are 50cc scooters highway illegal?
 

...or only if you fall below legal speeds?

I was curious, with all the super aeromodding and stuff like that, since the more powerful 50cc scooters seem to manage 40mph, I don't see why 55mph would be out of the question on flat ground, if not even better. (though gearing might be an issue admittedly)

The Federal Interstate requires that motorcycles be 250cc or larger, for non interstate highways you just have to meet the minimum speed limit, often 45mph to be legal, but being able to keep up with traffic is a great idea in a smaller vehicle.
There have been 50cc motorcycles that have top speeds of 90mph, but they are not by any means using scooter engines.
In my mind this falls under the rule of not doing something stupid and illegal at the same time, design the vehicle so you don't get pulled over and make sure it's fallowing all of the laws.
there are also 250cc engines out there that are going to get you better gas mileage then a scooter or motorcycle engine.

in MI the minimum size for the freeway is 125cc, but in order to go more than 40mph on state roads a vehicle must be registered as a motorcycle. this means it must have either an engine larger than 49cc or a multiple speed transmission. most "50cc" scooters purposely have engines under 49cc and cvt transmissions so that they do not need to be registered or insured. if you are caught going over 45 on a public road on a non registered noninsured vehicle, you can get in lots of trouble. that being said, if you register and insure your scooter as a motorcycle, you ought to be ok on rural highways. just not on expressways.

Again, this only applies to MI, as there are NO federal road laws. The Federal Government cannot legally pass road laws, they can threaten to take away highway funds though.

Waitasec, so does that mean even a Kawasaki eliminator 125cc can't legally be on the freeway despite running 55-60mph happily? First person said nothing under 250cc is legal second said there are no federal road laws so i'm confused now. The Ninja 250's are technically 249cc but can do 100mph, they wouldn't be legal either?

It was a long time back that I was told that you couldn't take a bike that was smaller then 250cc on the interstate, but I've had a number of people tell me that, of course I don't have a good source for that info so it could be wrong, or it might just be something weird with my state, so sorry if I was incorrect.
But you do have to maintain a safe speed and part of the safety of a motorcycle is being able to get out of peoples way, so having a small weird vehicle that only goes 55mph on a road where everyone drives 70mph might not be a safe choice.

my crystal ball is just buzzing and swarming on this



i wish in had a 4 place airbody with a 50 cc and lots of gears..

one of these days when fuel gets really tight .. we will see it

the answer is simple. each state differs.to answer this question you need to research your state's traffic and motor vehicle laws. what is considered a freeway legal machine in one state might not be in another.

Which further confuses things if you want to travel out of state....:D

You are free to travel through different states, regardless.

Agreed. your vehicle only needs to be registered and insured in your home state you can drive it in all the others. otherwise most motorcycles from Michigan would not be allowed in California. there is no catalytic converter requirement in MI yet. Capacity limits may be enforceable though. If your state says 250cc for the freeway, I might not be legal on your freeway. That said, I can keep up with freeway traffic @ 70mph, so I would not be likely to get pulled over.