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Old July 3rd 07, 03:32 PM posted to rec.bicycles.misc
David L. Johnson
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Posts: 1,048
Default Roof-mounted bike rack: fork mount or whole bike?

SMS wrote:
Bob Weissman wrote:
I've been using a trunk-mounted strap-on bike rack on my car, but
it doesn't exactly inspire confidence that my beloved bike won't
fall off at freeway speeds.


I managed to damage an aluminum frame on a trunk mount, because of how
the hooks grabbed the frame. I would think a carbon bike would be even
more subject to such damage.

I'm starting to look at roof-mounted racks and see there are basically
two kinds: the kind that hold onto the fork and require you to
remove the front wheel, and the kind that allow you to leave the
front wheel on.

Which is better? Obviously the fork mounts require more work, so
they must have some other advantage? Is there a problem with the
whole-bike mount which would cause me to regret choosing it?

(The bike is a 2007 Trek Pilot 5.0 and the car is a 2000 BMW 528i
sedan, if that makes any difference.)


The newer mounts that let you leave the wheel on will work with that
bicycle, i.e.
"http://www.thuleracks.com/thule/product.asp?dept_id=8&sku=594". I have
upright mounts that cannot be used with a carbon frame as they grip the
down tube, and would deform it.


I would distrust the mounts that clamp the middle of the downtube. But
the one you point out would place just as much force on the fork and
headset as a fork mount.

The advantage of the fork mounts is that they are cheaper to manufacture
and cheaper to purchase.


I think you are understating the advantages of a fork mount. The fork
ends are _designed_ to be clamped. Any fork strong enough to safely
support you while riding over a rough road are certainly strong enough
to hold just the bike on top of the car.

There are four main advantages to the "leave the wheel on" mounts:

First and foremost, it holds the bicycle in place by he strongest part,
the frame,


You seem now to be talking about a mount that grabs the downtube. The
center section of the downtube is by far not the strongest part,
especially under clamping force. But the link you provide is to a clamp
that grabs the top of the fork, and the front wheel, not the frame.

while all of the weight of the bike is on the wheels (just
like when you are riding).


The "weight of the bike" is 20 pounds. That is all that is being
supported on the rack. While riding, some of us provide considerably
more weight.

Second, it prevents the problem of bearing
wear (fretting) in the headset, which is a potential problem with fork
mounts.


Nonsense. The fork is still up there with either rack, and the steerer
is, yes, slightly moving as you go along. This also happens while
riding, and then there is considerably more force. Bearing fretting is
much less of a problem now than it was with older headset designs, and
you really can't blame roof racks for that.

Third, in gusty winds the whole bike sways, rather than the
frame exerting forces on the headset and dropouts as occurs with a fork
mount.


The bike then exerts pressure on that downtube clamp.

Fourth, you don't have to remove the front wheel and store it
somewhere


Don't most cars have a trunk?

There are two disadvantages of the upright mount. First, it costs more
than the fork mount. Second, it is harder to place the bicycle in the
rack if you are short, or if you have a tall vehicle.

With a bicycle that expensive, don't skimp on the fork mount, especially
with a carbon fork.


These rooftop racks that do not require all the "work" of removing the
front wheel have gone through quite a bit of re-design in recent years.
Those re-designs are probably a result of damage claims. I would not
use any rack that grabbed the downtube. Even steel bikes these days
have such thin tubing, especially in that area, that clamp damage will
be likely. For a while they heavily marketed racks that grabbed the
crank arm. While that would seem to be a strong point, these racks have
fallen out of favor, maybe with reason. I like the idea of securing the
bike where it is designed to be supported. Your fork supports you and
the bike just fine while riding. If it didn't, then the roof rack would
be the least of your worries.

Better yet, ride to the ride. Oh, and if you do use a roof rack, hide
the garage door opener.

--

David L. Johnson

When you are up to your ass in alligators, it's hard to remember that
your initial objective was to drain the swamp.
-- LBJ
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