blackmoon, thanks for the concern but dont worry the frame is cro mo, apart from knowing by research the and stickers, you can tell steel frames becuase they tend to hAve narrower tubes. and "generally speeaking" steel to alumnium is 50% less ductile, search for modulus of elasticity (i dont think i speel correctly) if your intrested.
matthurd i would suspect thelightest building to be friction drive road bike as even tho bmx's are small they tend to be engineered for much higher loads. but i could be wrong. anyone have bmx build weight?
by the way why feel free to post if think you have the lightest build
and if you intersted the motor adds about 3500 grams (the gb the mount and chain etc)plus 3500 for the motor. the frame is a rudge biframe 1980's cro-mo