Dear Tom,
Not to worry. Nothing in an on-topic steel frame made of any of the standard tube sets will be at risk, as far as I know. (Oversized steel and aluminum tubes are another story.)
We have been using Yakima GT bike carriers for about 20 years that are quite similar to your Mont Blanc Barracuda. We have mounted bikes with steel frames (Peugeot 1020, Reynolds 531, and other DB chromoly down tubes), as well as (WARNING!) bikes with off-topic oversized TI, and carbon fiber down tubes with no problems.
The general wisdom from Yakima (I worked for roof rack dealers) was that these down tube clamps were fine--as long as they were not over- tightened--on any old-style (531, Columbus SL, etc.) steel down tubes. One must take more care with one-of-a-kind and Olympic-caliber special-ultra-light steel frames. carbon fiber tubes, aluminum, modern oversized steels, and titanium tubes, especially the oversized and very thin-walled varieties of aluminum.
Leaving the jaws a bit looser, even on more "delicate" tubes (i.e., that are thinner-walled and more prone to crushing) should take care of your problem, even then. Just lay off the brute force when tightening the clamp(s).
Make sure that:
1) the clamp is just snug enough that it will not slip down the DT and cause instability, and 2) the wheel straps are absolutely secure if the jaw on the DT will be a bit looser.
Using a cable lock long enough to go through both wheels, around the frame, and through/around the arm may help stabilize it. Securing the arm to the DT with a toe strap or similar non-scratching strap might also help.
Regards,
Jon Spangler Alameda, CA USA
>
> Message: 2
> Date: Tue, 17 Mar 2009 13:04:43 -0800
> From: "Hansen, Thomas" <TH@HJTH.COM>
> Subject: [CR] Bike Carriers
> To: "CR List (E-mail)" <classicrendezvous@bikelist.org>
> Message-ID: <79311A41F6FA734EB6DBBD6E7C88ED0D06B4E32426@osu.HJTH.COM>
> Content-Type: text/plain; charset="us-ascii"
>
> Hey List, In my advanced age, I have become somewhat enamored of
> upright ha
> ndlebars and fenders. Unfortunately, the type of car top carrier I
> have al
> ways used, where one removes the front wheel and then clamps the
> front fork
> into the carrier, doesn't work because of the clearance. I also
> have a Mo
> nt Blanc Barracuda car top carrier, on which one leaves both wheels
> on and
> attaches the bike to the carrier with a foam padded claw on the
> down tube.
> It's very nicely made and has adequate padding, but I wonder if it
> can dam
> age our old 531 or Columbus tube frames. Anyone have any
> experience here?
> Thanks, Tom Hansen Los Angeles, California, USA,