Modern Vespa

In one of my replies to a post, I can't remember which one, I mentioned I had recently adjusted Cara Mia's rear spring rate. That was incorrect. Here's the story: Spring rate is the distance any given spring collapses (compresses) or extends (rebounds) and is expressed in lb./ins. The overall spring length, coil diameter, and wire diameter are the determining factors in this rate. Spring preload is used to set sag, or ride height, and does not effect spring rate. Shock dampening controls the rate at which the spring collapses or extends. So how do we GTS owners improve ride quality and/or handling of our scooters? Well, we don't, at least not very much with the factory coilovers. The only adjustment available on the stock shocks are the preload settings. And, as we know, this only sets ride height. Although the preload will slightly compensate for the riders weight, it can't compare with getting the optimum spring rate, and therein lies our biggest obstacle. As to shock dampening, there are no adjustments on the stock shocks. So, if you're a 450 pound scooter rider, say, then you might want to replace the stock springs with longer, thicker, and wider ones, so that when you hit a pothole you don't feel the impact go all the way up your spine. Conversely, if you're a small, lightweight individual, you might consider going to softer springs so that you won't feel like the scooter is going to jump out from under you. Now understand, this is not an indictment of the Piaggio coilovers. They do an outstanding job for the vast majority of riders. It's just that a completely tunable rear suspension, requires an investment in some after-market parts to do the job.

Proper way to adjust shock preload

Taken from the above, applies equally to Bitubo and standard...

Preload Adjustment 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.

Here is the Piaggio picture for adjusting preload.



Here is jimc's picture which may be less confusing:



Turning the ring counter clockwise while looking at it from above increases preload. You need to increase preload for carrying a pillion, for example. The Piaggio picture is somewhat confusing. Position 4 is actually the most preload for carrying a pillion. In that position the knurled ring is set with the spring under most tension all the way counter clockwise. The "ramp" on the knurled ring will be at its "deepest" setting.

Here are some common settings

Rider only position 1 or 2
Rider and Pillion position 4

You are correct sir. Well done.

When your stock shocks stop working correctly, replace them with some Malossi shock and your ride will improve 10 fold. I have Malossi shocks in front as well as in the back and the ride is sooo smoooth, I stopped bottoming out. 8)

I thought that the first post was insightful.

I'd like a suspension expert to explain how preloading the spring does not actually alter the effective spring rate, as if it didn't then preloading it for carrying a pillion would make no difference to ride height or performance of the suspension. Perhaps what occurs is that as a spring is compressed the effective spring rate increases ? Experts....??