So does anyone know the reason for the oversized wheels on the Thomas series Bachman stuff?.
They are built to “TOY” scale, not to prototypical. They are what they are, toys.
Bachmann wanted to give the model builders a bit more variety in ready made parts 
Travis Dague said:In the discussion of "Emily"'s scale over on the Bachmann forum, it is said that they are "Thomas" scale and are supposed to look like the TV program models, not the originals in the books. So blame the TV guys for taking liberties, not Bachmann!
So does anyone know the reason for the oversized wheels on the Thomas series Bachman stuff?.
Travis Dague said:To my eyes, they aren't oversize. Stirling Singles (Emily) had 8-foot driving wheels. Tank engines like Thomas usually had driving wheels in the 4'6"+ range. Carriage wheels (four-wheel) were in the 3'6" to 4' range. Goods wagons around 3' (with obvious variations for specialized stock). Tac can undoubtedly improve on my figures. The memory is fading.
So does anyone know the reason for the oversized wheels on the Thomas series Bachman stuff?.