Select a Helix Kit - N, 1 track

Step 4 of 4: Click a grade to see the helix with that grade, radius and vertical rise... (FAQ below the table)

3/4 Turn

 Vertical Rise 26" 660mm 26 1/4" 667mm 26 1/2" 673mm 26 3/4" 679mm 27" 686mm 27 1/4" 692mm 27 1/2" 699mm 27 3/4" 705mm 28" 711mm Helix Solutions Space Required (l x w)
Radius 13.5" 343mm 0 30" x 30" 77cm x 77cm
14.0" 356mm 0 31" x 31" 79cm x 79cm
14.5" 368mm 0 32" x 32" 82cm x 82cm
15.0" 381mm 0 33" x 33" 84cm x 84cm
15.5" 394mm 2.90% 1 34" x 34" 87cm x 87cm
16.0" 406mm 2.70% 2.80% 2 35" x 35" 89cm x 89cm
16.5" 419mm 2.60% 2.70% 2 36" x 36" 92cm x 92cm
17.0" 432mm 2.50% 2.40% 3.00% 3 37" x 37" 94cm x 94cm
17.5" 445mm 2.70% 2.50% 2.80% 3 38" x 38" 97cm x 97cm
18.0" 457mm 3.00% 2.40% 2.70% 2.80% 2.30% 5 39" x 39" 100cm x 100cm
18.5" 470mm 2.60% 3.00% 2.40% 2.70% 4 40" x 40" 102cm x 102cm
19.0" 483mm 2.30% 3.00% 2 41" x 41" 105cm x 105cm
19.5" 495mm 2.20% 2.50% 2.30% 3 42" x 42" 107cm x 107cm
20.0" 508mm 2.70% 2.20% 2.80% 2.50% 4 43" x 43" 110cm x 110cm
20.5" 521mm 2.60% 2.40% 2.80% 3 44" x 44" 112cm x 112cm
21.0" 533mm 2.30% 3.00% 2.10% 2.40% 4 45" x 45" 115cm x 115cm

FAQ

How do I select my helix from the table?

The table below lists Precision Model Railroad helix solutions which have the vertical rise shown at the top of each column.

  1. Find the column with your desired vertical rise in the heading row.
  2. In that column, review the grade options for each radius. Be sure to check the helix footprint in the "Space Required" column.
  3. Click your preferred grade for details of your helix.

HELP! I cant find a helix that fits my layout!!

If you are not able to find a helix that fits you layout, click here for our contact form. Tell us your available space, number of tracks, vertical rise, and preferred grade. We'll review your helix options and let you know what is available for your layout, including helix options not included in our store catalog. We're here to help you!

What do the blank cells mean?

Blank cells means there is no mathematical solution for a helix with that rise and radius (if there was, PMR would offer it!). This is because of one or more reasons:

  • The grade to achieve this rise would be too steep for model railroads.
  • The vertical clearance between the rail head and the lower surface of the next loop of the helix would be too low.

Why are there so few helixes below 15" radius?

Below 15" radius, only a few grades result in enough vertical clearance for a viable helix. at 13.5" for example, only 3.00% is viable. For 14", only 2.90% and 3.00% result in a viable helix. This means that if these helixes don't work for a given height, there is no solution.

Compare this to say 16" radius where we find helix solutions at 2.60%, 2.70%, 2.80%, 2.90% and 3.0%. With 5 different possible grades, it is much more likely that one or more of those grades passes through a given vertical rise.

In general, helix solutions are possible below 15" but more plentiful at 15" and above. Additionally, the larger radius results in lower grades which is beneficial for longer trains and reliable operations.