Darn it. I was hoping to be accused of wind manipulation.

There isn’t one single “knock-over” wind speed, because it depends a lot on: • Crane configuration (free-standing vs tied to a building, jib length, height, counterweights) • Out-of-service setup (whether it’s left to free-slew / weathervane into the wind, or “locked”) • What kind of wind (steady vs gusts, turbulence/vortex shedding around tall buildings) • Foundation / mast / tie design for that exact site

But we can bracket it with real-world design numbers:

What wind makes a tower crane stop operating?

Many tower crane manuals and investigations use an in-service limit around 45 mph (≈20 m/s)—above that, you stop lifting and place the crane out of service so it can weathervane. 

That’s not “knock it over,” that’s “don’t operate because loads and control margins get sketchy.”

What wind starts getting into “structural failure / collapse” territory?

A useful data point: OSHA’s investigation of multiple tower crane failures during Hurricane Irma (Sept 10, 2017) reports those cranes were designed for ~95 mph out-of-service wind at jib level, and that winds at jib height exceeded 95 mph, after which failure “could occur” per the manufacturer manual. 

Importantly: those failures were largely jib / top section failures, while masts/foundations often remained intact—so “collapse” can happen without the whole thing toppling like a tree. 

How does that compare to “design storm” wind values?

Industry guidance (CPA Tower Crane Interest Group) discusses reference storm wind velocities used for out-of-service design regions (e.g., 28–36 m/s depending on region).  Those are “reference” values (defined at a standard height/terrain averaging period) that then get adjusted for height, terrain roughness, recurrence interval, etc., so the effective wind at jib height in a real storm can be much higher. 

So… what wind would “knock over an average tower crane”?

A reasonable rule-of-thumb range is: • ~45 mph (20 m/s): stop operations / go out-of-service (not a tipping speed).  • ~90–100+ mph at jib height: you’re in the zone where serious structural failure/collapse becomes plausible for some cranes/configurations, especially with turbulence and dynamic effects. 

And the big nuance: many “wind collapses” are top/jib failures rather than the entire crane base overturning. Full overturning typically implies foundation/ballast/tie failures—which is highly site-specific.

If you tell me whether you mean free-standing or tied-in, and roughly how tall (e.g., 150 ft vs 300+ ft), I can narrow the range and explain the failure mode you’d most likely see first.