Front Fender Breakaway Options

On Tue, 11 Jan 2005 21:04:51 -0500, "Kyle.B.H."
wrote:

wrote:
On Tue, 11 Jan 2005 15:12:25 GMT, RonSonic
wrote:

[snip]


Help me out here. I'm having a hard time vidying what you'd ride over, into or
pick up on the tire that requires the breakaway fender. At least what wouldn't
be causing trouble already. Or that you'd hit with enough speed that it wouldn't
just be a minor nuisance. I could see branches and such being an issue, but we
usually aren't going fast enough over them that they'd do more than add drag
until getting ridden off.

Porcupines sprinting out into traffic? Caltrops?

Ron


Dear Ron,

It's much, much worse than you'd expect.

Fenders are often attached at the fork and also by a flimsy,
trailing metal loop that braces the back end of the fender.

If the fork support breaks on a light, poorly made, add-on
part, the fender hits the spinning tire and is carried
forward. (The mount can simply fracture from fatigue, or a
stick can be carried up into the back of the fender, jam,
and cause the same failure.)

Once the fork mount breaks and the fender is carried forward
by the tire, the trailing metal loop is dragged along with
the fender. The loop bends, shortens, jams with even more
force, bends some more, and stops the front tire in a
quarter revolution--a dead stop at any speed. You can
imagine the crash from such an abrupt front-wheel lockup.

When this happened to the uncle of a friend of mine at a
leisurely speed on a bicycle path, he broke his neck in the
crash and died of the obvious complications two years later.
The bicycle company settled out of court, since the fender
appeared to have fractured from fatigue.

I saw the bicycle. When the trailing metal loop gets caught
by the tire, it bends upward and toward the fork. As it does
so, it shortens and digs deeper and deeper into the tire. By
the time that the loop bends enough to reach the fork (which
stops it), the loop is buried in the tire.

I was astonished by how far the metal loop had sunk into the
tire without a pinch flat--imagine a half-inch slice removed
from a high-pressure road tire, right down to the rim. If
anyone had told me that a thin metal strut could sink so
deeply into the tire without an explosive flat, I would have
assumed that they were lying.

There are, of course, other outcomes, depending on what
breaks and bends, but a failed front fender that has the
traditional trailing brace usually means a violent disaster.

Carl Fogel

Carl,

By your frightening description, I don't see how something like SKS
Secure-Clips could solve the problem. Even if both stays disengage from
the fork, that rear loop could still catch on the tire - or would it?
Perhaps if the stays were disengaged at the fork, the metal loop would
be unable (or just less likely) to engage the tire and carry forward
into the fork.

Could the best solution then be fenders whose weak point is at the
stay/fender junction? Like the new-fangled Zefal fenders that clip into
notches in the fender body?

Kyle

Dear Kyle,

I don't know if there is any good system for front bicycle
fenders, but it's a very Bad Thing when anything tangles up
in your front wheel. If there's enough of a breakaway
designed into a fender, then the fender will, well, tend to
break away.

I expect that there are improved bicycle fender designs.

On street motorcycles, the solution is simply much heavier
mounting and much less violent motion. (We don't hear much
about car fenders falling into the front wheel, either.)

On off-road motorcycles with much wider front tires that
power through much deeper mud and water and bang around much
more violently, fenders are not so much a luxury as a
necessity. Two tricks are used.

First, there's the high-mount fender. Instead of sitting
close to the tire, the fender is mounted up under the bottom
of the triple clamp, the equivalent of the bottom of a
bicycle's steerer tube. The wheel moves up and down on the
suspension with up to a foot of clearance from the fender.

This gives a solid mount, it reduces the banging up and down
with the suspended front wheel, and it's a good way to avoid
mud clearance problems, where the wheel jams as thick mud
builds up between the tire and fender. But it's not much
good for trials work, where it's important to see the front
tire, not a fender half a foot above it.

So the usual trick is to have a sturdy fork brace connecting
the upper fork legs (the thicker bottom parts, as opposed to
the fork tubes, the thinner upper parts). You bolt a stiff
fender to the stout brace. The supports are much closer to
the fork legs, so there's less waving around and fatigue and
much less leverage if something breaks. There's no
bicycle-style trailing reinforcement hoop sticking back
horizontally from near the axle.

Typical motorcycle fenders are much thicker and heavier
plastic than bicycle fenders, so the unsupported ends work
fine.

Just how thick, stiff, and tough was a Preston Petty
off-road plastic fender? In the 1970's, we sawed them in
half and bolted them to the undersides of trials bikes for
skid plates to absorb the impact of hitting rock ledges and
three-foot logs. You needed a couple of huge C-clamps to
force a new fender half into place under the frame, but by
the end of the season the repeatedly smashed fender would
flap limply when unbolted.

Carl Fogel

Kyle.B.H. wrote:
Does anyone have any experience using nylon bolts for fender mounting?
Strong enough to hold 'em on and weak enough to break if necessary?

Zog The Undeniable wrote:
IME plastic fenders just shatter if you get something caught in them.

(am)But not the metal loop of left stay, metal bridge, right
stay. If you jam that against the tire at the crown you can
have a real problem. A breakaway some place is a good idea.

RonSonic wrote:
Help me out here. I'm having a hard time vidying what you'd ride over, into or
pick up on the tire that requires the breakaway fender. At least what wouldn't
be causing trouble already. Or that you'd hit with enough speed that it wouldn't
just be a minor nuisance. I could see branches and such being an issue, but we
usually aren't going fast enough over them that they'd do more than add drag
until getting ridden off.

Porcupines sprinting out into traffic? Caltrops?

In the most dramatic cases I never knew what started it but
once the mudguard jams against the tire the rider goes right
over with the bike. Results are ugly. Not common, but
sobering. One remembers the few incidents.

I've only seen the aftermath. Anyone actually flown by
mudguard trebouchet power?

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

Marvin wrote:
I've seen more than a quarter revolution. A woman pulled up at the
back door of my LBS with two obviously broken fingers and her mudguard
stays wrapped four times around the axle. Where the mudguard had hit
the tyre, the rim had been bent in to the point where it was about 6-8
inches from the axle, making the wheel look kinda heart-shaped. The
tyre had obviously blown out.

I ended up having to dismantle the whole front wheel with bolt croppers
because the stays, axle and spokes were all so tangled. Ever since
then I've been religious about fitting breakaways of some description.

Oh, and when I say "two broken fingers" I don't mean "strapped up", I
mean "not bending in the normal way". She'd come to get her bike fixed
before her fingers. There's real dedication for you...


What kind of "breakaways" would you suggest for the Planet Bike front
wheel fenders? ...a set of nylon screws to attach the fender stays to
the dropouts?

Jean

A Muzi writes:

I've only seen the aftermath. Anyone actually flown by mudguard
trebouchet power?

I was riding home from work, at night, several years ago, on a bike
with fenders. Coming down a hill I heard a "bang", the bike endoed
and I went over the bars. Over then I minor headache I was okay. I
never figured out what happened. The front fender was wrecked, the
wheel was tacoed, the tire was flat. I carried the bike a mile or so
until someone gave me a lift.

My suspicion was that I hit something in the road that caused the
wheel to collapse, jam against the fender/fork, and launch me.
However, I searched the road the next day and found nothing. I never
considered that something may have pushed the fender wire into the
wheel.

Joe

On Wed, 12 Jan 2005 02:57:40 GMT, Joe Riel
wrote:

A Muzi writes:

I've only seen the aftermath. Anyone actually flown by mudguard
trebouchet power?

I was riding home from work, at night, several years ago, on a bike
with fenders. Coming down a hill I heard a "bang", the bike endoed
and I went over the bars. Over then I minor headache I was okay. I
never figured out what happened. The front fender was wrecked, the
wheel was tacoed, the tire was flat. I carried the bike a mile or so
until someone gave me a lift.

My suspicion was that I hit something in the road that caused the
wheel to collapse, jam against the fender/fork, and launch me.
However, I searched the road the next day and found nothing. I never
considered that something may have pushed the fender wire into the
wheel.

Joe

Dear Joe,

Hard to tell in the dark in real life, isn't it? And by
morning, more traffic could have swept away any evidence.

It could have been a rock or stick. It doesn't have to be
very big to crash a bicycle.

Or it could have been that the fender mounts themselves
fatigued, broke, and jammed things up. The wreckage could
have damaged the wheel instantly, or the wheel could have
been damaged a moment later in the crash.

Glad you survived.

Carl Fogel

writes:

Hard to tell in the dark in real life, isn't it? And by
morning, more traffic could have swept away any evidence.

I doubt traffic would have removed the object. I was in the bike lane
on a sweeping left turn; the only traffic in the right lane would have
just come off a freeway and would be to the inside of the turn (away
from the bike lane).

It could have been a rock or stick. It doesn't have to be
very big to crash a bicycle.

Yeah, my guess is one of those.


Joe

Haven't had experience with the Planet Bike ones, however if they're
the Planet Bike Freddy range on the website those definitely look like
they have the potential to fail spectacularly. Nylon screws would
probably do the trick, alternatively the suggestion of cable ties
sounds workable. The SKS Secu-clips or similar would also work with
standard mudguard staysif you can find a pair separately.

Okay, now that I've grasped this concept that fenders can easily become part of
a jammed front wheel launch vehicle type problem....

This breakaway thing. Seems that more than a little thought needs to be put into
just what exactly is going to break away and what's going to be solid. Simply
mounting the thing with nylon bolts or cable ties may only increase the
frequency with which it tries to jam the tire. IOW debris that might only have
slightly jammed a solidly mounted fender, may cause the breakaway piece and it's
struts to get swallowed by the fork crown which then chokes.

I don't recall classic british roadsters having that sort of problem. And there
were a hell of a lot of them.

Ron

RonSonic wrote:

Okay, now that I've grasped this concept that fenders can easily become part of
a jammed front wheel launch vehicle type problem....

This breakaway thing. Seems that more than a little thought needs to be put into
just what exactly is going to break away and what's going to be solid. Simply
mounting the thing with nylon bolts or cable ties may only increase the
frequency with which it tries to jam the tire. IOW debris that might only have
slightly jammed a solidly mounted fender, may cause the breakaway piece and it's
struts to get swallowed by the fork crown which then chokes.

I don't recall classic british roadsters having that sort of problem. And there
were a hell of a lot of them.

Ron


Maybe the problem with most fenders these days is that they're in teh
middle between sturdy and flimsy? Perhaps fenders in the old days made
of steel with big thick struts and mounted with big fat bolts were more
immune to being sucked into a wheel by debris, wrapping around a hub,
etc... They also probably had more clearance...

Perhaps it's these middle of the road fenders that are the real killers
- weak enough to crumple with a little debris, strong enough to stop the
wheel quick.

So maybe the answer is to be at the extremes with either totally self
destructing fenders (individual stays, not L/R or F/B V's), that can
break away at both the fender and the fork, OR big tough ones with lots
of clearance like the old days.

Kyle

On Wed, 12 Jan 2005 22:50:13 -0500, "Kyle.B.H." wrote:

RonSonic wrote:

Okay, now that I've grasped this concept that fenders can easily become part of
a jammed front wheel launch vehicle type problem....

This breakaway thing. Seems that more than a little thought needs to be put into
just what exactly is going to break away and what's going to be solid. Simply
mounting the thing with nylon bolts or cable ties may only increase the
frequency with which it tries to jam the tire. IOW debris that might only have
slightly jammed a solidly mounted fender, may cause the breakaway piece and it's
struts to get swallowed by the fork crown which then chokes.

I don't recall classic british roadsters having that sort of problem. And there
were a hell of a lot of them.

Ron


Maybe the problem with most fenders these days is that they're in teh
middle between sturdy and flimsy? Perhaps fenders in the old days made
of steel with big thick struts and mounted with big fat bolts were more
immune to being sucked into a wheel by debris, wrapping around a hub,
etc... They also probably had more clearance...

Perhaps it's these middle of the road fenders that are the real killers
- weak enough to crumple with a little debris, strong enough to stop the
wheel quick.

So maybe the answer is to be at the extremes with either totally self
destructing fenders (individual stays, not L/R or F/B V's), that can
break away at both the fender and the fork, OR big tough ones with lots
of clearance like the old days.

That seems to make sense.

Ron