Submitted: 08-16-2012 by neilsprice
Thule "J" bar style racks clamp on to factory rack (on factory cross bars)
My vehicles: Jeep Grand Cherokee and GMC Acadia
I've had the J racks since getting our two Old Town Dirigo's a few years ago. They have performed perfectly. Just completed 4200 mile trip with them with no problems, but you should be aware of a few things and use common sense. I had concerns about stability and wind resistance for the long trip. The Dirigos are beamy and not super light (45# +). The Js held up to the task just fine and at hwy speeds.
Two areas of caution: These boats on their sides create a high profile and resistance. If your speed is 70 and you have a head wind of 20-30 (as we did) that's the same as 90-100...a bit much; I'd keep air resistance to 75 or so combined maximum. If the wind is to the side you'll feel strong buffeting at times, slow it down. Without wind we felt comfortable at 70. Kayaks were strapped according to instructions around J and under factory cross bars. Also had bow and stern tie downs to prevent sliding forward or aft.
Secondly air pressure will try to push the boats apart from the bow. The Js are attached to the crossbar in a clamp fashion tightened with two thumb bolts. These can slide on the crossbar. The edge of your factory rail will stop them in the front, but then the rear racks will tend to slide together (toward the center of the car), making a bigger air dam. I cut and taped a strip of wood to the crossbar between the opposing rear Js so they could not slide. (I saw another car with Js and the rear racks had come together making huge air resistance and although not separated one of the kayaks had lifted from being seated in the cradle....yikes I would not want to be behind that guy!) Check all tie downs every time you stop or if you here or feel anything unusual.
Caveat: I was thinking of replacing the Js with a rail rider or something that I could put an extended crossbar on in order to lay the boats flat. Figured less wind resistance would equal better gas mileage. I was surprised to find on this trip my mileage was better than expected (19+ with a big hemi V8, not great but hey, it goes!)I attribute this to mainly reduced speeds on many of the non interstate highways where we were running 60-65.