minimum switch frog radius number for 4-8-4? is a free Model Railroad Discussion Forum and photo gallery. We cover all scales and sizes of model railroads. Whether you're a master model railroader or just getting started, you'll find something of interest here.


New Member
What is the minimum frog number for a 4-8-4? I think a #4 frog turns into an 18" radius turn, but can the #4 frog on a switch be used safely (without derailments) on a 4-8-4? Or should I go up to a #6 for a good rule of thumb for minimum frog number? anybody?
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I have several 0-8-0s, 2-8-4s, 2-10-2s all Rivarossi that run 4s and 6s fine. The 611 Bachmann 4-8-4 does fine. My 2-8-8-2 does ok at slow speed but usually lifting the front truck is best. Good Luck, Tom


New Member
thanks for the reply.... Also, I know my bachmann daylight 4-8-4 (5449), can not do an 18" radius curve. Question is as long as I make the turn after the number 4 switch into a 22" minmum turn...will the 484 still make that #4 successful?


Coal Shoveler
My Proto 2-8-8-2 makes it OK, but I'm not blasting through at speed. My 2-8-4 also makes it OK.

These are Atlas #4s.



My other car is a 4-8-4
Keep in mind the Atlas #4's are actually #4.5's, and so are not as sharp a turn as an actual #4. So a loco that can make it through an Atlas #4 won't necessarily make it through a #4 from a different manufacturer.

For what it's worth, I have a Bowser 4-8-4 that can negotiate an Atlas #4 - at slow speed, and not very happily, but it will make it. My Spectrum 4-8-2 doesn't seem to have any problems.
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Only thing I know to do is lay it out on a temporary board and try it. None of mine have trouble on an 18 at slow speed though they look yucky.


I would go with a #6 it will look better and function better, Less likely for a derailments and you can go over them quick with no worries.

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