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15 inch curves

Started by wally, March 31, 2010, 09:00:12 AM

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Johnson Bar Jeff

Quote from: Jim Banner on April 01, 2010, 06:30:06 PM
I believe the problem with 4-4-0's is that the rear wheels do not swivel like the front ones do.  The front ones are much like a diesel truck and can swivel as a set.  The rear wheels are rigidly attached to the frame, at least as far as swiveling is concerned.  If the rear wheels are in a curve, they try to swing the front of the locomotive the same way - if the curve is to the left, the front of the locomotive swings to the left.  If this puts the king pin of the front truck over the center line of the track, there is no problem.  But if it puts the king pin to one side of center, the swing will put lots of side pressure on the wheels and off the track they come.  The problem is exacerbated by the distance between the rear wheels and the front wheels and is particularly bad in S-curves.

If you compare a 4-4-0 to something like a Pacific (4-6-2) which also has a 4 wheel pony truck, you will notice two things - the king pin on the Pacific is closer to the front drive axle than on the 4-4-0 and the front truck of the Pacific has some method of allowing side swing in addition to the rotation of the truck whereas the 4-4-0 does not.  While 4-4-0's in the real world can rock and roll down some really rough track, they cannot handle the extremely tight curve that a 15" radius represents.  Because of the side to side motion built into its leading truck, a model Pacific is more likely to handle 15" curves than a 4-4-0.

Except for the Mantua "General" and the Rivarossi eight-wheelers.  ;)

Thanks for the explanation, Jim.  :)

DaveMFnC

I know for a fact from experience that a Spectrum (Now standard line) 2-8-0 will handle 14-15 inch radius turns without a problem. I bent some flextrack to what I thought was 15" and undershot just a little bit, nevertheless, the 2-8-0 performed fine.
Getting back into the hobby, one guitar sale at a time ;)

ABC

Quote from: DaveMFnC on April 07, 2010, 01:16:41 AM
I know for a fact from experience that a Spectrum (Now standard line) 2-8-0 will handle 14-15 inch radius turns without a problem. I bent some flextrack to what I thought was 15" and undershot just a little bit, nevertheless, the 2-8-0 performed fine.
Not entirely correct, because Bachmann locos are unusual because some 2-8-0's may make 15" radius, but not all 2-8-0's will make 15" radius.Out of all my 2-8-0's only 1 would run on 15" radius and pretty poorly at that.