Tow Vehicle Recommendation? - R-pod Owners Forum

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offgrid

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Topic: Tow Vehicle Recommendation?
Posted: 19 Oct 2018 at 8:28am

Well, I guess I could try to coast down the WV rural highways too, but there's always a bunch of 15 to 25 mph hairpins on the way up or down and I'm not sure how well the rPod axle will hold up to going around the curves on one wheel.....

If you have properly inflated road tires and add in wind speed and vehicle speed to your mix of variables that you're keeping the same, I agree. Tow with whatever you want, as long as its "modern", ie, has a multispeed auto tranny, efi and good electronic engine controls, and it will probably show pretty much the same fuel economy on the same piece of highway going the same direction.

One thing that might help a little is to add one of the roof mounted spoilers to your TV to try to improve the drag coefficient. I'm thinking of trying that just of fun. I have access to the local airstrip here to run coast down tests to see if I can measure the effect, but I'd have to wait for a calm wind day, which are few and far between here on the OBX.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

furpod

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Posted: 19 Oct 2018 at 8:01am

LOL.. well, part of the difference for us is at nearly 8.5K pounds just in truck and passengers, we coast most of the way down. There are in fact a couple reverse grades you could call them coming down, but of course they are also easier on the way up. I gear down "coming home", (going back to my parents place) because, if not, the big eX would fall down that mountain.. I don't know, maybe 100 miles an hour. I have to brake a fair amount to keep it under 80, unless I kick the OD off.

But yes, it takes "X" horsepower to do "Y" work.. and it takes "X" amount of fuel and "Y" amount of air, to make that horsepower number.

So regardless of engine size, everybody gets the same mileage towing, +/- a few percentage points, when towing.

offgrid

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Posted: 19 Oct 2018 at 4:29am

How can both furpod and lostagain be seeing the fuel consumption they're seeing climbing and descending the same mountain range?

You put fuel/$ into you rig climbing a mountain. For a typical 9000 lb rig figure on about 1 gal per 2000 ft climb. Basic physics of potential energy, no getting around it. The trick is to try to get that back going down. But if the road isn't cooperating by providing you with a grade where you can just coast, there's a big part of that you don't get back. That part just is wasted as heat either out tailpipe if you're engine braking or into your discs if you're wheel braking.

This is the reason my Prius gets the same great fuel economy in town as on the highway. Regen braking puts that energy back in the battery for reuse by the electric motor. I originally wanted to get a Highlander Hybrid for that reason but its not up to towing an rPod.

I was unpleasantly surprised the first time I took my rig to the WV mountains, from sea level to 4000 ft or so. I expected bad fuel economy once I hit the mountains. Instead of my usual 14 mpg plus I got 9.5. Bummer, but I'm getting it back coming down, right?

Nope, I got 11 mpg. Why? Because I have to make 7 2000 plus foot climbs and descents to get to the final climb up to 4000. That's the Appalachians. Then, engine and wheel braking all the way down each ridge heating up the air for next to no benefit. On the way back I have one less climb so its a little better, not much.

All this is why comparing fuel economy towing is so confusing. Unless you're comparing running a dead flat highway at the same speed in a zero wind condition, there are way too many variables making the numbers bounce around. Even a 5 mph headwind will drop my fuel economy from 14 to 12.5 or so mpg.

To bring this thread back to rjmarlatt's original question. You probably don't want to get a new tow vehicle expecting some great improvement in fuel economy towing, you're likely to be disappointed. Almost certainly you'll never recover your investment with fuel savings. Most of the engineering that makes newer vehicles more efficient is washed out when you're dragging around a big heavy box.

My recommendation is to get a new tow vehicle because that's what you want to drive, make sure it meets your towing and other requirements, and enjoy. If your towing fuel economy improves along the way, that's gravy. And one requirement needs to be a big fuel tank, I'd say about 20 gal is the minimum. Less than that and you'll be looking for a gas station every couple of hours.

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

lostagain

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Posted: 18 Oct 2018 at 8:30pm

furpod, the thing that really sucks up the gas on the way to Sacramento is climbing from Dayton, to Moundhouse, then Spooner summit grade, then Echo Summit. Once you're past those, it's just a matter of wind resistance. And, yes, the trip starts at 4500 ft and ends about 100 ft above sea level. I just try to go a little slower and reduce the wind drag. There's not much more I can do besides keeping my engine in good repair and the tires properly inflated. Like I said, Chrysler/Dodge is not noted for wonderful fuel economy in any of their vehicles. But, the difference in gas savings will fall far short of buying my dream truck, so I'll just live with what I have and be happy.

Never leave footprints behind.
Fred & Maria Kearney
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2019 Ford F-150 4x4 2.7 EcoBoost

furpod

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Posted: 18 Oct 2018 at 6:08pm

Originally posted by fwunder

Originally posted by furpod

... 5-8 people and gear, or a cargo trailer, every trip.

Holy rest stop, furpod! How often did you have to pull over or, did you just dehydrate everyone before?! Are we there yet?! Star

fred

I won't go into details, but most legs, no stops. None of it was fun. My family is used to my military ingrained need to get there, get it done, and get back. My baby brother is also prior service, so he was no problem. Mom groaned a little first time up.. but by the last trip down after the funeral, she was "get home, now. not a peep out of her"..

fwunder

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Posted: 18 Oct 2018 at 5:40pm

Originally posted by furpod

... 5-8 people and gear, or a cargo trailer, every trip.

Holy rest stop, furpod! How often did you have to pull over or, did you just dehydrate everyone before?! Are we there yet?! Star

fred

2014 RPod 178 => MyMods and Buying Habits
2008 4Runner Limited 4.0-liter V6
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mcarter

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Posted: 18 Oct 2018 at 5:34pm

I have both a 2WD and a 4WD tow vehicle. The 4WD is a V8, the 2WD is a V6. Both have a 7000 lb tow capacity. The mileage on the 2WD is reduced more when towing than the 4WD. I use the 4WD for many things other than towing a Pod. To me it is a valuable asset. The 2WD my wife drives on a somewhat daily basis, and it gets very good mileage for an everyday driver. If I had to pick one to tow, I would choose the V8, 4WD. AND I do on most occasions. IMHO

Mike Carter
2015 178
" I had the right to remain silent, I just didn't have the ability."

offgrid

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Posted: 18 Oct 2018 at 4:20pm

TheBum, that makes sense.

Let's assume the same trailer and tow vehicle, the only difference is the engine. HP requirement is aero drag plus rolling resistance. So the aero drag will be identical and the rolling resistance will be nearly so, insignificantly more for the V8's slightly higher weight. And that will be true whether towing or not towing.

So, if the HP requirements to run down the road are nearly identical why wouldn't the fuel economy be the same for both? It won't because engine efficiency varies with loading. And the smaller engine is seeing a larger percentage variation in its loading than the larger engine is, so its fuel economy will likely vary more.

Nearly always the vehicle/engine combo has been designed so the smaller engine is a better match to its requirements when its lightly loaded/not towing. That way the manufacturer can advertise the highest possible highway fuel economy. Whether or not the larger or smaller engine is better towing will depend on where the engine ends up operating. The smaller engine is going to need to drop to a lower gear sooner and that's bad for efficiency because of the higher friction and pumping losses at higher rpm. It can easily be the case that the smaller engine is less efficient than the larger one when towing.

If anyone is interested, here's a cool calculator for fuel economy based on aero drag, rolling resistance, and engine/drivetrain efficiency.

https://ecomodder.com/forum/tool-aero-rolling-resistance.php

1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold

TheBum

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Posted: 18 Oct 2018 at 3:47pm

From anecdotal evidence, V8s or higher seem to have less of a difference in mileage between towing and non-towing than V6s do.

Alan
2022 R-Pod 196 "RaptoRPod"
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furpod

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Posted: 18 Oct 2018 at 3:37pm

From Carson City to Sacramento is almost all downhill.. I did that area 4 times in the last month, Sacramento to Winnemuca and back. My 6.8 V10 Excursion got 12.6 +/- a tenth going up, and 16.5 exactly, (again +/- a tenth) coming down.. 5-8 people and gear, or a cargo trailer, every trip.