fork problem



G

Gary Smiley

Guest
Here's the story:
I have a road bike (853 steel frame, carbon fork). I had a bike-rack mishap-
the skewer on my car-top bike rack released, causing my bike to tip over and
bending (thereby ruining) the aluminum dropout on my carbon fork. I found a
replacement- an Easton EC30 fork that I bought from Nashbar, and I had it
professionally installed. Here's the problem: something is wrong- when I
ride the bike, it veers slightly back and forth, similar to a car with a
misaligned front-end. It's kind of like a gyroscopic force is pushing my
front wheel from side to side. I checked the wheel for trueness and it's
true. So, for example, if I feel a slight force pushing my wheel to the
right, I will apply an opposite force to the left, and vice versa. I can't
ride "no-hands" any more. I brought it back, and the mechanic said that it
had a different rake, and that the front wheel was now closer to my
downtube, and that the bike would now be more "twitchy", more like a real
racing bike. But I disagree- the rake is the same (based on the fact that my
wheel is in the same position (relative to my downtube) as it was before.
Any ideas? Is my (threaded) headset screwed up? (It turns freely). Something
is "off". Should I take it to a different mechanic?
 
M

Mike Jacoubowsky

Guest
> I brought it back, and the mechanic said that it had a different rake, and
> that the front wheel was now closer to my downtube, and that the bike
> would now be more "twitchy", more like a real racing bike. But I disagree-
> the rake is the same (based on the fact that my wheel is in the same
> position (relative to my downtube) as it was before. Any ideas? Is my
> (threaded) headset screwed up? (It turns freely). Something is "off".
> Should I take it to a different mechanic?


I also vote for a change in the fork rake causing the difference (actually,
probably more correct to say that the bikes "trail" has changed, causing the
difference). When you say the rake s the same, because the wheel is in the
"same position", what exactly does that mean? For everything relevant to be
the same, there are at least two measurements you need to check-

#1: Front-center wheelbase. Measured from the center of the crank to the
center of the front wheel (pointed perfectly straight forward). You could
measure all the way back to the rear axle, but easier to measure to the
front.

#2: Height from the ground to the top of the handlebar. Assuming the same
stack height (spacers and headset) & stem, any difference you measure will
come from a taller or shorter fork, which changes the effective headtube
angle. Not much, but slightly.

Choosing a nearly-identical fork is not guesswork and doesn't happen by
accident. Having said that, most bikes are pretty tolerant of small changes
in fork rake & resulting trail. Actually, I think it's *people* that are the
adaptive feature here. I made the move from one bike to another with
identical setup & geometry, except that the fork rake on the new bike was
35mm and the older one 43mm. The difference was instantaneously picked up
and very obvious... the bike was quite a bit twitchier/faster/whatever. Felt
strange, but within a couple days it felt totally normal. Here's the weird
part. After that, switching between the two bikes you hardly noticed the
difference. Human adaptivity.

--Mike Jacoubowsky
Chain Reaction Bicycles
www.ChainReaction.com
Redwood City & Los Altos, CA USA

"Gary Smiley" <[email protected]> wrote in message
news:[email protected]
> Here's the story:
> I have a road bike (853 steel frame, carbon fork). I had a bike-rack
> mishap- the skewer on my car-top bike rack released, causing my bike to
> tip over and bending (thereby ruining) the aluminum dropout on my carbon
> fork. I found a replacement- an Easton EC30 fork that I bought from
> Nashbar, and I had it professionally installed. Here's the problem:
> something is wrong- when I ride the bike, it veers slightly back and
> forth, similar to a car with a misaligned front-end. It's kind of like a
> gyroscopic force is pushing my front wheel from side to side. I checked
> the wheel for trueness and it's true. So, for example, if I feel a slight
> force pushing my wheel to the right, I will apply an opposite force to the
> left, and vice versa. I can't ride "no-hands" any more. I brought it back,
> and the mechanic said that it had a different rake, and that the front
> wheel was now closer to my downtube, and that the bike would now be more
> "twitchy", more like a real racing bike. But I disagree- the rake is the
> same (based on the fact that my wheel is in the same position (relative to
> my downtube) as it was before. Any ideas? Is my (threaded) headset screwed
> up? (It turns freely). Something is "off". Should I take it to a different
> mechanic?
>
 
D

David L. Johnson

Guest
On Thu, 08 Dec 2005 20:03:17 -0500, Gary Smiley wrote:

> Here's the story:
> I have a road bike (853 steel frame, carbon fork). I had a bike-rack mishap-
> the skewer on my car-top bike rack released, causing my bike to tip over and
> bending (thereby ruining) the aluminum dropout on my carbon fork. I found a
> replacement- an Easton EC30 fork that I bought from Nashbar, and I had it
> professionally installed. Here's the problem: something is wrong- when I
> ride the bike, it veers slightly back and forth, similar to a car with a
> misaligned front-end. It's kind of like a gyroscopic force is pushing my
> front wheel from side to side. I checked the wheel for trueness and it's
> true. So, for example, if I feel a slight force pushing my wheel to the
> right, I will apply an opposite force to the left, and vice versa. I can't
> ride "no-hands" any more. I brought it back, and the mechanic said that it
> had a different rake, and that the front wheel was now closer to my
> downtube, and that the bike would now be more "twitchy",


OK, so don't go back to them. This is ********. My "twitchiest" bike is
the easiest to ride no-hands. This is either a misaligned fork or a
too-tight headset, or maybe brake/shifter cables that are pushing or
constricting the rotation of the fork.

> is "off". Should I take it to a different mechanic?


Yeah

--

David L. Johnson

__o | You will say Christ saith this and the apostles say this; but
_`\(,_ | what canst thou say? -- George Fox.
(_)/ (_) |
 
P

philcycles

Guest
Mike Jacoubowsky wrote:
>

Lots of interesting stuff snipped
>
>


>
> "Gary Smiley" <[email protected]> wrote in message

when I ride the bike, it veers slightly back and
> > forth, similar to a car with a misaligned front-end. I


Here's the key. I'll bet the headset is too tight. this is called a
Dutch roll and comes from too tight head bearings. It's more common on
motorcycles than bicycles.
Phil Brown
 
W

Wheels by BFWG

Guest
"philcycles" <[email protected]> wrote in message
news:[email protected]
>
> Mike Jacoubowsky wrote:
>>

> Lots of interesting stuff snipped
>>
>>

>
>>
>> "Gary Smiley" <[email protected]> wrote in message

> when I ride the bike, it veers slightly back and
>> > forth, similar to a car with a misaligned front-end. I

>
> Here's the key. I'll bet the headset is too tight. this is called a
> Dutch roll and comes from too tight head bearings. It's more common on
> motorcycles than bicycles.
> Phil Brown
>


Ditto this diagnosis. . . I just cured the exact same problem on a new road
bike by loosening the headset just a touch. . . gone and good to go . . .
 
Phil Brown writes:

>> "Gary Smiley" <[email protected]> wrote in message when I ride
>> the bike, it veers slightly back and forth, similar to a car with a
>> misaligned front-end. I


> Here's the key. I'll bet the headset is too tight. this is called
> a Dutch roll and comes from too tight head bearings. It's more
> common on motorcycles than bicycles.


I'll vote for that as well. With hands on the bars, the only way
you'll get a back and forth response is from over-correcting which is
a response to a binding head bearing. Besides, if the shop was so
sure about their assessment they ought to show you how much the fork
offset is different from the original one.

As was suggested, get out of there before they try to sell you the
Brooklyn bridge.

Jobst Brandt
 
philcycles wrote:
> >
> > "Gary Smiley" <[email protected]> wrote in message

> when I ride the bike, it veers slightly back and
> > > forth, similar to a car with a misaligned front-end. I

>
> Here's the key. I'll bet the headset is too tight. this is called a
> Dutch roll and comes from too tight head bearings. It's more common on
> motorcycles than bicycles.


I once managed to induce a similar behavior (not the roll, but the
bad steering feel) by installing a fender. The mounting bracket
stuck up and was rubbing on the lower headset cup. The effect
is similar: the drag was not enough to stop turning the headset
deliberately or steering the bicycle with the bars. But the bike felt
funny and was impossible to ride no-hands. Bending the bracket
instantly cured it, of course.
 
M

Mark Hickey

Guest
"philcycles" <[email protected]> wrote:

>> "Gary Smiley" <[email protected]> wrote in message

> when I ride the bike, it veers slightly back and
>> > forth, similar to a car with a misaligned front-end. I

>
>Here's the key. I'll bet the headset is too tight. this is called a
>Dutch roll and comes from too tight head bearings. It's more common on
>motorcycles than bicycles.


I'll bet on that as well.

Or it's always possible that he test-rode the bike during an
earthquake.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame
 
Gary Smiley wrote:
> Here's the story:
> I have a road bike (853 steel frame, carbon fork). I had a bike-rack mishap-
> the skewer on my car-top bike rack released, causing my bike to tip over and
> bending (thereby ruining) the aluminum dropout on my carbon fork. I found a
> replacement- an Easton EC30 fork that I bought from Nashbar, and I had it
> professionally installed. Here's the problem: something is wrong- when I
> ride the bike, it veers slightly back and forth, similar to a car with a
> misaligned front-end. It's kind of like a gyroscopic force is pushing my
> front wheel from side to side. I checked the wheel for trueness and it's
> true. So, for example, if I feel a slight force pushing my wheel to the
> right, I will apply an opposite force to the left, and vice versa. I can't
> ride "no-hands" any more. I brought it back, and the mechanic said that it
> had a different rake, and that the front wheel was now closer to my
> downtube, and that the bike would now be more "twitchy", more like a real
> racing bike. But I disagree- the rake is the same (based on the fact that my
> wheel is in the same position (relative to my downtube) as it was before.
> Any ideas? Is my (threaded) headset screwed up? (It turns freely). Something
> is "off". Should I take it to a different mechanic?


I did the same thing that you did. i was driving back from a triathlon
with some friends. We were in a parkinglot and there was a hotel with
one of those shade thingies by the entrance. I rode throught the thing
and heard an awful noise. One of my friends said "the bikes!!!". i got
out of the car and my bike had suffered the same thing that yours did.
Without room inside the car, I used the rack to bend the dropout back
into place and drove away. An angry Indian guy (from India) came out of
the hotel shouting at me. When i got home I finished straightening the
dropout with a wrench.

Since the dropout was bent half way, I kept using it. I figure that
even if the dropout cracks and the piece breaks, half of the dropout
would still hold the hub in place. I promised myself that I would buy a
new fork when I had money. this was over two years ago. I've been
riding the same fork without problems. Keep an eye on the obituaries.

anyways, as everone else suggested, I also think that your headset is
too tight, or the races are pitted. This is causing the fork to lock
instead of turning freely side to side. For these reason, the bike
wants to turn to one side or the other and you cannot ride no hands.

Andres
 
M

Mike Jacoubowsky

Guest
> when I ride the bike, it veers slightly back and
>> > forth, similar to a car with a misaligned front-end. I

>
> Here's the key. I'll bet the headset is too tight. this is called a
> Dutch roll and comes from too tight head bearings. It's more common on
> motorcycles than bicycles.
> Phil Brown


Could very well be the case. I should have brought it up (although it's
really not all that common for someone to overtighten a threadless headset
to the point that it's that tight. In any event, it's more fun talking about
fork rake & trail than a slightly-too-tight headset.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com
 
A

A Muzi

Guest
Gary Smiley wrote:
> I have a road bike (853 steel frame, carbon fork). I had a bike-rack mishap-
> the skewer on my car-top bike rack released, causing my bike to tip over and
> bending (thereby ruining) the aluminum dropout on my carbon fork. I found a
> replacement- an Easton EC30 fork that I bought from Nashbar, and I had it
> professionally installed. Here's the problem: something is wrong- when I
> ride the bike, it veers slightly back and forth, similar to a car with a
> misaligned front-end. It's kind of like a gyroscopic force is pushing my
> front wheel from side to side. I checked the wheel for trueness and it's
> true. So, for example, if I feel a slight force pushing my wheel to the
> right, I will apply an opposite force to the left, and vice versa. I can't
> ride "no-hands" any more. I brought it back, and the mechanic said that it
> had a different rake, and that the front wheel was now closer to my
> downtube, and that the bike would now be more "twitchy", more like a real
> racing bike. But I disagree- the rake is the same (based on the fact that my
> wheel is in the same position (relative to my downtube) as it was before.
> Any ideas? Is my (threaded) headset screwed up? (It turns freely). Something
> is "off". Should I take it to a different mechanic?


If you have the original fork, carefully measure both. A
suitable fork geometry is a combination of both the amount
of offset and the height. You'll find the 2 forks vary in
one or the other or both.

On a 'sport' model designed for use with 32mm tires,
replacing the original with a shorter 'race' fork may drop a
full cm from crown race to axle. In that case the top tube
will have acquired a slope; the head angle is increased.

Best to find the proper fork and a couple of measurements
will tell you what fork that is.

It's only recently that forks are considered
interchangeable, as the push to 'designer' forks led
manufacturers to standardize on a few basic designs. Now
you only need a suitable fork, not the exact
brand/year/model. Even so it's easy to get the wrong one.

What bike is it? For many popular models participants here
can provide the proper specs.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971
 
A

A Muzi

Guest
> Lots of interesting stuff snipped
>>"Gary Smiley" <[email protected]> wrote in message

> when I ride the bike, it veers slightly back and
>>>forth, similar to a car with a misaligned front-end. I


philcycles wrote:
> Here's the key. I'll bet the headset is too tight. this is called a
> Dutch roll and comes from too tight head bearings. It's more common on
> motorcycles than bicycles.


OK, it's certainly likely at that shop and may account for
some of his symptom, but the mechanic _admitted_ installing
a fork with different rake. . .

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

Gary

Guest
Thanks for all your help. First of all, the bike is a 1999 KHS Aero
Comp. It had a generic carbon fork, and unfortunately I scrapped it
when I replaced it so I'll never get the measurements. As I mentioned I
replaced it with an Easton EC30 carbon fork. I did loosen the headset a
bit, and it moves freely, but when I ride it it feels like the wheel is
stuck in some kind of groove in the road (although not as extreme). I
thought that maybe my tire might be too grippy, but when I swapped the
wheel with one from another road bike I got the same symptoms. It's
driving me crazy- I used to like my bike, but now I feel uncomfortable
with it. I guess the next step is to have someone actually look at it.
Here's what I'm going to do: Since I live in the Boston area, I'm going
to take it to Sheldon. (But not today - it's snowing like crazy.)
 
M

Mike Jacoubowsky

Guest
> OK, it's certainly likely at that shop and may account for some of his
> symptom, but the mechanic _admitted_ installing a fork with different
> rake. . .
>
> --
> Andrew Muzi


Andy: Since the fork was purchased from Nashbar, it's unlikely that the shop
mechanic "admitted" (as in takes blame for) installing a fork with a
different rake since he didn't apparently buy the fork from the place that
installed it. Part of this story involves the pitfalls of not doing
everything in one place at one time, since finger-pointing can drag out
solutions.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com


"A Muzi" <[email protected]> wrote in message
news:[email protected]
>> Lots of interesting stuff snipped
>>>"Gary Smiley" <[email protected]> wrote in message

>> when I ride the bike, it veers slightly back and
>>>>forth, similar to a car with a misaligned front-end. I

>
> philcycles wrote:
>> Here's the key. I'll bet the headset is too tight. this is called a
>> Dutch roll and comes from too tight head bearings. It's more common on
>> motorcycles than bicycles.

>
> OK, it's certainly likely at that shop and may account for some of his
> symptom, but the mechanic _admitted_ installing a fork with different
> rake. . .
>
> --
> Andrew Muzi
> www.yellowjersey.org
> Open every day since 1 April, 1971
 
R

Roger Loftus

Guest
Gary Smiley wrote:

> Here's the story:
> I have a road bike (853 steel frame, carbon fork). I had a bike-rack
> mishap- the skewer on my car-top bike rack released, causing my bike
> to tip over and bending (thereby ruining) the aluminum dropout on my
> carbon fork. I found a replacement- an Easton EC30 fork that I bought
> from Nashbar, and I had it professionally installed. Here's the
> problem: something is wrong- when I ride the bike, it veers slightly
> back and forth, similar to a car with a misaligned front-end. It's
> kind of like a gyroscopic force is pushing my front wheel from side
> to side. I checked the wheel for trueness and it's true. So, for
> example, if I feel a slight force pushing my wheel to the right, I
> will apply an opposite force to the left, and vice versa. I can't
> ride "no-hands" any more. I brought it back, and the mechanic said
> that it had a different rake, and that the front wheel was now closer
> to my downtube, and that the bike would now be more "twitchy", more
> like a real racing bike. But I disagree- the rake is the same (based
> on the fact that my wheel is in the same position (relative to my
> downtube) as it was before. Any ideas? Is my (threaded) headset
> screwed up? (It turns freely). Something is "off". Should I take it
> to a different mechanic?


Gary:

I want to suggest another unlikely possibility that will create exactly
the effect you describe. When you are riding straight ahead, the bike
will wander with that gyroscopic feel if the front and back wheels are
even slightly out of vertical plane. I tried to straighten a frame
once, and if the front and back were not perfectly aligned in the
vertical plane, well, you just couldn't ride it.

Maybe that's worth checking out in your case, especially if there was
any possibility of a minute tweak to the frame.

Roger L.

--
 
G

Gary

Guest
I did the same thing- bent the dropout back and actually rode on it
once. Maybe it would have been OK - but - once aluminum bends, and you
bend it back, it can fail without warning. I would always be thinking
about that on fast descents. I could never ride that bike without being
worried. No fun!
 
G

Gary

Guest
I was thinking of that - maybe the crown race was improperly installed,
or something. But that's what it feels like - a gyroscopic feel- left
for 2 seconds, then right for 2 seconds or so, back and forth. It's
rideable, but it's not pleasant.
How could I check that out? I would want a mechanic to try riding it,
but it's a 60cm frame and too large for most people. I'm 6-2. What tool
does one use to determine if the wheels are alligned in the vertical
plane (besides looking at it)?
 
R

RonSonic

Guest
On 9 Dec 2005 08:02:11 -0800, "Gary" <[email protected]> wrote:

>Thanks for all your help. First of all, the bike is a 1999 KHS Aero
>Comp. It had a generic carbon fork, and unfortunately I scrapped it
>when I replaced it so I'll never get the measurements. As I mentioned I
>replaced it with an Easton EC30 carbon fork. I did loosen the headset a
>bit, and it moves freely, but when I ride it it feels like the wheel is
>stuck in some kind of groove in the road (although not as extreme). I
>thought that maybe my tire might be too grippy, but when I swapped the
>wheel with one from another road bike I got the same symptoms. It's
>driving me crazy- I used to like my bike, but now I feel uncomfortable
>with it. I guess the next step is to have someone actually look at it.
>Here's what I'm going to do: Since I live in the Boston area, I'm going
>to take it to Sheldon. (But not today - it's snowing like crazy.)



While we're all speculating and getting our bets in before Sheldon takes a look:
I'm putting a buck on the height from axle to crown race is a little shorter on
this fork. That's tipping you forward, reducing rake and trail all at once.

That's the feel I've gotten in some of my less perfect MTB fork experiments.
Doesn't make a difference off-road, but on pavement there's this slightly
unnerving "gyro about to go bad" feel.

Ron
 
R

Roger Loftus

Guest
Gary wrote:

> I was thinking of that - maybe the crown race was improperly
> installed, or something. But that's what it feels like - a gyroscopic
> feel- left for 2 seconds, then right for 2 seconds or so, back and
> forth. It's rideable, but it's not pleasant.
> How could I check that out? I would want a mechanic to try riding it,
> but it's a 60cm frame and too large for most people. I'm 6-2. What
> tool does one use to determine if the wheels are alligned in the
> vertical plane (besides looking at it)?


Ok, here you go:

First, you need two straight boards or something, each as long as the
bike front to back. Place these on each side of the front and back
tires as high as possible without the spokes interfering with the
boards touching the tires or rims on their front and back. With the
straight edges drawn together front and back on each side of the front
and back tires, you should have perfect alignment of the rear wheel and
the front tire bound together in the straight ahead position. Check
this closely, because if the rear tire is not tracking the front
exactly (same exact plane looking down from the top) you have problem
number 1. Then, while the front and back are bound into alignment, use
a level to position the back wheel exactly vertical, then check that
the front wheel is exactly vertical also. A mismatch here is problem
number 2. If these two checks pass ok, all should be well and you
gotta look someplace else.

Roger L.

--
 
J

Jasper Janssen

Guest
On 9 Dec 2005 11:39:49 -0800, "Gary" <[email protected]> wrote:

>I was thinking of that - maybe the crown race was improperly installed,
>or something. But that's what it feels like - a gyroscopic feel- left
>for 2 seconds, then right for 2 seconds or so, back and forth. It's
>rideable, but it's not pleasant.


Since it happened in a sorta-accident, frame misalignment is possible.

>How could I check that out? I would want a mechanic to try riding it,
>but it's a 60cm frame and too large for most people. I'm 6-2. What tool
>does one use to determine if the wheels are alligned in the vertical
>plane (besides looking at it)?


A really long and perfectly straight ruler, either wood or alu. If it
touches both wheels at two points each simultaneously, it's straight.
Doesn't get much easier than that. If it doesn't it's time to break out
the big guns to see whats wrong: with the rear wheel removed tie a string
running from one dropout to the headtube and back to the other dropout. If
the string passes equal distances to each side of the seat tube, the rear
triangles are properly spaced. Checking that the headtube and seattube are
perfectly parallel is more difficult, but if it's really bad (ie, bad
enough to feel in the handling) you should be able to eyeball it as well.

If the frame's straight and you have horizontal dropouts, loosen the rear
QR and use aforementioned long board to make sure the wheel is in line
with the front wheel and then re-QR (QuickFasten?). Then see if the wheel
is equal distances from right and left sets of chainstays.


Jasper