Improving mid-range shifting
My New World Tourist can be adjusted to shift well either at the high end (small sprockets) or the low end (large sprockets). I haven’t been able to find a compromise that has it shifting smoothly throughout the range. It has twist grip shifters. Any suggestions?
There are two potential causes for this. The first would be the cassette spacing. Though rare, occasionally cassette spacing is not quite right. The result of this improper cassette spacing is as you describe, good shifting on the ends but not all the way through the range.
The other more comman problem is the allignment of the derailleur hanger. The hanger needs to be perfectly parallel to the wheel. If the hanger is bent a little, the shifting will suffer and no amount of adjustment will solve it.
Both of these problems will likely require a visit to your local bike shop. Most shops will have a derailleur alignment tool to check and adjust this.
The cassette issue is somewhat more difficult to measure. The cog center to center should be measured with calipers or a micrometer. With 7 speed systems, this distance should be 5.0 mm.
The other thing that could be influencing the shifting is the condition of the chain and cassette. It would be worthwile to check these things closely as worn drive train components can seriously impact shift quality.