Must have been having a senior moment, you're right of course, the wall thickness is half the difference between OD and ID. So English wall tickness is nominally 1.6mm while "Swiss" is 1.4 mm. That's a 12.5% reduction. Don't know if that's enough to create failure concerns, but 1.4mm in absolute terms doesn't intuitively strike one as very thick for an element like a steerer.
<email@example.com>; <FujiFish1@aol.com>; <firstname.lastname@example.org> Sent: Thursday, June 03, 2004 10:46 PM Subject: Re: [CR]Question about 1972 Motobecane Grand Record /Stronglightheadset
> The wall thickness is actually .1mm and .2mm less for French and Swiss
> respectively because the difference in diameters is twice the wall
> Also the real issue is the minor thread diameter and the root form. If the
> Metric threads have a shallow form that minimizes the stress riser the
> steerer may be just as resistant to fatigue or even better.
> I have ridden many miles on the Swiss 25.0 OD 22.2 ID and it seems okay (at
> least up to now!). I would speculate the biggest threat to the upper part of
> a steerer is overtightened stems.
> Joe Bender-Zanoni
> Great Notch, NJ----- Original Message -----
> From: "jerrymoos" <email@example.com>
> To: "Fred Rafael Rednor" <firstname.lastname@example.org>; <FujiFish1@aol.com>;
> Sent: Thursday, June 03, 2004 8:27 PM
> Subject: Re: [CR]Question about 1972 Motobecane Grand Record
> > The "opposite" arrangement, i.e. French threaded headset with 22.2 stem is
> > often seen on Swiss bikes, including my 1968 Allegro. This gives one a
> > little concern about the wall thickness of the steerer. French steerer
> > 25mm OD and 22mm ID are already (nominally) 0.2 mm thinner than English
> > steerers with 25.4mm OD and 22.2mm ID. The "Swiss" steerer with 25mm OD
> > 22.2mm ID is 0.4 mm thinner than English. The other problem is that with
> > some brands of headsets, it is difficult to insert a 22.2mm stem through a
> > French HS top nut.
> > Regards,
> > Jerry Moos
> > ----- Original Message -----
> > From: "Fred Rafael Rednor" <email@example.com>
> > To: <FujiFish1@aol.com>; <firstname.lastname@example.org>
> > Sent: Thursday, June 03, 2004 3:59 PM
> > Subject: Re: [CR]Question about 1972 Motobecane Grand Record /
> > Stronglightheadset
> > > Mark,
> > > If the steerer is built to French specifications, it's 25mm
> > > in diameter rather than 1 inch (i.e. 25.4mm), although people
> > > sometimes also refer to the French spec steerer as "1 inch".
> > > I would say that it's _nearly_ certain that the headset on
> > > this bicycle is French threaded. The reason I would not say
> > > it's 100% certain is because of an astounding experience I had
> > > this past weekend.
> > > I was working on a lightweight Peugeot from the same period
> > > as your Motobecane and found that the steerer tube was threaded
> > > for an English headset. Nevertheless, the inside diameter of
> > > the steerer was 22mm - i.e. the French standard. This was the
> > > opposite of my previous experience with "mixed-spec" steerers.
> > > That is, in the past I've worked on French bikes whose steerer
> > > tubes had French threading although the inside diameter would
> > > take a 22.2mm (i.e. "rest of the world") stem.
> > > I still have not fully recovered from this experience.
> > > Cheers,
> > > Fred Rednor - Arlington, Virginia
> > >
> > > --- FujiFish1@aol.com wrote:
> > > > Hey,
> > > > I currently have listed on Ebay a 1972 Motobecane Grand
> > > > Record frameset,
> > > > including a Stronglight Competition headset. Being a deeply
> > > > rooted
> > > > Italianophile, I cannot answer a couple of questions asked my
> > > > about the items, so I
> > > > humbly bring them to y'all ...
> > > >
> > > > 1) Is the headset definitely French threaded?
> > > > 2) Is the steerer 1" like English and Italian?
> > > >
> > > > View the Motobecane in question here, at Ebay #368115051,
> > > > or try this URL:
> > > >
> > >
> > RK
> > > > %3AMESE%3AIT&rd=1>
> > > >
> > > >
> > > > Thanks very much for the info kids!
> > > >
> > > > Ciao,
> > > > Mark Agree
> > > > Southfield MI