It most likely has an unbalanced tire, you guys should look into Dynabeads to balance the tires. As far as the shaking from the engine i highly doubt that, I personally and strokd_ge as well have gotten our Ruckus into the 60mph zone on the 50cc stock internal engine and that little thing sounds and feels safe at those speeds. That being said if there are a couple rucks out there consistently in the mid to high 50's im sure this engine will handle and respond to high speeds with mods very nicely.I hope the wobble ( or vibration, shuddering?) at higher speeds IS an unbalanced front tire and not the little motor struggling or suspension. I have had several bikes that sounded and felt like they were going to fall apart or explode near top speed (GZ250 was one). I need to be able to pin it and go wot 62 mph (or whatever top speed turns out to be) for a long time without wobbling, overheating, or worrying. That's how I've always ridden my small bikes. My little Sportcity 50 only had two positions...stopped and WOT. Top speed was 43 mph but you could ride it like that for hours.