From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Possibly dumb question......but,
Date: 13 May 2001 02:21:45 GMT

John Laird writes:

>>> ...what is the reason for the trend toward sloping top tubes on
>>> high end road bikes?  I've noticed a lot of those around the roads
>>> and in the magazines.

>> Many frame builders cannot achieve a horizontal top tube so they
>> purposely slope them, both up and down, enough so that you won't
>> think it is an accident. None of the excuses you hear hold water.

> Since most of the builders currently producing 'compact' frames have
> also been producing 'conventional' frames for years, your
> explanation doesn't hold water either.

"for years" ain't very long.  I know few frame builders who built in
the days of conventional steel frames in competition to Italian and
French steel frames.  The ones I know still build horizontal top
tubes.

>> With all the heavy money spent on bicycles, fashion has taken over.

> Fashion has always been with us, from the days of curly lugs and
> 'vibrant' stays to the present trends.

Filigree lugs had their validity in that they feathered out stress
without having to go paper thin at the edge of the lug.  Some
builders took this farther to make these lugs have elegant shapes.
Just because builders like Hetchins took it to the extreme doesn't
disqualify the use of filigree lugs.

> Aesthetics aside (de gustibus non est disputandum), is there any
> compelling reason NOT to slope the top tube now that few bikes are
> built with lugs whose angles are predetermined?

Yes.  You can see at a glance whether the frame is bent or not.  The
same goes for forks with a curl at the bottom instead of straight
blades and an angled crown.  Least important is aesthetics of a top
tube in-line with forward motion rather than one that is almost so.
The idea that slope gives a lighter frame is bogus because frame
tubing is thinner and lighter than seat post material and bar stems.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Possibly dumb question......but,
Date: 14 May 2001 16:16:49 GMT

John Laird writes:

>>>>> ...what is the reason for the trend toward sloping top tubes on
>>>>> high end road bikes?  I've noticed a lot of those around the
>>>>> roads and in the magazines.

>>>> Many frame builders cannot achieve a horizontal top tube so they
>>>> purposely slope them, both up and down, enough so that you won't
>>>> think it is an accident. None of the excuses you hear hold water.

>>> Since most of the builders currently producing 'compact' frames
>>> have also been producing 'conventional' frames for years, your
>>> explanation doesn't hold water either.

>> "for years" ain't very long.  I know few frame builders who built
>> in the days of conventional steel frames in competition to Italian
>> and French steel frames.  The ones I know still build horizontal
>> top tubes.

> I can think of Condor of London (established shortly after WW2) and
> Chas Roberts among other British manufacturers who offer both
> horizontal and sloping top tubes in their ranges.

So the up or down sloping top tube has become fashion but at the
outset it was a cover for unachieved horizontal top tubes.  I recall
when a lot of almost level top tube bicycles appeared as the cottage
industry first blossomed in the USA.  As I said, the high performance
multi speed bicycle was formerly exclusive to professional and
pre-professional amateur racing.

When the derailleur racing bicycle became common among affluent
society as a fitness symbol, bare functionality gave way to gimmicks
and fashion.  Professional racing has become a vehicle for advertising
for all sorts of fashionable oddities.  Just look at the pictures of
the ancients of 30 years ago with not much but one brand name on the
jersey.

> One manufacturer who was not just in competition with conventional
> Italian frames, but actually was a producer of Italian frames which
> now produces 'compact' models is none other than Cinelli.

Cinelli is not Cinelli of yore, it is a brand name owned by a
manufacturer of bicycles and bar tape.  Names are sold.

> While Specialized may not manufacture anything, they previously offered
> lugged steel frames of conventional design, and still offer welded
> aluminium frames of conventional geometry alongside their 'compact'
> models.

Yes, so what does that say about the concept of sloping top tubes.  I
suppose you notice that all cars have for the past 15 or more years
had the wedge styling with vertically diverging lines to the rear.  It
is a worn out and tiring fashion, something the roadster guys
introduced in the 1940's (with big wheels in rear, small wheels up
front) in contrast to the custom guys who lowered the rear of their
cars.

>>>> With all the heavy money spent on bicycles, fashion has taken over.

>>> Fashion has always been with us, from the days of curly lugs and
>>> 'vibrant' stays to the present trends.

>> Filigree lugs had their validity in that they feathered out stress
>> without having to go paper thin at the edge of the lug.  Some
>> builders took this farther to make these lugs have elegant shapes.
>> Just because builders like Hetchins took it to the extreme doesn't
>> disqualify the use of filigree lugs.

> Nevertheless, fancy lugs were usually used with butted tubes which
> worked perfectly well with plain lugs. When that fashion passed and
> plain lugs were once again the norm, frames did not begin to fail at
> the lug edges with any more frequency than they had previously.

Not so.  The lug made the joint and unless there was a transition,
tubes cracked at the edge of the lug.  Inexpensive bicycles did this
regularly.

>>> Aesthetics aside (de gustibus non est disputandum), is there any
>>> compelling reason NOT to slope the top tube now that few bikes are
>>> built with lugs whose angles are predetermined?

By the way, with any specific lug, about 5 degrees +- is possible.  A
good frame builder can form a lug to make such adaptations.  I've
watched enough special frames built that did so.

>> Yes.  You can see at a glance whether the frame is bent or not.  The
>> same goes for forks with a curl at the bottom instead of straight
>> blades and an angled crown.

> That is a justificatioin I've never heard before, and I agree that
> it holds some water. However, I have never damaged a frame or fork
> in such a way that it was not immediately obvious from the ride
> quality of the bike, or a brief inspection of the top- and down
> tubes behind the head tube.

I have a bit more experience with bent frames and forks and have
diagnosed enough poorly handling (pull to one side) bicycles at a
glance by this method.  No measurements are needed to verify this.

>> Least important is aesthetics of a top tube in-line with forward
>> motion rather than one that is almost so.  The idea that slope
>> gives a lighter frame is bogus because frame tubing is thinner and
>> lighter than seat post material and bar stems.

> I performed a brief calculation last week during my discussion with
> Mark Hickey on the same subject, which I duplicate below, which
> suggests that small weight savings are possible through the
> shortening of not only the seat tube, but the seat stays and top
> tube.

All this rides on the assumption that frames are too strong and have a
large load margin, because the extended seat post adds bending moment
to the seat cluster of the frame by the percentage increase in length.
This concept says we should ride BMX frames with long seat posts and
stems.  IN fat BMX is where this concept is driven to the extreme with
flat diamond frames having an 8" seat tube.  That fashion is much like
low rider pickup trucks with dinky broad wheels protruding beyond
sides of the vehicle.

Jobst Brandt      <jbrandt@hpl.hp.com>