I'm not assuming anything. It's funny how people can accuse and criticize others of making assumptions while making assumptions themselves. Just putting data down that someone building a bike might want to consider, especially when they're making suspension choices. I don't want to assume the guy is 150 lbs or 300 lbs, either. But it's something to consider when making these decisions. How heavy are the USD forks compared to stock? I know at least two of the bikes I converted, the USD was heavier. Where's he losing the weight? How much does a CB750 engine weigh? Or the frame? Where exactly is he going to drop 50lbs, because that's a lot of weight to lose? That's nearly 10% of the total mass. People are also suggesting he gusset the frame too, which adds weight. It was suggested that he match an R6 swingarm with the R1 front end. Which is heavier? A CB 750 has a 5 gallon tank, how many gallons is the R1. We haven't mentioned wet weight yet. 6 lbs per gallon.
No, but rims are a factor in the handling characteristics of a motorcycle. They also factor into how much breaking power he needs to stop the bike. No one has gotten into the part about converting to dual rotor. But ya know, no one has offered any thought as to what the unsprung weight actually is, either. Obviously, a 1978 CB750 could only be improved on braking, even if he goes with one floating rotor and dual pot caliper. Just a thought.
I bring up concern over lowering a motorcycle and now I'm a hater of USD shocks. I provide a weight comparison, and now I'm making assumptions about what the OP is or isn't going to do with his motorcycle. Sorry fellas, just bringing up things that someone building a motorcycle should consider when converting the entire suspension; or building in general.