Car-top cargo bags work on short roofs?

June 4, 2012 8:47 PM

Do car-top cargo bags really work on short roofs?

I have a BMW 3-series (3-box shape: short roof w/ trunk) with OEM load bars 28 1/2 inches apart o.c. and I'm going on a car camping trip this weekend with 2 kids and too much gear to fit in the trunk so I got a Thule Tahoe roof-top cargo bag.

It's 40 inches long and the instructions say 'It the distance between your crossbars is less than 40" drape the remaining length of the bag over rear crossbar'. I got the PDF of the instructions before I bought it but the picture is confusing and I really wasn't sure whether it would work without trying it. Now I've flopped it up there & it looks like it won't go flying off the roof, but it could very well shift around a lot while driving twisty mountain roads.

Food, stove, water jugs will go in the trunk. Only soft things on top: tents, sleeping bags, clothes.

It's 1/2 the price of a starter rigid cargo box and I'm not sure the mounting from one of those would work with my oversize crossbars anyway. At REI, I'd have to buy, then return if it doesn't fit. I've measured with dial calipers & looked at the boxes 'claws' & it's close, so close, but hard to tell for sure.

I know the bags aren't 100% waterproof and don't lock and that I'd have to find a place for a box when I'm not using it.

posted by morganw to travel & transportation (6 answers total)

Call Thule and ask. They're pretty helpful.
posted by fshgrl at 9:33 PM on June 4, 2012

Are you trying to place the bag on top of the bars or between the bars? Your bag looks like it has attachment points for the front and back, no side. Why not attach the front and then use other straps to keep it in place?

I have use a generic bag straight on the roof of my 2002 WRX from Utah>Oregon. Was not ideal, but we needed the room. If you tighten it, stuff will not shift. Especially since you have roof mounted rails already, it should keep it in a spot. Please limit the weight (It sounds like you know) since the sheet metal on the roof will dent VERY easily.

What about getting a basket like a Yakima Load Warrior? We picked one up used for $100 for our Outback and use it like crazy. I have a premium bag from REI that perfectly fits in it. Many attachment options, the bag is nestled, and I can fit 200+lbs (200 is max per Subaru, but I have done more) of gear up top.
posted by NotSoSimple at 9:40 PM on June 4, 2012

> Call Thule and ask.

Oh. Right. Of course. I'll try it.

> Are you trying to place the bag on top of the bars or between the bars?

Behind the front bar & on top of the rear bar. It "drapes" all the way to the end of the roof & an inch or so onto the rear window. I ought to take a picture....

> basket

I keep noticing those & thinking one could be more versatile & more secure. I'll check it out.
posted by morganw at 12:41 AM on June 5, 2012

Okay, so I had to drive halfway across the country (U.S.) in a little honda civic. All my stuff and me in just my little car. Tight fit, of course.

I thought to myself, "I should get a cargo bag for the top of my car! That will help!" So that is what I did, completely ignoring the fact that I don't even have bars on the roof. I thought to myself - "I will just strap it to the garment hooks! With four attachment points, there shouldn't be a need for the front and back attachments! I'll be fiiiiiine!"

....

Now I know you're expecting this to end in disaster, but! I also bought a box of $2 bungee cords. Stretched a couple from the back of the bag to the inside garment hooks, too. I was very nervous, and stopped every hour to make sure everything was okay. It was. Minor shifting, but barely noticeable. And that was going over 70 on I-80 for almost two days.

So, TL; DR

If you're really worried, get a couple sturdy bungee cords (or similar). Strap the going from the bottom of the back bar, under and over the bag, to the front bar. You could even criss-cross them for extra protection (strap one from the back right of the bag to the front left car bar, and strap the other from the back left of the bag to the front right car bar). Keep a couple exra in the trunk in case those two don't work out and you need to add more (but I bet they will work fine).
posted by Lt. Bunny Wigglesworth at 2:15 AM on June 5, 2012

Re Bunny's suggestion I've had poor result with bunge cords as they stretch under load. I'd use ratcheting cargo straps to double secure your bag to the bars. Two sets at the front and the same at the back. I do this with my surfboard and its good up to 70 mph
posted by dmt at 6:00 AM on June 5, 2012 [2 favorites]

Don't use bungee cords - use a couple of tie down straps for extra security and it will be fine.
posted by COD at 6:20 AM on June 5, 2012