Frame weak-points?

I have a Merida bike with "Shotgun technology" frame. The cross bar, and the diagonal bar down to
the pedals (downtube?) have been built around an alloy "double barrel shotgun" type of tubing for
extra strengthening. In other words two tubes side-by-side are in the middle of the cross bar,
and downtube.

http://www.merida-bikes.com/mou-19.htm

What intriques me about this, is the triangle of tubes comprising the tube from the seat post down
to the pedals, and the tubes from the pedals back to the actual wheel, and from the wheel back up to
near the seat, are all very thin normal tubes without this "double barrel shotgun" reinforcing
within the tubes.

Yet my totally ignorant impression would be that in almost any stressed situation such as a landing
from even a small jump, would put the forces on this rear "triangle" rather than on the crossbar,
and downtube.

It seems to me that the wrong tubes are reinforced

What parts of a frame fail most often, and where should they be reinforced.

TIA

Trentus

 

Trentus wrote:

> I have a Merida bike with "Shotgun technology" frame. The cross bar, and the diagonal bar down to
> the pedals (downtube?) have been built around an alloy "double barrel shotgun" type of tubing for
> extra strengthening. In other words two tubes side-by-side are in the middle of the cross bar, and
> downtube.

Yes it seems the strengthening is in the wrong place. I saw a courier screaming down a city street
on a nice new one of these yesterday. He did a right angle turn in front of a fast approaching bus
with just metres to spare. Before he could straighten up he was heading right at the high/sharp
curb. My heart sank. Without any sign of lifting the front, or moving his body or the bike in anyway
at all, he rode over it as if it was just flat pavement. Should I try this at home?

 

I thought that the rear triangle was a tetrahedron (??), which is one of the strongest structures
known to man! That's why you can get away with narrower tubes. The main triangle is just that - a
triangle - and is typically much longer than the rear triangle and is more likely to twist and flex.

Trentus <[email protected]> wrote in message
news[email protected]...
> I have a Merida bike with "Shotgun technology" frame. The cross bar, and the diagonal bar down to
> the pedals (downtube?) have
been
> built around an alloy "double barrel shotgun" type of tubing for extra strengthening. In other
> words two tubes side-by-side are in the middle of the cross bar, and downtube.
>
> http://www.merida-bikes.com/mou-19.htm
>
> What intriques me about this, is the triangle of tubes comprising the tube from the seat post down
> to the pedals, and the tubes from the pedals back
to
> the actual wheel, and from the wheel back up to near the seat, are all
very
> thin normal tubes without this "double barrel shotgun" reinforcing within the tubes.
>
> Yet my totally ignorant impression would be that in almost any stressed situation such as a
> landing from even a small jump, would put the forces
on
> this rear "triangle" rather than on the crossbar, and downtube.
>
> It seems to me that the wrong tubes are reinforced
>
> What parts of a frame fail most often, and where should they be
reinforced.
>
> TIA
>
> Trentus

 

"Phil Holman" <[email protected]> wrote in message
news:[email protected]... <snip>
> > What parts of a frame fail most often, and where should they be
reinforced.
>
> 1. The chainstay to dropout attachment on the drive side.
> 2. Chain stay to BB shell.
> 4. Seat tube to BB shell
> 3. Headtube attachment to downtube.

Anyone know a URL, or other easily found source, that names all the parts of a bike? As you may have
noted from my "descriptions" rather than technical terms for the various tubes on a bike, I don't
know much more than the obvious "seat", "wheel", "handlebars" etc. What's a chainstay, and where is
it.? What's a "dropout" a "dropout attachment" and where are they? What's a BB shell? (I can assume
a BB is a Ball Bearing) The seat tube, I assume is the tube down from seat to pedals. Headtube? (I
assume this is the tube that the steering goes through from handlebars to front forks.)

I'd love to know the technical terms for a lot more of the parts on my bike, if only so I can ask a
question and know I'm not causing confusion, or getting a wrong answer, because my description was
misunderstood.

TIA Trentus

 

http://www.sheldonbrown.com/glossary.html

"Trentus" <[email protected]> wrote in message
news:<[email protected]>...
> "Phil Holman" <[email protected]> wrote in message
> news:[email protected]... <snip>
> > > What parts of a frame fail most often, and where should they be
> reinforced.
> >
> > 1. The chainstay to dropout attachment on the drive side.
> > 2. Chain stay to BB shell.
> > 4. Seat tube to BB shell
> > 3. Headtube attachment to downtube.
>
> Anyone know a URL, or other easily found source, that names all the parts of a bike? As you may
> have noted from my "descriptions" rather than technical terms for the various tubes on a bike, I
> don't know much more than the obvious "seat", "wheel", "handlebars" etc. What's a chainstay, and
> where is it.? What's a "dropout" a "dropout attachment" and where are they? What's a BB shell?
> (I can assume a BB is a Ball Bearing) The seat tube, I assume is the tube down from seat to
> pedals. Headtube? (I assume this is the tube that the steering goes through from handlebars to
> front forks.)
>
> I'd love to know the technical terms for a lot more of the parts on my bike, if only so I can ask
> a question and know I'm not causing confusion, or getting a wrong answer, because my description
> was misunderstood.
>
> TIA Trentus