Ich das Problem gefunden.
Die Federn sind zu kurz.
Ich habe versucht, die Aufhebung der Front. Federn vollständig unverpackt bewegen (Ausführen a little 'rechts und links).
Ich muß eine dicke?

I found the problem.
The springs are too short.
I tried to lift the front. Springs fully unpacked moving (running a little 'right and left).
I must put a thick?

What's a thick? Is is something like a spacer?

Maybe it would help. But normally, even lowered springs should be that long that they fit tight while the wheel is in the air. They should'nt wobble like you wrote.

Are the springs you bought specially designed for the Materia & are they legal?

Yes, a spacer just to compress a little bit the spring, to avoid the whobble. Springs are fully uncompressed when the wheel is in the air and this is not a good thing.
But there is a good news. If I turn the spring fully clockwise, the whobble is reduced.
Another thing: I think to have found that my Materia is lower on the left side. Just a few millimeters, so I think to swap left and right springs. I will take this opportunity also to double check the plates and fixing bolts/nuts.

Ich habe nicht das Gummi auf der ursprünglichen Federn, am Ende der vorderen Spule und auch in der Mitte der hinteren Spule.
Jetzt habe ich das Gummi und es gibt weniger "clank", die auch auf der Rückseite.
Noch einige "clunk" auf der Vorderseite.

I didn't see the rubber on the original springs, at the end of the front coil and also in the middle of the rear coil.
Now I have this rubber and there are less "clank", also on the rear.
Remain some "clunk" on the front.