Sprocket tooth Combo? mileage at 75mph?

[monsterbronc]

Im in need of a chain and sprockets, and I want to gear it up for a bit better mileage. Im not sure but I think the drive sprocket is 18 teeth, and the driven I know is 48. and frankly Im tired of doing 60 mph at around 4500 rpm.(ish, My tach and speedo aren't perfect) but at speeds above 60-65, its revved way high, and Im afraid to go over 90, I dont think it can turn much faster without going boom.

I already went with a bigger rear tire, 120/80-18 and it helped a little, but since I need new sprockets, what would be the best combo for better mileage, without totally ruining my acceleration? I realize that in 1975 when this bike was built, highway speed limit was 55, so it was most likely geared for best mileage around there. in this day and age of 75 mph (everyone seems to do 85) im not running at my most efficient rpm.

I know my tach isnt quite right, so if one of you could tell me what my actual rpm at 60 would be with my current configuration, thats great too.

thanks

[Lucky 1]

I have a 1978 engine with the higher 4th and 5th and I went to a 40 tooth rear sprocket.

[TOOLS1]

I would go with a 45, or 43 tooth rear sprocket, and keep the 18 tooth front. Freedom Cycles on Hwy 71 in Grandview has really good deals on chains, and sprockets.
TOOLS

[Rodgil]

Use the search box (top RH of screen) for dozens of previous replies to "gearing" or "sprocket size". My 82 CB750F uses 18 front 46 rear. I dropped to 40 rear, highway revs went from 5,000 to 4,100. Still has plenty of power.