steam loco question

[nw-mailing-list at nwhs.org]

Just to complicate things, many street railway vehicles have  
cylindrical wheel treads rather than the 1 in 20 (?) taper that's  
characteristic in "steam" (as opposed to electric) railroad wheel  
treads.  Of course, the slippage of one wheel vis-a-vis the other is  
a bigger problem with street railways, which may have curves as sharp  
as 40 feet in radius.  The wear patterns on the inner and outer rails  
of street railway curves are a little different, but I haven't heard/ 
decided whether its the inner or outer wheel that does the slipping.   
(I'd bet on the inner wheel.)  Wheel profile is a big deal in rail  
transit systems, governed mainly by how much street running is involved.

I've read somewhere that the main reason for tapered treads is to  
reduce flange contact on tangent track.  Obviously, the "differential  
effect" of tapered treads will differ enormously depending upon the  
curve radius.

Since the original questioner focussed on steam locos, that obviously  
lack differential gearboxes, it has occurred to me that perhaps he  
didn't realize that standard RR equipment uses fixed wheelsets.   
About the only exceptions are Talgo passenger trainsets and some low- 
floor streetcars that have independently-suspended wheels.

pete groom

On Jun 27, 2006, at 7:51 PM, nw-mailing-list at nwhs.org wrote:

Yes there is a taper with the inside of the driver being slightly  
larger in diameter than the outside.  Does that work?  Well, I did a  
little math last night taking a 56" diameter driver on a 1000' radius  
curve through 180 degrees.  I won't do the math here but it turns out  
that the outside driver would have to make almost exactly one more  
revolution than the inside driver, or go about 14 feet further over  
better than 3000.  So what diameter on the outside driver would do  
the trick?  56-1/4" !

Harry

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