(F) Wheelbase less than gauge?

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chris stockdale
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(F) Wheelbase less than gauge?

Postby chris stockdale » Tue Feb 02, 2010 6:43 pm

Apart from a 20" wheelbase Lister sans centre balance weights yet for two foot gauge, does anyone know of either locos or rolling stock where the wheelbase is less than the (narrow) gauge?

I ask 'cos I am looking for excuses for a coming build (or three). I'll do it anyway, but thought it might simply be nice to Gnow.

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Postby csundstr » Wed Feb 03, 2010 2:28 am

Wheelbases shorter than the track gauge are generally not very reliable without additional balance wheels front and back. The physics make it unstable and make tracking around curves difficult.

It was not unheard of for some four-coupled locomotives with pilot and/or trailing wheels to have close-spaced drivers. Some of the Porter four-coupled locomotives had wheelbases as short as 36" and gauges offered wider than this. I would suspect few were sold in this configuration.

It is also difficult to accomplish with wheels of any significant size and since driving wheels are generally relatively large to provide a higher effective speed for each revolution they are rarely spaced this close.

Looking at the basic mathematics, assuming 15" gauge track (this is the Gnatterbox), with a 12" wheelbase you could feasibly use driving wheels with flanges about 11 inches in diameter, allowing for some clearance and mounting brakes on the outside of the wheels rather than between the wheels. Wheels with 11" flanges have a running (driving) surface about 8.75" in diameter, which means to achieve each mile per hour of speed the wheel needs to rotate at about 39 RPM. Typical industrial locomotives move at 4 mph in many cases, so the wheels need to turn at 156 RPM. A Lister CS engine ca. 1958 generates 8HP at 850 RPM, which means you can only gain an advantage of 5.5x through gearing, which results in a locomotive with almost no hauling power at full throttle speed of 4 MPH.

Small diameter wheels means low maximum speed and lower hauling capacity relative to the available horsepower (due to less gearing advantage being available). Note that this isn't a linear relationship. Wheels can be too large for an engine as well (due to inertial concerns).

On the other hand it has been done. I've seen several photos of several early or home-built locomotives with pilot trucks that had wheelbases shorter than their gauges. These trucks usually had wheels in the 9 inch to 12 inch diameter range with a wheelbase of approximately 24 inches for a gauge of 36" or standard gauge.

You can also see examples on many old narrow gauge Plymouth DLC6 or similar gas mechanical locomotives that have been rebuilt for standard gauge. Have a look through the Plymouth sections of the following website:

http://www.northeast.railfan.net/diesel104.html

Good luck with your build, but you will probably find the locomotives and/or cars rock back and forth and don't track very well. Problems in real life are often magnified in the small scale.

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Postby rockershovel » Wed Feb 03, 2010 8:44 am

I would suspect that just because something appears in the Porter catalogue, doesn't mean any were actually built.

Porter built locos over a wide range of sizes from stock parts and as anyone with experience of this approach will know, there are always combinations which work well, and combinations which work less well; ones which sell and ones which are really only hypothetical. The optimum working ranges are always considerably less than the possible range of alternatives.

Shay built at least one 10-ton, 15" gauge loco, but they never built another; several 10 and 13-tonne x 24" gauge examples, but these are a very small proportion of total production. Double Fairlies were never truly successful in the larger sizes. The viability of the basic design was affected by the varying relationship of design constraints as size changed.

it's true that a number of early locomotives were built with close-coupled leading trucks, the Norris 4-2-0 types for example, but this was soon discontinued as experience was gained
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Re: Wheelbase less than gauge?

Postby Steve Bennett » Wed Feb 03, 2010 9:31 am

Chris Stockdale wrote:Apart from a 20" wheelbase Lister sans centre balance weights yet for two foot gauge


It was originally 15" gauge though and converted to 2' gauge in preservation, I believe. Rides like a rocking horse :lol: and I suspect a model built to similar proportions would have the same motion. An idea for an Emett type layout maybe :wink:
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Postby rockershovel » Wed Feb 03, 2010 10:01 am

it's worth bearing in mind that the Fletcher Jennings loco 'Tal-y-Llyn' was originally built as an 0-4-0 and converted at an early stage because of its rough riding and instability. The crude nature of the conversion, effectively giving it the fixed wheelbase of a long-wheelbase 0-6-0, meant that the railway had to be re-gauged to accomodate it; presumably the improvement was felt to be such that this was worthwhile.

'Sgt Murphy' has been converted from an 0-6-0 to an 0-6-2 for the same reasons, the ex-Penryn locos 'Linda' and 'Blanche' have acquired leading pony trucks..

I'm sure there are plenty more examples if you care to look for them, but the moral is pretty obvious


it does occur to me that there is at least one eimco in preservation in the US which is 42" gauge, most US coal mines using 36" or 42" gauge; this might well have a wheelbase less than the gauge, but for a vehicle which mostly only moves a few yards at a walking pace, and is already notorious for its instability and rough ride, this probably isn't an issue.
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Postby chris stockdale » Wed Feb 03, 2010 12:45 pm

On Page 62 of Slate Quarry Album (2nd Edition) by Gordon and Ann Hatherill I found a drawing of a Maenofferen rubbish truck with a wheelbase of 21" i.e. a smidge less than the gauge.

These were double flanged - whether that makes a significant difference I await expert input!


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Postby Steve Bennett » Wed Feb 03, 2010 11:50 pm

Chris Stockdale wrote:On Page 62 of Slate Quarry Album (2nd Edition) by Gordon and Ann Hatherill I found a drawing of a Maenofferen rubbish truck with a wheelbase of 21" i.e. a smidge less than the gauge.


Yup, the wheels are close together to make it easier to tip, it takes less leverage to upend them. Not what you want on a loco though :wink:
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Postby MilesB » Tue Feb 09, 2010 3:38 pm

From memory there was at least one standard Bagnall 7" saddle tank (7" refers to the cyclinder diameter) which have a 3'0" wheelbase, but was built (or rebuilt) to run on the Whitehaven Lime Co.s 4'0" gauge line at Nantmawr, at the east end of the Tanat Valley.

Thats a gauge 33% greater than the wheelbase :shock:

That's about the most extreme I'm aware of.

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Postby Brack » Tue Feb 09, 2010 4:16 pm

the decauville type 1 has a 2' 10"ish wheelbase, and according to the catalogue was available in gauges from 50cm to 1m (3'3"ish). though whether any of them were built to the larger gauge, I'm not sure, all the ones I'm aware of are 50-60cm.

(yes, I know the measurements should be in metric)


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