Boom and Stick Length vs. Digging Force: The Real Trade-Off Behind Every Excavator Arm Configuration

2 days ago

4 min read

Most excavator buyers treat boom and stick length as a reach question and stop there: longer arm, more reach, done. What that framing misses is the actual trade-off happening inside the hydraulics every time a manufacturer offers a longer stick option — reach and digging force pull against each other on the same machine, and understanding why is the difference between speccing an excavator that fits your real work and one that just looks good on a brochure's reach chart.

What a Standard CAT 320 Arm Actually Delivers

CAT's standard 320 configuration, running a 5.7 m (18'8") reach boom with a 2.9 m (9'6") stick, digs to a maximum depth of 6,720 mm (22'1") and reaches 9,860 mm (32'4") at ground line. At that stick length, the machine generates 134 kN of bucket digging force under SAE rating — a number that exists specifically because that boom-and-stick geometry keeps the hydraulic cylinders working at mechanically efficient leverage angles through most of the digging arc. Operating weight for this configuration runs 22,700 kg (50,100 lb) with a 1.19 m³ HD bucket, 790 mm triple grouser shoes, and a 4.2 metric ton (9,300 lb) counterweight.

Why Reach and Force Can't Both Max Out on the Same Arm

A hydraulic cylinder's digging force depends on the leverage angle it's working through, and that angle changes constantly as a boom or stick rotates further out from the machine. Extend the stick and you move the bucket's working point further from the machine's pivot, which is exactly what buys you more reach — but it also means the stick cylinder is working at a progressively less favorable angle for most of that extended swing, which is why a longer stick configuration on the same base machine typically trades away some peak digging force to get that extra distance. This isn't a manufacturing shortcut or a flaw; it's the same lever-arm physics that makes a longer wrench easier to turn by hand but harder to apply full torque through at the very end of its swing.

Komatsu's PC210LC-11 makes this trade-off visible by actually offering it as a choice: the machine ships with stick options at 1,800 mm, 2,400 mm, or 2,900 mm, available in both monoboom and two-piece boom configurations. That's six genuinely distinct arm geometries on one base machine, and Komatsu publishes them as separate configurations specifically because a contractor digging deep basements wants a different stick than one doing shallow utility trenching at extended reach — there's no single "best" stick length, only the one that matches your actual digging profile.

How Far This Trade-Off Can Be Pushed

CAT's own 320 and 323 Super Long Reach configurations show how far that trade-off can be taken deliberately: a 174 hp SLR boom-and-stick package pushes maximum digging depth out to 37'10" and maximum reach to 51'1", against the standard configuration's 22'1" depth and 32'4" reach. Reaching that far means CAT adds a heavier counterweight on the SLR builds specifically to keep the machine stable with the bucket working at full extension — stability, not just force, becomes the thing you're managing once an arm configuration gets pushed this far past standard geometry. SLR configurations also typically require the boom and stick to be detached for road transport, a real logistics cost that a standard-reach machine doesn't carry.

Speccing the Arm to the Job, Not the Brochure

Deep basement, foundation, and utility work that needs real digging force close to the machine should default toward a shorter stick configuration, not the longest one available. Ditch cleaning, canal and pond maintenance, and any work where you're reaching out over water or an embankment rather than digging straight down is exactly where a long or super-long-reach configuration earns its added cost and reduced force. Most general excavation work sits comfortably on a standard configuration precisely because it balances both needs reasonably well — the specialized arm lengths exist for genuinely specialized work, not as an upgrade path for everyone.

Financing the Arm Configuration That Actually Fits Your Work

Excavation contractors, utility crews, and specialty outfits doing ditch or waterway work all depend on getting the boom-and-stick trade-off right for their specific jobs, not just the biggest reach number on the lot. The wrong configuration means either fighting a force shortfall every day or carrying reach capability you never use.

BFC finances and leases excavators nationwide, for startups and existing businesses, across every credit profile. We're a growth partner first — we'll help you think through reach versus force before you commit to an arm configuration. Apply for financing to get started.

For the full before-and-after on CAT's current medium excavator lineup, see CAT's Next Generation 320 and 323 excavators, and for hour-meter verification guidance on this generation of Komatsu excavator, read verifying hour meters on a used Komatsu PC210LC-11. You can also explore our full excavator equipment financing options.