Modern Vespa

So I've read of others with a wobble on their 300 GTS, I have it but only when between 35mph and 45mph. Does that sound normal for a GTS? How can I go about fixing it? The bike is only about a month old, I guess I can go back to the dealer but I kind of like to tinker and repair things myself if possible.

Wobble usually appears with one or both hands off the bars while decelerating through about the 30mph mark.

There is no single fix. The wobble is an inherent part of the design. That said, various things might mitigate the problem. See: FAQ: Is it normal for a GT/GTS to "wobble"?

Your dealer is unlikely to entertain your complaint. Ultimately, it's a minor flaw in an otherwise awesome bike, and the more you fixate on it the less happy you will be.

If it is under warranty let them fix it, it might be a bigger problem rear wheel bearing etc, or as simple as a bad tyre mount or bad tyre.

Unlikely.

Although not a GTS I had a wobble on my BMW bike, it turned out to be a defective front tyre, dealer changed it and all was good, Hope OP finds the problem as a 1 month old scoot wobbling is not acceptable and dangerous.

All GTSs wobble. It's not dangerous if you keep at least one hand on the bars.

I have two 2021 GTS Supers and one wobbles and one doesn't. Like Jess said, just don't take your hands off the bars and you'll never know it's there,

I find my HPE2 to be stable as can be, my 2012 wobbled.

Is yours a 23 or 24? Maybe check the tire pressure.

Perhaps the "wobble" happens depending on what colour your GTS is.....
eg. we all know that black bikes are faster

Wobble as in a tank slapper type of movement, or more of a deceleration gyration? I have not noticed it on my 22 yet, but I always keeps both hands on the bars when stopping, I have taken one off at highway speeds to adjust phone holder and did not notice anything.....

My BV also has the wobble. As you describe decelerating in the 60kph area, roughly 35mph, the wobble is there, but only when I take both hands off the handle bar.
If I have one hand on the handle bar, I do not even have to grab the bar, just rest my hand on it is enough, the wobble is immediately gone.

I would suspect any 'wobble' with the GTS300 might be caused by a relatively steep fork angle and those small wheels that produce limited gyroscopic stability, at least as compared to a motorcycle's larger and more massive wheels.

Perhaps a combination of fork angle, small wheels, and a short wheelbase.

I will say, that in spite of those possible factors, I've never noticed anything that I could call a 'wobble' with my 8000 mile, 2020 GTS, but about the only time I take a hand off of the bars is to momentarily reach up to open or close the faceshield on my helmet.

If you only sometimes take one hand of the handling bar you will never feel the wobble.

Try this:
On a free and straight road in good condition, go to speed 50mph, then take both your hands of the handling bar and let the scooter decelerate by itself.
I am almost sure that around the 30-35mph range the wobble will be there.

I Had it on my 2022, so I replace the front tire from new and its much better not perfect but better.

I have posted this video several times on this forum. It's quite old and not very good quality but it explains what wobble and weave are on 2 wheeled vehicles. Look at the video, understand it, and you'll never worry again about wobble and weave as you will know what to do.

My BV 350 also has it on decelerating between 35-30. Heavier bar ends reduced, but not eliminated, it. As noted a light touch from even one hand makes it disappear.

Ok that makes sense. I have done that on a few motorcycles and felt a slight vibration/wobble seems to more of two wheel issue as many motorcycles have a stabilizer strut to control that. I have a few BMW motorcycles that had that tendancy......

Just had a flashback to my harley days when I had a wobble, remembered that the wheel was out of alignement with handlebars, straigtened up, wobble was gone, wonder if that works on a GTS, I can imagine with such small wheels, a few millimetres would have a massive impact, specially if you are bumping up onto pavements etc to park outside shops.

All. GTSs. Wobble.

It's not broken. It's part of the design.

Mine (2006? GTS250) wobbles heavily usually during the downhill part of my commute and I survive it every day ) It will get better (=you will get used to it)

The imbalance of the gts' mono fork, with its suspension pivots, shock, rotor and brake caliper, all hanging from the left side (note how even at rest the front end heavily swings to the left) amount to what feels like at least 5kg more mass, to the left of the center of the fork. This likely causes a harmonic effect at a certain deceleration. I'm not thrilled with this quirk on an otherwise fantastic bike, but there are enough other assets that make it all worthwhile.

My sweet '65 Heinkel Tourist with its sensible symmetrical, Lambretta-esque front suspension, was rock steady at all speeds.

Keeping my hands on the gts grips is no hardship though. I can wave at passing bikes anytime over 33mph. I do miss my Tourist though.