We all know that drag forces are about 2/3 caused by aerodynamics, but we may not pay enough attention to the other 1/3, such as transmission losses, bearing drag, and tire deflection. This was brought home to me when BAK posted that Bob Barker told him that the CanAm 125 that he set records with back in 1973, seized up before the last timing light, but still set a record of 135 mph + and coasted three miles back to the pits! He said that the rear wheel, with the chain in place, would spin for 4 minutes when spun by hand. So I went out to my shop and because my landspeed bike was not in the shop, I grabbed the back wheel of my BSA B50 road racer which was on a rear stand and spun the wheel. It rotated grand total of 5 seconds. Obviously, there are some transmission losses here.
I had an old CB350 Honda front wheel under the bench, which is the drum brake equivalent of the front wheel on my Landspeed bike so I set it up in an old swing arm in a vise and tried the same thing. It spun an amazing (or so I thought) 4 - 1/2 minutes. The bearings are Japanese Koyos, and might even be the original bearings, which are sealed on one side only. So I popped off the outer seals and tried again. This time the wheel spun for 9 minutes 47 seconds. At this point I noticed that the wheel was not well balanced, so I wrapped some solder around the spokes on the light side and spun it again. The result was over 11-1/2 minutes before it stopped spinning, and I had to watch it carefully to tell when it actually stopped.
Now these experiments are not very scientific, but because I got an order of magnitude difference by just removing the seals and re-balancing, the results are significant.
The BSA rear wheel will never rotate very freely, because the design of the drive sprocket, which is mounted on a sleeve gear, which in turn runs on a bushing on the mainshaft, and which also rotates the layshaft and all the attached gears, has a huge amount of drag. Luckily, when in high gear, the mainshaft and sleeve gear rotate at the same speed, so the transmission losses are confined to spinning the gears and shafts on ball and needle bearings. Not much that can be done here without cutting the gearbox off the motor and substituting a more modern transmission, torque converter, or what have you?
The drive chain is another potential horsepower eater, but I don't know what would be better. If I were starting over, I would go to 428 chain (from the present 520), but that would require another whole set of rear sprockets and custom made front sprockets. Other than that, would a belt drive be more efficient? Also, a belt drive primary is available (with some modifications to fit the B50), which might help.
Tires are also part of the equation, and I'm presently using a radial 110/70-17 front tire on the back (running counter direction to the intended direction), and a 80/90-17 bias ply on the front, both with tubes, and running 50 psi tire pressure.
So I would be interested in hearing from others on what I could do (or what you have done) to reduce these other power losses.
Tom