Actually, this discussion and poll are a little flawed because almost all modern bicycles are built with tubing that is some mixture of steel and alloy in combination.
Cruisers used to be mostly just welded steel, until recently (and I'm not sure of the advent of the lighter frame, but know them by their oversized tubes that some people want you to drill through. And I think the alloy wheel rims arrived about the same time- circa early 80's)- so now they, like most road and mountain bikes are a form of "chrome alloy", and the relative weight and tensile strength of a frame derives from its percentage of steel vs. alloy mixture.
I know something of this because I raced USCF for 14 years back in the 70's and 80's. All aluminum bikes were introduced back then for road racing (Hi-E of Tennessee made a version) and they had great big oversized tubing that wasn't thought to be real strong and certainly not aero-dynamic, so generally smaller riders rode them. The Alan frame was a nice european version I still see occasionally for sale on e-bay). I had a frat brother who won a Teledyne Titanium bike they made in the early 70's and it was certainly light, with oversized but he was a mere 135 pounds- at 155 I kept on the standard Reynolds 531 or Columbus double-butted bikes.
But then in the late 70's I rode for the Cool Gear/ Exxon squad, and was given an ultra-light Exxon Graftek frame to ride, which was the very first prototype of the carbon fiber frame. I liked the material and had no problems, except mine always pulled slightly to the left. When the sponser fell through, I went back to a Columbus tubed Masi.
When I did my first build on a micargi cruiser almost a year now, I wondered here if anyone had tried to motor a Reynolds or Columbus frame. But now after messing with this thing for awhile, I don't think I'd choose to build up a Reynolds 531 or Columbus frame with a motor- they are just a little fragile I think- and certainly not a Reynolds 753 or Columbus SL tubed frame- I think the motor might break them at the seams. I have a 40 year old Peugeot PX10 I use for normal riding and it's gonna stay that way.
But what I am going to build is a Schwinn World Traveller I got for $5 last summer and you may have seen it here. I'll re-post. THe frame tubing is still pretty lightweight chrome alloy, but a little more rugged than a road racing bike. I'm waiting now on a 48 cc slant head kit, that I chose to keep the weight and vibration down (The Micargi cruiser, with 36 sprocket goes as fast as I want it to, at age 55!)
So anyway I think this bike may do well with a chrome tank, a chrome extended muffler, a narrow regular bike chain and sprocket on the motor and the newer slant head motor with needle bearings and steel sleeves which I hope will still pedal like normal- I'll probably leave the rear derailleur on, although I have a single freewheel I may go with. I project a finished weight of about 35-37 pounds, before fuel.
Happy motoring!
