Quote Originally Posted by Wald0 View Post
Not good?? 50MPG is about 4.65L/100km and that seems pretty good. sure you could get some Honda Airblade or Yamaha nouvo and drop that down to 3L maybe on 100km,

Main problem with small engine bikes is that you will have to rev them higher that big bore engines.
there just is not enough torque in small engines especially if your heavy as i am
My chevrolet Cruze gets an average of 34,7MPG, and does ~48MPG going 50MPH on the highway, so yes, 50MPG for a motorcycle is very lousy!

My modified MC-05-127 does about 105MPG, and about 95MPG when going 60MPH on the highway.

250cc is NOT a small bore! 50cc is a small bore.
For city riding, a 50cc needs to rev in the high revs to keep up.
You're right that you need to find a motorcycle that revs low in the environment you use it in.
For city and suburb riding, meaning 35-45MPH, and a level ground (no hills), a 110cc engine is just about perfect, and with the right sprocket change, you could get upto 120MPG.
If you're a bit heavier then me (I'm 160LBS), a 125cc might be more suited.

If you're going on the highway, doing 60MPH, a 125cc is revving to he top revs, and that's not good.
A 250cc has double the displacement, so theoretically can rev to half the revs, if you provide it with the right gear (sprocket) change.

Most 250cc bikes are geared to do 8k RPM @80MPH tops; or 6k RPM @ 60MPH.
If you don't need to go 80, but are satisfied with 60MPH, doing a sprocket change of ~25% lower teeth count, could get your RPMs down by 25%, or you'll be doing ~4500RPM @60MPH.
You can always downshift 1 gear to go to the top speed.

If you're a bit heavier then me, probably modifying a 300cc instead of a 250cc might be the better option for you.
A 300cc you might get lucky and get a good 85MPG out of. I'm aiming for 100MPG on a 250cc, but know that realistically I'll be more between 85 and 95MPG, with the right sprocket.