Grassroots Railroad Sports?

An interesting comparison of drive wheel diameter effect was on the PRR's Columbus-Sandusky line in 1956. There was a big coal traffic surge up to Sandusky and the Pennsy was short on operational power. They had tons of stuff in the dead lines but some of it had been parked since the Great Depression and couldn't be easily revived, the I1s 2-10-0s were beat to death, and the Q2s 4-4-6-4 Duplexes had all been kicked out of service with cracked boilers. So the Pennsy moved as many J1 2-10-4s they could spare and then leased a bunch of ATSF 5011-class 2-10-4s as well.

The big difference between the two engines was that the PRR J1s had 70" drivers (and there's a story regarding driver diameter there too) and the ATSF's 5011s had 74" drivers, the largest ever fitted to a 10-coupled engine. The consensus of the PRR crews was that while the J1s were worth a few more cars and were easier to start a train with, but the 5011s rode better at speed and could cover the Columbus-Sandusky run considerably. And of course the firemen preferred the oil-fired 5011s over the coal-fired J1s, but that's besides the point

Another that comes to mind is the Boston & Albany J-2 Hudsons. The B&A was a New York Central subsidiary, and had a much more sawtoothed profile than the rest of the NYC system, along with shorter hauls and a higher stop density with their passenger trains. Because they needed an engine that could handle hills better and accelerate away from stops faster, NYC took their J1 Hudson design, which had 79" drivers, and shortened them down to 75". Among other changes were the square sandbox with a higher capacity (for starting and climbing grades), and the short 4-axle tenders (no need for a high capacity tender with 200 mile runs, and it was less dead weight being towed around by the engine). The B&A was dieselized by the NYC fairly early on, since those diesels handled the grades even better, and the J-2s found themselves bumped into commuter service elsewhere in the NYC system, since those shorter drivers were nice for the frequent starts and stops of commuter service.

An easy way to get a little more speed out of an older engine design was to install thicker tires on the driver center to increase the effective wheel diameter. A visible example is on Frisco #1020, which was a 1910-built Pacific that Frisco dressed up for thee Firefly. They installed 2" thicker drivers to bump the diameter from 69" to 73", and then used a lot of sheetmetal to disguise that this was a 30 year old Pacific with a pencil-diameter boiler, tall shotgun stack, oddly large cab, and clunky Cole trailing truck. Note that the cars behind it are old clerestory roof cars that the Frisco disguised with balloon roofs and lower skirting to hide their age. This was a bucks-down effort, for sure.

Union Pacific's 4014 Big Boy is steaming through town again, on its way to Colorado. I didn't go this time.