Originally Posted by
stedalus
You've cherry-picked some nice corner cases there, which I respond to below, but the real point is that NDS and front tension don't have anything to do with each other. There is a spec for tension that applies to DS rear and front, or one for each. NDS is whatever is necessary to get the dish right. On a typical modern wheel, NDS tension will actually be a fair amount less than the front tension. On more exotic wheels, it might be greater, but it's not a sign of a better (or worse) wheelbuild as long as everything else checks out.
With a 145 mm OLD, there's very little dish in that wheel. With a typical 130-135mm hub, your NDS tension is not going to be so high. Also, I don't know what gauge spokes you're using, but based on those readings either your DS is overtensioned or your front is undertensioned (at least according to the specs you quote).
I've never seen that drastic a difference in spoke tension for front and rear, but I admit I have no experience with paired spoke and/or low spoke count wheels. In any case, I'd bet that the NDS tension is less than 140.
I used the tandem because I don't have an MTB, the tandem's wheels are much more highly stressed than any touring bike, and because the OP hasn't told us what his dropout spacing (DOS) is. However, if he's running 32H touring wheels and 1.6" tires, it seems to me there's some possibility that he's got 135 DOS. Never heard of a road tire dimensioned at 1.6". And that tire is sure not going to work on a 15mm road rim.
But even if he's running 130 DOS, I think you'd be wrong in your original assertion about tension: if he tensions his DS the same as his front, his NDS will be too low. On a 130 rear DOS bike, the front tension should be between the DS and NDS tension. All my road bikes are like that, and I never break spokes. A tourer trying to tension a wheel has to have something to go by, and plinking the front spokes will give him that, assuming that the front wheel was originally built correctly.
That's all he has to do: bring the rear tension up until his spokes are all tight, the wheel is round, and the wheel is dished correctly, i.e. rim same distance from the brake pads when inserted normally and 180° from normally. Then plink the rear spokes and the front, and adjust all rear spokes by the same amount, a little at a time, until the front plink is between the rear plinks in tone. Then readjust the dish, which will now be a bit out.
Spoke tensions are a little like tire pressures. We try to get them to come out to spec, but there's going to be some variation, which I attempted to indicate by the "~" symbol, and there is a good bit of leeway in the exact tensions. You're right that the NDS spokes on the Rolfs measure at less than 140 lbs. I should have gone out and measured them, instead of only relying on Rolf for info.