Why are 125cc sport bikes illegal in the US?

[chapstick]

Like the Honda CBR125, Aprilia RS125, etc.

It's not like it's too powerful. So why illegal? There are small displacement motor scooters.
to second poster. they are illegal because even though they sell the aprilia rs125 here in the states, it is only allowed on the track.

 

[James]

Due to low demand, the distributors do not import them into the country. And since they do not import them, they have not been inspected and tested to make sure that they comply with US regulations, such as emissions. Without that certification, they can not be legally licensed for the street.
Other countries have higher demand for such bikes because of either higher fuel or insurance costs for larger bikes, or because of tiered licensing systems. Americans have also always had a taste for larger displacement motors (in bikes and cars), and many highways have speed limits which would make it hazardous for smaller bikes.