Speed

Speed is determined by the track, not the engine.  2 ft gauge track was probably good for 25 mph psgr, 10-15 mph freight.

Some DownUnder input on speeds

G'day Irish and all,

Ok let's look at this a couple of different ways:

For steam locomotives, unless you can do something fancy with the steam circuit, there is a practical limit of about 300 rpm maximum for a reciprocating steam engine. So working backwards from your wheel diameter gives a maximum  speed of   300 x  Pi x 44/12 x 60 / 5280 = 39.3mph absolutely flat out

A more realistic 200 rpm gives a speed of 26 mph. 

For a real 30" gauge railway operating steam and diesel locomotives in Australia, Puffing Billy has a absolute maximum speed of 20 mph with these locomotives

and

Some of the curves on this line are down to 2.5 chains (155' radius) and are speed restricted down to 5 mph. As Dave has pointed out the track can be the speed limiting factor, Another factor that limits the speed is your ability to brake a train and hold it against a falling grade.

On 2' gauge in Queensland similar bogie diesel locomotives are hauling 1500T sugar cane trains at speeds of up to 80 kph  (45mph) on 60 lb/yard raisl and concrete sleepers. 

I hope that this helps give you a handle on what might be possible (subject to some back-dating and geographical constraints)     

Speed

The Maine 2 footers must have been run by Maine-iacs...40+ mph was fairly common on straight track, and the Forneys had drivers as big as, IIRC, 38".  A mile per minute happened perhaps more often than was wise, and the loco was reported to be very steady--though the consist, not as much.  I guess that I'll schedule the passenger locos to a max SCHEDULED speed of 40 mph.

I would both love and dread riding one of those Forneys at speeds in excess of a mile per minute...

The Maine 2-footers had very broad curves for 2 footers because the locos did not have blind drivers, so the tight curves concern wasn't a major factor.  Higher speeds will be needed to keep passenger traffic as motorcars start getting better roads to drive on...

The diesel express may well, if the track is good, be able to break 70 as the roaring 20's wind down?

practical limit of about 300 rpm

I am having difficulty restricting practical steam engines to 300 rpm. The N&W J's and many other mainline engines regularly ran at about 100 mph on 70" drivers. At about 18.32 feet traveled per revolution divided into 8800 ft / min (100 mph) results in about 480 rpm. That is substantially higher than 300 rpm.

So for the examples the absolutely flat out speed could be as high and scary as 62 mph and the realistic speed could easily be 42 mph. If the stories are correct Casey Jones ran sections of his last run on April 30, 1900 at 80 mph on 54” drivers which would calculate out to almost 500 rpm.

actually achieved

It being late, my math-fu is weak, but I did some digging.  it was with 35" and smaller drivers that the SR&RL locos sometimes hit the insane speed of in excess of 60 mph, so that's some insane RPM's.  Clearly, the trackwork was able to handle the speeds, as the 2-footers had wrecks, but as far as I was able to read, none due to speed.  Sounds like a good,well built loco on good track could be scheduled for as much as 60 mph, if mainline broad gauge (as 4' 8 1/2" was sometimes known to the two-footers) engines were hitting 100 on 70" drivers.  Brakes and managing a train on a downgrade are other stories...

Though I ne'er expect to have room for mainline running, I'm trying to really put the line together in my head.  (And stay OFF the tracks of the Downeastern Cannonball is on the way...)

Driver Diameter & Speed

The magic number to remember is 336. That's the driver RPM at which the driver diameter in inches and the speed in miles per hour are identical. A D&RGW K-28 with 44 inch drivers would be moving at 44 MPH at 336 RPM.

Mike

Useful number!

That is a very useful number indeed--thanks!  Those Maine engineers were crazy indeed, since it sounds like those Forneys were running at close to 600 rpm--YIKES!  That's going to help me out a lot.

The Railcar...

....built from a Rolls Royce for the Rhomney, Hythe & Dymchurch (England) 15" gauge was known to do 75 mph!! But the guy the owned the line was a race car driver so he probably thought it was slow!