I have a 44t rear sprocket and want to lower it to get more speed to compete with my 45+ mph mini bike. I know I most likely won't get 45mph but just want more speed. What would be the best sprocket size? 36t 34t 32t or 28t? or anything else?
I have used a 34 alloy sprocket I got from Kings Sprockets a few years back- with a stock 66 except for a billet intake, for several years- I'm heavier than you and this bike by its analogue speedo can get near 35, which I've never opened it up to, but it will cruise at 30.
Of course it's got 700C wheels- actually a back 700 c and still the front 27" inch here. I've had several spokes break on rear 27" inch wheels, but the slightly shorter spokes in 700C seem to make all the difference. The hub is a smooth sided high flanged flip flop hub, drilled then to match the inner disk brake drillings on the sprocket and attached with titanium bolts considerably smaller than rag bolts- s it's a very light affair.
The best part running a smaller sprocket is that the motor revs and vibrates considerably less at the same speeds. Another advantage is that as the sprocket gets smaller, there is generally more clearance for the chain in the rear stays, so it's easier to get rid of the tensionsr and match the chains with half links if you need to or a rear pedal derailleur.
If you ran 1.5 or 1.75 tires on 26 alloy rims, and unless you are in very hilly land, you could probably run a 34 or even 32 sprocket and get near the same speed I mentioned. The narrow tires help to pedal start the bike as well and a 415 Industrial trike chain with the same pitch but shorter plates is about half the weight of a 415 kit chain and really lessens chain drain too. You can really feel the difference peddling, so I'm sure the small motor does too.
Other things you can do is get a jug with a wider intake and a wider billet to match and then run a dellotto or CNS style carb, which aren't pricey these days, but never tried then here- just the NT speed carb. You might even be able to run a 28 with a larger intake and carb. You can also easily put a 700 or 27" narrow front wheel on the front- you have to change or adjust the brake- like you see on a chopper motorcycle, and youll notice a much better roll.
I also have a cruiser frame with 700 wheels- 28 or 32 mm wide tires and a 50 cc China girl with a 39 alloy sprock bolted to the hub- it will cruise in the high 20's but I don't push it much- just enjoy the quiet smooth ride- I've thought bout going to a 36 on that which might lag in a string wind, but I live in flat Florida.
i noticed your small chain rings and large rear sprocket for peddle work on all 3 bikes.
i'm set up the same way. easier on these old legs to get across a busy interrsection and also to start the eng.
nice bikes !