Kadee #5 on Passenger Cars - radius?

[etwiggar]

So I did a search and came close, but not quite to the answer of my question.  So here goes.
I have the Bachmann North Pole and Southern passenger car set.  Actually 2 sets.  I've had them at least 10 years, and the couplers have finally gotten to the point of needing replacement.  The local Hobby store recommended the #5 as being the standard, most common coupler.  Much nicer...should have done this 5 years ago.  Except...when I shunted the train into the siding and bam...multiple derailments, cars tipped over...and my son informing me "Daddy...bash!"  That's when I discovered the radius clearance doesn't work as well as the replaced whisker type coupler.   
Some searching here leads me to think I need to ask for the #148.  The clearance I'm looking for is essentially two 18" radius curves in a "S".  Does the #148 have a wider swing clearance? (Not sure of the terminology here, sorry!)

[Len]

Kadee couplers have a more or less pentagon shaped end, while the original EZ-Mate couplers have more of a circle shape. So the EZ-Mates are able to swiing slightly more than the Kadee couplers. But this shouldn't really be an issue.

The real problem is the S-curve you describe. Especially with 18" radius track. With body mount couplers, the ends of the car move towards the outside of a curve. Put two curves in opposite directions, like an S-curve, and the ends of two coupled cars are moving in opposite directions as they go through the 'S', resulting in derailments. So any time you have an S-curve, you should have a straight section between the halves of the 'S' to prevent this. Ideally it should be at least as long as the longest car that will be going through the 'S'. But half that length is better than no straight at all.

Len

[etwiggar]

Well, the #148 worked OK.  It still pulls a bit thru the "S".  Per Len's advice I went ahead and added a 3" straight between the switch and the curve.  That fixed the problem without having to replace all the 5's I just installed! I think I am going to try and find some Kadee #146's, which have a little bit longer shank(??) than the 148.  Just to try them out and see if that works.