just enough for the car to "wonder". The steering gets very light because there really isnt much rubber meeting the road. Okay, I'm done. I do hope you could follow what i was telling you guys/girls. I'm a flight instructor but a pilot first. I doubt many would comment but feel free.

That's an interesting analysis, but I think it's not correct.

The Cessna 152 has a gross weight of 1670 pounds, and an empty weight of 1081 pounds, which is a lot lighter than a Fit—very roughly half the weight. The Cessna has a wing area of 160 square feet, while the Fit has a "wing" area of about 70 square feet. The Fit is also hardly airfoil shaped; if anything, it's closer to an airfoil in reverse, with the blunt end at the back and the pointy end at the front. It does not generate large amounts of lift at highway speeds; indeed, modern cars are usually designed to generate negative lift (downforce) if anything. I would suspect the Fit is more or less neutral in that regard—no real lift or downforce.

The light steering is much more due to the design and adjustment of the power assist and the suspension angles (particularly caster angles, I think). It's also more a question of what you're used to—if you've previously driven vehicles with heavier steering or longer steering throws, which is a large portion of vehicles on the road, the Fit feels twitchier and perhaps dangerous even though it's perfectly controllable at highway speeds. It's a little like flying different airplanes with varying control forces; some are best controlled with the fingertips (some high-performance homebuilts in particular), and others need a more ham-fisted approach.

I should have used 172 since its 4 seater. If youve ever seen a Shorts 330/360, it has very skinny wings because most of the lift comes from the fuselage.

I would have to agree with DrewE. I've had my Fit up to slightly over 100mph on the interstate and it never felt like it was uncontrollable or going to fly off the road. If anything it seems to settle a little and get slightly more stable as you creap up to that speed. Gas mileage definitely plummets though! I would say that for every 5mph you go above 70 you lose roughly 2MPG.

-Dustin

You need to retake your low-speed aerodynamics course.

The Fit's shape hardly resembles an airfoil; the trailing edge is basically the exact opposite of the shape needed to generate lift. I'm a computer engineer, and I can tell you that. :nod:


Any wandering at speed might mean you should get your car aligned or check your tire pressure. :eek3:

And the trailing edge of a dump truck. The trailing edge matters a bit more.

The mess of drag back there coupled with the light weight and hard skinny tires is what makes things squirrely at speed, but mine's a lot more stable in the 70s than I expected. If it's a car issue and not rough pavement or odd winds (natural or traffic-made), then you ought to have it looked at.

Hah hah hah. I would question almost every statement in the original post. If you want to drive a car that actually gets light at 70 mph drive a '65 Corvair. I remember catching a crosswind driving north on Highway 66 out of STL and that thing tried to weathervane a little. You could still correct for it, but it took more steering than it should have. Eerie feeling.

Cheers.

Yeah, i've heard the Fit called a lot of things, but one of them was never "aerodynamic".

The roofline is too tall and the rear is not sloped enough. I think they did a good job of keeping the most amount of cargo space while attempting some sort of aerodynamics, but look at a Prius and you will understand what I mean. If you look at the rear wing of a Fit EV it attempts to reduce the drag that Charlie is talking about by sloping around the rear hatch. I'd like to get one for my car some day.

The Fit has the aero of a brick. It takes less time to coast down from 60 mph than your cessena unless you drop the flaps.
Cd for a Fit is like .35, not so good but not as bad as others.

My point is this. I never stated it was a clean airfoil (well yes i did). When its cutting through the wind its a turbulent experience like nothing I've drivin. I'm not complaining about the car doing these motions. I also never commented on the rear. Im just saying i def feel there is a pressure difference from the air going on top sand the wind going under it. The turbulence is most def in the rear because the body does let those two winds to meet back. Ill reverse my op. now that i think things through its turbulent air is what im indeed feeling.

I did a study once I bought my fit (ME analyst). The Fit has a relatively small cross section and aerodynamic front, there are a few downsides though. The mirrors are HUGE and spoil things a bit. The biggest and possibly worst thing is that our fit is too short. To get a MUCH lower Cd, you'd have to lengthen he car considerably. PLUS you'd also have lower the car considerably. That is just the aero portion though.
There is FAR more to this equation.

I remember my first course in aerodynamics..

Before I got my Fit, I had a 2005 2.4L Accord, and I was comfortable with a certain degree of coast and deceleration from neutral.

When I did the same for the Fit, I found that it coasted significantly longer than the Accord, and it decelerated much less to the point that it made letting others pass on track difficult.

Definitely not aerodynamic enough for lift... there was a quite detailed post about this when the GE8 first came out many, many years ago.
If it were more aerodynamic we'd get a whole lot more mpg's than we do now.

As mentioned, steering plays a part in that light feeling and drifting.. I've also noticed going to 205 wide tires also significantly reduced it for me.

OK, smart aleck, let's see the rigorous calculations. Reynolds number? Formula
https://www.gstatic.com/education/fo...lds_number.svg https://www.gstatic.com/education/fo...mber_var_1.svg = reynolds number https://www.gstatic.com/education/fo...mber_var_2.svg = density of the fluid https://www.gstatic.com/education/fo...mber_var_3.svg = flow speed https://www.gstatic.com/education/fo...mber_var_4.svg = characteristic linear dimension https://www.gstatic.com/education/fo...mber_var_5.svg = dynamic viscosity of the fluid

I surmise that it can be better. How do I know? After the Fit encounter rain, I see a lot of dirt accumulated on top of the rear bumper and below the hatch, which tells me there is turbulent flow in the area. Lots of down force in the rear. The rear wing on top of the hatch is not doing its job.

Your Cessna 172 will only rotate at 70 knots if it's configured for takeoff. If you push forward on the control yoke you'll never get off the ground.

You can also land a 172 at 70 knots.

indeed. I got a book on racecar aerodynamics and concluded that without a wind tunnel that had a rolling road, any mods I might make could do as much harm as good.

I recommend checking ecomodder forums to go really deep into this topic.

I've hit 170km/h in my GE (passing an Alberta driver. They are really aggressive and insist on passing you regardless of your speed and get mad when you pass them, which would be fine, however they slow down WAY too much in corners, like 60km/h in corners I usually don't think about and maintain the speed limit just fine).... on a track, where it is safe and legal to do so of course...........

It was perfectly stable, mind you this was the first drive on brand new Neo-Gen Tires, and mine is a Sport, I know the spoiler doesn't do much, but it might reduce lift. I will say the Fit REALLY doesn't like wind. 2500lbs with that side body profile that really catches the wind. I'd hate to drive one out on the prairies on a windy day.