Originally Posted by supcom
What's the issue? Do you think that you will overstress the bolt and have it break apart? Unless the bolt is defective, any force large enough to break it will have torn you bike up first.
Wrong. The fork is very well secured to the Thule bar, thanks in large part to the lawyer-lips on the dropouts. There is no way in hell the fork will part with the Thule head as long as it's closed, and the bike's fork, headset and frame are obviously a lot stronger than the Thule bar.
When the bike rocks sideways, it acts as a lever creating torque at the Thule head. How much torque? well, I saw the bike rocking on the car as I was driving and testing it on a bad road, and it was an alarming amount of rocking. I tried to reproduce the amount of rocking with the car stopped, by pulling on the side of the bike, to get an idea of the forces involved: I probably pulled a good 15Kg on the seat to get it inclined as much as I saw it "live" while I was driving. That means a torque of 150Nm. Given that the Thule head is about 15cm wide, with the retaining bolt at the center, that means the 150Nm torque is exerted on a 7.5cm lever, meaning the measly 5mm bolt, as well as the 3mm-thick aluminium lip of the load bar's railing are being pulled up with a force of 200Kg each time the bike rocks to a side, dozens of times per minute. I do NOT call this safe. And let's just suppose Thule didn't cut corners (which is what I think, but let's assume), the Ford aluminium load bar I have won't like this sort of treatment for very long.
Looks pretty secure to me.
A little math and common sense tells me it's pretty shoddily designed to me. I had expected the Thule head to be at least twice as wide, with a U-bolt on each side, to spread the load and stiffen the whole assembly to prevent rocking in the first place. But the way it's designed, it's really quite appalling. It might be reasonably safe with an ultra-light carbon bike, but not with a big steel tourer, that's for sure.
Anyway, I think the key to using this bar despite its shortcomings is to prevent the bike from rocking sideways, by tightening it down to the side of the car with with nylon straps. I have self-tightening straps, and I'll make a clever mount for the bars to use them, but I don't like having to come up with solutions to the problems of a product I purchased over 100 euros.