How to predict MPG? - Fiberglass RV


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Old 05-01-2011, 01:26 PM   #1
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How to predict MPG?

I'm trying to figure out if there's any way to predict whether a specific vehicle will get top fuel economy while towing. By top fuel economy, I mean better than most other tow vehicles... preferably around 20 mpg or better.

I'm in a somewhat different situation than most, in that I tow a trailer every day for work. With gas prices rising, I'm looking at cost cutting options like a more rounded trailer and/or a more economical tug. Currently my boxy 6x12 trailer and 2008 Highlander achieve about 10.5 mpg @ 65 MPH, or almost 12 mpg @ 57-58 MPH. I drive close to 20,000 miles like this for work, so at the slower speed that's about $6600/year at $4/gallon gas. I don't think I can slow down any more than that and still get all my work done, though.

I do think I can bump the gas mileage up to about 15 with a rounded trailer, and I'll probably make that change this summer. But getting back to my question...

I've seen plenty of numbers recently here from folks with 4 cyl engines who get 20+ mpg. This surprises me. My own experience with a 180 HP V6 Windstar, a 215 HP V8 Mountaineer, and my current 270 HP V6 Highlander has been that more power equated to equal or slightly better towing fuel economy. But all three were very close... in the 10 to 12 mpg range with the box trailer. The Highlander is the best of the three, and yet when towing the Burro it achieved only 11 (in high winds) to 16 (best conditions), averaging 14.3 over a 2900 mile trip. I also towed a 22' Rockwood (7.5' wide) with the Mountaineer and got about 10-11 mpg @ 55-60 MPH with that. It seems like wind resistance has a larger impact on gas mileage than do trailer length and weight. A 4x8 sheet of plywood weighs next to nothing, but if I towed it standing up like a sail (or 1/2" long trailer!) I am sure the mpg's would be terrible.

So I'm thinking, how can I find a vehicle that will get me 20 mpg with a rounded trailer? Is it hit-or-miss? Or is there a way I can have some confidence that what I buy will achieve such lofty results?

Looking on the Scampers forum's Records section, 75 vehicle/trailer combos are listed by their owners along with mpg results. I've studied them to try and draw some correlation between engine power and fuel economy. Some Subarus got 22 mpg towing, some only 16 or 18. Honda Elements towing 13'ers: a couple of them got 17, one got 23 mpg. This sort of thing makes me wonder if buying a vehicle for mpg is a hit-or-miss proposition, due to variation in engine parts manufacturing tolerances and such.

But there does seem to be somewhat of a general trend observable in those records, in that the little 4 cylinder engines sometimes (not always) have generally given better results then the V6's or V8's. A Chevy Colorado 4 cyl. is listed as giving 16 mpg @ 65, but 20 mpg @ 55. A Ford Escape was getting 24 mpg @57 (Floyd's?). A Honda Civic owner claims 31 mpg @ 65-70, towing a 13' Casita. A 4 cyl Jeep Cherokee getting 20.5 mpg @ 60. A PT Cruiser achieving 25 mpg @60 and 20+ @70. The Elements and Subies I already mentioned.

Any vehicle I buy will have to be able to handle a 3500 lb. trailer and 350 lb. tongue weight... if not from the factory, then with aftermarket mods (custom hitch? rear suspension help?).

I've toyed with the idea of a Jetta or Passat TDI. The VWs listed in Scampers are getting 25 mpg and up while towing. Can-Am in Ontario can install a custom receiver with WD hitch, but it's almost $2,000 for the job... and about 1400 miles away from me. And my last Jetta ('99 gasser) was somewhat problem prone... I'm leery of the upkeep costs for a VW TDI.

Short of buying a preowned vehicle with demonstrably good track record for towing mpg's (something that would be very difficult to find or obtain!), is there any way to fairly well ensure that a monetary investment in another tug will yield the kind of fuel economy I'm after? Thoughts, comments?
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Old 05-01-2011, 01:51 PM   #2
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I thought all of the Canyon and Colorado trucks were 5 cylinders, anyway a small engine that gets great mileage driving to the grocery store is not going to get good mileage towing because it's under powered. A bigger engine may not get as good fuel mileage but it will suffer less loss of mileage when towing because you would not be working it to death. I understand your dilemma.
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Old 05-01-2011, 02:36 PM   #3
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I had a Jeep Liberty CRD, towed a T@da and got 20 mpg. Only made the Jeep in 2005 and 2006 but they are selling used. Diesel though is above $4/gallon.
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Old 05-01-2011, 03:32 PM   #4
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Originally Posted by Greg H View Post
I thought all of the Canyon and Colorado trucks were 5 cylinders, anyway a small engine that gets great mileage driving to the grocery store is not going to get good mileage towing because it's under powered. A bigger engine may not get as good fuel mileage but it will suffer less loss of mileage when towing because you would not be working it to death. I understand your dilemma.
Our Honda CRV, a 4 cylinder, 180 HP, gets 22-25 mpg towing our Scamp 16, a little less towing the Casita 16. Our Honda has 140,000 miles and has never had a single issue. We have been all over the USA and Canada. I never felt it was straining and the temperature gauge has never moved off it's normal position.

We get 28-30 mpg on the highway and 22-25 mpg towing.

Norm
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Old 05-01-2011, 03:49 PM   #5
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Originally Posted by Mike Magee View Post
I'm trying to figure out if there's any way to predict whether a specific vehicle will get top fuel economy while towing. By top fuel economy, I mean better than most other tow vehicles... preferably around 20 mpg or better.

I'm in a somewhat different situation than most, in that I tow a trailer every day for work. With gas prices rising, I'm looking at cost cutting options like a more rounded trailer and/or a more economical tug. Currently my boxy 6x12 trailer and 2008 Highlander achieve about 10.5 mpg @ 65 MPH, or almost 12 mpg @ 57-58 MPH. I drive close to 20,000 miles like this for work, so at the slower speed that's about $6600/year at $4/gallon gas. I don't think I can slow down any more than that and still get all my work done, though.

I do think I can bump the gas mileage up to about 15 with a rounded trailer, and I'll probably make that change this summer. But getting back to my question...

I've seen plenty of numbers recently here from folks with 4 cyl engines who get 20+ mpg. This surprises me. My own experience with a 180 HP V6 Windstar, a 215 HP V8 Mountaineer, and my current 270 HP V6 Highlander has been that more power equated to equal or slightly better towing fuel economy. But all three were very close... in the 10 to 12 mpg range with the box trailer. The Highlander is the best of the three, and yet when towing the Burro it achieved only 11 (in high winds) to 16 (best conditions), averaging 14.3 over a 2900 mile trip. I also towed a 22' Rockwood (7.5' wide) with the Mountaineer and got about 10-11 mpg @ 55-60 MPH with that. It seems like wind resistance has a larger impact on gas mileage than do trailer length and weight. A 4x8 sheet of plywood weighs next to nothing, but if I towed it standing up like a sail (or 1/2" long trailer!) I am sure the mpg's would be terrible.

So I'm thinking, how can I find a vehicle that will get me 20 mpg with a rounded trailer? Is it hit-or-miss? Or is there a way I can have some confidence that what I buy will achieve such lofty results?

Looking on the Scampers forum's Records section, 75 vehicle/trailer combos are listed by their owners along with mpg results. I've studied them to try and draw some correlation between engine power and fuel economy. Some Subarus got 22 mpg towing, some only 16 or 18. Honda Elements towing 13'ers: a couple of them got 17, one got 23 mpg. This sort of thing makes me wonder if buying a vehicle for mpg is a hit-or-miss proposition, due to variation in engine parts manufacturing tolerances and such.

But there does seem to be somewhat of a general trend observable in those records, in that the little 4 cylinder engines sometimes (not always) have generally given better results then the V6's or V8's. A Chevy Colorado 4 cyl. is listed as giving 16 mpg @ 65, but 20 mpg @ 55. A Ford Escape was getting 24 mpg @57 (Floyd's?). A Honda Civic owner claims 31 mpg @ 65-70, towing a 13' Casita. A 4 cyl Jeep Cherokee getting 20.5 mpg @ 60. A PT Cruiser achieving 25 mpg @60 and 20+ @70. The Elements and Subies I already mentioned.

Any vehicle I buy will have to be able to handle a 3500 lb. trailer and 350 lb. tongue weight... if not from the factory, then with aftermarket mods (custom hitch? rear suspension help?).

I've toyed with the idea of a Jetta or Passat TDI. The VWs listed in Scampers are getting 25 mpg and up while towing. Can-Am in Ontario can install a custom receiver with WD hitch, but it's almost $2,000 for the job... and about 1400 miles away from me. And my last Jetta ('99 gasser) was somewhat problem prone... I'm leery of the upkeep costs for a VW TDI.

Short of buying a preowned vehicle with demonstrably good track record for towing mpg's (something that would be very difficult to find or obtain!), is there any way to fairly well ensure that a monetary investment in another tug will yield the kind of fuel economy I'm after? Thoughts, comments?
Mike G.

We have towed both a "square" and a "round" trailer with the same tow vehicle.

The Square trailer was a 15.5 ' 1982 Sunline. It was the lightest and the widest of the trio. We had the worst mileage towing it and got 20 mpg towing it.

The first Round trailer was a 1995 Casita 16 with front bath. It was the heaviest and shortest of the three and we averaged about 23 mpg.

The second Round trailer was a 1991 Scamp 16 with side bath. It was a about the weight of the Sunline but we got 22-25 mpg. I give a range because so far we have only towed the Scamp 1600 miles.

We have towed somewhere around 30,000 miles. We do not travel as fast as you, typically in the upper 50s.

Our son towed with an Element and neither towing or not got the mileage of the CRV. I think the Element is a little boxier.

It appears to me that your problem is going to get magnified. Gas in CT this week was $4.39 for regular and the state is raising the gas taxes again, among the highest. As well I see the EPA has shut down more drilling operations in Alaska. I would not be surprised to see $5.

Our Honda is 7 years old, 140,000 miles. If Honda would sell their diesel here I would buy one in a minute. I've considered the VWs but am leary of all the negative reports from users.

Hope this helps a little.

Norm
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Old 05-01-2011, 05:07 PM   #6
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Jim, what made you decide to sell the CRD? Tell me your likes and dislikes about the Jeep.

Norm, with the CRV the biggest thing I wonder about is whether the receiver attachment will handle 350 lbs tongue weight. Would it need some extra reinforcement?

I suppose If I buy a vehicle that's 5 to 8 years old, at least the investment is low and I can try it out for fuel economy without much at risk... and if it's not acceptable, resell it without losing much.
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Old 05-01-2011, 05:20 PM   #7
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350 pounds hitch weight is too much for a CRV, certainly without some kind of WD. We had an opportunity to buy a 2005 Casita 17 for $6500 and passed because they are too heavy for us. As well 3500 #s exceeds the European rating for the Honda.

I'm personally more comfortable keeping the weight under 3000 #s. I wouldn't and haven't towed anything larger than a Casita 16. As well I actively seek to keep the hitch weight down.

Part of our reason for choosing the Scamp 16 was it's lower total weight and lower tongue weight, not to mention I can standup in a Scamp and can't in the Casita.

Certainly one advantage the Europeans have over us is the availability of all those 4 cylinder diesel engines from European, Japanese and even American manufacturers. Ford has some great little diesel vans in the UK.

Until a more appropriate Tow Vehicle comes along we'll stick with our Honda.

Hope this clarifies,

Norm
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Old 05-03-2011, 09:15 PM   #8
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Mike, I think you're stuck with larger tow vehicles when you are in the 3,500/350 lb range. My guess for the best fuel economy would be a Sprinter van -- one of the earlier 5 cylinder models. I have one, and it gets 22 MPG driving 75 MPH through the mountains with 6,000 pounds of cargo inside. I used to make a trip like that three times a month. It is rated to tow 6,000 pounds. I have towed with it, but not very far (and it was a 5,000 pound boat). My Sprinter is the longest, tallest model. For the best fuel economy and towing ease, I would recommend the smallest model you can live with... they're still pretty big!

I tow my 13' Scamp with a Scion xD (Toyota Urban Cruiser in Europe). It has a 1.8 liter 4 cylinder and gets 24 MPG towing at 55 MPH. My all time average over 60,000 miles is 35 MPG. I have gotten 42 MPG driving insanely slow. There is no way I would tow 3,500 pounds with it... and I bet a 350 pound tongue weight would rip the hitch off the car... so I am not recommending it for your job.

One thing I will say is that you are going to see people post very different MPG numbers... towing AND not towing. This is NOT because of engine tolerances... this is because of different driving habits and situations. Driving just about any car on my normal commute to work, I guarantee I will get about 20% higher than the EPA highway mileage. This is partly because of my driving style, and partly because of the roads, terrain, and traffic patterns.
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Old 05-03-2011, 09:58 PM   #9
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Sounds like the best option (maybe the only option) to approach 20 mpg towing a cargo trailer is a small diesel. Used Sprinter prices are pretty high, but if the right deal came along it might be a good one to try, thanks. Might keep my eyes open for a good Liberty CRD, too.

It's always possible to hit an oddball (in any model) that gets unusually low or high mpg's. I guess it's an unavoidable risk. But you're probably right that the most prevalent cause of varying results from different owners is the driving style. As far as my driving style goes, the recent fuel price increases have induced me to modify my own driving habits. I'm up about 1 to 1.5 mpg by driving 5 MPH slower. Unfortunately I don't think I can slow down more and still get my work done, so I've about reached the limit of that.
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Old 05-03-2011, 11:15 PM   #10
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Cool You asked the one million dollar question.

Phew! We would all like the answer to your question. What you get and how it works depends on a lot of factors.

A heavy trailer will get worse MPG than a lighter one if it experiences a lot of starts and stops whereas long drives on relatively flat freeways will be more affected by the aerodynamic shape and not so much the weight.

Different tugs would probably give better results for each scenario.

The laws of physics are the laws of physics.

Air resistance increases as the square of the speed.

50 mph = 2500 and 70 mph = 4900, almost twice as much.

"Driving at higher speeds increases aerodynamic drag (wind resistance), reducing fuel economy. The new EPA tests account for aerodynamic drag up to highway speeds of 80 mph, but some drivers exceed this speed."

from: Many Factors Affect MPG

Remember, you can fool Father Time, but not Mother Nature.
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Old 05-03-2011, 11:59 PM   #11
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WOW! I am NOT joking...
I knew I'd seen that most-aerodynamicClick image for larger version

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Did they nail it, or what?Click image for larger version

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1950 "COLE" : 13 ft.; 6ft headroom; 61/2 ft wide; 800 lbs!!!
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Old 05-04-2011, 06:34 AM   #12
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When towing gas MPG will be about 20% less than your avg MPG.
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Old 05-04-2011, 07:08 AM   #13
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Hi: All... I have always said that fuel economy and trailer towing shouldn't be used in the same paragraph. The secret un scientific thing is to find the sweet speed...at which max MPG's are obtained. My old Escape 5.0 and V6 GMC pickup combo was 58 MPH. You just have to get used to feeling like you're going backwards. Our best mileage was 18.5 tuggin'. 26 not tuggin'...but in OD the truck had no guts either!!!
Alf S. North shore of Lake Erie
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Old 05-04-2011, 08:00 AM   #14
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When towing gas MPG will be about 20% less than your avg MPG.
I could wish! My Highlander gets 23-24 mpg when not towing. 20% less would equate to about 18. With my cargo trailer I'm getting 11 mpg, some days 12.
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