The other thread seemed to be getting stale, so I thought I would report on the results of installing a 39 tooth sprocket on my 2016 T120.
I purchased a steel/alloy combo from Supersprox, in silver/black. The part number was: RSB1521-39, silver/black, drawing # 2012.
My bike lift was tied up with my Trophy, so for installation, I put the centerstand up on a 1" board to give the tire extra clearance for removal (not sure it was necessary). Removed both mufflers. Pre-checked the alignment by using digital calipers to see if I could measure the chain-bolt distances accurately. Measuring from the front of the aluminum block to the indent where the bolt screws in, I found pretty much equal distances of something like 1.83 inches on both sides. So I knew I could measure distances accurately on the setup, and that they were equal from the factory. I marked the outside flat of both bolts so I could keep track of turns, just in case.
Removed the axle, tying up the rear brake, changed the sprocket, using blue locktite with 55 nM torque, and with a bit of fussing, got the wheel back on. I turned the adjustment bolts in about 8 turns each. When done adjusting the chain, the clearances on both sides matched to something like 1.38 inches on both sides. I will double check the alignment with a string later, but for now it is definitely not out of alignment. The axle is now near the center of its movement, which makes one wonder if 39 teeth weren't planned, but they installed 37 teeth to meet Euro 4 specs.
As for the results, they are great. It is only about a 5% change, but it really makes the bike easier around town and starting off. It just seems more natural starting out from a light, etc. On the highway, 3,000 rpm is 65 miles per hour in 6th. It is not a huge difference from stock, but it is enough to be noticeable.
As others have found, I would say changing the rear sprocket from 37 to 39 teeth is worth the effort.
I purchased a steel/alloy combo from Supersprox, in silver/black. The part number was: RSB1521-39, silver/black, drawing # 2012.
My bike lift was tied up with my Trophy, so for installation, I put the centerstand up on a 1" board to give the tire extra clearance for removal (not sure it was necessary). Removed both mufflers. Pre-checked the alignment by using digital calipers to see if I could measure the chain-bolt distances accurately. Measuring from the front of the aluminum block to the indent where the bolt screws in, I found pretty much equal distances of something like 1.83 inches on both sides. So I knew I could measure distances accurately on the setup, and that they were equal from the factory. I marked the outside flat of both bolts so I could keep track of turns, just in case.
Removed the axle, tying up the rear brake, changed the sprocket, using blue locktite with 55 nM torque, and with a bit of fussing, got the wheel back on. I turned the adjustment bolts in about 8 turns each. When done adjusting the chain, the clearances on both sides matched to something like 1.38 inches on both sides. I will double check the alignment with a string later, but for now it is definitely not out of alignment. The axle is now near the center of its movement, which makes one wonder if 39 teeth weren't planned, but they installed 37 teeth to meet Euro 4 specs.
As for the results, they are great. It is only about a 5% change, but it really makes the bike easier around town and starting off. It just seems more natural starting out from a light, etc. On the highway, 3,000 rpm is 65 miles per hour in 6th. It is not a huge difference from stock, but it is enough to be noticeable.
As others have found, I would say changing the rear sprocket from 37 to 39 teeth is worth the effort.