Hi Richard,
the first answer is very simple:
There is an old, everlasting discussion about what "G" Scale is.
So, as long as some people beating their heads, let me say that:
G Scale is MAINLY everything on 45 mm gauge.
That are scales from 1:32 upt to 1:19
But its also everything in scales between 1:32 and 1:29 that uses OTHER track than 45mm gauge.
Why?
let me give a try:
prototypical there are different gauges from several narrow gauges over standard up to broadgauge (spain, russia...)
If u calculate that down by scale u get different gauges in modelling.
Now comes the big chaos!
While gauge 1 is scale 1:32, its reduced quite heavy, what makes standard-prototype-stock looking nearly the same as the less reduces narrow-gauges in scale 1:22,5.
That means, while the gauge 1 standardgauge-track with 45mm has the same model-gauge as LGB narrow gauge track, the gauge 1 is reduced MUCH more from prototypical measurments. means: all u see in gauge 1 seems to be more fragile and fine as it will in gauge 2.
So does the rails.
Now, having completely different customers in mind, the manufacturers did what aimed on their customers:
the LGB narrow gauge had to become a durable toy, while most gauge 1 models are expensive high-detailed adult-models.
So, while the narrow-gauge modeling started to grew adult, the some kind of elitist gauge 1 scene tried to get the other customers with becoming less detailed and therefor cheaper.
Not to be "checked out" from other systems, some manufacturers tried to hold on on the 45mm gauge, no matter what it means in scale.
Others dont matter about anything like piko. They use scale 1:27 on 45mm tracks. that ist neither standard gauge nor narrow.....its just the measurement that makes standard-stock beeing nearly as big as 1:22,5 LGB to run on 45 mm track!!!
While the ones care less about, others are going to be detailed:
Bachmann has US rolling stock in 1:22,5 for a 45mm track. but looking on it, the calculation between gauge and scale doesnt fit. 1:22,5 and 45mm makes a European 1000mm-Gauge.
So the F-Scale came up: scale 1:20,3 what makes the 45mm track (to be able to use e.g. LGB-track) exactly the scaled gauge.
puzzeled?
yes, its weird.
but prototypical building, construction and operations are weird, too.
So with G-scale modelling, there are two mainstreams:
the one tries to fit EVERYTHING to 45mm gauge,
and the other that wants to have the exact downscaled gauge (or otherway round the exact scale for calculating from 45mm up)
more puzzled?
ok, i´ll stop.
If u want to use most used rolling stock, look to use the track they call "Code 332" or like this. That code just gives the heigth of the rail. That is as far as i know aristo, LGB, piko, thiel....
looks a bit clumsy, but is stable and works fine.
All other things are a bit for counting rivets, so its at yours to see what u want.
But dont wonder:
its the "rivet-counting-thing" that makes some layouts looking so extraordinary fine!!!!! Because the finest Details are balanced!
But there is no use having a perfectly scaled 1:20,3 scaled layout with exactly downscaled rails (some people differ between the used rails from different RR companies!) and then let run an LCE on it. And thats why the LCE (aka LGB or piko-locos) dont run on some tracks: toy meets pro-modeling!
Every branch has its right to exist....
Greetings
Frank