[ST] RE: Nervous Front End (long)

["Keith Tynan" <keith@xxxxxxxxxxxxxxx>]

> Date: Thu, 05 Apr 2001 22:36:31 -0500
> From: ira <ira@xxxxxxx>
> ...
> How many of you have had dramatic experiences with the front suspension?
> What mods, other than RaceTech, have you done, and were they satisfactory?
> Anyone put a steering damper on the bike? What about replacing the springs
> without revalving?  Could there be issues with excessive lateral
> play in the
> front wheel?

Tollah,

Get ye to the FAQs: http://www.triumphnet.com/st/ -> FAQs -> Suspension

IMHO, slapper tendencies with stock suspension are more likely to be as a
result of poor rebound and compression damping (front and rear). Sort the
suspension out (f & r) and you're unlikely to need a damper within the ST's
speed range. I would say it's unlikely to be head or wheel bearing play, but
check this first to be certain.

If, however, you start playing with the geometry (by increasing the front
pull-through, or jacking up the rear), then the resulting decrease in trail
is going to bring the weave threshold* within the ST's speed range - hence
your desire for a damper will increase. It's always going to be a balance
between quick steering (low trail) and high speed stability (high trail).
The numbers are not big - 5 mm pull-through will only drop 2.1 mm off the
wheelbase - but the effects are quite noticeable. (Even 10 mm pull-through
on and ST wouldn't shorten the trail as much as the stock S3 or Daytona.)
Tyre profile also has a lot to do with this.

I currently run 5 mm pull-through on the front, which nicely quickens the
steering at 'normal' speeds, but which has sacrificed a bit of top-end
stability (not much though). Being a relatively mild tweak, I don't consider
it necessitates a damper.

I hope to get a track day in sometime this year, and I'm thinking of
increasing the pull through to 10 mm - I'll report back if I think this
warrants a damper.

* ALL bike steering systems have resonant oscillations. The first harmonic
(high frequency) occurs around the 40-50 mph region, the second (low
frequency) occurs at anything between 130-180 mph depending on geometry.
Manufacturers of road machines usually try to engineer this point to be
beyond the bike's speed range - or fit a damper as standard. Third and
subsequent harmonics are well into the realms of fantasy.

Regards,
- --
BRG
email: keith@xxxxxxxxxxxxxxx
'00 Sprint ST BRG 'Wolfram'


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