Bicycle Mechanics - downtube shifter cable tension

How tight should the cable tension be when the shifters are in their most relaxed position? Taut? A half inch of movement? More?

They should be as tight as they need to be to consisitently shift into the next up gear.

The only reason they go slack in this last position is the travel limit screws on the derraileur takes the load off the cable. So really slack or tight at that point is meaningless. It is what it is. As long as your derraileur shifts up cleanly from adding in the next click then you're golden.

For friction shifting I like to have the cables just snug with almost no slack in the "most relaxed" position.

For indexing, you need to have the cable tight enough that the first click completes the shift but that is an automatic outcome of proper adjustment.

I usually have mine set so I can "pluck" them. If they are looser, then you have wasted movement in your shift levers as you take up the slack.

Thanks for the responses guys. I'm running friction on the front with an indexed rear.

It definitely is wasting travel with the front when getting out of the innermost ring due to its slackness now that I think about it. It also rubs a bit when in the loosest point (but for this I need to tighten up the limit screw).

My indexed rear is very slack at its loosest yet also is shifting smoothly. I guess I may leave this one alone if whether or not it shifts properly is the only concern.

For your indexed rear shifter, you'll need a tensioned cable for shifting to your second lowest gear (aka second biggest cog) for your indexing to work. Generally, there shouldn't be much slack in an indexed (or friction) shifter cable. You can have some play with your friction shifter shoved forward, but why waste shifting time and movement as you pull back and and take up slack. (Wouldn't want Tom B. to get the jump on you in a field sprint!) A tight cable, a taut ship, blah blah.

My indexed rear is very slack at its loosest yet also is shifting smoothly. I guess I may leave this one alone if whether or not it shifts properly is the only concern.
I am surprised this shifts properly but, since it works, I can't argue with success.

My experience is that for index shifting, either front or rear, the cable is pretty tight in the most slack position and moves the derailleur nearly immediately when the lever is moved. However, if yours shifts well certainly don't "fix" it.

Regarding indexed: Cable tension shouldn't be used as a metric to tell you anything. It is, how it is when it shifts fine. Some bikes need to have this tight, some have a bit of slack.

My indexed rear is very slack at its loosest yet also is shifting smoothly. I guess I may leave this one alone if whether or not it shifts properly is the only concern.

Mine too - whenever I change the cables I start off really tight but can't get the full range. Eventually I remember how loose it was and think to myself, "that can't possibly be right!" but it shifts great so no complaints.