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)
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7/8 Turn |
Vertical Rise | 4" 102mm | 4 1/4" 108mm | 4 1/2" 114mm | 4 3/4" 121mm | 5" 127mm | 5 1/4" 133mm | 5 1/2" 140mm | 5 3/4" 146mm | 6" 152mm | Helix Solutions | Space Required (l x w) | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Radius | 13.5" 343mm | 3.00% | 1 | 30" x 30" | 77cm x 77cm | ||||||||
| 14.0" 356mm | 2.90% | 3.00% | 2 | 31" x 31" | 79cm x 79cm | ||||||||
| 14.5" 368mm | 2.80% | 2.90% | 2 | 32" x 32" | 82cm x 82cm | ||||||||
| 15.0" 381mm | 2.70% | 2.80% | 3.00% | 3 | 33" x 33" | 84cm x 84cm | |||||||
| 15.5" 394mm | 2.90% | 3.00% | 2 | 34" x 34" | 87cm x 87cm | ||||||||
| 16.0" 406mm | 2.80% | 2.90% | 2 | 35" x 35" | 89cm x 89cm | ||||||||
| 16.5" 419mm | 2.60% | 2.70% | 2.80% | 3 | 36" x 36" | 92cm x 92cm | |||||||
| 17.0" 432mm | 2.40% | 2.50% | 2.60% | 2.90% | 3.00% | 5 | 37" x 37" | 94cm x 94cm | |||||
| 17.5" 445mm | 2.40% | 2.80% | 2.90% | 3 | 38" x 38" | 97cm x 97cm | |||||||
| 18.0" 457mm | 2.50% | 2.60% | 2.70% | 2.80% | 4 | 39" x 39" | 100cm x 100cm | ||||||
| 18.5" 470mm | 2.20% | 2.30% | 2.40% | 2.50% | 4 | 40" x 40" | 102cm x 102cm | ||||||
| 19.0" 483mm | 2.70% | 1 | 41" x 41" | 105cm x 105cm | |||||||||
| 19.5" 495mm | 2.20% | 2.30% | 2.40% | 2.50% | 2.60% | 5 | 42" x 42" | 107cm x 107cm | |||||
| 20.0" 508mm | 2.10% | 1 | 43" x 43" | 110cm x 110cm | |||||||||
| 20.5" 521mm | 2.30% | 2.40% | 2.50% | 3 | 44" x 44" | 112cm x 112cm | |||||||
| 21.0" 533mm | 2.00% | 2.10% | 2.20% | 2.30% | 2.40% | 5 | 45" x 45" | 115cm x 115cm | |||||
FAQ
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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.
- Find the column with your desired vertical rise in the heading row.
- In that column, review the grade options for each radius. Be sure to check the helix footprint in the "Space Required" column.
- 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.