CJ wrote:I think the probable reason it works so well is the way Ergopower shifts. It was very noticeable during my measurements that there's a large over-travel on the downshift - much larger than with Shimano shifting. With this , the mech goes a good 2mm further before the shifter clicks – and then settles back. The settling back may leave it 1mm out, but the 2mm overshift has already carried the chain onto the sprocket – and apparently there are enough chain links between the guide pulley and the sprocket to accommodate the odd millimetre of residual misalignment without complaint.
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The overshift may well explain why it is more tolerant than might otherwise be expected. I also note that chains and sprockets just keep getting better and better too; they seem to increasingly either run relatively smoothly or shift, with less of that 'will I won't I' chittering and clattering inbetween.
Years ago overshift was something that was useful in pre-index systems too; using suntour powershift levers and suntour RD with a standard spaced block there were about four clicks per shift which meant that you could overshift a little (anything up to just less than one click); the downshift would go better and the alignment would still be perfect after the shift. Once click too many didn't always run sweetly after the shift though. I had one set of (cheap) shimano friction levers that had built-in overshift, i.e. there was some deliberate (I assumed) backlash in the RH lever between the lever itself and the friction clutch. With many setups this meant less post-downshift trimming than normal. However it presumably also meant that the RD was pulled hard into the limit screw every time bottom gear was selected, which I can't think was a good thing.
Related to all this is 'float' in the guide pulley. Without any float there is less tolerance to running whilst misaligned, and faster wear in the guide pulley teeth should this occur. There is presumably an interplay between 'float' and any sticking friction/stretch in the cable, as well as how abruptly the shift is made too, all of which would be expected to affect how well aligned everything is during and after the shift; however I wouldn't claim to understand how this all works exactly. However I do note that modern mech designs increasingly have little or no float in them; maybe this means that they shift well for longer as the mech wears in the pivots etc; it certainly requires that the indexing is more accurate if silent running in gear is to be achieved when everything is new; maybe some shimergo-type setups can only be expected to work well if there is 'float' present...?. Occasionally I've extracted 'the last five minutes' out of a worn RD in an accurate indexed system by replacing the guide pulley for one with no float in it. More often it has been 'wear vs float' when trying to get a system set up right and I suppose once a RD gets a bit worn an imperfect indexing system will be more likely to start to behave badly.
AndyA wrote: ...It indexes ok with half a turn of the barrel adjuster either way, it's not proven finnicky in use....
overshift or not, that is about as good as you can expect it to be, comparable with the tolerance seen in a system with all new matched parts, and (IME) more likely to keep working even when the RD gets a bit worn and the cables start to get a bit sticky.
cheers
