Bars wobbling on straight, flat roads!?

[steve mac]

Afternoon all.

I noticed on the way to work today that my bars were wobbling gently from side-to-side, we're not talking a tank-slapper obviously, but a bit disconcerting nonetheless.

Found a flat, straight bit of road and took my hands of the bars and it still happens so I know it's not down to too tight a grip. Even tried this several times throughtout the journey on completely different road surfaces.

Bike wise it's a curvy '01 SVS, standard forks and rear shock, rear ride height raised about 1" with some shorter dog-bones and pre-load wound up max. Rear tyre is starting to square off but not enough to affect geometry and it was a straight road anyhow...

I'll see what happens tonight when I back the pre-load off but in the meantime, does anyone know if this sounds symptomatic or bearings, wheel balance etc.?

Cheers, Steve.

[Sid Squid]

Tall at the rear can get you in to unstable steering territory, a worn back tyre will worsen this.

If it still does it with a good tyre on it may be worth a closer look.

[steve mac]

Thanks Sid.

I understand the changes in geomerty will put more weight on the front and make the steering a bit sharper / flickable - that's why I did it.

What I don't get it why a worn back tyre might worsen this - at least not when going straight.

Can you show me the light mate?

Cheers, Steve.

[Sid Squid]

As the tyre wears flat in the middle the contact patch gets wider, depending on the specifics of the tyre's interaction with the road; camber, load, carcass flex etc, the exact point of drive, (either forward or reverse: braking/engine braking), may not be exactly centred along the axis of the bike, as the steering tries to self centre - a function of the castor and trail - the contact patch centre moves around, also the fact that the steering apparatus, (forks, wheels, 'bars etc), has mass and therefore, if moving at sufficient speed, momentum, causes the steering to pass through the centre position, and the process repeats itself in the other direction, thus the oscillation of the front end.
In this circumstance, that is; off the throttle or just light a throttle, the front tyre will often damp out the oscillation by scrubbing on the road, sometimes just the weight of your hands on the bars will be enough to change the resonant frequency and still it.
Generally it will only turn into a 'tankslapper' if there is relatively little contact of the front tyre, for instance when hard on the throttle, or when the front end is lightened over a bump, but the reasons are similar; the front wheel is trying to line up with the rear.

[Wiltshire7]

oscillation

thats a damn good word. im gonna start using it.

'how r u oscilating today?'
im not convinced i know what it means though :(

[Flamin_Squirrel]

oscillation

thats a damn good word. im gonna start using it.

'how r u oscilating today?'
im not convinced i know what it means though :(

:lol:

A pendulum, for example, oscilates. It basicaly means move back n forth.

http://dictionary.reference.com/search?r=2&q=oscillate

[Scoobs]

oscillation

thats a damn good word. im gonna start using it.

'how r u oscilating today?'
im not convinced i know what it means though :(

PMSL! :lol:

[Warren]

im having the same confusion.
check wheel bearings, wheel alignment, chain tention, brakes arnt rubbing,

i even got my wheels balanced and feels slightly wobbly,

could be just me being paranoid tho.

[jonboy]

oscillation

thats a damn good word. im gonna start using it.

'how r u oscilating today?'
im not convinced i know what it means though :(

:lol:

A pendulum, for example, oscilates. It basicaly means move back n forth.

http://dictionary.reference.com/search?r=2&q=oscillate

An oscillation is an eliptical path not just a linear movement back and forth.


.

[Stig]

I can concur, and on top of this (not in this case I realise) having wider bars can give the same result.

[Flamin_Squirrel]

oscillation

thats a damn good word. im gonna start using it.

'how r u oscilating today?'
im not convinced i know what it means though :(

:lol:

A pendulum, for example, oscilates. It basicaly means move back n forth.

http://dictionary.reference.com/search?r=2&q=oscillate

An oscillation is an eliptical path not just a linear movement back and forth.


.

You mean sineusoidal, I'm an engineer you know! I just didn't want to confuse the guy with further geometric jargon :lol: Hence the word, 'basicaly' :wink:

[embee]

sounds a bit like your ar$e-uppards set up won't help, but other things are steering head bearings loose (tight tends to give a slow weave at low speed, loose tends to give wobbles typically at around 40mph and worse on overrun).

Also front tyre not suited to the bike (carcass stiffness) or wrong pressure can do it.

I'd suggest check the fork legs/yokes aren't twisted (suspension bumps can then input a turning effect)

[jonboy]

You mean sineusoidal

Look this is a "U" rated site so please refrain from using language like that in future. :twisted: :lol:


.

[weegaz22]

oscillation

thats a damn good word. im gonna start using it.

'how r u oscilating today?'
im not convinced i know what it means though :(

:lol:

A pendulum, for example, oscilates. It basicaly means move back n forth.

http://dictionary.reference.com/search?r=2&q=oscillate

An oscillation is an eliptical path not just a linear movement back and forth.


.

you would know wouldnt you? :wink:

[Warren]

oscillation

thats a damn good word. im gonna start using it.

'how r u oscilating today?'
im not convinced i know what it means though :(

:lol:

A pendulum, for example, oscilates. It basicaly means move back n forth.

http://dictionary.reference.com/search?r=2&q=oscillate

An oscillation is an eliptical path not just a linear movement back and forth.


.

you would know wouldnt you? :wink:

well tell you what . . . i dont know.

[jonboy]

oscillation

thats a damn good word. im gonna start using it.

'how r u oscilating today?'
im not convinced i know what it means though :(

:lol:

A pendulum, for example, oscilates. It basicaly means move back n forth.

http://dictionary.reference.com/search?r=2&q=oscillate

An oscillation is an eliptical path not just a linear movement back and forth.


.

you would know wouldnt you? :wink:

Fixed now, with forks done and head-race bearing tightened up.

You haven't been about much, you you doin'?


.

[weegaz22]

oscillation

thats a damn good word. im gonna start using it.

'how r u oscilating today?'
im not convinced i know what it means though :(

:lol:

A pendulum, for example, oscilates. It basicaly means move back n forth.

http://dictionary.reference.com/search?r=2&q=oscillate

An oscillation is an eliptical path not just a linear movement back and forth.


.

you would know wouldnt you? :wink:

Fixed now, with forks done and head-race bearing tightened up.

You haven't been about much, you you doin'?


.

been working and trying to get the flat i bought sorted so havent had much time to come on the board, but seeing as summer is here i think ill be on a bit more now

[Stig]

................but seeing as summer is here i think ill be on a bit more now

It is :?: :shock: :shock: must have missed it :roll: