Straight line instability?

[Mike Reef]

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

[Phil, Squid-in-Training]

> 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

[Rick Onanian]

On 16 Aug 2003 14:16:02 -0700, Mike Reef > wrote:
> 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.

> - Mike
--
Rick Onanian

[David L. Johnson]

On Sat, 16 Aug 2003 17:49:32 +0000, Rick Onanian wrote:

> On 16 Aug 2003 14:16:02 -0700, Mike Reef > wrote:
>> 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.
>
> 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
(_)/ (_) |

[Ron Hardin]

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


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

[ottodog]

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" > wrote in message
om...
> 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

[David L. Johnson]

On Sun, 17 Aug 2003 03:33:04 +0000, jobst.brand wrote:

>> 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]

[David L. Johnson]

On Sun, 17 Aug 2003 09:57:48 +0000, Ron Hardin wrote:

> 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.
(_)/ (_) |