Straight line instability?

Quoted message said:

Is this normal? If not, what is the cause of it? Is it specific to the bike, geometry,
and/or setup?

Nope. And all of the above could be culprits.

1. Check/adjust the headset preload/bearings. They could be too tight.
2. Check/adjust the front and rear dish. I'm not sure what happens when the front wheel is off, but
when the rear is off, the bike will constantly drift.
3. Check/adjust the front wheel bearings. This probably isn't the problem.
4. Check/adjust the alignment of your ass. Maybe you're sitting funny?
5. A long shot: is your seatpost too high, and so you have to rock side to side to pedal, thus
causing weight shift? This isn't likely, but maybe your form is too jerky? (no offense)
6. Check if the frame is bent.
7. Check if your wheels are all the way in the dropouts, and if the rear wheel has the long
slot-type adjustment for aligning the wheels.

--
Phil, Squid-in-Training

Mike Reef said:

both hands off the bars to stretch my back while having a drink from the bottle. The front wheel
started swerving back and forth, not

Is this normal? If not, what is the cause of it? Is it specific to the bike, geometry,
and/or setup?

I'd expect this on a road bike except at higher speeds.

Bike, setup, and especially geometry could certainly do it, and would certainly have an effect.

If it steers to one side, then your frame is probably bent.

Quoted message said:

- Mike

--
Rick Onanian

"Mike Reef" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

I have a stock 1998 Cannondale R300.

Ever since the bike was new, the front end has always felt very twitchy and requires a conscious
effort to keep the front wheel perfectly straight. I find myself pushing forward on the bars to
force it to go straight.

Although it's not something I normally do, today I sat up and took both hands off the bars to
stretch my back while having a drink from the bottle. The front wheel started swerving back and
forth, not greatly, but enough that I didn't dare leave my hands off the bars for more than 5
seconds.

Is this normal? If not, what is the cause of it? Is it specific to the bike, geometry,
and/or setup?

- Mike

Here's an enlightening article about 'speed wobble' or 'shimmy' that may be applicable to you:
draco.acs.uci.edu8h.5.htmlOpen ↗

Rick Onanian said:

Mike Reef said:

both hands off the bars to stretch my back while having a drink from the bottle. The front wheel
started swerving back and forth, not

Is this normal? If not, what is the cause of it? Is it specific to the bike, geometry,
and/or setup?

I'd expect this on a road bike except at higher speeds.

Nonsense.

Quoted message said:

Bike, setup, and especially geometry could certainly do it, and would certainly have an effect.

If it steers to one side, then your frame is probably bent.

I'd be quicker to assume the fork would be misaligned, since that is common (with steel forks
at least).

But the description seems to be more of someone who is uncomfortable riding no hands -- or riding
that bike at all -- than of a mechanical problem.

--

David L. Johnson

__o | If all economists were laid end to end, they would not reach a _`\(,_ | conclusion. --
George Bernard Shaw (_)/ (_) |

David L. Johnson writes:

Mike Reef said:

Quoted message said:

Quoted message said:

both hands off the bars to stretch my back while having a drink from the bottle. The front wheel
started swerving back and forth, not

Quoted message said:

Quoted message said:

Quoted message said:

Is this normal? If not, what is the cause of it? Is it specific to the bike, geometry, and/or
setup?

Quoted message said:

Quoted message said:

I'd expect this on a road bike except at higher speeds.

Quoted message said:

Nonsense.

Quoted message said:

Quoted message said:

Bike, setup, and especially geometry could certainly do it, and would certainly have an effect.

Quoted message said:

Quoted message said:

If it steers to one side, then your frame is probably bent.

Quoted message said:

I'd be quicker to assume the fork would be misaligned, since that is common (with steel forks
at least).

Quoted message said:

But the description seems to be more of someone who is uncomfortable riding no hands -- or riding
that bike at all -- than of a mechanical problem.

Let's clarify whether the complaint is shimmy or that the rider must lean to one side to ride
straight ahead while riding no-hands. From what I see, it's shimmy which has nothing to do with
frame alignment. I saw no complaint abut aversion to riding no-hands.

Jobst Brandt [email hidden] Palo Alto CA

I have a bike with no rake to speak of and it rides no-hands as described. It comes from no
countersteer at the start of a correction. With a decent rake, moving the seat right turns the
front wheel left _then_ right as the front of the wheel is late in following (opposite of the
gyroscope effect). The left-then-right is the countersteer that makes a right turn work when you
tip the seat right.
--
Ron Hardin [email hidden]

On the internet, nobody knows you're a jerk.

Ron Hardin said:

I have a bike with no rake to speak of and it rides no-hands as described. It comes from no
countersteer at the start of a correction. With a decent rake, moving the seat right turns the
front wheel left _then_ right as the front of the wheel is late in following (opposite of the
gyroscope effect). The left-then-right is the countersteer that makes a right turn work when you
tip the seat right.

I agree with this. My mountain bike has a similar "stability" issue -- I can't ride it with no hands
for more than a couple of seconds, but the fork rake's so little that I can make a U turn on some
trails and any driveway. It may be that CD decided that the agility / stability compromise should be
in the direction of agility?

David

I saw this on my CD. I found the headset preload too loose. I also had a slight "rattle" in the
headset. After tightening, the problem was much improved.

Chris

"Mike Reef" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

I have a stock 1998 Cannondale R300.

Ever since the bike was new, the front end has always felt very twitchy and requires a conscious
effort to keep the front wheel perfectly straight. I find myself pushing forward on the bars to
force it to go straight.

Although it's not something I normally do, today I sat up and took both hands off the bars to
stretch my back while having a drink from the bottle. The front wheel started swerving back and
forth, not greatly, but enough that I didn't dare leave my hands off the bars for more than 5
seconds.

Is this normal? If not, what is the cause of it? Is it specific to the bike, geometry,
and/or setup?

- Mike

jobst.brand said:

Quoted message said:

But the description seems to be more of someone who is uncomfortable riding no hands -- or riding
that bike at all -- than of a mechanical problem.

Let's clarify whether the complaint is shimmy or that the rider must lean to one side to ride
straight ahead while riding no-hands. From what I see, it's shimmy which has nothing to do with
frame alignment. I saw no complaint abut aversion to riding no-hands.

From the original post: "Ever since the bike was new, the front end has always felt very twitchy and
requires a conscious effort to keep the front wheel perfectly straight. I find myself pushing
forward on the bars to force it to go straight."

This certainly does not sound like shimmy. I don't understand what he means by "pushing on the
bars", though.

He continues:

"Although it's not something I normally do, today I sat up and took both hands off the bars to
stretch my back while having a drink from the bottle. The front wheel started swerving back
and forth, not greatly, but enough that I didn't dare leave my hands off the bars for more
than 5 seconds."

Again, "swerving" is not how people tend to describe shimmy. Perhaps the idea of an over-tight
headset or some other mechanical glitch would make sense.

--

David L. Johnson

__o | And though I have the gift of prophecy, and understand all _`\(,_ | mysteries, and all
knowledge; and though I have all faith, so (_)/ (_) | that I could remove mountains, and have not
charity, I am nothing. [1 Corinth. 13:2]

Ron Hardin said:

I have a bike with no rake to speak of and it rides no-hands as described. It comes from no
countersteer at the start of a correction.

My first good bike had lots of rake, and the next one, a track bike, had almost none. But I could
always ride the track bike no hands, while the road bike would always veer to one side. Eventually I
found out that the fork was misaligned on the road bike, but certainly a lack of rake is not a cause
of this instability.

--

David L. Johnson

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

David L. Johnson said:

Again, "swerving" is not how people tend to describe shimmy. Perhaps the idea of an over-tight
headset or some other mechanical glitch would make sense.

I've been involved with shimmy a lot of years and have heard all sorts of descriptions of the
phenomenon. I guess you got to be an old timer to recall when the shimmy was a dance that pretty
much did what a vehicle wheel does when it shimmies.

streetswing.comz3shimy.htmOpen ↗

On the other hand, from Webster's Dictionary:

Main Entry: 1shimmy Pronunciation: 'shi-mE Function: noun Inflected Form(s): plural shimmies Date:
1837 1 [by alteration] : CHEMISE 2 [short for shimmy-shake] : a jazz dance characterized by a
shaking of the body from the shoulders down
3 : an abnormal vibration especially in the front wheels of a motor vehicle

Jobst Brandt [email hidden] Palo Alto CA