Some electric skateboards start to wobble quicker than others at higher speeds. This is even those that have dampeners.
The ones that I've found that wobble less are the ones with wider trucks and wheels. The lower the truck is to the ground the more stable it is also. Many people sometimes take out their bushings and get harder bushings for more stability too. A bi- directional damper for better steering helps eliminate the speed wobble some too and makes it more smooth. Many beginners get the dampeners at a local skate store.
Also tightening the trucks will help some boards eliminate some of the wobble at high speeds. The biggest reason is the rider and not knowing how to handle the wobble. Many people are too tense and don't really relax when it happens and don't keep their body weight forward
Best thing I can do is just to ride soft, keeping my knees and feet less tense. Standing up to high creates drag and just makes the wobble more. The narrow electric skateboards are less stable but more responsive and the wider boards are more stable in general but less responsive.
The first thing I would do is to adjust the truck when you get it and if you need different bushings for your weight. If the trucks are too tight or too lose it can be a factor in speed wobble. Finding just the right sweet spot is what usually needs to be done to get comfortable with the new board.
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