B
On Jun 19, 10:05 pm, Michael Press <[email protected]> wrote:
> In article
> <d0f865db-c487-4390-9743-250519259...@d19g2000prm.googlegroups.com>,
>
>
>
> "[email protected]" <[email protected]> wrote:
> > On Jun 19, 7:26 am, [email protected] wrote:
> > > On Jun 19, 8:23 am, John Forrest Tomlinson <[email protected]>
> > > wrote:
>
> > > > Yeah. Perhaps rider error, perhaps oil. If I heard later his tire
> > > > flatted just then I wouldn't be surprised either. But NOT severe
> > > > frame flex for those bikes specifically.
>
> > > not severe flex, but just enough under load- or something else about
> > > the frame- last year at the tdf there were a couple of occaisions
> > > where the csc rider was unable to negoiate the curve on a descent,
> > > whereas other riders did- anyone re-watching the tdf2007 dvds might
> > > just take a note of the number of times a csc rider had trouble on a
> > > curve
>
> > Side load on a head tube, or just about any frame
> > part, during a descent is essentially zero. Bicycles
> > lean into corners rather than scrubbing tires like cars.
> > I could see issues from either an ultra flexy fork or
> > flex in a really long steerer and headtube (which can
> > contribute to shimmy), but hardly any of these guys
> > ride such a frame.
>
> I do not think it is that simple.
> What you describe is true for a constant curvature turn.
> Descents require very hard changes in the
> bicycle's aspect. This puts forces every
> which way on the front of the bicycle.
>
I don't think it's that complicated. Although the bike lean
angle changes as you enter and exit turns, it does so
gradually. Turns are initiated by small amounts of
countersteer and your COG is more or less in plane
with the wheel. While descending, you never turn the
handlebars very far, even if you really have to slow
down to enter a turn. The majority of the force on the
headtube is not side load, but fore-aft from braking
force. There are exceptions, like if you are doing a
slow-speed technical MTB descent, but they're not
relevant to Schleck's Cervelo.
You can put a side load on the head tube while climbing
or sprinting when you lean the bike and pull on the
handlebars. When descending, you would rarely
put that kind of force on the handlebar. I think if you're
descending on the road and you manage to put a large
side load on the head tube, you're going to fall down,
and it has nothing to do with magical frame-flex
properties.
Ben
> In article
> <d0f865db-c487-4390-9743-250519259...@d19g2000prm.googlegroups.com>,
>
>
>
> "[email protected]" <[email protected]> wrote:
> > On Jun 19, 7:26 am, [email protected] wrote:
> > > On Jun 19, 8:23 am, John Forrest Tomlinson <[email protected]>
> > > wrote:
>
> > > > Yeah. Perhaps rider error, perhaps oil. If I heard later his tire
> > > > flatted just then I wouldn't be surprised either. But NOT severe
> > > > frame flex for those bikes specifically.
>
> > > not severe flex, but just enough under load- or something else about
> > > the frame- last year at the tdf there were a couple of occaisions
> > > where the csc rider was unable to negoiate the curve on a descent,
> > > whereas other riders did- anyone re-watching the tdf2007 dvds might
> > > just take a note of the number of times a csc rider had trouble on a
> > > curve
>
> > Side load on a head tube, or just about any frame
> > part, during a descent is essentially zero. Bicycles
> > lean into corners rather than scrubbing tires like cars.
> > I could see issues from either an ultra flexy fork or
> > flex in a really long steerer and headtube (which can
> > contribute to shimmy), but hardly any of these guys
> > ride such a frame.
>
> I do not think it is that simple.
> What you describe is true for a constant curvature turn.
> Descents require very hard changes in the
> bicycle's aspect. This puts forces every
> which way on the front of the bicycle.
>
I don't think it's that complicated. Although the bike lean
angle changes as you enter and exit turns, it does so
gradually. Turns are initiated by small amounts of
countersteer and your COG is more or less in plane
with the wheel. While descending, you never turn the
handlebars very far, even if you really have to slow
down to enter a turn. The majority of the force on the
headtube is not side load, but fore-aft from braking
force. There are exceptions, like if you are doing a
slow-speed technical MTB descent, but they're not
relevant to Schleck's Cervelo.
You can put a side load on the head tube while climbing
or sprinting when you lean the bike and pull on the
handlebars. When descending, you would rarely
put that kind of force on the handlebar. I think if you're
descending on the road and you manage to put a large
side load on the head tube, you're going to fall down,
and it has nothing to do with magical frame-flex
properties.
Ben