Shimano Nexus Hub
Over the weekend I made a major modification to the trike. I exchanged the rear derailer and cassette gears with a new wheel with an integrated transmission. the main advantage of an internal hub transmission is super smooth shipping and the ability to shift when stopped. I chose the "red-band" Shimano Nexus 8-speed hub and had Harris Cycles build me a wheel around this hub. I chose this particular hub for it's gear range and high efficiency.
Instead of multiple sprockets and external shifter, the internal hub has just one sprocket and an internal shifter that locks various internal planetary gears. The gear range is determined by the number of teeth on the sprocket and the size of the wheel. I decided to choose my rear sprocket size based on the gear that I normally spend my time in, instead of trying to match my old gear ratios. The reason I did this is because the hub transmission is most efficient in 5th gear with a 1:1 ratio where the hub gets locked to the sprocket. According to my tests on the stock 11-34-tooth cassette I spent most of my time on the 20 and 17-tooth sprockets. For my initial setup I installed the 20-tooth sprocket. It was good enough to test the whole setup, but it was immediately obvious that this gear was too low. With the new wheel I had them send me a 20, 19, and 17-tooth sprocket. The 19 would be too close to 20 so I tried on the 17. I soon noticed that the 17t sprocked was too thick for my chain. I went to the local bike shop and he traded me my 20t for an 18t off a kids bike. He didn't have any 17t sprockets. I gave it a shot for about 50 miles and was happy, but it wasn't quite there yet.
After talking with Harris Cycles I found that they don't make sprockets with less than 18-tooth for 3/32" chains and they are all for 1/8" chains. I guess people would normally use the hub with a larger wheel than 20", so the bigger sprockets would be ok. Since I can't put a bigger wheel on the trike I decided to make the thicker 1/8" sprocket work with my 3/32" chain. So I used the table belt sander and milled 1/32" off the back side. After I tested it for fitting the chain I attached it to the hub. The size of the 17t sprocket is enough smaller than the 20t that I needed to pull off another link of chain. I don't need a chain tensioner, but I may have to play around with the rear idlers some. I haven't ridden with this new setup yet, so tomorrow is the day.
Instead of multiple sprockets and external shifter, the internal hub has just one sprocket and an internal shifter that locks various internal planetary gears. The gear range is determined by the number of teeth on the sprocket and the size of the wheel. I decided to choose my rear sprocket size based on the gear that I normally spend my time in, instead of trying to match my old gear ratios. The reason I did this is because the hub transmission is most efficient in 5th gear with a 1:1 ratio where the hub gets locked to the sprocket. According to my tests on the stock 11-34-tooth cassette I spent most of my time on the 20 and 17-tooth sprockets. For my initial setup I installed the 20-tooth sprocket. It was good enough to test the whole setup, but it was immediately obvious that this gear was too low. With the new wheel I had them send me a 20, 19, and 17-tooth sprocket. The 19 would be too close to 20 so I tried on the 17. I soon noticed that the 17t sprocked was too thick for my chain. I went to the local bike shop and he traded me my 20t for an 18t off a kids bike. He didn't have any 17t sprockets. I gave it a shot for about 50 miles and was happy, but it wasn't quite there yet.
After talking with Harris Cycles I found that they don't make sprockets with less than 18-tooth for 3/32" chains and they are all for 1/8" chains. I guess people would normally use the hub with a larger wheel than 20", so the bigger sprockets would be ok. Since I can't put a bigger wheel on the trike I decided to make the thicker 1/8" sprocket work with my 3/32" chain. So I used the table belt sander and milled 1/32" off the back side. After I tested it for fitting the chain I attached it to the hub. The size of the 17t sprocket is enough smaller than the 20t that I needed to pull off another link of chain. I don't need a chain tensioner, but I may have to play around with the rear idlers some. I haven't ridden with this new setup yet, so tomorrow is the day.
posted by Ashley Guy at 8:50 PM
0 Comments:
Post a Comment
<< Home