Originally Posted by boredom.is.me
20mm minus the wall thickness. Think about it. A 80% FSA with one of my 25/12 fans would yield a diameter of 18.76mm. Area of I.D. minus Area of hub equals FSA.
With the 25/OT you would need a diameter of 18.53mm. Just shoot for 19mm.
Do you know how many amps your 25/12 set up would pull with a Fiago 5800 on 3s? I'm wondering if the batteries would have to be bigger than this model could handle with that setup. You could probably get close to 1:1 with a 25/10 and a hi KV Losi on 2s I would think.