Well, you DO intend to cruise over 30 mph, correct? Faster? The build has to be able to reliably perform the task you intend for it, or you could lose everything you invested into the vehicle and then some. If you ever have a breakdown, you'll need a plan to get it home safely as well.
Front suspensions on mountain bikes can also have ball-joint failures. Such a failure has the potential to be an extremely unpleasant experience, and worse, if it occurs at speed.
On a front-suspension trike, I have been able to comfortably/safely/reliably cruise 35 mph using ebike components and non-crap mechanical disc brakes. And on roads that were known to be okay, have even cruised 40-45 mph, but an unanticipated pothole destroyed a steering spindle at 40 mph, and a racoon weeks prior to that was ramped and sent it airborne also at 40 mph landing on the wheel of the side where the spindle broke, and on tires rated for 32 mph. To withstand higher speeds than 35 mph without something critical to the vehicle's continued safe operation failing, I need stronger components all over the vehicle, especially since I ride in traffic with boobus Americanus. Anything less is opening the door to all kinds of unwanted and/or unpredictable circumstances when operating the vehicle at desired cruising speed. In my case, getting the rear-wheel caught in a pothole at speed could easily get ugly, where you have zero control over its direction until the rear wheel regains sufficient traction to accelerate. This makes rear suspension a necessity for faster speeds on bad roads in traffic.
If you intend to use a quality full-suspension mountain bike as a base chassis for this Leafbike motor riding on bicycle-grade components, you probably don't want more than 35 mph cruising speeds. You might get good results at even higher speeds with a dedicated downhill bike, but increased speed will quickly eat into your potential range because an upright ebike has as much drag as a decently streamlined small car(eg. Toyota Yaris) or more. 30 Wh/mile @ 30 mph can quickly turn into 100-150 Wh/mile @ 60 mph, which considering how light the vehicle is, the latter is extremely wasteful(There exist 2,500 lb electric cars that consume that amount of energy @ 60 mph). Requiring more battery. The Leafbike with mods can yield excellent results reliably, but without mods, at 72V, it's still a 2,000-2,500W continuous motor in the best of circumstances. With the right winding, that still might allow a 40 mph cruising speed without overheating on a fully stock motor, even on an unfaired upright bike. With motor mods like hubsink, that might become 3kW or more continuous without overheating the motor, and where continuous rating soon becomes less important than 1 hr rating given how quickly you can drain a battery using these levels of power. You'll need the motor's wiring sized accordingly. There are people who run these motors at 8 kW peak. You can have quite some scoot on such a light vehicle with this motor and rest of the bike prepared for the power/torque it can deliver. Taking off like a car is very doable. If you want the battery to last, you'll need to size it to where your typical use case uses no more than 50% of charge, then charge it to no more than 90% every day you use the bike.
If you want to use this motor's full potential without killing yourself, the bike will also need to be up to the task. I'm in the process of making mine up to the task. When mixing with cars in traffic, the vehicle needs to be able to perform like something akin to them if not superior to them in many facets to do so safely. That means braking, cornering, acceleration, wet weather performance, maneuverability, ect. at least comparable to a car. You mentioned roads with speed limits up to 65 mph, and earlier mentioned a desire for a 40 mph cruising speed.
A modest 96A phase current in a 20" wheel has the potential to wheelie your bike even in a 3T wind if you're light enough. The Phaserunner/Frankenrunner is capable of that. If you go to a higher turn-count wind, it's assured. I know this because my trike wants to go sideways at this tiny bit of current running through the motor with a 20" Schwalbe Marathon Plus round it. And that unexpected wheelie is the least of the things that can go wrong, because wheelies can be really fun if you know what you're doing. Better have good torque arms.
Which is why I'm throwing this out there. Hope you find the right chassis for the job you intend for it. You're getting a motor that's capable of a lot of performance for its weight. Make sure the bike itself can use it.
A fatbike? I'd initially trust it to like 30 mph, max.
Regardless of what you do, this motor will have no problem accelerating it up to speed. A Frankenrunner will do okay with this motor even in a 3T wind. It will be slower than most cars, but fast enough to quickly get into trouble. My 46.8V pack got me to over 40 mph with the body removed and I didn't even top it out, using a 3T in a 20" wheel in a Phaserunner set to 96A peak current and the CA3 set to 3,000W peak. A correctly sized Sabvoton could make it very dangerous to operate and would have no problem getting you quickly up to whatever speed you want. Make sure you really want to move at that speed on whatever it is you're riding, as it will be extremely tempting to push things to the limit on a regular basis.
I found out mine was good for 35 mph cruising over typical roads, even though it was capable of going significantly faster for extended periods without the motor or controller ever overheating and was quickly capable of reaching those > 35 mph speeds. And thankfully, I did not find out that 35 mph was the max safe cruising speed the hard way. Making a death machine is very easy! (And cool!) Is that what you want?
I spent a lot of time riding in a detuned 350W mode, as on flat ground, with the body installed, this was good for 30-35 mph with light to moderate pedaling. If I had 8 kW peak available, I wouldn't have gotten to use it much given what my max safe continuous cruising speed was, as I'd be there in a few short seconds from a stop. But your vehicle will probably have a significantly different energy consumption vs speed graph than mine. But even then, 8 kW peak would get an upright to over 50 mph pretty easily. And quickly. And the right-sized Sabvoton and properly selected battery pack could easily do it.
Do you really want that on a fatbike with fatbike components? A Phaserunner/Frankenrunner is perfectly capable of reaching above your target cruising speed of 40 mph, and it will get there "quickly enough", even if not nearly as quickly as the Sabvoton would. And it will probably be too much for your fatbike. 72V in a 3T wind motor might get you 60+ mph top speed with a properly-sized Sabvoton. The Phaserunner could do it for short durations before overheating and scaling back power. Which might make a higher turn-count motor more ideal for acceleration/torque up to whatever you think the safe cruising speed is for your bike if you're going to really run 72V.
In a 20" wheel, if you insist on 72V, you will probably end up with a 45 mph top speed using a Phaserunner/Frankenrunner in a 4T wind in a 20" wheel, if you limit the Frankenrunner to 2,500W. It will need a heatsink. Power will be the limiting factor to top speed. Your motor won't overheat, stock.
The Sabvoton with a 3T wind would make all kinds of unsafe operating conditions possible and include the capability of quickly destroying components, until you upgrade the motor with cooling mods and also the rest of the bike.
. Just wanted to make sure I understand what you meant. Thanks
