Like
Jay Strongbow posted above, it depends on your typical trainer speeds.
You'd probably want close shifting in the 14 to 20 mph range. Maybe your small chainring would have the closest shifts there.
Here's a chart of speed vs cadence on a typical 34/50 and 11-28 in 11 speed bike. Note that the 34 chainring has close shifts all the way to 20 mph. (Here's that setup on Mike Sherman's Gear Calculator,
34-50 & 11-28 if you want to change cogs or use different cadences, the charts update on the fly.)
View attachment 314460
Using a 52 ring instead of 50 adds .6 mph at 15 mph, to about .9 at 25 mph.
My Kurt Kinetic fluid trainer is a good steady workout for me at 14-16 mph. ( I keep the chart handy, since it's interesting to see watts at different levels of effort.)
I would guess that your trainer is somewhat similar. In any case, you can get on it and see the speed where you are spinning easy, and the speed where you are pushing hard, and that's the range you want the closest shifts.
If you are at the 19-22 mph range a lot, it would help to have a 16 cog and an 18 cog. (It's common for cassettes to have 14,15,17,19.) To get the 14,15,16,17,18,19,21, you probably need a 12-25.
From Kurt, watts at different speeds. Fluid trainers have a predictable wattage that goes up dramatically at faster speeds. Kurt trainers are similar to riding up a 1% grade, not a flat road.
Mph Watts
13 110
14 126
15 143
16 162
17 173
18 206
...
22 319
26 473
30 675
35 1005
Thanks, I guess I could have ignored the trainer part and just asked this: If you are riding on flat, unvaried terrain, does it really help keep things smooth to have as few >1 tooth jumps as possible? I realize that's a YMMV question. Anyway, likely going for the 12-25 or 11-25. Thanks.
I really like close shifts on flatter rides. I'll trade off some close shifts for low gears if it's hilly.
I have the
Abbey cassette tool that makes cassette swaps fast and easy.
To hang on fast-for-me rides, I've put on a 12-25 so that I have very close shifts at 20 to 24 mph, where I need all the help I can get. At 95 rpm, the speeds are 19.6, 20.7, 21.9, 23.3, 24.9 mph.
But at 15-20 mph or 25-35 mph, most cassettes are pretty similar. Those speeds are the 11-15 cogs on the two chain rings.
