RTTs and fuel economy

[LocalmotionSC]

My girlfriend and I are in the middle of a long north american road trip (4 months on the road so far). Our plans were altered dramatically when our 1987 Sportsmobile "Big Blue" was totalled in a flood outside of Detroit Michigan the day before we crossed into Canada.

Needless to say it has been quite an ordeal dealing with the insurance company, searching for a new vehicle, and trying to figure out how to register a vehicle in a state I don't live in. Also camper vans, sports mobiles, expo rigs, etc are much less prevalent here in the Northeast compared with out West.

The silver lining of all this is that we have the opportunity to re-imagine our trip around a new rig. I think if we had been able to find a comparable Sportsmobile nearby we would've jumped on it. Since we haven't found much in terms of vans or small RVs (tiger, sunrader, etc) we started to think more creatively. The more we brainstormed the more we realized the thing we disliked most about the sports mobile was the fuel economy. When we first got the van we were getting 12-17 but over the last 7k miles we probably averaged 12.5 mpg. We began to think about getting a fuel efficient car and an RTT. At the top of our list is the Tirbo Diesel Jetta Wagon which gets 40-50mpg highway.

My question is whether an RTT affects fuel economy significantly. I'm sure its different rig to rig so I'm specifically curious how it affects the fuel economy of diesels, cars or smaller engines. Also is there a significant difference in fuel economy between the more aerodynamic fiberglass style and the soft RTTs?

Thanks for the help expo! Any feedback is appreciated.


If you want to check out our adventure so far through the West, Texas, Arkansas, and the Midwest check out our blog:

NAWWAL.NET
"Not all who wander are lost"

 

[tarditi]

RTT is more an effect of wind resistance than weight - if you work out a fairing on the leading edge you may not het too bad of a hit if the RTT is generally the same footprint as the vehicle roof. That said, a TDI jetta is pretty narrow-roofed compared to something like a Tahoe, Land Cruiser, or other full size SUV, so it may not work out so well.

Frankly, you could strap a twin mattress on it and drive around to see how it impacts your MPG. That's likely a fair representation.

 

[screwball48]

What about something like a jumping jack trailer. Small enough for a small vehicle to tow yet spacious enough for two on an extended trip. Towing may have the same effect on MPG as an RTT would but the trailer could be left at campgrounds for trips into town. http://www.jumpingjacktrailers.com/6x8-tent-trailer.php
(No affiliation)

 

[stingray1300]

It might be fair to asses your mpg hit being about 10%. My truck gets 21mpg, but with the RTT it gets about 19.
.
*YMMV* :sombrero:

 

[Mike S]

We have some data on this subject. As Frenchy pointed out, there are a number of variables.

- Horsepower/torque of the vehicle
- Aerodynamics of the roof tent - hardshell vs. folding tent, the difference is significant
- Aerodynamics of the vehicle - windshield slope, etc.
- Weight of the tent
- Mounting position/height of the tent
- Driving style
- Driving conditions and speed

All these things play a role to one degree or another.

 

[concretejungle]

All good posts. The type of tent you have, the type of vehicle and how you drive it all work together. A "fold over" type RTT that is like a huge brick on top of your car will affect your MPG more the faster you drive. I had one and running 70 to 75MPH was not enjoyable and the truck didn't like it. Under 55mph and i didn't hardly know it was there.

I switched to a hard shell RTT and the milage is a lot better. I only lose maybe 1-2mpg compared to not having it up there.

 

[proper4wd]

With regards to registering the vehicle, contact Its Easy

they will likely be able to register it for you in your home state, pending local laws on vehicle inspection etc

http://itseasydmv.com/index.php

We used these guys in the car biz and they are a life saver.

And about the RTT, I have one on my Xterra and still see 19ish mpg. Did not notice much of a change with or without it. 90% of my driving is under 45mph but even on the highway it still gets close to 20mpg.

 

[eviioiive]

i set mine pretty far back on my suburban and was under 2mpg loss

 

[Scoutn79]

The mileage loss is going to be in direct proportion to what you ar putting it on. IE a big diesel rig will see nothing measurable as a loss but in your Jetta idea I bet you loose 10 mpg. Those cars are designed to be very slippery through the air. Adding a big amount of wind resistance is going to kill the aerodynamics.
Case in point. I had a Honda CRX that got 60 mpg on the highway. I traveled from Colorado To Ohio with a very light weight tiny cargo rack with a tool box on top. The tool box was situated so the wind side cross section was 12" by 20" and (IIRC this was almost 30 years ago) I lost 15 mpg...25% on a very aerodynamic car.

Darrell

 

[LocalmotionSC]

Wow, thanks for all the input guys.

Your responses confirmed my assumption that it really depends on the vehicle, the engine, etc.

I'm hoping to get a hard shell with pretty good aerodynamics and hopefully the Jetta Wagon TDI fairs better than its gas counterpart would. I'm not really sure why I think this will be the case, but I just feel like a diesel will have less trouble pushing a little extra air out of the way. It sounds like I'm looking at anywhere between a 2-10mpg loss which is around a 5-25% loss. I would hate to lose 10mpg but I guess its still a lot better than the Sportsmobile was getting. I don't mind driving a little slower to get better fuel economy so maybe I'll be able to keep the loss to a minimum.

Proper4wd - thanks for the recommendation I'll look into that company they could be a lifesaver if they can make something work for us.diesel

If anyone has any other creative alternatives to the Jetta/RTT idea let me know. I'd love all the input I could get. I'd like to get 18+ mpg with a van/truck/rv or 30+ with a car/rtt or car/trailer combo. I'm even considering going back to sleeping on the ground and just getting a decent tent. Any ideas whether a small (maybe teardrop) trailer or a RTT would be a bigger hit to mpg?

Thanks for the input guys

 

[Idahoan]

Might look for a Honda Element with the Ursa Minor top.

 

[LocalmotionSC]

I talked to someone who used the Maggiolina Air Top and the VW Golf TDI. He said he experienced around a 2mpg decrease in fuel economy with this combination. This is better news than I was expecting. 2mpg amounts to roughly a 5% decrease in fuel economy.

 

[Scoutn79]

The diesel may be less effected than a gas engine. I would have to see the 2mpg loss to believe it tho.

Darrell

 

[fike]

I can get 24 or 25 MPG on the highway with my 2010 2.5 liter manual trans Subaru Forester and a small Maggiolina on top. That is averaging about 70 MPH on relatively flat terrain. If there is a headwind or steep mountain roads, it can be much worse. In Nova Scotia last year, i got about 21MPG driving over the mountains in high winds and rain.

 

[Binksman]

If it's any help, I my cousin got a new TDI Jetta wagon this year. He's either got a roof box or mountain bikes loaded on the roof, and he gets lower 30s for mileage driving at NJ-PA highway speeds (70-75 mph). His roof box is one of the larger, boxier designs that is probably very similar to a RTT with a cover and deflector.

I'm looking at getting one of these to replace our rusting ZJ, so I grilled my cousin pretty thoroughly