Wayne...I presume driver size is the wheel without the flanges. If so, they scale to 51.65". Took the measurement with calipers....
BTW...Spectrum is Bachmann's line of "fine" models.
That's correct, Gus, the size is measured over the wheel tread. Looks like the drivers are too small, and the price too big.

Wayne,
What project do you have in mind?
I'm planning to build a TH&B Gs Consolidation, Marc. I purchased a Bachmann Spectrum to use, as outlined by the TH&B Historical Society's "Focus" magazine. While the resultant model looks good, the over-size drivers sorta bugged me. I have an old Bachmann 2-8-0 (the Reading model) with 60" drivers, but it would probably need to be repowered. Just now, while I was hunting for this stuff, I found that I already have the wheels and chassis


I actually used the TH&B's lettering scheme as a model for that of my Grand Valley locos.
Bachmann's latest 2-8-4 was also under consideration for my TH&B interchange, but I don't think that the 201/202 were ever used in Port Maitland.
Wayne