I am not interested in speed just pulling and mountain climbing.
You can have the best of both worlds if setting your bike up with the optional SickBikeParts jackshaft sprockets, being a 9 tooth on the right hand side of the jackshaft and a 48 tooth on the heavy duty one way bearing.
The final drive only needs to be a 2 speed system (i have tried a 3 speed system, and it was pointless because i never used the midrange gear ratio) but you will still need to install the 30 tooth dished sprocket, to allow the chain to easily jump from the 24 tooth sprocket to the 36 tooth sprocket.
If you want to be a bit sneaky, you can order a 38 tooth sprocket with a 9 speed chain tooth relief that fits the heavy duty one way bearing, but you will have to hunt it down from another supplier, as it's not a stocked item at SickBikeParts. The 38T drops engine rpm (compared to the SickBikeParts 36T) by 300 revs in top gear at a theoretical 31 mph, keeping the engine below the heavier vibrations that occur upwards of 4,800 rpm. The 66cc engine doesn't make any extra power going over 4,800 rpm using a modified standard exhaust, so the 38 tooth sprocket works out perfectly. Another benefit is that the big end connecting rod bearing will last a heck of a lot longer if keeping max rpm below 4,800.
The best option for the rear cassette is an 8 speed system (being cheaper and in pratice, much better than a 9 speed system) using megarange gearing of 34T - 11T.
It's the 11T cassette sprocket that is the secret weapon in your gearing arsenal because it gives back useful road speed from the low range jackshaft ratio.
You'll be able to sit on 25 mph at 3,400 rpm, with a modified standard exhaust, and that's towing a trailer. Another benefit is that the 66cc engine has low vibration below 3,500 rpm with maximum torque at 3,800 rpm.
If installing Jaguar's torque pipe (and if the law allows you to get away with a pipe hanging off the side of your bike), you'll get even more midrange rpm pulling power.
The 34T cassette sprocket allows excellent hill climbing power, but a sneaky trick is to order a 29'er, nine speed cassette with a 36T sprocket and jailbreak both the 8 speed cassette and the 9 speed cassette, then replace the 34T sprocket with the 29'er 36T sprocket. This gives the maximum possible ratio spread on the rear cassette i.e. maximum possible pulling power (using low range jackshaft gearing of 9T - 48T) and the optional SickBikeParts 24T sprocket and acceptable road speed with low rpm using a 38T final drive sprocket to an 11T cassette sprocket.
Next point is to use 9 speed chain for the final drive, because it has narrower width to the outer side plates than an 8 speed chain, yet retains the same inner width as 8 speed chain.
This has significant advantages in that ghost shifting is eliminated because it allows for more mechanical error when running on the cassette sprockets, especially when operating in second gear with the chain sitting next to a 36T first gear sprocket, as shown by the photo.
