Steam Pulling Power observations

[mike_lawyer]

Hi guys,

Over the past week, I have been conducting some tests of my N scale steam locomotives, in particular two Kato Mikados with GHQ pewter shells, and two Broadway Limited M1a 4-8-2s.  I am operating with 21 inch radius curves.  Rolling stock is a mixture of MTL and Atlas freight cars with low profile plastic wheels.  I do have a decent number of 50 foot boxcars in that string of cars.

At the outset, all of the locomotives are very good pullers.  The Kato Mikados can haul about 35 cars easily, probably more.  One of the tests I conduct is not only how many cars can thr locomotive pull when starting on straight track, but also how many cars can each locomotive reliably start on a curve?  The Mikados can start about 35 cars from a stop on a curve.  Beyond that and you get some wheel slippage.

For the BLI M1a's, I found that I can reliably haul about 30 cars, including starting on a curve.  That is pretty impressive straight out of the box.  One con however is that the traction tire driver is spun only by the siderods.  I have found that the traction tire drivers on both locos can sometimes not make complete contact with the rails where there might be slight dips in the track.  I have  noticed slight eccentricity on the traction tire drivers on both M1s.  This can cause wheel slippage at startup under heavy load.  Both M1s can start trains of about 30 cars on curves, and can probably haul 35-40 cars if starting the train on straight track. 

[brokemoto]

I do not have any experience with Original Poster's locomotives except for the Kato 2-8-2 and those only with the plastic shells from the factory.  I do not recall my trying any more than twenty or twenty five cars and a caboose on straight and level.  I seem to recall that I could get twelve or so loaded MT gondolas and a MT wood caboose up a one per-cent grade at twenty SMPH.   The best on that were the MP 2-6-0 and the B-mann SPECTRUM 2-8-0. They would pull fifteen of those loaded gondolas and the MT wood caboose up that one per-cent grade at twenty and fifteen SMPH, respectively.  The 2-6-0 is re-fitted with a B-mann SPECTRUM USRA standard tender.

On a 2,2% grade, the 2-8-0 would get ten loaded gondolas and the caboose up that hill;.  the 2-6-0, only nine.

I run smaller to average sized steam.  On the MPs, the traction tire does much for the 2-6-0. It does not do much for the 4-4-0.

The two that are anemic that surprise me are the modified B-mann USRA 0-6-0 and the MDC/Athearn 2-8-0.  While swapping in any of the SPECTRUM  tenders will markedly improve the performance of the 0-6-0.  still, its pulling power is not that much.  Someone (@SkipGear  [?])did mention that moving the driver pair with the tires does improve the pulling power,  I have yet to try this.  The MDC/thearn has two pairs with tires, but this does not seem to help it.  The MDC/Athearn 2-6-0 does better.

[randgust]

One of the 'genius' things of the Kato Mike is that the drawbar is through the trailing truck, which in turn is mounted right behind the trailing driver.

Most N scale steam puts the drawbar connection on a post under the cab.   If you have a trailing truck, you have to think what that does on a curve.  It REALLY wants to yank the locomotive sideways under load, which does three nasty things....

1)  Messes up whatever lateral design is in the frame for flanged driver movement through curves
2)  Forces the lead driver against the outside rail, increasing likelihood of derailment, literally crabbing through it.
3)  Forces the rear driver HARD into the lower rail, which may compromise contact of the traction tire.

Now, put in any vertical hump or dip and watch that lead driver climb off.  Now, go to smaller flanges, it gets much worse.

I don't know about the BLI design, but I ended up moving the drawbar for my Life Like 2-8-4 up behind the rear driver, and what a difference that made.
I've noticed that even my rebuilt Trix Decapod goes reasonably nuts under heavy load in curves, fighting all of the above, only combatted by playing around with washers on the drivers to cut down on the crabbing.

It's really a design flaw.  You really want that tender drawbar as close to the last powered axle as humanly possible

[mike_lawyer]

Agree completely with the drawbar observation, that is a real advantage for the mikado.  Also, the Kato Mikado has a real advantage with the traction tire driver not being connected to the siderods.  On the M1s, with the traction tire only connected to the siderods, it creates a slight eccentricity such that the traction tire simetimes makes intermittent contact with the rails under heavy load.  I am not sure why more manufacturers do not make traction tire drivers that are disconnected from the siderods and powered by axle gears, as to me it is a superior design for traction.

[TVRR]

Agree completely with the above comments, I'm rather surprised that the latest MP 4-6-2 has outstanding pull for a small steamer. Mine will pull an 8 car Kato passenger string without any difficulty and 25-30 40' freight.