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Topic ClosedProud new owner of a rpod 193
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GlueGuy View Drop Down
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Posts: 2627 		Direct Link To This Post Topic: Proud new owner of a rpod 193
    Posted: 17 Jul 2020 at 5:21pm
I don't think you can just take the frontal area; exposed or not. A significant portion (in fact, I think the majority) of the drag from trailer towing is the "suction" at the rear. That's why very aerodynamic things (e.g. airplanes) have the pointy part in the rear; it's to reduce the turbulence/suction/drag imposed by the back end of whatever it is.
bp
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lostagain View Drop Down
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Posts: 2586 		Direct Link To This Post Posted: 17 Jul 2020 at 6:14pm
So a giant dunce cap on the back of the trailer is what I need?Confused  Too much time on my hands after returning from camping.
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Fred & Maria Kearney
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KerieG View Drop Down
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Posts: 8 		Direct Link To This Post Posted: 17 Jul 2020 at 9:09pm
Wow thank you all for the explanations. We are still debating what to do. Its a chicken or egg thing. We have a Honda Pilot AWD with 5K towing capacity but I REALLY want that 193. But ugh this pandemic is both making me crazy and need to get out of this house but also the idea of trading in a vehicle right now is a pain in the butt. 

Thank you all for the info! Lots to consider. 
Kerie
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offgrid View Drop Down
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Posts: 5290 		Direct Link To This Post Posted: 18 Jul 2020 at 5:06am
Originally posted by KerieG

Wow thank you all for the explanations. We are still debating what to do. Its a chicken or egg thing. We have a Honda Pilot AWD with 5K towing capacity but I REALLY want that 193. But ugh this pandemic is both making me crazy and need to get out of this house but also the idea of trading in a vehicle right now is a pain in the butt. 

Thank you all for the info! Lots to consider. 

Good for you in recognizing that the tow vehicle you have isn't up to towing that trailer. You have a decision to make, smaller trailer or bigger tow vehicle. I have a Highlander which is a good all around mid sized SUV with I think the same towing capacity as your Pilot. It gets used 90% of the time with no trailer behind it. Paired with the 179, it is a good match and provides what my wife and I find is an ideal size rig for two people.  I wouldn't want anything bigger, and wasn't interested in owning a pickup truck again. Others have different needs, opinions, and budgets.
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offgrid View Drop Down
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Posts: 5290 		Direct Link To This Post Posted: 18 Jul 2020 at 5:54am
Originally posted by lostagain

Nope, it's not clear, at least to someone as slow as me.  But then I rarely drive fast.  The back of the truck is 6' wide and 4.5' high to the top of the tonneau covered bed.  The trailer is 7' wide and about 8.5' tall with the same curved front as an r-Pod.  There isn't a lot of trailer showing looking at the truck and trailer combined from the front.  And there are no cantilevered wheel with phenomenal wind resistance sticking out the sides.  Ermm  So what would be the Cd x A?  

The reason aerodynamicists separate A and Cd is so they have separate shape and scale factors.  That way they can do small scale wind tunnel testing of a shape and then scale it up to full size using the frontal area A. 

Since the tow vehicle and trailer share an air stream they effect each other, so, think of the rig as a single shape, It doesn't work to try to calculate their areas and drag coefficients separately. In this case the rig has a frontal area of say 55 square feet, the area of the trailer, which is larger than the tow vehicle. 

We don't know what the Cd is, which is why the manufacturer's 55 square foot restriction seems pretty bogus. The other reason is that just slowing down 5 mph has about the same impact as say the difference between 45 and 55 square feet would, everything else being equal.  My guess is that the manufacturers just use A because it is fairly easy to measure. No one knows the Cd of each combination of tow vehicle and trailer. It allows them to place some kind of limit on the size of trailers being towed which they could use to protect themselves from litigation I suppose. 

I came up with the roughly 0.4 Cd for my rig by backing into it using fuel efficiency and rolling resistance numbers. But its a rough assumption, and similar to what other boxy vehicles are. The way to find out would be to do coast down testing. For me, that would only be worthwhile to test out the effect of a spoiler on the back of the SUV or removing the a/c or something like that.
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lostagain View Drop Down
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Posts: 2586 		Direct Link To This Post Posted: 18 Jul 2020 at 8:17am
Oh, heck, I'm just not going to think about it any more.  My truck is balanced with the trailer to the point that it drives smoothly, has no tail wagging the dog issues, gets above average mileage, does fine with strong cross winds, and has plenty of reserve power.  So I'll just keep plodding along with the cruise control set at 55, smiling as I drive, and arriving relaxed and ready to so some more serious relaxing at the destination.  
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Fred & Maria Kearney
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offgrid View Drop Down
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Posts: 5290 		Direct Link To This Post Posted: 18 Jul 2020 at 10:01am
Originally posted by lostagain

Oh, heck, I'm just not going to think about it any more.  My truck is balanced with the trailer to the point that it drives smoothly, has no tail wagging the dog issues, gets above average mileage, does fine with strong cross winds, and has plenty of reserve power.  So I'll just keep plodding along with the cruise control set at 55, smiling as I drive, and arriving relaxed and ready to so some more serious relaxing at the destination.  

Sounds like a good plan to me. Besides, while you're in CA you'll be driving at the legal speed limit for towing. Tongue
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KerieG View Drop Down
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Posts: 8 		Direct Link To This Post Posted: 01 Sep 2020 at 4:25pm
Welp we did it! I think we're the first 193 owners in the PNW. Still working on upgrading the tow vehicle but I couldn't pass up the 193 that was on the lot.  Super excited! 
Kerie
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StephenH View Drop Down
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Posts: 6285 		Direct Link To This Post Posted: 01 Sep 2020 at 4:44pm
Congratulations and welcome! Just take it easy until you can upgrade. I hope you have many fun adventures and make many great memories with your new RP193.
StephenH
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KerieG View Drop Down
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Posts: 8 		Direct Link To This Post Posted: 01 Sep 2020 at 4:56pm
Thanks! 
Kerie
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