Just read the last article. A couple of excerpts:
"For typical light duty service where the vehicle Is not subjected to long periods of high speed or load operation and is run primarily on paved streets, plain cast iron is a good choice"
"When faced with continuous high speed or severe load conditions, the engine will be subjected to long periods of high temperatures. Moly is then a good choice because of its scuff resistance."
"In a dusty environment such as gravel pits, sand or rock mines, or operating on a dirt or unpaved roads, chrome is the best choice."
Now a quote from another one:
"Cylinder pressure forces the rings down in their grooves and, because of side clearance, gets behind the rings and forces them out against the cylinder wall. The top ring benefits the most, as there is much less cylinder pressure present at the second ring."
"Usually, the rings are bevel-cut to promote twisting. The top ring is often beveled on its top inside edge, which causes positive twist. That pushes the lower inside edge against the ring groove and creates an oil seal, while also allowing cylinder pressure to get behind the ring. The bevel of the second ring is machined in the lower inside edge to create negative twist and press the lower outside edge of the ring face against the cylinder wall for oil-scraping."
"The barrel face of the top ring is slightly curved, resulting in a very narrow contact point between the ring and the cylinder wall. Because the outward pressure on the ring is concentrated on a small area, the seal is tighter. The barrel-shaped face also allows the ring to maintain a proper seal as it rocks in its groove when the piston changes direction. As an added bonus, the barrel-face adapts easily to the cylinder wall during break-in and is able to maintain a positive seal as it wears."
My thoughts....
For both top and second identical rings, which basically would be the top ring shaped like the second ring.
The second ring is more porous for better oil distribution, the top is tapered for better seal against the combustion chamber (more pressure active surface less contact surface) during intake and combustion cycles, and metal treated for durability.
I guess cruising around on weekend in summer would fall in that 'typical light duty' category. I guess that would be around town and going to a park? While not off road usually and not racing, these 'muscle' bikes would be ridden harder than a moped, and extra stressed with load pulling all that weight wherever they go. Touring in mountains or countryside would go through dusty roads. Plus, these bikes have a general opinion of running hot. I'd say if installing a turbo in one of these, the engine would definitely appreciate those proper expensive rings.
