[Ducati] squirmy rear wheel at speed?

[Andrew]

Sounds like the bumpy ride on I95 at speed was working the rear suspension
of your bike in a manner yet untested. My guess is that there are no real
issues with "loose frame or swing-arm components" but it is a matter of
making adjustments to the rear suspension.  I would, however, check the
torque setting on all the major component bolts/nuts.

Sounds as if the preload on the rear shock is approximately right; sag
should be between 7/8" and 1 1/16".  You may well already know this but just
in case, to check sag properly you should fully gear up, sit on bike while
someone steadies front end and holds you and the bike from falling over
while someone else measures from center of rear axle to reference point on
frame - call this measurement A.  Next make the same measurement from center
of axle to same reference point on frame with the rear suspension fully
unloaded - call this measurement B. Subtract A from B, the result is sag.
For the problem you describe (i.e., rear wheel wobble) I would set the sag
at the lower end of the range (i.e., 7/8").

I am not sure if your bike's rear shock is adjustable for both rebound and
compression damping but if sag is OK, you may want to next adjust
compression and/or rebound damping.  My suggestion is to adjust one of these
characteristics at a time a couple of "clicks" and take the bike for a test
ride.  Given the problem you describe (i.e., rear wheel squirm) I would try
stiffening the rebound and/or compression damping.

If the problem still persists you may want try a stiffer spring for the rear
shock.

BTW - from the road description you provide (I95 and Rt. 1) it sounds as if
you are in the Phila area.  I live in Phila area.

Hope this helps.

Cheers,
Andrew

-----Original Message-----
From: ducati-bounces at ducati.net [mailto:ducati-bounces at ducati.net] On Behalf
Of Wright, Dirk
Sent: Sunday, June 11, 2006 7:34 AM
To: Ducati Owners Group
Subject: RE: [Ducati] squirmy rear wheel at speed?

I should clarify that I actually have a 900 Sport, with a Sachs shock. The
original fork springs were really soft, so I don't know if the rear is the
same way. 


-----Original Message-----
From: ducati-bounces at ducati.net on behalf of Wright, Dirk
Sent: Sun 6/11/2006 6:34 AM
To: Ducati Owners Group
Subject: [Ducati] squirmy rear wheel at speed?
 
Hi all, I took my 900SS on the interstate for the first time yesterday. I
went 50 miles non-stop @ average speeds of 65-75 mph to do a day of overtime
at work. What I noticed was the way the rear wheel felt like it didn't have
as much traction as the front. I'm not sure if it actually had less
traction, but it felt squirmy, like it was moving around on a slick surface.
The wind at that speed is just tremendous, and I'm a large person, so I
guess I have a large "sail area", but I found the rear end dancing around to
be distracting. The tire is a Michlen Pilot, virtually brand new, and pumped
up to the proper tire pressure. After the ride, I checked for looseness back
there by gripping the tire and pushing and pulling it laterally to the
frame. Nothing seems amise that I can find. The bike has less than 1,000
miles on it. At slower speeds the rear feels much more solid. I check the
axle position as indicated by the pointers on the slider on the swing arm
and both sides are pointing at exactly the same mark on the swing arm. The
bike tracks straight. During the ride, I was buffeted by wind from trucks,
etc. and it was strange to have the rear move more than the front. Maybe
this is just normal and my inexperience is showing, but on the way home I
got off the interstate and took a break. The interstate was far bumpier than
I expected and I was getting worn out just dealing with bumps at 70 mph.
Route 1, which runs parallel to I-95, was much smoother and I took that the
rest of the way home. My shoulders really hurt at the end of the day. On the
suspension, all I've done is: replace the fork springs with much stiffer
ones, tighten the rear preload by one complete turn, and increase the rear
bounce by two clicks. When I sit on the bike, the rear goes down a small
amount but the front doesn't move. Maybe I need more preload on the rear? Do
the make stiffer springs for the rear? Any suggestions are appreciated!

Dirk
'02 900SS