I would like to know where I can find a 100 tooth sprocket for # 25 chain. Since I am having trouble getting a front sprocket smaller than 9 teeth, my only other option is to go larger than 89 teeth on the rear sprocket. The final setup would be 9-100 sprockets for about an 11:1 reduction. Note than it doesn't have to be exactly 100 teeth but anything close to that such as 98, 102.... Also note that the bolt holes need not line up with my E-300s as I can have those drilled. Even a split (2 piece) sprocket would be acceptable.
The only option we know about for a #25 sprocket over 89 teeth is having the sprocket custom made by Rebel Gears. http://rebelgears.com/customsprockets.html
It doesn't seem worth the cost to get a rear sprocket larger than 89 teeth. It appears there would be some clearance issues with 100 tooth rear sprocket and since I am already at about a 10:1 reduction (9:89 sprockets), adding 10 teeth to the rear is similar to just subtracting 1 from the front. I already have an 8 tooth sprocket but am trying to figure out a way to get it mounted. It does NOT have a D bore on it and the bore in too small to go on the motor shaft. If I had a machinist bore it out and make the D bore, the chain would hit the motor shaft and not rest of the teeth properly. No easy solution to get it to work that I know of.
I wish someone would mass produce these 100 tooth sprockets for # 25 chain. It appears the E300s will accommodate it, perhaps with just a little but of modding to make it fit. Even better would be if someone made a motor with a 2:1 reduction built in but without an offset sprocket, then very little change in the stock sprockets would be needed, perhaps just dropping it from 11 front to 9 front to get it to 40% of the original top speed (6 MPH instead of 15 MPH). That should work well offroad.
Also, I noticed with my low "gearing" 9-89 sprockets that I am getting great mileage. That makes sense cuz to go half the top speed takes about 1/4 of the power but I am only going half as fast so the battery "distance" should (in theory) double. I was seeing about 10 miles on a pair of used 7Ah 12V batteries. I suspect using a pair of properly cycled good quality 9Ah batteries instead, 15 miles per charge would be possible on flat pavement with no strong headwinds. That, at about 7.5 MPH top speed (9-89 sprockets), would take about 2 hours. That is much longer than the advertised "up to 40 minutes" on a single charge. It is actually triple (3 times as long).
I called Rebel gears and they seem to want about $60 shipped for an aluminum sprocket in the 100 tooth range for # 25 chain. That is quite a bit more than I paid for the 89 tooth I have now. It won't even fit on my E300S without first modifying the rear motor mount cuz it is in the way of the chain for anything larger than about 89 teeth. Not sure yet if it will be worth the money. I would actually like to get 108 teeth so then with the 9 tooth front, that will be a 12:1 reduction with a top speed of about 6.5 MPH (10 kph) on flat pavement.