Fuel Consumption Towing ??? (Whiskey-Tango-Foxtrot) - Page 22 - 2014+ Jeep Cherokee Forums
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post #211 of 217 (permalink) Old 06-14-2017, 05:21 PM
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Since this is going into dyno talk, I will add this. No dyno is accurate. They will give you a ball park number, but depending on the type of dyno, your numbers could be very different from one dyno to the other. Dyno's are really just used for comparisons. If you dyno a car on a dyno, mod it, and dyno again on the same dyno, then you get the ball park add of the part, environmental factors will throw these numbers off, that is why I said ball park. I know some people have dyno'ed a car in hot weather, 90+, and then dyno'ed again in 40 degree weather and got a gain in performance, all do to the weather changing. I know vendors like to do this to show bigger gains then actual.


Example, when I had my Evo, I only put down 200awhp on a dyno. Not very good considering it puts out 300hp stock, but again types of dyno's play into your number. I modded it and went back to that same dyno, and my car put down 240awhp. From that you could tell my mods increased my HP by ~40awhp. I really didn't care about the total number, I just wanted the gain. That same car went to another dyno and put down 319awhp. I gained 80whp just by changing dyno's. Man I miss that car it was fast.

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post #212 of 217 (permalink) Old 06-14-2017, 05:28 PM
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Back in my dyno days, the Mustang brand dynos always gave lower numbers than the Dynojets. I never used a Mustang dyno, but my Trans Am was run on three different Dynojets between 2001 and 2004, and the results were within a couple of hp each time.

If I recall correctly (and was told correctly), the Mustang dyno design applied a drag to the drum that was supposed to take into account the vehicle weight, but the Dynojet was only spinning up the drum's mass.

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post #213 of 217 (permalink) Old 06-23-2017, 06:25 PM
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10+ days, @SS_Syndicate. How's the fuel economy holding up?
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post #214 of 217 (permalink) Old 06-24-2017, 01:59 PM Thread Starter
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Originally Posted by Rojhan View Post
10+ days, @SS_Syndicate. How's the fuel economy holding up?
Seems to still be better, but it's tough to tell. My wife's commute is pretty short so we are still on the same fill up from after our trip. Our little errands of late have been in our new toy. (I got my new 4runner)

For a few reasons.... we have opted to take the KL on the big overlanding trip in a few weeks. In prep, I plan to make an airfoil or wing to help direct the wind above the tent more efficiently on the trailer.

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post #215 of 217 (permalink) Old Yesterday, 02:22 AM
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I see two things that are hurting you with that trailer. First, a very non-aerodynamic piece protruding well above the roof height of your vehicle (flat plate being forced through the oncoming air) will cause much more drag than an aerodynamic shape of the same total surface area. The Coefficient of drag of a flat plate is 1. Any improvement in the leadedge shape will reduce that and improve your mileage.

Second, the empty space between your upper level and lower storage area on your trailer induces interference drag. Two bodies close together cause more drag than a single body of the same surface area because the airflow between them becomes turbulent and adds drag to both surfaces.

The third thing is your speed. While I understand your concerns about driving slower, the total drag increases exponentially with speed. Slowing down just 5 MPH, so long as that doesn't put you into a poor gear ratio range, will show a significant improvement, while 10 MPH may be dramatic.

Here's a good article on drag. Ignore the part about induced drag (which results from generating lift in an airplane), but pay particular attention to the paragraphs on FORM DRAG, and most especially INTERFERENCE DRAG. Understanding those two may help you improve on your trailer's design in relation to drag, and therefore gas mileage.

https://en.m.wikipedia.org/wiki/Parasitic_drag

My recomendation would be: since you designed and built the trailer yourself, either lower the top level closer to the height of your Cherokee, or add a vertical "V" shaped fairing to the front. If possible close the space between the upper and lower levels at the front of the trailer, and don't leave holes that generate turbulence, which increases drag. Good luck!
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post #216 of 217 (permalink) Old Yesterday, 08:21 AM Thread Starter
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Originally Posted by RGH2CO View Post
I see two things that are hurting you with that trailer. First, a very non-aerodynamic piece protruding well above the roof height of your vehicle (flat plate being forced through the oncoming air) will cause much more drag than an aerodynamic shape of the same total surface area. The Coefficient of drag of a flat plate is 1. Any improvement in the leadedge shape will reduce that and improve your mileage.

Second, the empty space between your upper level and lower storage area on your trailer induces interference drag. Two bodies close together cause more drag than a single body of the same surface area because the airflow between them becomes turbulent and adds drag to both surfaces.

The third thing is your speed. While I understand your concerns about driving slower, the total drag increases exponentially with speed. Slowing down just 5 MPH, so long as that doesn't put you into a poor gear ratio range, will show a significant improvement, while 10 MPH may be dramatic.

Here's a good article on drag. Ignore the part about induced drag (which results from generating lift in an airplane), but pay particular attention to the paragraphs on FORM DRAG, and most especially INTERFERENCE DRAG. Understanding those two may help you improve on your trailer's design in relation to drag, and therefore gas mileage.

https://en.m.wikipedia.org/wiki/Parasitic_drag

My recomendation would be: since you designed and built the trailer yourself, either lower the top level closer to the height of your Cherokee, or add a vertical "V" shaped fairing to the front. If possible close the space between the upper and lower levels at the front of the trailer, and don't leave holes that generate turbulence, which increases drag. Good luck!
You are a little late to the show but I appreciate your efforts...

The tent on the trailer has to be where it is for several reasons. If it were able to be lower I would gladly lower my GOG. Remember, this trailer is used with several vehicles. This is actually the whole point to having the trailer. We use several vehicles depending on how far and the type of terrain we are covering. My large complaint (and foundation for this post) was that it caused such a drastic change with the KL yet only yielded small losses when towing with other vehicles. I don't want to drone on about these other vehicles, but trust me.... there is absolutely no reason they should perform more economically than the KL, Especially given your drag argument.

Since our firmware updates we have seen some economic improvements. (A measured 3-5 MPG, and vehicle calculated 2-4 MPG, improvement). This puts us in a realm where I really don't have an argument anymore. This said... Jeep still has a ton of work to do when it comes to economy. Our KL really should be our highest economy vehicle and it isn't. Compound this with the rather limited fuel capacity and Jeep missed the mark pretty big given the demographic they are targeting. (Explore.... but don't get to far from the pump, LOL)

.

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post #217 of 217 (permalink) Old Yesterday, 10:26 AM
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Got this mpg on the way to Arkansas from SoCal pretty much the whole trip at 65-70.
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