Side Rack Instead of Yakima Rack

Jack

Senior Member
Joined
Nov 18, 2007
Messages
416
Location
Portland OR
When I removed the factory rack from our Fleet to lay down flexible solar panels, I had intended to install Yakima tracks so I could carry the chairs and a few other items that I had been carrying on top.

We meander, so we generally change location most days. The problem with gear on top is that if we decide we want to setup the chairs after popping the top and setting up, we have to drop the top, get the gear and then pop-up again. It’s a minor hassle, but more often than I care to admit, we just don’t do it.

Well, the first thing I noticed after taking off the rack, the gear on it, and the Zamp panel was about a 1 mpg improvement in gas mileage. I really liked that and began to think about alternatives to a rack on top.

The solution was a side rack, inspired by FWC’s surfboard rack. It holds our two chairs, which are now easy to get at, even for lunch on the road. It can also carry our folding crab pot and clam gun. I think a kayak or canoe would be too wide, so a side rack isn’t for everybody.

The other thing I really like about the side rack? $40 instead of $400+ for Yakima.

Materials: 4’ 2x2” x 1/8” Al angle, 6’ x 8’ poplar cut down the middle to make a right-angle. I should probably have gotten 6’ of Al angle so I could run a second bar across the bottom to carry more odd stuff.

side rack 0.jpg
Side rack.jpg
 
Excellent idea to use the jack brackets....and you seem not to overdo it with too much weight.

You camper fits really low on the truck sidewalls.

We have about 5-6 inches height which gives more storage space.

David Graves
 
Vic Harder said:
are you worried about the paint scuffing on the truck's bed? Rough roads & dust = sandpaper?
I got some paint protection film that I plan to put on when the weather warms up.
 
Mighty Dodge Ram said:
Interested in hearing about new mpg numbers.
We've made two short trips (mostly main roads) and gone from about 15.5 to about 16.5 mph according to the Ranger's mpg reading. We will complete our vaccinations in two weeks and plan on a 4 week trip on varied road types. This should give us a much better picture of mpg. The directors chairs on top I'm sure created a lot of turbulence. I'll post an update.

As an aside, while vaccination will protect us from serous Covid19 consequences, we will continue to wear masks and distance to protect others in case we get contagious.
 
Hi Jack

I am interested in your notion of trying to improve fuel mileage.

For the hundreds of Freeway miles we put on getting to somewhere interesting , so am I.

Do you know what the little stick on fins are called that a lot of the young folks add to their street racers ?

They are supposed to break friction on a trailing edge....I think :) ?

I have seen them on commercial trucks lately so they must have some effect.

I have toyed with attaching some to the rear top and maybe sides of the Hawk.

Like you I try not to carry anything up top unless and until we reach the dirt.

David Graves

PS Our 2016 Tacoma has essentially the same thing on much of the body side trim.
 
I'm not a mechanical engineer, but I do know that it's turbulence that creates the drag that's the main drag on your mpg. And it's usually tricky to find and to identify what you need to do to reduce turbulence. It's worth noting that today's cars pay as much attention to the aerodynamic shape of the back (probably more) than the front. In my case, the chairs and rack were obvious.

The spoilers on race cars serve two purposes - reduce turbulence but making the airflow more laminar, and often to increase the downward weight on the rear wheels as the car goes faster. The fins are there to make the airflow more laminar.

Without the benefit of a wind tunnel or a test road, it's hard to know if an investment in fins, fairings and such is worth it.

The test road is an interesting technique: You need a seldom traveled road with a nice hill that, coasting, will get you up to 60 or so mph and that drops down to a relatively flat or slightly uphill stretch. From the top of the hill, only coasting, you see how far your vehicle will coast, first without changes, and then with changes. Just make sure any head or tail winds are the same for each run. The greater the coasting distance, the less drag.
 
The drag UNDER the vehicle is really important too. Those lower lips you see under the bumper on trucks make a significant difference. They also interfere with approach angles, and can get ripped off.
 
The other obvious MPG mod I daydream about is to make some sort of fairing for the front corners of the camper main box.

On my Chevy these are perhaps a foot wider than the truck cabin and cry out for some sort of slipstreaming.

But then , I do a lot of day dreaming. : )

DG
 
Very cool! Im a mechanical engineer but by no means an expert on the subject of fluid mechanics. A couple things stick with me though- you guys probs already know this. Amount of the drag force is related to velocity squared. So as you go quicker it really works against you. The other thing is that frontal area is multiplied by the coefficient of drag. I would guess that your roof top rack probably increased your frontal area more than your side rack- but you know this. I would also guess that the rack up top compared to the rack on the side didn't really change your overall vehicle coefficient of drag much. Both additions are going to be draggy.

So, you are thinking that your gas mileage will improve and I agree with you. This would be based on your frontal area being less. I also like your idea to measure drag with the repeatable hill. Neat idea to give you a quick look.

--------
I just went through a design/build on a rack to carry my ski's. If I had seen your post I probably would have done as you suggested vs what I built. Im happy with my thing but it grew beyond just carrying my skis and now needs a place in my garage for storage and it is not small. In my case the frontal area of my truck did not grow but the coefficient of drag may have changed. Good or bad I dont know. https://www.wanderthewest.com/forum/topic/21386-hitch-mounted-ski-rack/


Steve
 
Consider the shape that a falling water drop is always drawn as, or even pictured with high speed photography. The bottom or front is hemispherical because that shape offers the greatest volume for the least frontal area or the least drag. Look at the tail, water wouldn't form that way by itself, something else is doing that. Drag, air drag in this case. The surface tension of water is high so the air drag from the laminar boundary layer stretches out the tail in an effort to stay attached to the surface.

Those little fins are properly called "Vortex Generators". https://en.wikipedia.org/wiki/Vortex_generator Aircraft pioneered their use. Then they showed up on rally cars at the top of the rear window and on the underside of F1 rear wings. Shortly thereafter they showed up on the rear of under-belly trays, and the street scene glomed onto them.

If you can see the chair bags ruffling in the wind while going down the highway it would probably benefit from having a smooth outer surface. A 'door' or fairing of some sort. Could be as simple as a piece of plastic sheet covering the whole that is attached with high strength velcro.
 
So my Chevy 3/4 ton with camper would have to reach at least 45 MPH for the little fins to impart any effect on fuel consumption ?

Dang, the kid down the street with the 335 HP Subaru said they were all the rage.....

What is a chair bag ?

David Graves
 
Tell me more about the box on the front of the camper between it and the truck back window!
I too think that could be valuable space!
 
DavidGraves said:
So my Chevy 3/4 ton with camper would have to reach at least 45 MPH for the little fins to impart any effect on fuel consumption ?

Dang, the kid down the street with the 335 HP Subaru said they were all the rage.....

What is a chair bag ?

David Graves
The bag that most camping chairs come with to store them in.
 
Oh sure, bags with folding chairs inside them.

Our chairs stow inside.

Is there anything simple that can be done to improve airflow and mileage for highway speeds with our campers ?

David Graves
 
DavidGraves said:
Is there anything simple that can be done to improve airflow and mileage for highway speeds with our campers ?

David Graves
If you dig WAY back through either the Truck Campers or Four Wheel Camper Discussion sections, there was fairly lengthy discussion on, and examples of adding a fairing in front of the cabover. From what I remember, those who had added one were getting a mile or two a gallon increase. It may have been part of the discussion on what to do with the space under the cabover with examples instead. The discussions happened around the same time.

Good Luck....
 
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