MotorTrend Long-Term Review - AirDam - Chevy Colorado & GMC Canyon
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post #1 of 31 (permalink) Old 04-19-2017, 12:51 PM Thread Starter
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MotorTrend Long-Term Review - AirDam

Not sure if this has been posted elsewhere, but here's a very good assessment of the impact on removing the airdam. Spoiler alert...no impact! Well, except for more ground clearance.


2016 Chevrolet Colorado Z71 Diesel Review - Long-Term Update 5

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post #2 of 31 (permalink) Old 04-19-2017, 01:26 PM
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Originally Posted by CaptainSlow View Post
Not sure if this has been posted elsewhere, but here's a very good assessment of the impact on removing the airdam. Spoiler alert...no impact! Well, except for more ground clearance.


2016 Chevrolet Colorado Z71 Diesel Review - Long-Term Update 5
Well I guess you didn't read it or I misread it? I read a 4% drop in highway MPG (about 1) BUT a small gain in city (probably because of weight removed, they took the side steps off too)...Not bad right? But why take the side steps off during a air dam test? just to screw up the test?Stupid......

I'll rip that thing off, I almost never drive my truck on the highway.
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post #3 of 31 (permalink) Old 04-19-2017, 01:28 PM
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I know GM has taken a lot of heat for the low hanging air dam, how difficult it is to remove, and how little of an impact it has on fuel economy.

I wonder if they will make any changes when the truck eventually sees it's first refresh / face lift.

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post #4 of 31 (permalink) Old 04-19-2017, 01:56 PM Thread Starter
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The difference is insignificant in my opinion. I trust that GM did extensive wind-tunnel testing that yielded the actual airdam design, however real world driving shows minimal difference. GM was very likely chasing a mpg target and 1 mpg put them over a threshhold goal.


I did appreciate the GM engineer's comment that they are aware of how difficult it is to remove..."obviously are very much aware of for our future." Hopefully this means they will at least improve on the upside down screw design.


Also note the engineer's comment regarding the airflow issue. She could not "envision a situation in which the Colorado's engine is harmed with the air dam removed."
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post #5 of 31 (permalink) Old 04-19-2017, 02:07 PM
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Also note the engineer's comment regarding the airflow issue. She could not "envision a situation in which the Colorado's engine is harmed with the air dam removed."
Well we know she wasn't a contributor in the owner's manual compilation.
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post #6 of 31 (permalink) Old 04-19-2017, 02:15 PM
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Well I guess you didn't read it or I misread it? I read a 4% drop in highway MPG (about 1) BUT a small gain in city (probably because of weight removed, they took the side steps off too)...Not bad right? But why take the side steps off during a air dam test? just to screw up the test?Stupid......

I'll rip that thing off, I almost never drive my truck on the highway.
Without the air dam, the truck had a 4% drop on the highway versus with the air dam on our Real MPG cycle. Compared to the EPA results, the Colorado without the air dam improves 9.3% on the highway.

As for the side steps, well they were coming off anyways because I was sick of bashing my shins on them. After much discussion with our Emissions Analytics team, they didn't believe that removing the side steps would make a difference in our test results.
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post #7 of 31 (permalink) Old 04-19-2017, 02:31 PM
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There is no way the air dam weighs enough for that to be a factor in any mileage differences. The side steps may be a different issue, but more likely they offer some aerodynamic impacts.

I think the air dam was simple a part of the chase for MPGs. Any improvement from air dam would have met a costs analysis benefit: Even if it is 0.1 MPG improvement, when that is added to other 0.1 MPg improvements, pretty soon you reach 0.6 MPG improvement, and with the round off error can claim an additional 1 MPG better achievement.

The costs of the air dam itself are minimal, plastic is relatively cheap and light. The real expenses are the $#$%^% 12-13 screws and clips, along with the labor to attach the air dam.

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post #8 of 31 (permalink) Old 04-19-2017, 05:41 PM
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That was a good little article but it is a shame about the side steps being removed as well leaving us just to guess. Science 101, reduce testing to only 1 variable.

You have 2 things occurring here. The air dam effectively pushes a lot of air around and underneath that would otherwise run in to the undercarriage and result in turbulence. It's feasible that it's pushing a lot of air unnecessarily at slow speeds and the city mpg gain is because at those slower speeds the air hitting the undercarriage doesn't matter much. There isn't a whole lot of it. But much energy is expended pushing it around the truck.

The other issue related to the steps is that weight matters when starting and stopping, but not at steady speeds. So removing the steps might have had no weight effect (who knows about aero) during the highway portion but have been of some notable help at slow city start/ stop duty cycle. I'd bet that with air damn, w/o steps, would be the best combo in all circumstances.

But look from GM's perspective, a $2 piece of plastic that gains a proven 1 mpg is such a no brainer. They would do 150 little pieces of plastic if they all made gains even a fraction of this.

I really wish they would build full under body coverings, that's efficient and out of the way and 100% provides real improvement which is why I built one for my Vette.

As for me and my truck, I don't even notice the dam and will probably just leave it on my future lifted Canyon for the gain in highway mpg but more for the improvement in front end planted feel at highway speeds (a sure proof of better aero btw).

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post #9 of 31 (permalink) Old 04-19-2017, 05:45 PM
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Dam if you, Dam if you do not....
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post #10 of 31 (permalink) Old 04-19-2017, 06:17 PM
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That was a good little article but it is a shame about the side steps being removed as well leaving us just to guess. Science 101, reduce testing to only 1 variable.

As for me and my truck, I don't even notice the dam and will probably just leave it on my future lifted Canyon for the gain in highway mpg but more for the improvement in front end planted feel at highway speeds (a sure proof of better aero btw).
Yeh, one variable at a time. There are some ways to test multiple variables with less tests than variables, but requires much more sophisticated measuring and sampling than any of us here would ever want to undertake. Works best with the number of variables to be tested in the double digit range and where at least some of the variables have more than 2 points: For example, speed & gear the truck is in can have multiple settings, where as the air dam only has two: ON or OFF. The test method works extremely well, but it blew my mind the first time we used it.

I guess I don't see how the air dam provides for a better planted front end. I would think it would either cause the front end of the truck to lift up slightly, or no effect, just pushes the air around the sides of the truck. I have one theory on the pushing the air around the sides of the truck that might result in a more stable ride, but I am not sure I can explain it without a whole lot of hand waving and beer.
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post #11 of 31 (permalink) Old 04-19-2017, 06:40 PM
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A buddy of mine has a custom tube chassis '69 Nova with a bad ass 700 hp MoTown 427 that he built, it felt light in the front end at 140 mph and adding a road skimming air dam (made of Mad Max worthy welded up aluminum) made a huge difference. I can't imagine our flimsy plastic deals that are more than 8" off the ground on a truck speed governed to around 100 mph make that much of a difference at all as far as "ground effects" go.

To further drift off topic, was riding in a friend's 5.7 Tundra, was semi napping and awoke when I felt it stuttering. Looked ahead and noticed we were going fast. Looked at the speedo, the crazy SOB was going 115 with our two dirt bikes in the back. We got to Utah in no time

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post #12 of 31 (permalink) Old 04-19-2017, 06:43 PM
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I guess I don't see how the air dam provides for a better planted front end. I would think it would either cause the front end of the truck to lift up slightly, or no effect, just pushes the air around the sides of the truck. I have one theory on the pushing the air around the sides of the truck that might result in a more stable ride, but I am not sure I can explain it without a whole lot of hand waving and beer.
Think of it like an reverse airplane wing. By smoothing airflow to one of less turbulence, you create a low pressure area under the vehicle, which leads to better planting of the nose. This concept is used in many vehicles in form of front flaps(in front of wheels), bumper lips etc., Its just that as compared to others, the chevy airdam is a bit too low for a 4x4
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post #13 of 31 (permalink) Old 04-19-2017, 06:58 PM
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The goal of the entire thing was to improve ground clearance for wheeling trails and light offroad, he said as much in a previous update. The mpg test was for observation's sake. It wasn't meant to be hugely scientific, and I'm glad to see what the results were. Even if they were tainted by also removing the steps.

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post #14 of 31 (permalink) Old 04-19-2017, 08:27 PM
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I know GM has taken a lot of heat for the low hanging air dam, how difficult it is to remove, and how little of an impact it has on fuel economy.

I wonder if they will make any changes when the truck eventually sees it's first refresh / face lift.

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I just wish they'd flipped the hardware for the 17 as they'd promised after the flack they caught in 16.
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post #15 of 31 (permalink) Old 04-20-2017, 10:11 AM
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"Statistically Insignificant" that line in the second to last paragraph sums up the entire article.

I had a digital speedo DIC error right out of the dealership of +1 MPH. Compared to GPS at 70 MPH, level road, no wind.

So far I've got. . .

GPS MPG running better than DIC mileage (but I suspect the accuracy of iPhone GPS/Odometer app isn't quite 100% over a 500 mile drive). Speedo has a +4-5 MPH error at 70 MPH. 265/65R/18
Dam off
Leveled front
Larger tires and wheels
Cap on back
Yakima cross bars on cap

Diesel RPM hasn't changed with current vehicle weight. . . One driver. . . Not much cargo. . . does torque overcome drag? I think it probably does. So too does driver technique. I could easily get 30 MPG highway if I drove it accordingly and regardless of drag/no drag devices on the vehicle.

Just about to put 500 highway miles on it in the next three days. I'll get a good idea of mileage then. First work commute with cap and bars.

As far as annual increase and or decrease in fuel costs, won't be noticeable and I drive 24k miles/year. I have been wanting to own a truck again for many years, but slugging 15MPG around was tough to justify. 25MPG is a little easier to accept. Now. . . if I could vacate California and 24k miles a year. . . that would negate everything.
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post #16 of 31 (permalink) Old 04-20-2017, 12:10 PM
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I trimmed my air dam by 2" so do I lose only 2%?


Or maybe 5% because I lose the 4% plus an additional 1% for keeping the weight of the remaining plastic and screws?

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post #17 of 31 (permalink) Old 04-20-2017, 12:51 PM
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I trimmed my air dam by 2" so do I lose only 2%?


Or maybe 5% because I lose the 4% plus an additional 1% for keeping the weight of the remaining plastic and screws?
So 1" = 1% ? But you gain .01% for keeping screws? Or was it 2% because overall is 100% but you removed 5% of the plastic?

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post #18 of 31 (permalink) Old 04-21-2017, 11:49 AM
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So 1" = 1% ? But you gain .01% for keeping screws? Or was it 2% because overall is 100% but you removed 5% of the plastic?


I'm just asking as you are


But my guess is that if 2" is 1/2 the size of the air dam, then 1/2 of 4% = 2%.
As there may not be a linear correlation, any trimming could cause complete loss of 4%.
Then I'm left with the remaining weight of the dam plus screws totaling, idk, 1% additional loss.


Go figure, you do the math, your mileage may vary, etc.

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post #19 of 31 (permalink) Old 04-21-2017, 12:07 PM
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I'm just asking as you are


But my guess is that if 2" is 1/2 the size of the air dam, then 1/2 of 4% = 2%.
As there may not be a linear correlation, any trimming could cause complete loss of 4%.
Then I'm left with the remaining weight of the dam plus screws totaling, idk, 1% additional loss.


Go figure, you do the math, your mileage may vary, etc.
Well, if 2" is 1/2 the size of the air dam, then 1/2 of 4% = 2%.
As there may not be a linear correlation, any trimming could cause complete loss of 4%
Then if you have a complete loss and you still have the weight of the plastic and the screws,
my math tells me you will loose at least 10 MPG on regular fuel. If I were you I would buy a new one and hope like hell
it is identical to the old one. BUT only use half the screws to install it! Man you screwed up big time!

Now I gotta go, I'm shopping for a Prius pick up.

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post #20 of 31 (permalink) Old 04-21-2017, 01:26 PM
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Just my two cents - on a road trip to the Grand Canyon my Colorado got 30.2 MPG highway.

I just took the air damn off and added fogs (and bed liner). I am road tripping to Yosemite in a couple weeks.

Will keep everyone posted on the diff.

**but I got a 4 cyl WT lol in case it matters**

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