Why hydraulic flow (GPM) matters more than horsepower for running attachments.

[Ryan Calloway]

We get a lot of buyers who fixate on horsepower when they’re shopping, especially if they plan to run attachments like augers, breakers, or grapples. It’s an easy number to latch onto. But when it comes to actually powering attachments, hydraulic flow usually matters more, and it trips people up constantly. So here’s the plain-language version of why.

Horsepower moves the machine. Flow runs the attachment. Think of horsepower as the engine’s overall strength, mostly about driving the tracks and turning the pumps. But your attachments don’t run off horsepower directly. They run off hydraulic oil being pushed through them. That push is your flow, measured in GPM or liters per minute. An auger spins because oil is flowing through its motor. A breaker hammers because oil is cycling through it. Not enough flow, and that attachment runs weak or slow no matter how much horsepower is on the spec sheet.

Two machines, same horsepower, very different attachment performance. This is the part people miss. You can have two machines with similar horsepower, but if one delivers more hydraulic flow to the auxiliary circuit, it’ll run a demanding attachment noticeably better. The horsepower number alone won’t tell you that. You have to look at the auxiliary hydraulic flow specifically.

Flow is speed. Pressure is strength. You want both matched to the tool. Flow (GPM) largely controls how fast an attachment runs, an auger’s spin speed, a breaker’s cycle rate. Pressure (PSI or MPa) controls how much force it can deliver. A good attachment machine balances both. But the mistake we see most is people checking horsepower, buying the machine, then discovering the auxiliary flow is too low to run the attachment they wanted at full performance.

What to actually do before you buy:

Find the auxiliary hydraulic flow on the spec sheet, not just engine horsepower.

Check the flow requirement of any attachment you plan to run. Augers, breakers, and mulchers in particular have a flow range they need.

Make sure the machine’s aux flow lands in that range. Too little and it underperforms. Way too much without the right setup isn’t ideal either.

Confirm the machine actually has an auxiliary circuit and enough of them if you want to run two functions at once, like a powered attachment and a thumb together.

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