One (1) tooth change on countershaft sprocket same as a four (4) teeth change on rear sprocket, so your 16/48 combination will result in a top speed less than the 16/45 combination. Going with this 1:4 ratio, 17/48 would be very comparable to 16/45. Obviously, "smaller" front sprocket = less top end speed, same as "larger" rear sprocket = less top end speed. With a 16/48 combination, your bike will have more "grunt," quicker acceleration whilst sacrificing about 6 mph top speed, more thrilling around town to ride !
I cannot imagine ANY chain manufactured today being near the lower tensile strengths of 1969-1971 chain steel. I don't know anything about stretch/wear characteristics of Vietnamese chain, i do know the Vietnamese chain tensile strengths are less than Japanese manufacture chain. I use Japanese manufacture DID non-O-ring and O-ring.
16 tooth front is not that small of a sprocket by today's standards and any modern Japanese 600cc four is making around 105 -110 hp and uses a #520 chain, the CB750 makes 68 hp and uses a #530 chain. When we were racing between 2003-06, my kid's Yamaha R6 (dyno'd at 111 hp) was running 13 and 14 tooth front sprockets, we were running approximately 60 races (and 60+ practice heats) per season with chain adjustments every 10th race and NO FAILURE what so ever. Of course, we were using Sprocket Specialist sprockets and DID Racing Gold #520 O-ring chain.
Myself, i am a fan of O-ring chain, even though O-ring chain sucks a couple horse power. Some pro-level racers don't use O-ring chain and they replace the the non-O-ring chain every other race, depending on course and operating conditons. I like O-ring on the street in potentially prolonged filthy operating conditions, because O-ring chain is nearly maintainence free, requires periodic but infrequent lubing, even much more infrequent adjusting, is easily cleaned and sprockets will not wear out, almost ever.
Our CB750's only make 68 hp, nothing close to a 110hp 600 four. So, my opinion, a good range tensile strength O-ring or non-O-ring chain should be able to handle any front/rear sprocket combination utilised on a 69-76 CB750. Because a Vietnamese manufacture chain is lower tensile strength than a Japanese manufacture chain, assuming chain care and operating conditions equal, stretch/wear should be less a factor with a Japanese chain. O-ring does not a chain make stronger, it makes it less suceptible to wear because the links and pins are more protected from dirt and water. I don't know that a Viet Namese chain will be unsuitable on a stock CB750, but i will hazard guessing the tensile strength of a Viet Namese chain is greater than chain steel manufactured during 1969-71. Like i said earlier, for a few dollars more, i use the higher tensile strength Japanese chains.
