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I'm considering making some modifications to my Niro EX with 16" wheels to make it more aerodynamic. Living in Chicago I'm not willing to get rid of side mirrors and shaving door handles seems to be much more expensive than it'd be worth. I'd prefer to keep the roof rails for when I use my cargo box and I am aware of the huge aero loss with a cargo box so I always remove the aero bars and cargo box when not using them.

I am considering the solid "Mooneyes" hubcaps, closing out the rear wheel wells, and lowering the car by an inch or so. Though this isn't an aero mod, I've already brought the tire PSI to 40, though I've known hypermilers to go way higher.

I've seen other people do deflectors below the front bumper and the joint between the hood and windshield, sideskirts, and boat tail of various lengths, but those are usually on older cars that would appear to have had much less engineering go into the aerodynamics so I'd be less confident that they would make a difference on the Niro.

To validate the modifications I'd perform coast down tests with and without the modifications while datalogging on an Arduino with a GPS. Then I'd do a best fit curve on the data to determine the coefficients of rolling resistance and aerodynamic drag. I'd have to know atmospheric pressure and vehicle weight, but those should be attainable from weather.gov and online specs.

Has anyone tried and validated any of these aero mods or more?

Thanks,

-Will
 

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Ecomodder.com has a wealth of information and a forum. Almost everything you mention has a potential downside and little upside. Lowering the car an inch has the best chance for a decent gain. I doubt that would change negatively affect aero friction under the car and would knock off an inch of frontal area on each tire. Could be a 3% gain.

Coast down tests are cool, but difficult. Start with 36 psi versus 40 psi cold fills (or use TPMS for operating temperature) to see if you can tell the difference. There is one, but it is small, and the downsides from the higher pressure are well documented: lower tire life (which I suspect costs more than any increased efficiency savings), increased noise and reduced comfort. 40 psi isn't crazy, but it is on the way!

When it comes to tires, narrower is better. I looked at the options myself, but to keep speedo accuracy requires an odd truck size. Other options have fewer decent tire models available so I gave up looking. But that is a really great place to potentially increase efficiency. Narrow tires do have a negative impact on handling and braking of course (better snow performance might be a consideration in Chicago).

Not a lot of info in the link you posted, but it appears weight savings was a major focus. Not impressed with the mpg acheivements with hypermiling, that is old news, here is 76.6 mpg cross country unmodified in the wintertime. That's in the Niro (not even the most fuel efficient trim), not a modified already more aero stock Ioniq!
 

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2018 Kia Niro LX Hybrid
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Shedding weight would be the easiest way to increase fuel mileage without much risk of adverse effects. Tire Rack lists the weights of the wheels they sell. Look to find wheels that are lighter than stock. The Enkei RPF1 fits the Niro and is listed as one of the lightest on a lot of forums at around 15 pounds.

If you want to get more extreme you could take out the rear seat. I would take it out and build a flat floor if I didn't have kids. That would get rid of a lot of weight.

In the words of Colin Chapman, “Simplify, then add lightness
 

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I've heard someone say putting water pipe insulators on the lower grill to reduce the air that flows into the engine bay increased their mileage slightly.
 

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Increasing tire pressure to 40 psi does not wear out the tires faster. I’ve run my tires at 40 psi since my 2018 was new. Just had to replace the last 2 stock tires at 62,000 miles due to nails(I live in a neighborhood with LOTS of new houses being built). They get rotated at every oil change. That is the key to longevity with tires.


On a 2006 Chevy Colorado I had 15 years ago I put a grill block on it. Just cardboard duct taped over the grill. Got 34 mpg on that tank! It worked but I was monitoring coolant temps the whole time with an OBDII scanner. NEVER trust the factory idiot gauge.
 

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Increasing tire pressure to 40 psi does not wear out the tires faster.
Do you have a theory why Kia recommends 36 psi? Obviously Kia would enjoy higher sales if they can boost the EPA ratings by simply raising recommended psi.
 

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Yes I do have a very good theory as to why. It is the rule of the worst possible scenario.

Auto manufacturers have to protect their backsides. This means designing and programming cars for the worst case scenario because their are people out there who will do stupid things with their cars. Take the tire pressure for example. Tire pressure and gas mileage do go hand in hand and higher pressure has been proven time and time again to be more efficient, and we can all agree on that. At the same time, auto manufacturers know someone out there is going to take their Niro, load it up beyond the maximum payload capacity, then take the car to Death Valley where they will drive too fast for too long on the cheapest gas they can find.

It is this scenario that they have to take into consideration when programming the car and when recommending things like tow ratings, payload capacities, and tire pressures. At the same time, engineering limitations and recommendations have to be met. So it is a balancing act to keep their lawyers happy, the bean counters happy, their parts suppliers happy, and their customers happy.

When it is all said and done, there is almost always wiggle room left on the table for all aspects of a vehicle. It is our decision as a consumer to either stay within those factory bounds or to take responsibility when we go slightly outside of the recommended settings. Because in the end, they are just recommendations.


There is also a law of diminishing returns. At some point you will still gain MPG when increasing tire pressure, but the rate of gain starts to get less and less. They (auto manufacturers)have to think not only about fuel economy but also tire longevity on less than perfect roads but also NVH(noise vibration and harshness). The higher the pressure, the rougher the ride is going to be. Not everyone is willing to sacrifice a smooth ride for a slight bump in fuel economy.
 
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