The only times I saw this effect of a derailleur clamp (dents)
were on bikes of standard tube size--one Japanese, a Sekai 5000,
and one British, a Bob Jackson made out of 531 light gauge tubing. It still
would have taken a real gorilla to do this, but I've seen many frames and
bikes with rust under and around a derailleur band. Also, two product
development rumors--that Columbus developed ribbed tubing to reinforce the
brazed area (can't quite believe this; a ft. derail bracket could be silver
brazed at very low temperature) and that Suntour developed the "endless
clamp" derailleur band to traumatize light tubes less (this seems more
likely.)
David Feldman
<chuckschmidt@earthlink.net> Cc: <classicrendezvous@bikelist.org> Sent: Sunday, March 25, 2001 11:04 PM Subject: [CR]re: Front Derailleur Clamp Problems
> Dear CRs:
>
> I have a "theory" regarding the disadvantages of clamp-on front
> derailleurs, as commented on by Chuck Schmidt (below):
>
> I have seen seat tubes with small dents caused by clamp-on front
> derailleurs and I have seen lots of seat tubes with rust underneath the
> clamp when it chips the paint.
>
> Chuck Schmidt
> South Pasadena, California
>
>
>
> I suspect that the cause of vintage front derailleur problems (scraped
> paint, dented or rusted seat tube) is actually caused by a minor misfit
> between the front derailleur (inner) clamp diameter and the seat tube's
> outer diameter .
>
> Consider that Campy made the NR seatpost in something like ten sizes,
> ranging from 25.0 mm up to 27.4mm. I recall that most Italian and French
> frames (in the early & mid-70s) used seatposts (seat tube inner diameters)
> of around 26.2 mm up to 26.8 mm, while British frames and the Schwinn
> Paramount used a 27.2 mm post (with a correspondingly larger outer ST
> diameter).
>
> Since most seat tube thicknesses were relatively constant (around 0.9 mm
> for Columbus SL.) the seat tube's outer diameter would then vary
> proportionally to the seat post size.
>
> So, if Campy made the front derailleur clamp to "best fit" Italian frames,
> then the FD clamp would be a bit undersized for British and American
frames
> which used 531 tubes, with a 27.2 mm ST inner diameter (seatpost size).
> With the "undersized" front derailleur, it would then be easier to scrape
> off the seat tube paint or dent the seat tube.
>
> After I dented the seat tube on my first (British) racing bike, I started
> filing down the NR front derailleur's inside clamp surface, where the
> fixing bolt passed thru. I filed it down enough to remove the semi-sharp
> edge on the far side and also remove some inside clamp metal to get a
> smoother fit.
>
> In later years, the seat post diameters seemed to stabilize around 27.2
mm.
> All of the newer front derailleurs are more carefully made and seem to fit
> better as well.
>
> I do not like a braze on front derailleur at all. The derailleur cuts into
> the brazeon's paint very easily which causes it to peel off or flake off
if
> the derailleur is adjusted or changed. Retrofitting a newer derailleur
into
> an older brazed on casting has given me grief more than once.
>
> regards,
>
> Andrew Gillis (overcast but good riding in Long Beach, CA)