I tend to be a curious person, and my curiousity has led me to ask many questions. Many of my questions have been unanswered, so I sought to try things myself.
After about four years of wondering, buying motorcycles, fixing motorcycles, riding motorcycles, and thinking about motorcycles, I think I know what I want.
I'll start with my conclusion:
There are many amazing two-wheeled machines. The best of them is the BMW Airhead.
It is reliable.
It is nimble.
It is durable.
It is capable.
It is practical.
It is available.
Parts are still available. An R90S was recently built from new parts. The design is sensible and exacting. You can throw it around, or ride it comfortably.
Not all airheads are perfect. The best years are probably 1976-1978.
The wire wheels are forgiving enough and repairable enough to take you offroad, anywhere. The heavy flywheel means you won't be spinning your tires unduly. The cylinders sticking out may save your leg in a low-side especially if you also have luggage on. The carburetors are accessible immediately. The gas tank is large, fuel economy is decent. The community is excellent and there is a lot of information on them.
They are a simple design and feel like they were built by riders, for riders.
You can find more comfortable, faster, more appliance-like, and cheaper bikes. But the value of the airhead is that it can do all things decently.
BMW setup the bikes with less trail than other machines, about 3.5" inches. The steering is light as long as the bearings are set properly light. It is extremely forgiving. The suspension travel is incredibly high for such a machine.
BMW went wrong when they tried to alter the recipe. They went to the mono swingarm, which exposes the brake arm and makes it vulnerable. They went to a 21" front wheel on the G/S, which is not what this bike is about. They put on a lighter flywheel, so you can spin your tires in the dirt. Why?
The /5's short wheelbase was a bit too short. The lengthened it out. If you have something like an R90/6, R75/7, or R100/7, you probably have one of the best motorcycles ever made.
The limits are such that you wouldn't want them to be any higher on the street. Its offroad ability is sufficient in road trim, to take you most anywhere you want to go. You can repair it anywhere, mostly with just the stock tool kit. The wire wheels are strong and durable, but mendable when needed.
It's predictable enough that you can flog it about without dropping it. In the right cases, you can slide, push the limits, and have more fun than anyone else around you.
The UJMs of the 80s were fantastic, but harder to work on, heavier, and had cast wheels. Good for the road, but not off. Modern bikes can be very apt, but often suffer from lack of real world applicability. Twitchy throttle off idle, light flywheel, and not fixable on the side of the road. They also have limits so high that once you're pushing them, you're feeling more fear than excitement.
And the limits for all bikes are the same when there's an oil patch ahead. Better to be at a lower limit when you hit that.
The BMW airhead is the best motorcycle of all time, because it is the best compromise of all time.
This is based partly on experience, and partly on theory. But, I'm betting I'm right. And if you want a touring bike out of the wind, there was the R100RS.
This was easy on the /5: https://www.youtube.com/watch?v=mkGDrsy0EiY
There were points where the front would slip on oil. The rear would slip on oil. The front would want to kick back up after it regained traction. But, I could always hold it together. That, to me, is a good motorcycle. The /6 and /7 should be no different in that regard.
On a more serious note, I have a 1974 Yamaha RD-350 in good condition. Looking to trade for an airhead.
I'm also thinking about working on airheads as a side job. If you have any around San Antonio, Texas, let me know.
Don't get caught up into fads or unrealistic expectations. You aren't going to be pushing your R6 on the street to its limits. Your Goldwing is really too much bike for just getting groceries. And those clubman bars aren't making the bike any easier to handle. If you want to talk about bikes and what it a good motorcyclist and motorcycle are, let me know.
Update: I no longer think this, though do still have some fondness for Airheads. Happy to explain more if you're interested.