absurdtools

Trad Rack Builder

Which cam fits a given crack, how well it will sit, and the whole Camalot range drawn to scale for comparison.

What fits

The whole rack, to scale

Z4 #0
7.5–11.8 mm
Z4 #0.1
8.8–13.8 mm
Z4 #0.2
10.4–17.5 mm
Z4 #0.25
12.4–21.2 mm
Z4 #0.3
15.3–26 mm
Z4 #0.4
18.7–33.2 mm
#0.3
13.8–23.4 mm
#0.4
15.5–26.7 mm
#0.5
19.6–33.5 mm
#0.75
23.9–41.2 mm
#1
30.2–52.1 mm
#2
37.2–64.9 mm
#3
50.7–87.9 mm
#4
66–114.7 mm
#5
85.4–148.5 mm
#6
114.1–195 mm
050100150200 mm

Why the ranges overlap so much

Look at the bars: every size overlaps its neighbours heavily, and that is deliberate rather than wasteful. A crack is not one width — it flares, it pinches, and the good placement is often two inches from where you first tried. Overlap is what lets you find a piece that fits the constriction rather than the average.

Aim for the middle of a cam's range. A cam near full expansion is close to tipping out and is the classic way to place something that looks fine and is not. A cam fully closed is usually solid but can be genuinely impossible to retrieve, which is how cams get left on routes. Somewhere around half to two-thirds retracted is the sweet spot.

Ranges here are the published Black Diamond Camalot C4 and Z4 figures, because they are the de facto reference other brands are described against. Other manufacturers differ, sometimes by a useful amount at the small end — check your own gear rather than assuming a colour means the same thing across brands.

How to use

  1. Measure or estimate the crack width.
  2. Find the cams whose range covers it.
  3. Aim for placements in the middle of a cam's range.
  4. Build a rack from the rock you actually climb on.

Frequently asked questions

Why does a cam need to be in the middle of its range?

Because a cam placed near the tips of its range holds poorly and can walk or pull. Too open and there is little camming action left; too closed — over-cammed — and it may be impossible to remove. The middle of the range is where the mechanics work as intended.

What is cam walking?

A cam moving deeper into a crack from rope movement and vibration, often ending up somewhere it fits badly or cannot be retrieved. Extending placements with a sling reduces rope movement at the cam and is the standard prevention.

How do I know if a placement is good?

Both by the cam's position in its range and by the rock around it. A perfectly sized cam in a flaring crack, behind a loose block, or in soft rock is not a good placement. Reading the rock matters at least as much as reading the cam, and it is the part that takes experience.

What should a first trad rack contain?

That depends heavily on the rock you climb — granite cracks and limestone pockets demand very different racks, and gear from a partner or a shop's advice for the local area beats any generic list. A single set of cams and a set of nuts is the common starting point, extended from experience.

Do cam ranges differ between brands?

Considerably, and colour coding is not standardised — the same colour means different sizes across manufacturers. Mixing brands on a rack is normal and works fine, provided you know the actual ranges rather than relying on colour.

Is this enough to start placing gear?

No. Trad climbing is learned from experienced partners or instructors, on the ground first and then on easy terrain, and judging placements is a skill that cannot be read. This tool compares sizes; it does not teach protection, and nothing here is instruction.

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