In article ,
Michael Daly wrote:
If the car makers provide four fixed points, as per BMW and the CRV, there's no
reason you can't bolt on a couple of rails like this and have full
adjustability.

The most generic mounting system is raingutters. These have gone out of
style on cars, but still remain on full size vans, where they are often
used for mounting racks used by construction workers and the like.

Second place would be tracks or rails like those sometimes found on wagons,
vans, and SUVs.

Note that raingutters, tracks, and rails allow positioning the racks at
varying positions (which may be helpful for those with longer boats),
while fixed mounting points limit the options one has for crossbar spacing.
Old wagons with raingutters typically have the largest possible crossbar
spacing.

As far as bolting on rails to fixed points, you'd have to either DIY some
rails, or get some rack company to offer the rails. Also, if different
car companies have fixed mounting points different distances apart, of
the rooflines of vehicles were different shapes, then the bolt on rails
would need to be specific to different vehicles. Plus, bolt on rails that
extend much beyond the mounting points may not be as stable compared to
built in rails anchored at the ends of the rails.

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Timothy J. Lee
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On 4-Apr-2006, (Timothy J. Lee) wrote:

These have gone out of style on cars,

It wasn't style that made them go away, it was poor performance in wind.
They increase drag and noise.

As far as bolting on rails to fixed points,[...] or get some rack company to
offer the rails.

And that's a problem? They offer a gazzillion versions of roof racks now.

Also, if different
car companies have fixed mounting points different distances apart, of
the rooflines of vehicles were different shapes, then the bolt on rails
would need to be specific to different vehicles.

Nonsense. You just lack imagination. If the rail mounts on a standard foot,
then only the foot needs to match the roof profile. The rail can be attached
at any point with the appropriate track underneath. I have a ski box that
goes on a Thule rack without forcing the rack to be located at a specific
point.

Plus, bolt on rails that
extend much beyond the mounting points may not be as stable compared to
built in rails anchored at the ends of the rails.

Some built-in roof rails on station wagons and trucks are flimsy and others
are not. It all depends on the designer. And an overhang need not be any
more or less stable than the part between the anchor points. In fact, anchoring
at the ends is not the most weight-efficient means of providing a stiff, stable
support.

Mike