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Building a Powerful Ebike

Posted: Jan 03 2019 3:02am
by Callbrin
I am planing to build a powerful ebike [my 2nd one] but I not sure what I need.

First I'm either gonna need a fat bike or a regular bike with 150mm dropout for obvious reasons but I'm not sure what to get as I dont want any of those frames that look like dirt bikes like the grey borg or stealth bomber.

List of Bikes For possible use: ... op?ie=UTF8 [already have andf it is 155mm rear dropout but is a cheap walmart bike] ... X0DER&th=1 [Rear Dropout width is unknown but its made of steel so I might be able to stretch it] ... rk:10:pf:0 [Looks cool but unsure if its worth it to get this]

List of Possible Kits ... r-Kit.html [8000w] ... 266fbaab20 [5000w] ... B01GSR8MLW [3000w Has option for fat wheel]

Now The Problems:

Rear dropout width

battery size [thinking maybe running 96v instead of 72v]

Trusted kits [I want a lot of torque but I dont want to overspend. Do I even need 5kw? The torque is rated at 190nm and around 65mph so the 5kw looks best bust the battery sizing is and issue then.

Possible Batteries For Diy Battery ... p-battery/ [3000mah 5C] ... a-battery/ [21700 Cell, 5000mah 1.95C] ... p-battery/ [3200mah 3.125C]

I dont want a lot of voltage sag but I want the batteries to not struggle giving full power and then some to the motor

Re: Building a Powerful Ebike

Posted: Jan 03 2019 3:34am
by ScooterMan101
You are going to need a better bike than those listed above, for high power builds.

Disc Brakes a must , 180 or 103 mm disc rotors. Quality Calipers.

I don't know about the powerful motors much because they are DD hubs. which are very heavy, so they need the type of frame you think you do not want. You are better off getting at least the Frame Called the Vector Storm , or the one from Australia the FUTR Alpha .

A motor like the QS 205 or others like it for a high power build.

Or get the Tangent , or LightingRod's Big Block.

Re: Building a Powerful Ebike

Posted: Jan 03 2019 5:03am
by Callbrin
In that case Would 3000w be enough? The kit I posted says 150nm but is it? or more closely to this one in terms of torque: ... :rk:1:pf:0

If it is actually a lot more torque than the cheap ebay one, is it worth it for an upgrade from a 1500w DD

Re: Building a Powerful Ebike

Posted: Jan 03 2019 5:15am
by Callbrin
ok new plan: I will get the mongoose dolomite unless someone recommends something better for a fat bike.

I will get this kit: ... th=1&psc=1 [3000w Fat bike rim version for 26"]

Now it says for the fat bike version that the width is 175mm and as far as I know the Dolomite is 190mm. SO will this be a problem or can I just squeeze it together or use washers/gaskets

Re: Building a Powerful Ebike

Posted: Jan 03 2019 5:50am
by MadRhino
65 mph is very fast for a bicycle. Most of them are not safe to ride that speed, and those that you linked are very far from it. Fat bike tires are not fit. If you want tires wider than 3 inch, you will need motorcycle tires to ride 65 mph. Fat bike frames are not fit either, none of them that I know.

You need a bike that is safe to ride much faster before building it, for it will have to ride fine and safe at 65 mph AFTER you add the weight of motor, batteries, etc... The kind of bikes that are making good rides at that speed are few, and expansive. Even after you have one, you will need to improve, mod, building it better, to make your ebike suitable for that kind of performance. I suppose that you know, that big hub motors are pulling much more than their rated wattage in acceleration.

Then, ebikes that are riding 65 mph have huge batteries when they are built with safe chemistry. So, most of us are using RC lipo because of their high C rate and density. They are not the ‘plug and play’ type. They need careful monitoring and safety measures.

This was only to make you conscious of the task and goal requirements. Probably much more work and money that you were thinking of, If you want to build a 65 mph bike that is not a suicide machine.

Building a Powerful Ebike

Posted: Jan 03 2019 10:25am
by E-HP
What I'm gathering from your post, and combining some of the elements of your other thread on torque, is that you are not as concerned about speed, but torque. In addition, you're not as concerned about how that torque is applied to hill climbing, but rather acceleration. If you can confirm or clarify what your goal is, you may get better advice, since there is a lot of expertise and experience here. I'm mentioning this, because I was provided similar advice when I first posted here, and that advice was like gold, and really helpful.

Anyway, let's assume that you want more torque, and mainly for greater acceleration (if you want something else, this will still apply); then go here:

Choose a battery voltage, and capacity just to get you started, say 52 V 16 aH. You can adjust later, after you get an idea of what this tool can do for you. Then choose a controller that has adequate current capability, so the controller is not the bottleneck; say 40 A. In the motor drop down, scroll all the way to the bottom and select "Show All". This will reveal all motors that are simulated in the tool. Now you're ready to look at the torque characteristics of a large number of e-bike motors.

For acceleration, determine what range you want to simulate, say 0-20 mph. To accelerate through that range quickest, you want the highest torque at 0 mph and 20 mph, ideally as flat a torque curve as possible, if you want hard acceleration through that range. (If you're used to mph rather than kph, you can select the units in the dropdown below). After selecting a motor, press the "Simulate" button. For a 9C+ 2705 motor, for example, torque starts at 75 N-m and about 47 N-m at 20 mph. If you choose the MXUS 3005, the torque curve starts at 85 N-m and goes to 48 N-m by 20 mph. That motor should accelerate harder, all other things being equal (wheel diameter, etc.). However, you also need to look at the shape of the torque curve (actually area under the curve), since that may reveal that it wont' pull as hard at 10 mph for instance, so acceleration will be affected. Flatter is better, and dipping downward quickly is less desirable.

You can also look at the torque curve for things like hill climbing, but in those cases, you may want to pay more attention to the speed you want to climb at, and the torque available at that speed. It's a great tool to learn the different characteristics of various motors, and then if you look further into the design of those motors, you will learn what the build characteristics of the motors that give them those qualities (speed, torque, power, and their respective performance curves).

EDIT: I forgot to mention, you may notice that upping the voltage will not increase the maximum torque of the motor, but it will flatten the torque curve, so more torque is available at speeds above zero, where the torque is maxed out. Greater area under the curve, so quicker and pulling harder for longer.

Re: Building a Powerful Ebike

Posted: Jan 03 2019 10:47am
by tahitiboob
in the simulator what engine to choose to match at most qs273

thank you

Re: Building a Powerful Ebike

Posted: Jan 03 2019 11:14am
by Smoke
I was thinking about a big direct drive hub motor for a while.

They have some virtues like a pretty straightforward conversion process but they also weigh a lot and if you want something that works well over a large range of speeds you need higher voltage which means more battery cells and usually more expense in the BMS, controller and charger.

Mid-drive systems have a bit more mechanical complexity but their gearing allows them to be much more compact and light weight. If you design your drivetrain properly you can have a gear for pulling trailers or climbing steep hills, a gear for quick starts, a gear for a ~high cruising speed and more gears in between.

Which is best is determined by how you are going to use it, how much battery you want to buy/carry and how heavy you are willing to go.

I determined that 3kw mid-drive with a 3 speed IGH was the direction I want to go for a commuter/cargo bike. My top speed will be gear limited, probably less than 45 mph but that's fine for me. It won't be light but I'm putting weight in to my battery rather than the motor so range should be excellent. It won't be cheap because all the parts add up quickly and I'm building it with parts that should (hopefully) handle the power and speed safely.

If you look at a lot of the nicer conversions, they usually are not a first attempt because most people fall in to the trap of a cheap kit and wind up with something not quite up to their expectations.

You can either jump in to get your feet wet or spend a lot of time figuring out the right setup for you. I'm going with a lot of time which is why I have a lot of parts rather than a bike but I'm expecting I can make the end result 100% tailored to me after I build my frame.

Re: Building a Powerful Ebike

Posted: Jan 03 2019 11:37am
by E-HP
To the OP, MadRhino’s advice is spot on. It’s relatively easy to build a powerful bike, but if you don’t look at the entire system and build it to match, bad things will happen. I learned that lesson with on of my motorcycles and I’m lucky to be alive to benefit from it.
Basically, if you build power and don’t build up your braking, suspension, tires and chassis to match it, you’re really not looking at if you will die, but when. Even reliability has to be increased, since even having a chain pop off at speed, can turn you into a mangled puddle of carnage on the pavement.
You may be able to build the power you want, but aren’t going to build a bike that can safely deal with it using a kit and Walmart level of bike as your starting point. That’s why people invest in a solid chassis built for the power.

Sent from my iPhone using Tapatalk

Re: Building a Powerful Ebike

Posted: Jan 03 2019 11:45am
by 2old
Question about the Dolomite; I squeezed the 190 (actually was 200+) rear to 135 before aftermarket rear motors with greater width were available, but needed to space out the freewheel for a conversion. That said, listen to those above about speed. My "errand" bike goes 35 mph and even with the excellent road system here, that's the fastest safe speed I can envision on a bike without suspension. If you want to go faster, you need to start with at least a FS downhill frame IMO. The Dolomite steel frame is very sturdy for slower considerations. We added a home-built sidecar for carrying a physically challenged girl in a wheelchair to it and the system was unusually robust.

Re: Building a Powerful Ebike

Posted: Jan 03 2019 12:06pm
by Callbrin
The reason I did not want to get any of those dirt bike looking frames is because I will be using it to get around everywhere at not always for around 90% of the time go more than 30. Unless someone can recommend a good bike to use Then I assume I have to get something like this: ... e-package/

Maybe this bike tho: ... 6404041011 [unable to find the rear dropout width so IDK if it would even work]

Also Yes I am more concerned about acceleration and from the 2 reviews on the 3kw kit it seems like more than enough for me

For the batteries. Is Lithium-ion possible?[ hopefully] if not, any links to where I can study up on lipos?

Bike For 3kw Hub Motor

Posted: Jan 05 2019 2:53am
by Callbrin
So I really dont want to get an enduro bike frame for the 3kw hub motor that I will be buying : ... th=1&psc=1

So I've been trying to find full suspension bikes to use that can also fit a battery in it as well inside the frame.
Here are a few I found. ... 0&LH_BIN=1 [unknown reardropout, asked seller]

Mongoose Dolomite with LUNA LANDER FAT SUSPENSION FORK [rear fat tire for some suspension]

Any ideas on bikes that might work and that can fit a large battery?

Re: Bike For 3kw Hub Motor

Posted: Jan 05 2019 3:31am
by Chalo
Too much motor, not enough bike. The kinds of bikes you're looking at are complete garbage, likely to self-digest from human power only. Add 4HP and you might well become grated topping for your busted BSO.

Re: Bike For 3kw Hub Motor

Posted: Jan 05 2019 6:28am
by dustNbone
Agreed. Spend the money on a quality (barely) used bike off Craigslist or something. There's tons of them, and after xmas is a pretty good time to get one as people are looking to make space for the new crap they'll also never use.

Help with bikes

Posted: Jan 05 2019 7:37am
by Callbrin
I want to out fit a bike with this 3kw kit : ... +motor+kit

I dont want an enduro frame because stealth

I've been trying and failing to find bikes that would work. It seems that bikes with plus sized wheels might do the trick as most seem to have a wider rear dropout by default.

Examples: ... YAQAvD_BwE

or ... dltrpswprf

Obviously these arent the best of bikes but could work. please help on finding ones that would work and fit a large battery pack. at this point I'm fine with a hard tail because of the extra space in the frame. thanks in advance

Re: Help with bikes

Posted: Jan 05 2019 9:30am
by MadRhino
Please, stop starting a new thread everytime you try finding another suitable bike.

You have 2 choices:

1- you continue looking for cheap bikes, then you turn to building slower with a smaller motor.

2- you stand with building with a big 3kw hub, then you start looking for used DH bikes.

DH bikes are not easy to build. They never have the space for batteries in frame, because they are made with big tubing, big shock and linkage. DH bikes are stiff and sound to build a fast and powerful bike that is safe, but new DH bikes are 8 to 15 thousand dollars for a complete bike, 2 to 4 thousand for a frameset. So, you need an old one and spend the time to restore it. Enduro ebike frame and such Chinese box frames are cheaper, easier to build, capable for a big hub... but very far from the ride quality of pro DH frames, for a fast build especially.

There are some ebike dedicated box frames that are good (not best but good) to build a fast ebike, but they are also pretty expansive. They are closer to DH bikes than Chinese box frames, and builders like them because they are ready for battery and motorization. To mod a pro DH bike is PITA, for dropouts, battery, geometry... lots of work but potentially more discrete than a box frame, and suspension design for a better ride.

Lets say: the bikes you linked so far, are potentially suitable for a 1000w motor kit and 25 mph top speed. Above 30 you need a tough frame, above 40 you need a tough FS frame, and above 50 you need the very best of them DH bikes with upgraded components.

Re: Help with bikes

Posted: Jan 05 2019 3:34pm
by Callbrin
sorry about that, I'll stop. also I saw this thread ... =1&t=85489

and thought maybe this might work with this frame what do you think? or would it be a bad idea because it would hit the front tire?

Re: Help with bikes

Posted: Jan 05 2019 3:41pm
by Callbrin
also could I use a fat bike with something like the Luna Lander Fat Suspension Fork? since the fat tires would also provide some rear cushioning to make up for no full suspension

Re: Building a Powerful Ebike

Posted: Jan 05 2019 7:14pm
by MadRhino
The DHI is a good frame to build a powerful bike. It is stiff enough to be built safe to ride 60 mph. The required components though, might be expansive, and require some technical knowledge to fit and tune. The GT DHI frame does clear 3 inch tires. The one I prefer is the 2007. I would build it on 24 X 3.

Fat bike forks are not suitable for high speed, neither fat bike tires. That option would limit your build to be safe up to 40 mph at the very best.

Re: Building a Powerful Ebike

Posted: Jan 05 2019 8:30pm
by Callbrin
thanks. now I have an idea on what to look for. I did find some other bikes But only front suspension. I have 3 Questions.

1. is there a limit to smaller tire sizes on a bike made for 27.5 like putting 26" or 20" rims on it?

2. With the frame shown before and the thread with the battery box. what would be my limit on battery size?

3. I dont plan to go off-road or anything like that. just through my town on roads. So do I need rear suspension or would getting a plus sized bike for wider tires be good enough?

Re: Building a Powerful Ebike

Posted: Jan 05 2019 9:31pm
by MadRhino
24 inch bicycle wheels are the smallest that would be good with the DHI. 19 inch motorcycle wheels are about the same diameter. Going smaller would require serious mods, if you plan functioning pedals at least.

Bigger tires than 3 inch are useless for street riding an ebike. Fat bike tires are made for slow riding loose terrain. They are expansive yet very thin, not reliable at high speed. Tires are not making a suspension. Suspension is required to keep the wheel in contact with the ground according to speed and surface condition. The faster the ride, the bumpier the road, the most dangerous it is to ride and corner without suspension. Suspension must be tuned according to weight, speed and terrain. Tire choice, thread, carcass type, width, PSI, gum hardness... must be according to riding conditions.

Motorcycle wheels are very heavy, stealing performance and range off your bike. They are rated for much faster speed than your ebike will ever do. They can be a good choice though, for those who are riding extreme puncture conditions, like desert thorns or steel debris on the pavement. At some point of extreme conditions, bad choices can become a fair compromise.

Battery size and weight, are according to those factors:
Desired speed and range.
Efficiency (hills, weight).
Cell type and chemistry.

Re: Building a Powerful Ebike

Posted: Jan 06 2019 4:43am
by Callbrin
ok so that DH frame actually has a thru axel. Any way to convert it to fit a hub motor? also I was thinking that I could split the batter into 2 and hang them off each side on the top tube but how could I do that?

If these obsticle are too much I might just Make a bigger battery for my 1500w ebike to go faster with more torque? Would that be easier than trying to make a more powerful DH ebike?

Re: Building a Powerful Ebike

Posted: Jan 06 2019 5:47am
by MadRhino
Open dropouts would be useless as well. Powerful builds require custom dropouts or torque plates each side. We cut them off 1/4 inch steel minimum. Many threads can be found about dropouts and torque plates, open, through axle or pinch type. Ideally, your custom dropouts will be bolted to the actual through axle plates.

Overpowering your actual motor is easy. You need first to evaluate how much it can survive. You would still need to hold the extra torque with custom dropouts. Making it significantly faster, would make it unsafe for the frane snd components that you have.

Re: Building a Powerful Ebike

Posted: Jan 06 2019 6:04am
by MadRhino
Easy to split a battery that you assemble yourself. Many are using RC lipo bricks, ideal for high power bikes. I usually fit the basic battery to the front of the DH fork, 4 bricks of 6s 8Ah in a quick release bag that is inserted into a holder made out of an alu ‘No Parking’ sign. Next 4 bricks are in a top tube or frame bag. When eequired for longer rides, replacement battery bags can be carried in luggage bags or back pack. Making batteries modular is best to always ride optimal weight, not carrying the weight that you don’t need.

Re: Building a Powerful Ebike

Posted: Jan 06 2019 8:38am
by tolkaNo
Build a giant dh comp/team