Poor Traction with some locos.

[Butler]

Hi

i have a reasonable size layout with 4 tracks OO in a complete loop. I mostly run EMUs and diesels, but have a good selection of steam locos too. I just find that I have so many problems running steam, especially large Pacifics . My tightest curve is 2nd Radius, but I run the bigger locos on 3rd Radius. All of my diesels will pull easily a 7 coach train around the tightest bend,  its the bigger steam that just slip. Well nearly all of them. But the smaller Standard Tanks, class 4 , Fairburn etc, Will pull the same train fine. I don’t get it. I have run Unrebuilt West Country fine, B of Brit, fine, but M Navy, Brittania, simply slip. Is this to do with the length of the loco wheelbase?

Any help appreciated

B

[ikcdab]

The coupled wheelbase might be a factor on tight curves. The longer the wheelbase, the more friction there is on the curve. 

Loco weight is also a factor. Some need more weight over the coupled wheels.

[Butler]

Hi

Thanks, funnily enough I just tried a Duchess on the same track, same load, no problems. That’s got to be one of the longest wheelbases, except perhaps 9x , but don’t intend running oneof those! Maybe a good clean up of track, wheels is called for. It is strange how some locos don’t run as well as others. I’ve found some ( mainly steam with bogies) derail more than others. I’ve got 1 tender that keeps derailing, I can’t see anything wrong. Maybe the wheel flange spacing?

B

[zarniwhoop]

2 hours ago, Butler said:

I’ve got 1 tender that keeps derailing, I can’t see anything wrong. Maybe the wheel flange spacing?

More commonly described as 'back to back' - you can get gauges for it, there have been innumerable arguments about what is the correct back-to-back for OO (in part, it depends on the dimensions of the check rails on the points).

 

But for plain track it doesn't really matter (although I suppose that excessively narrow wheelsets in the rolling stock may hunt, and on locos might reduce adhesion - but if so, moving the loco wheels out might lead to much higher friction on tight curves.

 

All I can add is that my only OO is a plain track test oval for running-in, with 18" radius curves (laid with a tracksetta gauge) and using a West Country with several carriages causes it to slow noticeably at the ends of the loop (the board is only about 3'6"x5'), the EMUs, 33s and 'Little Ed's (class 73) don't seem to slow quite so badly.

 

Oh, and clean wheels on both locos and rolling stock (avoid plastic wheels) help to reduce friction.

 

ĸen

[DCB]

It depends a lot on the age of the locos, a 1963 Hornby Dublo West Country should pull 20 plastic coaches, a new Hornby West Coutry might manage 6.   The curve resistance will usually mean the loco slips to a stand immediately it gets off the curve as the resistance helps the traction when pulling roud the curve.  Generally 7 is something I would expect most big RTR steam to manage on a level layout but they are rare, most people's level is 1 in 100 or worse.

Adding ballast is the logical answer, if you can get the loco body off but usually the speedo drive breaks or it doesn't come apart till you really tug it and then the hidden screw you  missed snaps a great chunk out of the body and you glue your fingers to the body with super glue while trying to repair it.  Then with the etra weight the drive gears strip.  Stick to diesels and Hornby Dublo / Wrenn locos or Cast white metal bodies on RTR Chassis.

[locomad2]

Much already said, one criticism of modern stock reviews is they don't publish pulling power in grams like model mags of the 60's and 70's. In mid 70's Model Railway Constructor compared up to then most locomotives and published haulage power in grams, I've still the article and prehaps up date it with locomotives more recent.

 

Adding weight helps but not all modern stock is easy to get at plus puts extra strain on running gear, motors and gears. One of my projects was to see if 100 Hornby dublo wagons can be hauled round a layout, with non pin point axles, a mighty weight. It broke a few locomotives either burnt out motors, de quartered wheels and sheared a 10BA bolt used as a coupling pin. Added to that lots of coupling got ripped off bogies, tender & wagon chassis. In the end only one managed it, & 2 got near.

[The Johnster]

The best you can do is to get as much weight in to the loco body over the driving wheels, which will improve pickup as well as haulage.  This is not as easy as it used to be as much space is taken in modern locos by DCC related gear; chips, servos, loudspeakers and such.  Once you have done this to the best of your abiltiy, have a look at the stock.  Most modern stuff runs freely enough but older stock may have less efficient bearings.  It may also have plastic wheels, which pick up dirt and do not run smoothly, and plastic axles which wear down easily and do not run well.  Check that all bogies can swing freely and have sufficient vertical play as well.

 

Also worth checking that your track is level, and the pieces are smoothly joined to each other, and that the buffers are not contacting on the curves, which will increase rolling resistance because the bogie or vehicle cannot run evenly on curve if it is held by the buffers.  The larger you can make the radius of your curves the better, and my practice is to make the minimum curve the next radius up from that recommended by the manufacturers.  I use Peco Streamline flexible  track with Peco medium radius turnouts on the scenic part of my layout, except for small radius for the loco release crossover, but have no,3 radius setrack and turnouts in the fiddle yard.

[bike2steam]

Lack of, or poor , lengthy running-in of a new loco, overloading a new motor, CAN cause poor traction.

 I've lost count of the number of times I've purchased a s/h loco off someone, who said it was a poor runner, slung away the motor, and replaced it, run it in properly, and found it no problem. Saved  40 or 50 quid on a loco for the sake of a motor for a tenner. 

[Butler]

Thanks for all the comments, invedentally what is the back to back tolerance supposed to be? Is it taken on the inside of the wheel ?

B

[Il Grifone]

20 hours ago, Butler said:

Thanks for all the comments, invedentally what is the back to back tolerance supposed to be? Is it taken on the inside of the wheel ?

B

 

It depends on the standard. The NMRA publish theirs andquote tolerances. Most British R-T-R up to about 2000 used the old Hornby Dublo standard with a B2B of 14.2mm*. No tolerance was quoted, but I try for +/- 0.1mm. Later Hornby used BRMSB standards*, again no tolerance quoted . nowadays it seems most wheels are to NMRA standards?

Note the important dimension is the check gauge (B2B + flange thickness.).

 

* Never specifically stated AFAIK, but they measured as I stated. (Rolling stock - I have never measured a later production locomotive, not possessing any.)

Edited March 27, 2021 by Il Grifone

[Sam Moss]

Also depends on the age of the locos. i had two Spam Cans at one point, identical models other than there was about 3 years between manufacture. The older one had much darker, brass tinted wheel plating compared to the new the one which was a much brighter nickel colour. The older walked all over the new ones from a traction point of view. 

 

[Il Grifone]

Nickel wheels tend to be more 'slippery'. 3 rail dublo locomotives with non-plated wheels seem to have more grip than the nickel ones.

 

I forgot to say the B2B is measured between the inside edges of the wheel flanges. The NMRA website covers it all in detail.