Re: Cannondale Mtn Bike Recall

Jobst Brandt said:

Steve Gravrock writes:

http://www.cpsc.gov/cpscpub/prerel/prhtml07/07211.html

Quoted message said:

Quoted message said:

> "Cannondale Announces Recall of Mountain Bicycles; Lefty Forks Can
> Break Unexpectedly"
Of course that stupid design would be dangerous.

That was my reaction the first time I saw a Lefty, but now I'm not
so sure. It looks wrong because it's asymmetrical, but that's
actually not uncommon. Most modern forks have a spring in one leg
and dampening controls in the other. That includes basically all air
forks. The Lefty just combines both into a single leg. Supporting
the hub on one end also seems questionable at first, but it's common
on wheelchairs.
The CPSC announcement doesn't say exactly what went wrong, but I'd
guess that either the lower part of the fork leg separated from the
upper, or the fork leg separated from the steerer.
Does anyone know why Cannondale moved away from their old design
that put the suspension above the crown of what was otherwise a
rigid fork? That seemed pretty sensible to me, especially back in
the days when suspension fork flex due to uneven compression was a
major problem.

Consider the difference between a cantilevered spindle, extending from
a single fork leg and one that is supported on both ends with wheel
bearings close to those ends. Bending loads from the cantilevered
spindle are more than ten times as great and propagate up the fork
leg that is otherwise not loaded in bending from the spindle.

Looking at automobile wheel support, the size and design of axles and
spindles support is done with care, having large transition radii and
solid anchoring in housings and steering knuckles that do not look
like the features visible on the Cannondale struts.

What we need next is this design with a disk brake to make all the
problems work together to enhance failures.

But the single-sided hub mounting eliminates the disc brake wheel/
ejection concern, even with the brake mounted on the rear of the mono-
strut.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

email hidden said:

Consider the difference between a cantilevered spindle, extending from
a single fork leg and one that is supported on both ends with wheel
bearings close to those ends. Bending loads from the cantilevered
spindle are more than ten times as great and propagate up the fork
leg that is otherwise not loaded in bending from the spindle.

That makes sense. I'd thought about it only in terms of the load on the
hub bearings. It seems like that increased bending load could
contribute to the crowns breaking, if that's indeed what happened.

Quoted message said:

What we need next is this design with a disk brake to make all the
problems work together to enhance failures.

It looks like all of Cannondale's current mountain bikes come with disk
brakes, including Lefty-equipped models.

Tom Sherman writes:

http://www.cpsc.gov/cpscpub/prerel/prhtml07/07211.html

Quoted message said:

Quoted message said:

Quoted message said:

>> "Cannondale Announces Recall of Mountain Bicycles; Lefty Forks
>> Can Break Unexpectedly"

Quoted message said:

Quoted message said:

Quoted message said:

> Of course that stupid design would be dangerous. That was my
reaction the first time I saw a Lefty, but now I'm not so sure. It
looks wrong because it's asymmetrical, but that's actually not
uncommon. Most modern forks have a spring in one leg and dampening
controls in the other. That includes basically all air forks. The
Lefty just combines both into a single leg. Supporting the hub on
one end also seems questionable at first, but it's common on
wheelchairs.

Quoted message said:

Quoted message said:

Quoted message said:

The CPSC announcement doesn't say exactly what went wrong, but I'd
guess that either the lower part of the fork leg separated from
the upper, or the fork leg separated from the steerer. Does
anyone know why Cannondale moved away from their old design that
put the suspension above the crown of what was otherwise a rigid
fork? That seemed pretty sensible to me, especially back in the
days when suspension fork flex due to uneven compression was a
major problem.

Quoted message said:

Quoted message said:

Consider the difference between a cantilevered spindle, extending
from a single fork leg and one that is supported on both ends with
wheel bearings close to those ends. Bending loads from the
cantilevered spindle are more than ten times as great and propagate
up the fork leg that is otherwise not loaded in bending from the
spindle.

Quoted message said:

Quoted message said:

Looking at automobile wheel support, the size and design of axles
and spindles support is done with care, having large transition
radii and solid anchoring in housings and steering knuckles that do
not look like the features visible on the Cannondale struts.

Quoted message said:

Quoted message said:

What we need next is this design with a disk brake to make all the
problems work together to enhance failures.

Quoted message said:

But the single-sided hub mounting eliminates the disc brake wheel/
ejection concern, even with the brake mounted on the rear of the
mono- strut.

That may be, but the torque of a hub brake adds to the bending load on
the strut that is supposed to telescope freely axially while
supporting load and brake bending moments. I haven't seen a
motorcycle with such a front end, but I'm sure there are some in the
woodwork.

Jobst Brandt

Quoted message said:

Tom Sherman writes:

http://www.cpsc.gov/cpscpub/prerel/prhtml07/07211.html

Quoted message said:

Quoted message said:

>>> "Cannondale Announces Recall of Mountain Bicycles; Lefty Forks
>>> Can Break Unexpectedly"

Quoted message said:

Quoted message said:

>> Of course that stupid design would be dangerous. That was my
> reaction the first time I saw a Lefty, but now I'm not so sure. It
> looks wrong because it's asymmetrical, but that's actually not
> uncommon. Most modern forks have a spring in one leg and dampening
> controls in the other. That includes basically all air forks. The
> Lefty just combines both into a single leg. Supporting the hub on
> one end also seems questionable at first, but it's common on
> wheelchairs.

Quoted message said:

Quoted message said:

> The CPSC announcement doesn't say exactly what went wrong, but I'd
> guess that either the lower part of the fork leg separated from
> the upper, or the fork leg separated from the steerer. Does
> anyone know why Cannondale moved away from their old design that
> put the suspension above the crown of what was otherwise a rigid
> fork? That seemed pretty sensible to me, especially back in the
> days when suspension fork flex due to uneven compression was a
> major problem.

Quoted message said:

Quoted message said:

Consider the difference between a cantilevered spindle, extending
from a single fork leg and one that is supported on both ends with
wheel bearings close to those ends. Bending loads from the
cantilevered spindle are more than ten times as great and propagate
up the fork leg that is otherwise not loaded in bending from the
spindle.

Quoted message said:

Quoted message said:

Looking at automobile wheel support, the size and design of axles
and spindles support is done with care, having large transition
radii and solid anchoring in housings and steering knuckles that do
not look like the features visible on the Cannondale struts.

Quoted message said:

Quoted message said:

What we need next is this design with a disk brake to make all the
problems work together to enhance failures.

Quoted message said:

But the single-sided hub mounting eliminates the disc brake wheel/
ejection concern, even with the brake mounted on the rear of the
mono- strut.

That may be, but the torque of a hub brake adds to the bending load on
the strut that is supposed to telescope freely axially while
supporting load and brake bending moments. I haven't seen a
motorcycle with such a front end, but I'm sure there are some in the
woodwork.

eh? you've never seen a vespa? only 10 million made since 1946.

jim beam said:

Quoted message said:

Tom Sherman writes:

Quoted message said:

Quoted message said:

Quoted message said:

>> Does
>> anyone know why Cannondale moved away from their old design that
>> put the suspension above the crown of what was otherwise a rigid
>> fork? That seemed pretty sensible to me, especially back in the
>> days when suspension fork flex due to uneven compression was a
>> major problem.

Limited travel for MTBs and probably in comparison to mass produced
standard forks just to expensive for touring cycles. The design
principle survives in a bike with limited space in the area of the fork
blades: Speed machine by HP-Velotechnik.

Quoted message said:

Quoted message said:

Quoted message said:

> Consider the difference between a cantilevered spindle, extending
> from a single fork leg and one that is supported on both ends with
> wheel bearings close to those ends. Bending loads from the
> cantilevered spindle are more than ten times as great and propagate
> up the fork leg that is otherwise not loaded in bending from the
> spindle.

You're writing here about completely different designs, right? Headshock
vs. Lefty Monofork.

Quoted message said:

Quoted message said:

That may be, but the torque of a hub brake adds to the bending load
on the strut that is supposed to telescope freely axially while
supporting load and brake bending moments. I haven't seen a
motorcycle with such a front end, but I'm sure there are some in the
woodwork.

eh? you've never seen a vespa? only 10 million made since 1946.

8" wheels and thus extremely short fork blades.

Günther

Quoted message said:

That may be, but the torque of a hub brake adds to the bending load on
the strut that is supposed to telescope freely axially while
supporting load and brake bending moments. I haven't seen a
motorcycle with such a front end, but I'm sure there are some in the
woodwork.

Jobst Brandt- Hide quoted text -

- Show quoted text -

Whilst we're on the subject, I saw one of these on the London-Brighton-
London yesterday:

http://www.use1.com/products/sub_antidive/sub_80mm_detail.php
http://www.use1.com/products/sub_antidive/detail.php
http://www.use1.com/products/sub_antidive/technical.php

I've no idea how it rides, or whether it's a valid concept, although I
did notice the shaft's anodizing was badly abraded where it enters the
upper. I pretty sure it had happened in an unacceptable mileage
judging by the general appearance of the bike (very new looking) and
the rider (very obese looking). The shafts on my Marzocchi fork (also
aluminium) appear much better coated/ sealed, as the bike gets ridden
in invariably filthy conditions (head-to-toe mud), and with no
maintenance at all the fork remains unblemished, smooth and holds air
for years at a time, which I find remarkable given my experience of
Rock Shox and and Manitou forks in years past.

It's always a good ride just to look at the weird and wonderful bikes
on display. I saw some guy pushing what appeared to be a genuine Lotus
bike (a la Chris Boardman) up Ditchling Beacon:

http://www.grouplotus.com/eng/track_record.php?section=17&page=25&id=13

I can't find a good page on these, which is surprising given their
iconic status (at least here in the UK), and don't know whether they
were mass produced or not.

Tom