Cheapest high torque fast bike?

Haien · Mar 30, 2020

So I have been looking on amazon at the 1000w kits avaliable for cheap, and through some research I have come to understand that you can easily put 2000-3000w in them for short periods at a time. What is the easiest way to do this? I heard you can probably use a 60v battery with the included controller, though this seems very uncertain and risky. Would it be better buying a 72v 40 amp controller? If so, which one? I am limited to amazon .de as I live in Europe.

Battery wise, the ones available on amazon don't seem to ship here and are very sketchy looking, doubt they can output much current. The ones I can get here are way too expensive, so the best option seems to be assembling my own battery. I can get 60 Samsung INR18650-25R 2500mAh for $200, 80 for $250 or 100 for $300. Would a 20s 2 or 3p work for the 40 amp controller? Or would I need at least 4p (as in 10 amps per cell in parallell)? Might it be worth having a lower voltage for allowing higher amperage with the same amount of cells? I can also get 80 Samsung INR18650-35E 3400mAh 10.5A for $300, would this be a good alternative?

Thanks in advance!

dogman dan · Mar 30, 2020

The cheap recipe for a 40 mph bike starts with a motor typical of the 1000w kit. They are 27 or 28 mm wide dd motors rated at 500w. They easily handle 1500 to 2000w. At 3000w, using a 72v 40 amps controller, they will melt down in about 40 -60 min.

But if you limit your time, and are just hauling ass on relatively flat terrain, you can pretty reliably run 700 watt hours through them before they actually melt. Drilling holes in the cover helps too but mostly with faster cooling once you stop for a few min. Statorade also a way to improve cooling.

The cheap battery is RC lipo. Only those lipos are cheap enough, and strong enough, for a small 72v 10 ah battery to run at 40 amps. And about 10 ah is the most you can run continuously at full speed before the motor melts.

Usually you will have 40 mph when the battery is full, then about 35 mph later on in the run. As the battery drains, it loses voltage, so the 3000w is really just when you start, then it pulls 2000w continuously later. About a 40 min ride, and your battery is empty, and time to be home letting the motor cool. If its hot, and you ride hills off road, you WILL still melt motors in the summer.

You could still run a good quality 18650, but the battery will have to be bigger, and then you are almost sure to melt your motor, simply because you are carrying enough watt hours to ride too long.

Balmorhea · Mar 30, 2020

13.5A to 20A per cell, continuous, is too much for commonly available 18650 cells. You’ll get a lot of voltage sag and short battery lifespan. If you want high power for cheap, you need to look at salvaged automotive cells or radio controlled airplane packs.

Most of the cheapest hub motor kits from eBay or Amazon are too high speed (in terms of RPM per volt) for what you have in mind. For instance, a hub motor that is set up to spin at 30-40kph on 36V will spin at 60-80kph on 72V, but won’t have nearly enough power to get close to that speed range. It will be stuck running at a smaller fraction of its free motor speed, and efficiency will be poor.

Leaf Bike will custom wind a 1500W motor to run at an RPM your available power can actually support. Theirs is not the cheapest motor you can buy, but it isn’t expensive, and it offers very good value for its cost. Use the Grin Technologies hub motor simulator to estimate how much motor power a given speed range will require (or how much speed a given motor power will allow). Then you can figure out your requirements regarding motor RPM per volt, torque per amp, and battery power.

If you use the cheapest motor kit available to you, you probably will not know any of the motor’s technical specs, and whether it offers a good match of power to speed will be a matter of luck. But understand that no such kits are designed to run on 60-72 volts, so if you raise the voltage, they’ll try to turn at a faster speed than their power allows them to approach.

Haien · Mar 30, 2020

dogman dan said:
The cheap recipe for a 40 mph bike starts with a motor typical of the 1000w kit. They are 27 or 28 mm wide dd motors rated at 500w. They easily handle 1500 to 2000w. At 3000w, using a 72v 40 amps controller, they will melt down in about 40 -60 min.

But if you limit your time, and are just hauling ass on relatively flat terrain, you can pretty reliably run 700 watt hours through them before they actually melt. Drilling holes in the cover helps too but mostly with faster cooling once you stop for a few min. Statorade also a way to improve cooling.

The cheap battery is RC lipo. Only those lipos are cheap enough, and strong enough, for a small 72v 10 ah battery to run at 40 amps. And about 10 ah is the most you can run continuously at full speed before the motor melts.

Usually you will have 40 mph when the battery is full, then about 35 mph later on in the run. As the battery drains, it loses voltage, so the 3000w is really just when you start, then it pulls 2000w continuously later. About a 40 min ride, and your battery is empty, and time to be home letting the motor cool. If its hot, and you ride hills off road, you WILL still melt motors in the summer.

You could still run a good quality 18650, but the battery will have to be bigger, and then you are almost sure to melt your motor, simply because you are carrying enough watt hours to ride too long.

As I don't intend on commuting on this bike, I probably won't run it fast for long stretches. I would rather just use it as a toy with the capability of going faster and farther. If I would ride far it would probably be in like 20mph, which probably won't even make the motor warm. For this purpose 18650s are good right? Though it may be a waste buying 80 cells just for having a capability I barely use.

Haien · Mar 30, 2020

Balmorhea said:
13.5A to 20A per cell, continuous, is too much for commonly available 18650 cells. You’ll get a lot of voltage sag and short battery lifespan. If you want high power for cheap, you need to look at salvaged automotive cells or radio controlled airplane packs.

Most of the cheapest hub motor kits from eBay or Amazon are too high speed (in terms of RPM per volt) for what you have in mind. For instance, a hub motor that is set up to spin at 30-40kph on 36V will spin at 60-80kph on 72V, but won’t have nearly enough power to get close to that speed range. It will be stuck running at a smaller fraction of its free motor speed, and efficiency will be poor.

Leaf Bike will custom wind a 1500W motor to run at an RPM your available power can actually support. Theirs is not the cheapest motor you can buy, but it isn’t expensive, and it offers very good value for its cost. Use the Grin Technologies hub motor simulator to estimate how much motor power a given speed range will require (or how much speed a given motor power will allow). Then you can figure out your requirements regarding motor RPM per volt, torque per amp, and battery power.

If you use the cheapest motor kit available to you, you probably will not know any of the motor’s technical specs, and whether it offers a good match of power to speed will be a matter of luck. But understand that no such kits are designed to run on 60-72 volts, so if you raise the voltage, they’ll try to turn at a faster speed than their power allows them to approach.

So if I use 18650 I will need at least 4 in paralell to get enough current? This at 72v might be a bit much, as 80 cells are expensive. But that would, assuming the cells are goid for 10 amps each, work right?

The cheaper ones seem to be wound for 30mph at 48v (which the controller included is rated at) at about 20 amps according to the 1000w figure. If the speed theoreticaally is proportional to the voltage, 72v would give me 45mph, assuming the current is sufficient to overcome air resistance, this, 40mph, is what other people get with this setup so I dont see why I wouldn't be able to.

I agree that I won't know the specs of the motor I get, so would it be a better bet going for a lower voltage controller with high current, as I value acceleration highly? Like maybe a 52v one with 40 or 60 amps? Because then the current will support the speed which shouldn't be over 35mph anyway and there would be lower risk of overheating the motor (if I don't constantly accelerate or climb hills)?

DogDipstick · Mar 30, 2020

I kind of just did the whole template that dogman did. Got an excellent 40 mile per hour bike for about $1,300.... excellent name brand and all high-end but I bought most of my stuff used for cheap and there was a lot of do-it-yourself. if you know what you're looking for you can build a really powerful battery without too much trouble or cost.

Qs V1 205 is an excellent motor compared to the leaf bike motor and quite cheaper... That alone what take the leaf out of contention.... If you are looking for a large direct drive hubs.

Balmorhea · Mar 30, 2020

Haien said:
As I don't intend on commuting on this bike, I probably won't run it fast for long stretches. I would rather just use it as a toy with the capability of going faster and farther. If I would ride far it would probably be in like 20mph, which probably won't even make the motor warm. For this purpose 18650s are good right? Though it may be a waste buying 80 cells just for having a capability I barely use.

You can make it work with 18650 cells if they are rated for very high current. Examples include Sony VTC5, Samsung 20S, and LG HD2C. The battery interconnects must also be capable of carrying high current, which rules out normal nickel strip construction.

If I were building a bike like you describe, I’d go for a higher power cell like this:
https://www.ebay.com/itm/20-SPIM08HP-3-7V-8AH-LITHIUM-ION-BATTERIES-25C-200A-SUPER-CELLS-POWERWALLS-EBIKE/173305036284?

Get a high current speed controller that can accept a range of voltage, and then you can increase or reduce the number of cells to get the characteristics you want. Current has more effect on acceleration, and voltage has more effect on top speed, though changing either one will have some effect on both.

Haien · Mar 30, 2020

DogDipstick said:
I kind of just did the whole template that dogman did. Got an excellent 40 mile per hour bike for about $1,300.... excellent name brand and all high-end but I bought most of my stuff used for cheap and there was a lot of do-it-yourself. if you know what you're looking for you can build a really powerful battery without too much trouble or cost.

Qs V1 205 is an excellent motor compared to the leaf bike motor and quite cheaper... That alone what take the leaf out of contention.... If you are looking for a large direct drive hubs.

Don't you think you could get it for less than that? 1000w kit for $160, homemade 18650 battery/hobbyking battery $200, controller $100?

I would rather not go with another motor as this is supposed to be as cheap as possible, the 3000w figure can be 2000w instead if that fits batteries and my wallet more.

DogDipstick · Mar 30, 2020

Haien said:
Don't you think you could get it for less than that? 1000w kit for $160, (I paid 200 shipped ) homemade 18650 battery/hobbyking battery $200 ( that is what I paid) , controller $100? ( I paid 70$)

I would rather not go with another motor as this is supposed to be as cheap as possible, the 3000w figure can be 2000w instead if that fits batteries and my wallet more.

Yes, but you can also try.. but end up paying more in the end.... and have a junk bike still....

So at the beginning tI thought I would maybe build the 600$ bike...but....

My motor is 1Kw but I hit 8Kw bursts. The forks are high quality (600$ new). The frame is high quality ( 1499 new) The crank, bracket, display, shunt, datalogger, AcDc converter. Lights. 19" rubber for a vintage Motorcycle on DOT 76mph tires with a Zero throttle.... All new ... Nigh tq street eating 100A 8Kw 83v 45mph downhill Frame and Dwlink suspension with dual pot hydros on Hayes 8inch with brand new stem bb bar brakes chainrings pedals... chain... derailer and all trigger shimano Ispec...

No I would rather have the 1300$ bike. Also note that this was NOT my first ebike.

You will not get there with 600$, my bike performance.... and the 40mph you want.. for long range.. like my 20-40miles....

But take your time and buy used, or DIY, and yeah.

Neither any HK lipo or 18650, 21700, 38120 would come close to the power/$ my battery has.

QS V1 motor is much better than cheap kit motor.. and still close in price. Cheap kits are for starting hobby but do not spend alot of money in the interest of reliability. I even think Bafang mid drive is cheap, though popular.

If everything was bought new, who knows how much my bike would have cost.

I do say there are many kits in the range you want, please do as you like. Ask here and the people with more experience will answer.

Only the basic power package for my bike? Yes cost only ~600 with everything basic with ~25 mile range, 27mph average and 40 mph peaks.... However, it s not junk. 200$ motor 200$ battery 100$ controller 100$ display. You can still buy good in the 600$ budget..for your needs absolutly... DIY, and careful choice.... lol but budget is always gone over for me...

much better than the 140$ kit. I have a Qs motor and a 72v 50 Amp controller of medium quality ( Kelly KEB series)

flat tire · Mar 30, 2020

High torque fast ebikes aren't cheap.

markz · Mar 30, 2020

Cheapest
- YESCOMUSA ebike kit in a 24" bicycle rim, for that extra torque you want.
- Battery, always the dilemma. NKON will tab weld for you for extra 0.55euro, then you buy 18650 holders and solder away, or just solder directly onto the can which needs a high heat soldering iron and flux for the solder to stick. Atleast with the tabs, its very quick and very little heat is put into the can. Get EM3EV.com to build you a battery. Home Depot lawn equipment battery. Radio Controlled LiPo battery. Then what about a charger, again dilemma's man, only money can solve and a bit of time, hence cheap and money, dilemma.

MikeSSS · Mar 30, 2020

Aero bars are for fast, even fast climbing.

Torque Sensor pedal assist is great for aero bars. Throttle has to be out on the front of the aero bars.

Also, aero bars carry a lot of your weight on the arm cups, that reduces saddle weight and saddle pain.

Non sense speed limiting is a bad thing.

Life on the aero bars can be most excellent.

Haien · Apr 1, 2020

DogDipstick said:
Haien said:

Don't you think you could get it for less than that? 1000w kit for $160, (I paid 200 shipped ) homemade 18650 battery/hobbyking battery $200 ( that is what I paid) , controller $100? ( I paid 70$)

I would rather not go with another motor as this is supposed to be as cheap as possible, the 3000w figure can be 2000w instead if that fits batteries and my wallet more.

Click to expand...

Yes, but you can also try.. but end up paying more in the end.... and have a junk bike still....

So at the beginning tI thought I would maybe build the 600$ bike...but....

My motor is 1Kw but I hit 8Kw bursts. The forks are high quality (600$ new). The frame is high quality ( 1499 new) The crank, bracket, display, shunt, datalogger, AcDc converter. Lights. 19" rubber for a vintage Motorcycle on DOT 76mph tires with a Zero throttle.... All new ... Nigh tq street eating 100A 8Kw 83v 45mph downhill Frame and Dwlink suspension with dual pot hydros on Hayes 8inch with brand new stem bb bar brakes chainrings pedals... chain... derailer and all trigger shimano Ispec...

No I would rather have the 1300$ bike. Also note that this was NOT my first ebike.

You will not get there with 600$, my bike performance.... and the 40mph you want.. for long range.. like my 20-40miles....

But take your time and buy used, or DIY, and yeah.

Neither any HK lipo or 18650, 21700, 38120 would come close to the power/$ my battery has.

QS V1 motor is much better than cheap kit motor.. and still close in price. Cheap kits are for starting hobby but do not spend alot of money in the interest of reliability. I even think Bafang mid drive is cheap, though popular.

If everything was bought new, who knows how much my bike would have cost.

I do say there are many kits in the range you want, please do as you like. Ask here and the people with more experience will answer.

Only the basic power package for my bike? Yes cost only ~600 with everything basic with ~25 mile range, 27mph average and 40 mph peaks.... However, it s not junk. 200$ motor 200$ battery 100$ controller 100$ display. You can still buy good in the 600$ budget..for your needs absolutly... DIY, and careful choice.... lol but budget is always gone over for me...

much better than the 140$ kit. I have a Qs motor and a 72v 50 Amp controller of medium quality ( Kelly KEB series)

Yes your bike sounds fantastic for the price, though I don't think I would go for a expensive (quality) motor for significantly more money just because it will be a bit better. I am a student without a job, but if I had the money and opportunity I would want yours.

As for battery, I have looked around a bit and the rc batteries avaliable are really expensive here, a 14,8V 5200mAh 40C battery is a bit over $100, and five of those are just barely at the amperage limit. 18650s are cheaper, but still expensive as I would probably need 5 parallell for the current draw and 20 series, making 100 cells. Quite a lot for a toy, though good range in 1000w mode I suppose.

Haien · Apr 1, 2020

flat tire said:
High torque fast ebikes aren't cheap.

Everything is relative. Also if I by fast mean quick as in good acceleration, 3000w can go a long way, at least up to 20mph.

dogman dan · Apr 1, 2020

High torque, fast bike, BATTERIES are not cheap. Cheapest way to get a battery able to handle high amps is lipo.

Lipo is DANGEROUS. This is why my lipos were outside the house, in a bunker, when my "safe" 18650 pack burned my garage down. :lol: The good news was I had good insurance, and was able to live in my house again less than a year later.

So if cheap is you aim, go lipo, and keep em outside.

Best high torque fast bike, would never include starting with the cheap 500w rated motors. But since they are cheap, its kind of fun to melt one down once a year or so. Spend a bit more good money on the controller, and as high c rate lipo as you can afford. 20c type will do, but are saggy compared to 30 or 40c types.

If all you want is a 30 mph bike, then your 18650's can do fine, with 14s, and a 30 amps controller. ( the stock cheap kit) 40 mph club means a LOT more battery is needed. I often suggest sticking to 48v if budget is an issue.

flat tire · Apr 1, 2020

Haien said:
Everything is relative. Also if I by fast mean quick as in good acceleration, 3000w can go a long way, at least up to 20mph.

Cheap is relative, but you don't mention what your budget is. It's helpful that you clarified what you mean by fast. Unfortunately 3000W does not go a long way even under 20.

First, conditions make a lot of difference in what the motor can take and not all 2-3kw configs are equal. You could be using all the power intermittently, for short times, in arctic weather. Or you could be in 100* heat trying to race everywhere at full throttle.

Even somewhere in between those extremes a 1000W hub kit will not last long overclocked on 2-3kw input power from the battery with a user who wants to be "quick". A significant factor for overheating independent of the power level is the max phase current which determines peak torque. In other words you could have phase current from 40 to max saturation amps in the 100s and still be drawing no more than 3kw. Unfortunately you will want to ramp that up pretty high to get powerful take offs.

The bare minimum hub motor to get for a bike where "quick" or "fast" are anywhere in the owner's mind is the QS205 v3. You can get enough power (10+kw) from one of these to get into dangerous territory speed-wise without getting the motor too hot. That motor will power wheelie well into the 30s mph without straining. So the acceleration is also terrific.

If you really want an ebike but can't afford properly specced parts for your ideal vision, you are probably better off not overclocking your 1kw kit unless you are very careful and install a temp sensor or you will just waste more money on the same compromised setup while burning out parts.

Also you want to allocate at least twice your $200 on a battery, that's just ridiculous. Even then you'll be left very much wanting.

DogDipstick · Apr 1, 2020

Yeah I do admit after a while you must give a hub motor a rest ( when off road. ) . A Bafang mid drive or some similar mid drive will chug along all day, albeit a little slower than you may like.... on the "30A 14s" config goal.

Hub motor tries really hard and uses loads of fun power. You need serious power to waste if you want to climb fast on a hub motor.... and that becomes the expensive combo... But a mid drive if you go slow enough you can go all day slow. A hub motor is tearing it up or hot when off road.... and if you go to slow on a hub motor to long the heat builds up.

Mid drives like to climb like a goat sometimes. Hub motor is for racing busses on the daily commute. I did feel like my Bafang was very underpowered though. Lol.

markz · Apr 1, 2020

Batteries are expensive, its as simple as that.

Now, do you want to cheap out on some mystery dangerous basement built battery off ebay or amazon and save some coin, or do you want to know for a fact you have a properly built battery, built by a reputable company or person, or do you want to gamble?

goatman · Apr 1, 2020

I bought 200 used 25r last year for $2 each. right now im running 17s4p of 25r at 2500 watts, if I hop on the bike and go for a typical ride, I spend about 1/3 of the ride at 65km/h average speed will be about 36km/h(stopping at red lights kills the average speed) but im usually cruising at 45km/h and my range is about 20km, if I baby the ride at 30km/h ill get 30km range. ive got around 8000km on the 25rs but I built two 2-17s4p that I swap between my bikes or parallel for longer range like 80km range at 30km/h and theyre getting tired.

if I run 17s4p at 3500 watts the volt sag is too bad
id be looking for a 40 amp controller with higher voltage like this from grin

https://www.ebikes.ca/shop/electric-bicycle-parts/controllers/c7240-gr.html

it works from 36v to 72v so you can build whatever size battery you want, if you can find a controller like that where you are you should be ok

goatman · Apr 1, 2020

I should mention if I run them at 5p and 40 amps the volt sag aint bad like 4/5 volts on my tired pack. I charge to 4.1v/cell and discharge right to 3.0v/cell sometimes less, if my packs voltage is low sometimes my sag will dip down to 2.8v/cell or 48v so I don't have to walk the bike home but these are 25r's they can take a little abuse.

Sunder · Apr 1, 2020

Haien said:
Yes your bike sounds fantastic for the price, though I don't think I would go for a expensive (quality) motor for significantly more money just because it will be a bit better. I am a student without a job, but if I had the money and opportunity I would want yours.

As for battery, I have looked around a bit and the rc batteries avaliable are really expensive here, a 14,8V 5200mAh 40C battery is a bit over $100, and five of those are just barely at the amperage limit. 18650s are cheaper, but still expensive as I would probably need 5 parallell for the current draw and 20 series, making 100 cells. Quite a lot for a toy, though good range in 1000w mode I suppose.

There's the old engineering saying "You can have it cheap, fast, and reliable. Which two do you want"?

Everything has already been said about being disappointed if you try to cheap out. Either it's going to be disappointing in performance, or you're going to be replacing parts regularly.

As an anecdote, in RC racing - which is what those RC LiPos are made for, most people move their packs from "race" status to "practice" status in 7-10 cycles, and dispose of them after 30-50. You can take two things from this:

1. If you go down that route, you may need to treat battery packs as consumables, and spread the cost over time. (50 cycles = 1 year of weekend fun, assuming only one charge per weekend? But after the first 2-3 months, performance will drop.)

2. If you have friends in RC racing, ask them to put out out the word you're willing to buy near end of life packs that haven't puffed dirt cheap, and then build them into a monstrously over sized battery, that you baby. So like if you expect to be drawing 3kw, build a 6kwh (this thing will be like 20kg) pack and you're only drawing at 1/2C

Anyway, sacrifices have to be made somewhere. You can't have a fast, cheap, and reliable bike, or someone would have already mass produced it and made a killing.

The only way to do that is make some else's loss your gain, and the only legal way to do that is buying second hand. Next few months, there will be a lot of people desperate for extra cash as they are out of work. Don't take advantage of them, but if you see a good offer, help them out if you have spare cash.

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