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Proper way to adjust shock preload
or Sag, as it is sometimes known.

As a guide a scooter should have 25-30mm of loaded sag at the front and 20-22mm at the rear.

To measure the static sag get the scooter on its centrestand with the rear wheel off the ground.

With the rear wheel in the air measure from the centre of the axle to a fixed point on the bodywork (the bottom of the cowl panel for example). Write this measurement down. We shall call this S1.

Now get an assistant and sit on the scooter with the wheel on the ground off the stand.

The assistant should then push on the seat and allow the pressure to release slowly, allowing the suspension to extend gradually. Ask them to measure the distance from the static bodywork point to the centre of the axle. We shall call this measurement S2.

Then get your assistant to lift the back end by about three centimetres and allow to settle again. This measurement is S3.

Find the average of S2 and S3 by adding together and dividing by two, then subtract S1.

Congratulations, you've just measured your sag. This sag can be dialled out by adjusting your preload using the supplied c-spanner and moving the knurled ring on the rear shock.

If you have too much sag, you should increase the preload and vice-versa.

For example if your average of S2 and S3 is 4cm, (it should be actually at 2.2-3 cm, as above), you will have to try to dial out 1-1.8cm of sag.

This is the same method used for setting a Bitubo shock. However to set the rebound, it is just a matter of timing. Push down and the scoot should return to normal in about 1 second. Less than a second and the rebound is too soft, more than a second and it's too hard.

Hope this helps.


Performing the Preload Adjustment

What to do
You need to increase the preload if you'll be carrying more weight
(like when you'll be carrying a pillion, for example).

Here is the Piaggio picture for adjusting preload:

Looking at this picture, you can increase the preload
by turning the ring counter clockwise while looking at it from above.

Here is JimC's clearer picture (IMO):

Looking at this picture, you increase the preload by twisting the shock
so that the peg fits into a position with a higher number, like Position 3 or 4.

Position 1 (where the ring is twisted all the way clockwise) has the least preload,
so it is the proper position when you are riding by yourself and you're fairly light.

Using Position 4 adds the most preload, so it's the proper position
when you're carrying a pillion and both of you have substantial weights.
In this position, the knurled ring is set with the spring under the most tension (all the way counter clockwise).


Other Pointers
* If your preload hasn't been changed recently, it helps to spray the mechanism with WD-40,
so that it moves more easily.

* Until you're practiced at this adjustment, it really helps to wear gloves,
so that you don't bust your knuckles against nearby parts.

* If you're inseam-impaired (a bit too short for your bike),
please be aware that increasing the preload will raise your scooter seat upwards.
Last Updated Fri Apr 30, 2010 7:09 am
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