Roof Rack Design Considerations

[s.e.charles]

search started to swirl so i bailed. plenty of fabrication stories but we're not there yet.

anyone have any design criteria NOT to do when designing a roof racking system. NOT a roof rack specifically.

but an appurtenance installed at the highest point of the vehicle. NOT which screws to use, or what material, but the considerations which would go toward a system allowing SOME carrying capacity, draining of water accumulation, and MINIMALIZING road noise.

theory is what's required now; details can be worked out as we go along.

thanks

 

[4000lbsOfGoat]

Keep it as tight to the roof line as possible (i.e. as low as possible) and put a solid air dam across the front to minimize noise.

 

[ExpoMike]

I agree, keep it as low on the roof as you can. Here is the Baja Rack I put on my Cherokee, which is about as low as I can get. I did have to make a front air dam (no pics) as it would make "hum" above 40mph. Air dam solved the problem.

 

[billiebob]

use tubing, not pipe, keep it light and simple
a bit of triangulation or gusseting helps add rigidity
think tie downs. a hole in the center of triangular corner gussets lightens the rig and add tie offs.

do you need point loading like will you be standing up there and dancing or will the loads be evenly distributed dead cargo only
you don't mention if this is a base for an RTT

 

[billiebob]

I agree, keep it as low on the roof as you can.

View attachment 677155

cannot mount a dish like that in snow country....
very nice rack

 

[Metcalf]

Don't mount stuff on the roof.
If you need to carry stuff on the roof, or even in excess on the rear bumper, you have the wrong size vehicle.

 

[NatersXJ6]

I don’t know about “not dos”, but a few wish list things and positives I’ve come up with after 7-8 years hauling stuff on my Jeep:

1) Keep it smooth from front to back to allow long items to hang over each end without issues.

2) make it say to install skid-resistant protection, rubber pads, sliders, tube covers, something. A canoe or lumber or steel tube can strip coating fast.

3) Consider wiring paths, you almost always add lights if they weren’t already included in the first build.

4) Put a lot of thought into your preferred tie down methods, I like the expanded metal surface of mine because I can use bungees or ratchet straps nearly anywhere on it, but some areas/configurations are still difficult. I’m glad I don’t have the aluminum slat style, as needing t-nuts and extra tools would really cut into spontaneous use.

5) Any sort of aerodynamic modeling, mock up, etc… will be helpful.

6) Exocage styles look cool but whistle and make it hard to wash your windshield effectively.

7) Easily removable means easy to repaint.

8) lightweight tube can be very strong

9)building a roof rack is an excellent reason to buy a tube bender

others I’m sure when I think of them!

 

[ChasingOurTrunks]

I've built a few, and there's good advice here in this thread so far, but a few things to add:

1) Strength should come from the design, not the material. The roof rack should be as light as possible to maximize actual carrying capacity and, more importantly, to minimize weight up high when not in use. Gussets and braces are the name of the game here.

2) Edges - make sure there are no sharp edges or ridges or places to get caught up on the rack. Even a well fabricated 90 degree corner can be like a scalpel if it catches you the wrong way when getting down off a rack. A slightly raised bit of metal might seem like no problem, till it catches your partner's ring and degloves their finger. The nature of roof racks is that we are almost always interacting with them at some kind of height off the ground, and its often getting down from that height that makes otherwise harmless bits and pieces or design elements much more hazardous.

3) If possible, look for ways to take advantage of professional produced accessories when designing how you attach stuff to the rack (like using T-slot compatible cross bars). That way if you ever want to mount up a specialized Thule carrier (say, for a bike or a kayak or something specialized), you can do so easily.

4) Consider the actual specs of the rig, and know that they are very likely to be "On Road" specs. 300 lbs weight limit on the roof is likely an on-road figure; off road it can be reduced dramatically as the forces are usually a lot more sudden and extreme. So, even if my car can handle a 300 lbs roof load, there may be no sense in designing a rack that can take 300 lbs if my intention is to take my car off road, because the rack mountings are likely only good for 100 lbs in an off road situation, and I can design my rack accordingly. Similarly, often DIY fabricators look to commercial options for inspiration. If one were to look at, say, Rhino Rack and decide that since they use rivets through the roof shell therefore that will be a good enough attachment method for a DIY option, they may be in for a bad time. (Youtube link to Ronny Dahl's vid on his experience with on vs off-road ratings for his Rhino Rack).

 

[4000lbsOfGoat]

Similarly, often DIY fabricators look to commercial options for inspiration.

OP didn't mention what type of vehicle we're talking about here but take a look at Prinsu racks. They are about as well-designed as a roof rack can be.

 

[s.e.charles]

thanks for the input and thought fodder guys. more than this for now will only lead to specific decisions which i'm not prepared to make yet.

 

[NatersXJ6]

thanks for the input and thought fodder guys. more than this for now will only lead to specific decisions which i'm not prepared to make yet.

maybe also consider whether or not you will need or want solar panels. I surface mounted my solar panels on the rack and now almost anything I carry runs the risk of bouncing on/scratching/breaking the panels. If I build custom, the panels will likely go in some sort of slide-out racks below the carrying surface or with a removable carrying surface if needed.

 

[thebmrust]

Don't mount stuff on the roof.
If you need to carry stuff on the roof, or even in excess on the rear bumper, you have the wrong size vehicle.

Then why are vehicles designed with roof racks?
I have a suburban. We travel with 2 adults and 3 large dogs. That’s 2/3rds of the cargo space inside. We don’t have a trailer. How do you suggest we carry items if we don’t use the OEM roof rack? And no, towing anything is not an option.

 

[s.e.charles]

... How do you suggest we carry items ....

it's an internet forum; some things are inevitable.

 

[1000arms]

Don't mount stuff on the roof.
If you need to carry stuff on the roof, or even in excess on the rear bumper, you have the wrong size vehicle.

... Hmm, just what size vehicle do I need to carry a 105 pound 20' Old Town Canoe XL Tripper? ...

...

I'll agree that avoiding carrying things on the roof is a good practice, but sometimes the roof is useful for other than keeping the rain/snow/sun/... out of a vehicle.

My "roof rack" on my 98 Jeep Wrangler TJ ran front brush guard to rear bumper. 1" tubing (.120 wall) and 3/4 #9 flat expanded metal mesh combined with a welding gun be quite useful.

I could carry 24' lengths of steel, canoes, lumber, and/or 4'x8' sheets of plywood. Yes, I was careful about how much weight I carried and how I drove, but that Jeep carried things in to places that large vehicles couldn't.

The rack sat high enough to be able to remove/install my hardtop and remove/install/use my softtop.

I also had a small tent I could set up on the expanded metal mesh. Camp in 6" of standing water? Sure, why not?

The hood could be lifted and supported the usual way.

The rack was removable without the need for a metal saw.

... Hmm, I even managed to include a few design thoughts. ...

 

[Metcalf]

Then why are vehicles designed with roof racks?
I have a suburban. We travel with 2 adults and 3 large dogs. That’s 2/3rds of the cargo space inside. We don’t have a trailer. How do you suggest we carry items if we don’t use the OEM roof rack? And no, towing anything is not an option.

Do whacha want, but nothing ruins vehicle dynamics quicker than weight up high ( or behind the rear axle ). A roof rack is a double hit because you typically have to add weight ( the rack itself ) to carry any decent amount of weight.

Towing something is always an option, put people rule it out because they think it will be 'worse' than having stuff on the roof. The majority of times it is likely the better answer if you are pushing the vehicle size and/or GVW. Especially if you are doing any off-highway activities.

Back to my original statement.....if you are having to carry stuff on the roof ( or lots on the rear bumper) the size of the vehicle is wrong for the task. ?‍♂️