The radius shown for curves is the minimum.
It is recommended that where possible curves should be double that shown, plus an extra allowance
if speeds over 10 mph are likely.
Thus, for high speed running on 7¼, the radius should ideally be not less than 75 feet.

MODEL TRAINS.
The resistance of a model passenger carrying train can vary considerably.
Some years ago I measured the force required for starting and sustained movement of several fully laden passenger cars, and found that there was wide variation but all the figures were below 10 lbs. for different cars over a varying gradient.

Since then, I have used that figure as a rule of thumb.
However, it is too high for most modern passenger cars with ball or roller bearings, for which about half or three-quarters of that figure would be appropriate, on level track. Resistance rises dramatically on
gradients, being about four times as much for a 1:100 slope as it is on the level..

I am told that an average taken from a sample of modern passenger trolleys, in good condition, was about 8 lbs per ton load.

Drawbar pull.

The drawbar pull on model locomotives can vary widely, both with different models, and even with different examples of the same model.
Rough figures for typical models of the larger main-line prototypes (say, 4-6-0 size) , are, 39 lbs. for a 3.5" gauge loco, and 60 lbs. for a 5" gauge one.
However, around 90 lbs. has often been recorded for the latter.

Models of narrow gauge prototypes can easily give higher figures, whereas the smallest models, for
example, a "Tich" might be only 3 or 4 lbs.

When laying model track, remember to allow for expansion with changing temperature.
Set the gap according to the ambient temperature at the time.
80°F  = minimal gap;
60^o F = 1/8"
35-40^o = 3/32"
( This allows for an expansion of 12 ft lengths of aluminium rail, and would result in the gap closing to zero at about 85^o F.
Steel rail would need a gap of approximately half the above.)