Recommend a rear sprocket size for TSDZ2 and NuVinci

[AF7JA]

Yesterday I was working on my commuter eBike. There were two things I wanted to accomplish. The first was to switch from 27.5" wheels to 26". The other was to install a NuVinci hub.

I had the Nuvinci built into a 26" wheel and all of that was ready. Most of it was the little stuff, putting tyres on, making the cables and the like.

One thing I noticed was that it was slower than I liked. I was able to start, with no issues in the highest setting on the NuVinci. The NuVinci has a 20 tooth gear and the front has a 42 tooth gear.

Last night I ordered a 14tooth cog for the rear. Here is the data from Sheldon's Gear Calculator, the assumption is 60 rpm and 26x1.5 tyres, the table is in mph. That 17.7 is very close to what I was seeing on my test ride last night:

I am thinking of changing that order to 13t:

I have a throttle, so I also calculated with a cadence of 80rpm:

I did look at the big TSDZ2 thread. The only mention of rear sprocket seems to be about going larger. I am also very open to the idea of a larger chainring. Any suggestions or thoughts??

 

[amberwolf]

Two points:

The NV hub has a torque input limit, beyond which it's possible to damage it, though you'll experience slippage before this happens most likely. I don't recall what the limit is, but craig calfee has a recent thread with the entire manual and the last page has it.

The smaller your sprockets are, the faster they wear, and the more possible it is for the teeth to slip upward on the teeth and skip under load. The larger the sprockets are, the more teeth are engaged at any point, so the better they handle loads and wear.

 

[AF7JA]

I went with a 14t sprocket and a 52t chainring. While I was at it I also installed a BMX chain, but that has little to do with speed.

Before the change, I was basically going about 17mph. After the change, I am easily hitting the low 20s'.

Sure, on long runs it would creep up into the low 20s' before, but it was a really slow process. I am going to say the calculator post in the original post was about right for the original configuration. At this point, it can quickly pull up to about 22. Keep in mind, this is using the original programming. It isn't a very strong motor, I am now actually using the gears.

At this point I am satisfied.