New E Fat bike build help!

[Tcmcec]

I’m new to this group and electric bikes. But I own an electrical contracting company and grew up racing motocross so I feel I should have no problem tackling the build and riding a fast ebike.

I’m looking for some info on good reliable conversion kits, batteries, controller, donor bike, etc etc

Here is my wish list:
- 40mph+
- rear hub drive
- pedal assist
- 20 minutes of full power ride time
- dirt bike style twist throttle
- budget is 1500-2000 US

Any advice would be awesome.

 

[e-beach]

I’m new to this group and electric bikes. But I own an electrical contracting company and grew up racing motocross so I feel I should have no problem tackling the build and riding a fast ebike.

I’m looking for some info on good reliable conversion kits, batteries, controller, donor bike, etc etc

Here is my wish list:
- 40mph+
- rear hub drive
- pedal assist
- 20 minutes of full power ride time
- dirt bike style twist throttle
- budget is 1500-2000 US

Any advice would be awesome.

Hi Tcmcec. Welcome to ES!

Let me start by saying at least you have a reasonable budget in mind. Most who want 40+ mph usually don't realize the cost of a bike that can take the stresses of 40mph+. What nubees don't think about is that the weight of the batteries and motor cause inertial forces that most bikes are not made for. If you want to go 40+ mph for a short time, a lot of high quality bikes can handle it. If you want to go that fast for long periods, (and speed is addictive) then a high quality downhill bike is what you want along with moped tires. (16 inch moped tires on 20 inch bike rims? )

For that kind of speed you will need higher then average voltages. Start by thinking 60v or higher. That means a controller that can handle it. If a controller is listed as being able to handle a high voltage it probably can. Otherwise if you have a generic controller you may have to open it and check out the specs on the caps and fets to see what voltage it an handle.

For higher torque, you will need more amperage. (Generally speaking, volts = speed, Amps = torque)

Your motor will apply torque forces on the rear dropout that will deform your dropout unless you use a torque arm. Especially if you are using regenerate breaking. Torque arms are always an issue with adapting a bike because the dropouts are not made for motors. If you can find a bike frame with flat rear dropouts then it is easier to find a functional dropout. Dropouts that can clamp around the axle are always an advantage.

The cheapest and most energy dense batteries are RC Lipo from places like Hobby King, but they are also the least stable and if handled improperly can burn your house down. Just ask Dogman Dan!!!

All lithium calls can burn, but the least energy dense cells, like LiFePO4 are less of a risk.

For motors and batteries check out these sites first to see what they offer:

Ebikes.ca
Em3ev
Yescomusa 26in Rear Electric Bicycle Motor Conversion Kit 48v 1000w

Edit: And remember the best place to put your battery pack is in the triangle. It is the best place for the weight. (think motorcycle engine.)

And read-read-read everything you can on ES because it has all been done before.

 

[dogman dan]

Yeah, doable for that budget, but maybe no so much, if you want a really good riding bike.

Trying to say, just the bike alone for that quality ride pushes 3 thou these days. But in between, there is a tolerable ride there in the used MTB's, that are now maybe 5 or more years old, but were not ridden to death yet.

What you must avoid, is anything in that category of an MTB that you buy new for less than 300 bucks. You simply need real shocks on it for starters, and some decent frame rigidity. Bike shaped objects just won't do. I have ridden even the best of that category, and gotten semi tolerable ride, but not really very good. The cheap stuff does not have shocks with dampening or adjustability, they are simply springs. You rode the motorcycles, and will be severely disappointed in the ride of a BSO type bike.

Fat tires are not for speed as well. stick to 26" MTB, and put as wide a tire on it as possible. Later maybe, with more budget, go to moped rims and tires.

For the motor, a larger, more powerful rear direct drive motor is the ticket, and usually 72v power if you want up to 40 mph.

Lastly, I also wanted a fatter tire for sand, plus a bit more speed than fat bike tires inflated to 10 psi tolerate. I found my solution very cheaply in a honda 100. In fact, it handles better than any of my more budget bike based e bikes ever have. But,, its handicap is that it is simply not allowed on the single track bike trails in my area. So I still ride both, e bike on the trails, and the honda on roads, or other trails not in the national monument bike trails system. Those trails and roads are open to motorcycles, quads, jeeps.

Part of my decision to go back to gas, was just because that type of motorcycle riding roads is huge in my area, and starts at the end of my driveway. Its just too good not to be riding both. But the tore up jeep roads just don't ride well on bike tires. Too steep, too rocky, etc.

 

[Tcmcec]

Thanks for all the great info. After doing a bunch of research I think I’m going to go with a 1500w rear hub, 40 amp controller and a 52v 17.5 or 20ah battery. I realize it won’t have the speed I want, but I think it will be plenty for a fat bike setup. Besides eBay, Amazon, ebikes.ca, and em3ev, is there any recommendations for kits and parts. Em3 seems to have the best pricing on batteries.

 

[Bullfrog]

Tcmcec,

Others have better recommendations if you really want to go 40 mph. If you do, stop reading now and ignore everything below except the vendor recommendations.

Might check with "Mad Rhino", he has a good bit of Direct Drive experience and is very helpful...I didn't see him post on this thread yet. Direct Drive is definitely the way to go if you want to go 40 mph.

How are you going to use this bike...on pavement, off road, or both?

The reason I ask is I would highly recommend a mid drive BBSHD if you are going to mainly ride off road.

If you plan on riding hilly terrain and off road, a MAC geared hub motor (12T is my favorite) would be my recommendation.

And lastly if you are going to ride fairly flat pavement and/or basically commute, Direct Drive hub motor.

Don't know if this will work for you but I took Mongoose Hitch fat tire bike (steel frame) I bought at Walmart and put a Suntour Raidon fork on it, Maxxis DHF 27.5x2.8" front tire by changing front wheels and used a Maxxis FBR 26x4.00 rear tire. Went with a 14s6p battery with HG2 cells (allows extra amperage if you upgrade controllers), and the BBSHD motor. Geared it with a 30t front and a 22t White Industries 72 engagement point freewheel in the rear. That is my off road set up and it works great with a top speed of about 20 mph.

I am an old MX racer too so excuse me if I missed the boat on your intentions . We race through the single track trails now and it hurts when you crash at 20 mph but not as bad as faster speeds...it just takes a loooong time for me to heal up now :lol: .

EM3ev for batteries is the way to go.

Grin Tech has good everything.

California ebike carries more of the little pieces and parts you'll need.

All have awesome customer service...of course I like to support Grin Tech since they make this forum possible and I use the heck out of the Motor Simulator they provide.

 

[jpacadd]

Another vote for BBSHD in a good used mountain bike.

Big advantage to BBSHD is that the bike transmission changes the gearing for the motor.

My stock controller BBSHD gets up to 35mph fairly quickly and easily goes a half hour at full throttle with my 17.5ah bottle mount batteries. You can get larger batteries.

If you want to go faster you can buy the BBSHD from Luna and get the Ludicrous controller, which IIRC boosts power by 50%, that is if your battery BMS will allow it. Not difficult to bypass the BMS though if you want to risk it. I have not done this but others have.

My rig is a 2009 Giant Trance X3 with Fox suspension and hydraulic disc brakes, works awesome as an off-road ebike. https://www.reddit.com/r/ebikes/comments/eudj5t/40_today_so_took_the_bike_out_and_found_this/

 

[dogman dan]

Fat bike tires are NOT for 40 mph. Go with a big fat tire on an MTB.