Re: Limiting factors for speed of a steam locomotive

bcp Wrote:
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> I've read that the 110% guideline is pretty ac-
> curate in the mid range.  Large drivers have
> more room for proper balance weights, so can
> run faster than 110%.  Small drivers are harder
> to balance.

trainrider47 Wrote:
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> That old rule of thumb is exactly that, an old
> rule from the drag freight era. Modern engines
> such as 844, 611 and others could easily ex-
> ceed that limit due to improved counterbalanc-
> ing and improved pilot and trailing truck lateral
> control.  611 was even able to exceed driver
> diameter × 1.5!


Quite right on both counts -

It's an OLD rule of thumb, and "modern" steam engines with Boxbok or Scullin disk drivers definitely had higher top speeds than older engines with spoked wheels — especially narrow-gauge engines.  I used to wonder why the K-36 and K-37 engines – with their counterweights so close to the reciprocating rods – couldn't have been balanced better for higher speeds.  OTOH, they were primarily limited by the curvature of the line, with less than 30 miles or so of straight running between Alamosa and Antonito, so why bother?

- El Abuelo Histœrico, Greengo y Curmudgeoño de los Locomoturas Viejos y Verdes,
aka Der Grossväterlich DünkelOlivGrünDampfKesselMantelLiebHabender