First Build, know what I want, not how to get there.

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theloadedquestion

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Hello all,
I currently own a fat bike ebike I got for free as an abandoned package (I work in shipping). Best score ever! It has got me hooked and I've put over 300 miles on it in the just under 3 months I've had it, but now I want more power, and, being a huge nerd, have proceeded to try and learn everything I can about electric vehicle and battery technology, and am ready to embark on my first build/modification.

As the title says, I do know pretty much exactly what I want from the bike I will build, from performance to riding conditions, but the part where you guys hopefully come in is that I'm not entirely sure how to get to that end result. First here's a picture of what I am starting with, and for economical reasons really hope I can use in my build and still achieve my goals.

KUHc4c7.jpg


Made by dj-ebikes it comes stock with the bafang 750w hub motor, a 25A controller, and a 48v 13Ah battery with no information on it's max continuous amperage capability or bms, and I can't get any answer from dj-ebikes on that either. So, I'd probably want a new motor, new controller and lcd display, and a new battery to run it all, but use the rest.

So, here is the performance I'm after, as well as the conditions and terrain I plan to use it in.
- A top speed of 35-40mph
- Decent torque/acceleration (125 N.m.+)???
- Desired range @ 20mph 20-25 miles
- Climb relatively short but steep hills with ease
- Road/Commuter riding (minimum performance needs)
- Trail/Offroad riding for fun (where I'd like it to shine)
- Western Washington weather, mild and plenty of rain
- Budget around $600 (excluding battery)

I know a heavy fat tire bike isn't the most nimble option for serious trail/downhill riding, but with my current budget that "perfect" ebike will have to wait until the next build.

The motors and kits I have been looking at are:
MXUS 4504 3000w (4t) - Haven't found paired with a good "kit"
Leafbike 1500w snow fat bike conversion kit
https://www.leafbike.com/products/b...h-snow-fat-tire-bike-conversion-kit-1081.html
kun ray electric fat bike motor kit 72v 3000w - $450
https://www.aliexpress.com/item/4001116307016.html
Leili 3000w 72v electric fat bike conversion kit - $600-800 (seems to vary widely)
https://www.ebay.com/itm/Leili-3000...-or-Regular-Tire-Conversion-Kit-/123326859463
niubo 5000w/72v ebike kenda fat tire conversion kit - $699
https://www.ebay.com/itm/Niubo-5000...878602?hash=item1cef99318a:g:NI0AAOSwYy9fIlFT

Most of these are a tad out of my budget but if that's what I need to get the bike I want then so be it. But aside from these choices I'm very open to any other suggestions. Maybe even not buy a kit at all, but the individual components? That seems more expensive from my research, but probably better performance.

And then, of course, the battery. This will be a 48v or 52v build, that part is for sure. But what sort of capacity, max continuous discharge, and bms would I need for my goals? For instance will cells rated at 10A max continuous in a 14s4p configuration do the trick? And what about bms? I keep seeing so many pre-assembled batteries sold come with 30A bms, which seems weak, but maybe I'm not understanding something, or maybe the packs are made with low C, low A cells, I don't know. I'd be open to buying a battery but that frame makes me think I might have to build my own due to lack of room in the triangle. The most "powerful" batteries I can find are sporting a 50A continuous bms, but that's probably good enough for my needs?

Hopefully I've covered my needs well enough for some good feedback, but I'll also gladly answer any questions if it will help.
Thanks!
 
I run a leafmotor 1500w kit. 52v, 40a controller/BMS, 14s5p battery.

Top end 37.5mph (only when battery is fully charged then after 3-4 miles will start to slow). At 50% battery it tops out at about 31mph
Range nailing it 20-25miles 100% to 40% ish.
Don't know torque but it's quick.
Laced on a 26" 2.25" tyre @40psi
I weigh 75kgs
Bike weighs about 30kgs ish I'd say
Pulls about 1800w max fully charged on acceleration.

So I'd say for what you want you'll want 3k ish and a bigger battery. Maybe 14s8p.

Sent from my CLT-L09 using Tapatalk

 
40 mph in mountain trails is very fast for any hard tail bike, on fat tires especially.

I suggest targeting torque instead of speed. 30 mph does seem well enough for that bike IMO. You just need the power to make it in the mountain, and that would be a major improvement already.
 
Sell that bike, and get a very high quality full suspension DH bike as a starting point.

Your desires equal small motorcycles, and requires a much stiffer frame, rugged suspension, and wide tires, but not fat low pressure tires. Many actually put their strong rear hub motors into moped rims, and run motorcycle tires at least in back.
 
MadRhino said:
40 mph in mountain trails is very fast for any hard tail bike, on fat tires especially.

I suggest targeting torque instead of speed. 30 mph does seem well enough for that bike IMO. You just need the power to make it in the mountain, and that would be a major improvement already.
Click to expand...

The 35-40 mph top speed is for commuting on city streets, not trail riding. The torque and acceleration I'm targeting, which I did mention although maybe not specific enough, is for the trail riding, where I will essentially never top 20-25mph, and that only rarely. This will be a dual-purpose build, a specialty, full eMTB style build will have to wait until next time. Thanks man.
 
Hickbeard said:
I run a leafmotor 1500w kit. 52v, 40a controller/BMS, 14s5p battery.

Top end 37.5mph (only when battery is fully charged then after 3-4 miles will start to slow). At 50% battery it tops out at about 31mph
Range nailing it 20-25miles 100% to 40% ish.
Don't know torque but it's quick.
Laced on a 26" 2.25" tyre @40psi
I weigh 75kgs
Bike weighs about 30kgs ish I'd say
Pulls about 1800w max fully charged on acceleration.

So I'd say for what you want you'll want 3k ish and a bigger battery. Maybe 14s8p.

Sent from my CLT-L09 using Tapatalk
Click to expand...

Thanks, this is useful. I'd probably be running it on a 52v 18Ah pack with a 50a bms, or something thereabouts, but I think the stock controller is only 40a, so I'd have to swap that out I think? I was strongly considering the leafmotor 1500w but I also kind of want something with room to upgrade in the future, maybe a 3000w that I can run at 52v, but can also upgrade to 72v at some point if I desire (I probably will)
 
dogman dan said:
Sell that bike, and get a very high quality full suspension DH bike as a starting point.

Your desires equal small motorcycles, and requires a much stiffer frame, rugged suspension, and wide tires, but not fat low pressure tires. Many actually put their strong rear hub motors into moped rims, and run motorcycle tires at least in back.
Click to expand...

I've considered that. Two things stop me from going that route. My concern that it would become a money pit project, getting completed god knows when at who knows what outrageous cost. And two, this has become my commuter bike, saving me $20+ a day in uber costs, and if I sell it for a whole new build I will have nothing to ride in the meantime, and will be back to spending all my spare (potential ebike hobby) money on uber. So yeah, like I said in the OP, my perfect, dedicated eMTB build will have to wait for a future project, and instead my goals for this build are more modest and focused on versatility (and frugality), with the potential to be repurposed in future builds for more power (the main reason I'm looking at 3000w motors instead of 1500w motors).

For this build I'm looking for modest performance in both categories, city street commuting, and light to moderate trail riding. I'm looking for a modest 35 mph or so top speed on the city street for commuting, and reasonable toque and acceleration for the trails.
A 3000w rated motor may be a bit of overkill for my relatively modest goals with this build, but I was mostly considering that route for the potential to repurpose it later in a more dedicated, high power build. But that would be at some unknown future date.
Thanks man
 
Anyone used this motor/kit?
https://www.aliexpress.com/item/4000111726045.html?spm=2114.search0302.3.84.485b7e52icmVWP&ws_ab_test=searchweb0_0,searchweb201602_0,searchweb201603_0,ppcSwitch_0&algo_pvid=c133ff7a-23e5-4791-acf7-868d48ec6585&algo_expid=c133ff7a-23e5-4791-acf7-868d48ec6585-11

Seems like a too good to be true price, so it probably is.
 
theloadedquestion said:
Thanks, this is useful. I'd probably be running it on a 52v 18Ah pack with a 50a bms, or something thereabouts, but I think the stock controller is only 40a, so I'd have to swap that out I think? I was strongly considering the leafmotor 1500w but I also kind of want something with room to upgrade in the future, maybe a 3000w that I can run at 52v, but can also upgrade to 72v at some point if I desire (I probably will)
Click to expand...

You need more volts, not amps.
Comparing going from a 40A to 60A controller (120A phase amps) . No change in speed.
https://www.ebikes.ca/tools/simulator.html?motor=Leaf%205T&batt=B5220_GA&cont=C40&hp=0&axis=mph&cont_b=cust_60_120_0.03_V&motor_b=Leaf%205T&batt_b=B5220_GA&hp_b=0&bopen=true

Comparing same 40A controller with higher voltage battery:
https://www.ebikes.ca/tools/simulator.html?motor=Leaf%205T&batt=B5220_GA&cont=C40&hp=0&axis=mph&cont_b=C40&motor_b=Leaf%205T&batt_b=B7223_AC&hp_b=0&bopen=true
 
theloadedquestion said:
Anyone used this motor/kit?
https://www.aliexpress.com/item/4000111726045.html?spm=2114.search0302.3.84.485b7e52icmVWP&ws_ab_test=searchweb0_0,searchweb201602_0,searchweb201603_0,ppcSwitch_0&algo_pvid=c133ff7a-23e5-4791-acf7-868d48ec6585&algo_expid=c133ff7a-23e5-4791-acf7-868d48ec6585-11

Seems like a too good to be true price, so it probably is.
Click to expand...

It is a common motor and the price is fair. You have to consider shipping cost.
 
If that really is a 750 watt hubmotor (I have my doubts) then you can probably replace just the controller, verify if you have enough power, then get a bigger, better battery. Most likely you can get to 30MPH with just a better controller. If you really want 40MPH, then do as others say and start from scratch.
 
LeftieBiker said:
If that really is a 750 watt hubmotor (I have my doubts) then you can probably replace just the controller, verify if you have enough power, then get a bigger, better battery. Most likely you can get to 30MPH with just a better controller. If you really want 40MPH, then do as others say and start from scratch.
Click to expand...

Tried that already. First thing I tried and wasted $120 on a 35a KT controller I can't use lol.
 
still wrong tire for 40 mph, dirt or street. Ever hit a manhole cover at 40 mph and done a rear wheel wheelie at 40 mph? I have, and its not fun. 40 mph commute bike needs serious tires, sturdy frame, and rear suspension. your bike has none of that.

I never said what you want will be cheap. But don't listen to us, who have poured money into that pit. Ride what you got if saving money is the goal. I did, and in 5 years I saved enough to clear $20,000 in charge card debt. Instead of a new car payment or old car maintenance costs, I rode enough to put that payment to old debt.

You gotta decide what you want, save money on your commute or go fast. I'm a notoriously cheap bastard, which is why I rode 300cc scooters for the last few years, and just upgraded to an old but well running bmw touring motorcycle. I balk at spending what a good 40 mph e bike costs.

However, you can build a 40 mph bike on the cheap, for fun on the weekend. It won't stand up to a long daily commute, but will be a blast on saturday. Start with a cheap piece of shit full suspension bike. Then get a cheap ass 48v 1000w direct drive rear hub kit for it. For a brief ride, say 40 min, those hubs can take 3000w. Then get it a 40 amps 72v controller, 3000w. For battery, you run 20s RC lipo battery from hobby king. 10 ah max, because if you run 15 you ride long enough to melt the motor. You will have 40 mph out the door, and 35 mph for the rest of the ride. VERY fun.

if you want to commute on this thing, then you need to run it on 2000w. 48v 40 amps. only 30 mph, but 2000w will still take off from the stop light real nice.
 
LeftieBiker said:
Well, the controller does have to be compatible with the motor. :(
Click to expand...

Oh it's compatible all right, it's just not realistically installable due the to hardwired nature of this OEM build. It's easier to just replace the whole kit, and will get me closer to my goals anyway so that works.
 
dogman dan said:
still wrong tire for 40 mph, dirt or street. Ever hit a manhole cover at 40 mph and done a rear wheel wheelie at 40 mph? I have, and its not fun. 40 mph commute bike needs serious tires, sturdy frame, and rear suspension. your bike has none of that.

I never said what you want will be cheap. But don't listen to us, who have poured money into that pit. Ride what you got if saving money is the goal. I did, and in 5 years I saved enough to clear $20,000 in charge card debt. Instead of a new car payment or old car maintenance costs, I rode enough to put that payment to old debt.

You gotta decide what you want, save money on your commute or go fast. I'm a notoriously cheap bastard, which is why I rode 300cc scooters for the last few years, and just upgraded to an old but well running bmw touring motorcycle. I balk at spending what a good 40 mph e bike costs.

However, you can build a 40 mph bike on the cheap, for fun on the weekend. It won't stand up to a long daily commute, but will be a blast on saturday. Start with a cheap piece of shit full suspension bike. Then get a cheap ass 48v 1000w direct drive rear hub kit for it. For a brief ride, say 40 min, those hubs can take 3000w. Then get it a 40 amps 72v controller, 3000w. For battery, you run 20s RC lipo battery from hobby king. 10 ah max, because if you run 15 you ride long enough to melt the motor. You will have 40 mph out the door, and 35 mph for the rest of the ride. VERY fun.

if you want to commute on this thing, then you need to run it on 2000w. 48v 40 amps. only 30 mph, but 2000w will still take off from the stop light real nice.
Click to expand...

Awesome, thank you this was very helpful. I really would be happy with 30-35 top end speed, maybe 35 true top, 30 or so as a realistic cruising top speed. But you have brought up some great points here and stuff to consider. Thanks again.
 
dogman dan said:
still wrong tire for 40 mph, dirt or street. Ever hit a manhole cover at 40 mph and done a rear wheel wheelie at 40 mph? I have, and its not fun. 40 mph commute bike needs serious tires, sturdy frame, and rear suspension. your bike has none of that.
Click to expand...

Okay, a couple questions. Frame and suspension I understand completely, but what exactly is so bad about bigger tires? I would think that would be a plus for this application, not a minus. And after all, motorcycles made for street use have pretty fat tires, not skinny little bicycle tires? And there are plenty of fat tire kits and motor laces in the 3000-5000w range, but if they are dangerously unsuitable for those power levers, why offer them? I also think this frame seems very solid, and should hold up to most anything I plan to throw at it, but I could be wrong I'm no engineer or expert. The suspension, however, is another story and a very good point. So, if I were to abandon this frame and start from scratch, would something like the following bicycle work as a starting point?

https://offerup.com/item/detail/798635466/

Edit: no disc brakes, so I guess not suitable anyway

This is as cheap as it gets, but at least it has front disc brakes, and the 24" wheel size might be nice laced with a 1500-2000w leafmotor, maybe 5T, or even 4T with the 24" wheel size?
https://www.ebay.com/itm/Mongoose-2...085230?hash=item2f4837e3ae:g:A6AAAOSwJlRe8sCD
 
The problem with bicycle fat tires is not their size. It is their low thickness and weight that is making them weak. Some are better than others, heavier wire beaded construction, yet in general they are made for a specialty purpose, which is slow riding on loose surfaces.

You realize that a 3.0’’ tire that weights 1.5 kg, will need to be well above 2 kg at 4.0’’ to maintain its construction and relative stiffness. 4.0’’ motorcycle tires are much heavier than that.
 
theloadedquestion said:
...what exactly is so bad about bigger tires? I would think that would be a plus for this application, not a minus.
Click to expand...
Not simply "bigger tires" as you state, but "fat bike" tires are not stable at high speeds. What are they designed for? Snow/mud/sand, run at relatively low pressure, and not at your desired 40MPH.

theloadedquestion said:
And after all, motorcycles made for street use have pretty fat tires..
Click to expand...
Motorcycle street tires yes can be "pretty fat" but are constructed much differently than "fat bike" tires, they are designed for high speed stability, cornering, etc. In fact, you may want to use them for sustained high speed road use.
 
MadRhino said:
The problem with bicycle fat tires is not their size. It is their low thickness and weight that is making them weak. Some are better than others, heavier wire beaded construction, yet in general they are made for a specialty purpose, which is slow riding on loose surfaces.

You realize that a 3.0’’ tire that weights 1.5 kg, will need to be well above 2 kg at 4.0’’ to maintain its construction and relative stiffness. 4.0’’ motorcycle tires are much heavier than that.
Click to expand...

Ah, yes, that makes sense, and they are quite "soft" even at relatively high psi. I guess it is that softness and lack of sturdiness that is the problem in any high speed/high power applications. So what am I looking at then? A 2.8 tire with thick, sturdy rubber and heavier wire beading?
 
Not simply "bigger tires" as you state, but "fat bike" tires are not stable at high speeds. What are they designed for? Snow/mud/sand, run at relatively low pressure, and not at your desired 40MPH.

Motorcycle street tires yes can be "pretty fat" but are constructed much differently than "fat bike" tires, they are designed for high speed stability, cornering, etc. In fact, you may want to use them for sustained high speed road use.
Click to expand...

Understood thanks, that pulls it all together and I understand now. Now, could I not just replace the stock tires with a more suitable ones, using the same rims, or no? Anyway, even if yes I am starting to see why people were suggesting starting from scratch with a new donor bike. I do love this bike though, just got the bug now and want just a little more power on the trails and speed on the roads.
 
theloadedquestion said:
Ah, yes, that makes sense, and they are quite "soft" even at relatively high psi.
Click to expand...
And at higher pressures higher speeds they can blow off the rim or get hemorrhoids.
 
This is an expensive hobby my friend. [emoji1787] I will never have money again. Lol

Sent from my CLT-L09 using Tapatalk

 
theloadedquestion said:
...could I not just replace the stock tires with a more suitable ones, using the same rims, or no?
Click to expand...
Maybe, probably not. Important: What is the rim bead width? That will dictate your tire width choices.
 
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