Written by Jeff Frost
Myth: to make an engine take sharper curves, install blind tires.
Blind locomotive tires are tires that do not have flanges. The sketch shows a flanged tire and a blind tire. On the outside the tires have a lip that will bear against the wheel center for its proper placement on the wheel center.
The flanged tire has a 1:20 taper from the outside edge to the fillet and is a minimum of 5-1/2″ wide for standard gauge steam engines. The taper will help the wheels find their home on the track and keep the flanges from rubbing the rail on straight track.
The blind tire has a small taper on the inside and outside edges of the wheel and the center is turned straight. The blind driver is a minimum of 6″ wide for standard gauge steam engines. They are turned straight to allow them to move laterally on the rail when going around curves without creating extra resistance.
Blind drivers are used on locomotives that have a long rigid wheel base to help the engine take curves easier. Because blind tires don’t have flanges to keep them from walking off the rail, the tires are slightly wider and are also set so the back-to-back of the blind tires is slightly smaller than the back-to-back of the flanged tires.
With long rigid wheel bases, if all the drivers have flanges, that can create problems when going around curves as the flanges will bind on the rails. The driving axles don’t have a lot of lateral movement (3/16″ when new, 3/4″ is condemning) so by having blind drivers on the middle drivers, those wheels can move more than if they had flanges, making it easier to go around curves.
Some of the very early 4-4-0’s had blind tires on the lead driving wheels (the B&O #25, the William Mason is this way). The early 4 wheel lead trucks did not swing and pivot but just pivoted like car and tender trucks. By installing blind tires on the lead driving wheels, the engine was able to take sharper curves. With a swinging 4 wheel lead truck, blind drivers would not work as the front of the engine would be allowed to swing out of alignment of the track.
It is a common thought that for an engine to take a sharper curve the railroad should just install blind drivers. That is not really the case…
With a sharper curve, the lead and trailing trucks will need to swing more/farther away from the centerline of the engine. The rockers and swing links might not allow the extra movement needed to take sharper curves. The truck frames could interfere/bind on the locomotive frame if the engine takes a sharper curve. The lead and trailing wheels might hit the locomotive frame as they swing farther away from the locomotive centerline and closer to the engine frame.
For 1:8 scale
The IBLS standard for 1:8 scale tires is a minimum width of ¾”. There is no maximum width and many wheels are wider than ¾”. For blind tires, I would recommend having the blind tire be a 1/16”-1/8” wider than the flanged tires, having the straight turned part be around 3/8”-7/16” long in the middle and the tapers to the inside and outside of the wheel be around 5.5-6 degrees, with the prototype being 5.65 degree taper.
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Jeff Frost is the author of the book “The Live Steam Hobby“.
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