Yes if you have a long enough transition from flat to 4% i think a pair of them might be able to pull a couple cars up a 4% grade. otherwise Your problem is going to be unwanted uncoupling at the transition area. As the rear truck on the lead climbs and the lead truck on the one behind it is still flat it can cause the couplers to miss aligne and uncouple.
An excellent point above by tjdreams about the (grade) "transition area". I have used some steep grades in my N scale layout, and the transitions from flat to graded sections gave me problems with both uncouplings and derailments. Problems with grade transition areas can be specific to certain locos. For me, my Kato F3 A unit derailed at a certain grade transition, while the matching Kato F3 B unit had no problems there. Eventually I fixed the grade transitions, which was caused by my poor tracklaying, but it was a frustrating time. Also I discovered that Kato N-scale Unitrack is not a good fit for areas containing grade transitions. I would guess that any sectional track having built-in roadbed might not be a good match for use in grade transition areas. For me, the uncouplings and derailments at the grade transition areas were a bigger problem than the steepness of the grade. I am not a Z scale modeler, but I would guess that such problems would be at least as difficult in Z scale as they are in N scale.
Is it too late to add to this discussion the notion that it might be a good idea to differentiate the grade? starting at 1% to accomodate the change from level to rising, than soon up to 2%, with possibly 3% on straight stretches and in curves a lesser steep climb, because of forementioned factors (resistance). Here a rough sketch of what I am trying to explain: Btw superelevated track can easily be made by glueing a strip of evergreen strip on the trackbed (rubber /cork) on the outer rail of a curve. Cheers, Matt
I am wondering if it's also possible to gently press Unitrack in the center to achieve a slight bow in the track, so as to ease the transition. For a piece at the base of a grade, maybe place a wooden dowel or pencil at each end of the track piece and gently press down in the center, eyeballing the result and working until it looks right. I haven't tried this, but plan to when I get underway with my new railroad. The risk will be minimal, at most ruining one piece of track.
