Hub Motor Cooling Compared: Statorade vs HubSink vs Vented Covers
Three ways riders cool an overheating hub motor: Statorade ferrofluid inside the motor, HubSink fins on the outside, and vented side covers. Here is how they compare, and why most riders use the first two together.
The two bottlenecks
A direct drive hub motor makes its heat in the stator, in the middle of a sealed shell, surrounded by an air gap. The heat has to get from the windings to the shell, then from the shell into the air. Fixing only one of these leaves you limited by the other. More detail is in why ebike hub motors overheat.
Comparison
| Method | What it fixes | Keeps motor sealed | Notes |
|---|---|---|---|
| Statorade ferrofluid | Stator to shell | Yes | Grin measured heat conduction rising from 1.8 to 4.3 W/°C on one motor. Made no real difference to shell to air. |
| HubSink fins | Shell to air | Yes | 50 to 60% better shell to air cooling in Grin wind tunnel testing. Up to 20% more total heat flow on top of Statorade. |
| Vented side covers | Moves air through the motor | No | Lets in water, dust and grit. |
| Lower controller current | Makes less heat | Yes | Works by giving up power. |
Why use Statorade and HubSink together
Statorade moves heat into the shell and HubSink pulls it out of the shell. Together they give the biggest drop in motor temperature, which is what lets the motor handle more power. See how to run more power through a hub motor without overheating. Source: Grin Technologies and the Endless Sphere testing thread.
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Hub motor cooling FAQ
What is the best way to cool an ebike hub motor?
Heat has to get from the windings to the shell and then from the shell to the air. Statorade ferrofluid fixes the first step and HubSink fins fix the second, so using both gives the biggest drop in temperature.
Is Statorade or HubSink better?
They solve different bottlenecks. In Grin Technologies testing, Statorade made virtually no difference to shell to air cooling, while HubSinks improved it by 50 to 60%. Statorade substantially improved heat flow from the stator to the shell. HubSinks added up to 20% more total heat flow on top of Statorade.
Can I drill vent holes in a hub motor?
Vented side covers move air through the motor, but they also let in water, dust and grit, which is a problem for trail and wet weather riders. Statorade and HubSink keep the motor sealed.
Does cooling let me run more power?
HubSink does not make power. Your controller and battery do. Better cooling lets the motor handle more of that power without overheating, and HubSink guarantees at least double the power or no more overheating at your normal power.