Steam locomotive non history

[The Johnster]

A Stirling 8 feet single had 18 times 28 inch cylinders.Let us  rebuild it  with five feet drivers and 18 times 17.5 inch cylinders and  identical valve areas

Performance and piston velocity is unimpared.

The false idea was that big wheels rode better(Somehow true on uneven roads) and had better traction coefficient .

If true,electric trains would have 2 meter drivers today.

 

The idea that a better coefficient of traction could be achieved by larger drivers made the incorrect but perhaps understandable; the idea was that a greater 'footprint' area of the tyre was in contact with the rail.  This was a fairly scary proposition in the early days when, if you thought about it, this is predicated on a degree of deformation under load of the tyre and/or the rail, both of which are made of brittle cast iron.  Cornwall, mentioned above, seems to have been an attempt to provide the largest possible driving wheel diameter (you can't get much more than 10'6" in the loading gauge) in conjunction with the lowest possible centre of gravity, and the thing looks like it was designed for speed rather than traction.  It could do 80mph, not bad for the 1840s!  

 

The GW Harrison singles were an attempt at high speed as well, and could have probably run quite fast if they had ever been ballasted to actually grip the rails, and Pearson's Bristol and Exeter 9 footers were certainly designed with the idea of running fast, using the broad gauge's ability to lower the centre of gravity in relation to the track gauge to get away with what would have probably been a bit top heavy on a standard gauge loco.