I'd get a geared hub if I lived in a less hilly environment, to take advantage of its pros, but I know I'd probably kill it in a few rides here. If they can come up with a way to shed heat, that would be a game changer.
In my MAC, I used distilled water and added Motul MoCool for corrosion protection. Worked great and it wasn't slippery if any leaked on the rear brake rotor.
Prior to the water, I tried low viscosity ATF. It cooled great but I got a tiny amount on my rear rotor and it made it feel like my bike sped up when I applied the brakes.
For a MAC, about 4.5-5.0 ounces is what you need to thermally connect the stator to the housing. A good bit less should work for a DD hub motor.
But in the long run, I chose to not run ANY cooling fluid and put my 10T MAC in a smaller/26" wheel. One nice thing about a MAC is you can change the motor from one wheel to another by just buying an extra shell/housing and lacing it to a different wheel. Back when EM3ev was selling the MAC, I bought a few extra housings and had them lace one to a 26", 27.5", and 29" rims so I can go back and forth depending on what size tire I want to run. My 12T MAC usually goes in the 29" wheel and my 10T usually goes in the 27.5" wheel with a
Schwalbe Super Moto-X 27.5x2.8" tire.
When I use the 26" wheel, I run a
26x3.0" Duro Beach Cruiser tire:
https://www.amazon.com/Alta-Bicycle...locphy=9011660&hvtargid=pla-673067767644&th=1.
For the 29" wheel, I use a
Maxxis DHR II 29x3.0" or a
Maxxis Hookworm 29x2.5". The DHR II works great on the pavement but it does wear a little quicker than the other tires I mentioned.
The tires above can be used with any motor. In addition, Schwalbe offers the "Pick Up" that is designed for Cargo bikes so it is pretty tough but the widest size is a 2.6". I have not had good luck with Vee Tires...a couple came apart and a couple got punctured fairly easily...they would probably be OK on a bike without a motor
.