roofbag & mileage?

http://roofbag.com/

I don't know about mileage hit (I assume 5 to 10 mpg), but someone else posted this warning on another site about using the Roofbag without a rack:

"Customer Reviews

Rated on 2008-10-22 I have a 2008 Prius without any sort of roof rack. I purchased the 15 cu. ft. Roof Bag and installed it with no real issues. Then it started to rain--the straps soak up the water and transport it to the interior of the car, where it drips all over the seats. This is completely unacceptable! To add insult to injury, I can't get in touch with their customer service department. The recording either states their business hours (which I called well within) or that all their representatives are busy, then asks you to leave a message, and that's it."

Makes sense. I don't know what you'd do to stop this.

 

Mileage hit would be noticeable. Drastic is a relative term. I would guess 5 to 10 on the highway, also, but less impact around town.

 

The Prius MPG Simulator predicts fuel economy for a variety of conditions, including the adding of certain external cargo.

The following driving conditions put it in the neighborhood of your 47 MPG without any external accessories:

• 71 MPH, steady speed
• Level terrain
• Smooth dry pavement
• No winds
• Outside air temp 70F
• All windows up
• 300# load, driver and cargo
• Goodyear Integrity tires inflated to 44 front, 42 rear
• E10 fuel

Here are the choices for roof-mounted cargo and the resulting adjusted fuel economy from the simulator:

• Small enclosed aero carrier: 39 MPG
• Medium enclosed aero carrier: 33 MPG
• Large enclosed aero carrier: 29 MPG
• 2 medium coolers front to back: 39 MPG
• 2 medium coolers side by side: 32 MPG
• 2 large coolers front to back: 36 MPG
• 2 large coolers side by side: 27 MPG
• Small heap of "stuff" on roof: 26 MPG
• Medium heap of "stuff" on roof: 23 MPG
• Large heap of "stuff" on roof: 21 MPG

I don't know which of these most closely matches the soft pack. (The simulator provides no further definition for any of them.) Even so, you can get a pretty good sense of how much anything on the roof impacts fuel economy negatively.

The simulator also predicts fuel economy with a rear luggage hitch filled to the following heights:

• Empty: 45 MPG
• 12" high: 40 MPG
• 24" high: 38 MPG
• 36" high: 37 MPG
• 42" high: 36 MPG

From a fuel economy perspective, you're likely better off with a hitch device.

 

docarya, I know your concerns. I had them as well two years ago and looked at all the options I could find. Bottom line is that I created a system similar to the roof bag giving these results-- 7500 mile trip, two adults, two teens, and all the camping gear, some of it on the roof. My goal was 50 mpg, didn't make it, but close, 49.74. I was still very pleased. In addition to the favorable aero design on the roof, the other key was that we only drove 60 mph. That was our choice, other's choose differently. If you are interested in more details you can read my journal of that trip at--
http://www.priusownersgroup.com/?page_id=2840

PA P

 

Yes, I regret I didn't take detailed pics of that set-up. The picture in the journal may be a bit clearer to you after this explanation.

1. I mounted our Saris roofrack (eBay deal) with front air deflector, then added the two bike trays, each a few inches in from the outer edges of the roof.

2. I placed a rubberized non-slip pad (like what is placed under throw rugs on hardwood floors) over the whole roof area in order to protect it.

3. I got a tarp that was about the same width as between the bike rails and a bit more than twice as long as the roof area. I placed this tarp on the roof-- between the bike rails and one end of the tarp at the back edge of the roof and the other end layed up over the front rack and down over the windshield.

4. I packed the things we wanted on the roof-- tents, sleeping bags, and hiking boots-- into dry bags. In case you don't know, these are the bags used for to carry gear for watersports such as canoeing. They are waterproof. This is where we got ours-- http://www.sierratradingpost.com/p/4690,68407_Seattle-Sports-All-Purpose-Dry-Bag-Large.html We used four bags-- three length-wise up front with the front of these bags tucked a bit under the front rack and air deflector. The fourth bag was in the back, crossways, between the back rack and the other three bags. If you are still following-- the bags are laying on the back half of the tarp which is on the non-slip pad.

5. I then threw the front half of the tarp up over the bags. So the tarp is now forming a large "C" with the bags in between. I added a number of extra grommets to the tarp, so I could cinch the sides together and the back together.

6. This may be hard to follow, but it is only a detail, so not so critical--- I cut piece of hardwood, about 1/2" by 1" and long enough to reach between the two bike rails. I drilled a hole in each end so I could use the sliding fasteners that came with the bike rack to attach this piece of hardwood between the back ends of each of the bike rails. Before attaching it I stuck it through the back of the tarp where I had laced the tarp together. The tarp was long enough that it stuck back past the rear rack cross bar about a foot. The bike rails were a bit longer than that yet. With this in place I could then slide the hardwood piece toward the back of the bike rails until the tarp became taunt. This also formed a type of "boattail" (if you are into areodynamics) for the rack.

7. Finally, I made a bungee cord that was long enough to criss cross back and forth over the tarp just to keep the wind from getting in any where and to keep it all on the roof.

As I said earlier, we were very satisfied with this set-up. Packing and unpacking took more time than if we would have used our Thule rooftop box (now collecting dust after one use and taking a 10 mpg hit). But for our trip we usually stayed at one place for 2-5 nights, so that wasn't so bad. I also need to add that our camping equipment is more along the line of backpacking equipment than RV equipment.

I hope this was all somewhat understandable!

PA P

 

The above sounds ... complicated. Here is a much simpler approach.

There is a guy who recently used an AeroPACK on a 3000 mile trip.

It worked well to carry soft camping gear, and mounts behind the Prius. No racks, no aero drag, no MPG hit and much less than roof systems.

http://priuschat.com/forums/gen-ii-prius-modifications/60696-soft-pack-mounts-hatch-glass-3.html