I need to get up to speed for recommending a kit

Hi guys,

It´s been a long time since my last post, no I am not studying anymore I am a dad and all that... The thing is I have a friend asking me questions and I know that things have easily changed a lot since when I used to be here. So here I come with some newbie questions.

He wants some kit for putting on a road donor bike, not very powerful, he says 60km of autonomy, but (I think that´s way too much), he wants something light, not necessary very powerful, I guess that something around 350w it´s fine (just to fell a little bit more power than most of the things out there), he likes Swytch bikes but he doesn't want to wait for it, so it seems he likes the minimalist look.

Battery technology? ! I don´t have any idea, in my time LIFEPO4 was one of the safest options, lipo for the bravest... whatever but it´s for someone that is definetely not gonna be tinkerin, so safe and reliable.

I wonder if a bafang mid-drive motor is a good idea, but since it´s gonna be a road bike and he likes the clean look, maybe a small hub motor is better (but change my mind if you want), with one of those batteries in a bottle.

Rear of front? I remember that rear was better in terms of vibrations in the fork, but is it really a problem with low power systems? also it´s way easier to install, which it seems like a good idea for this user.

A quick search and I saw this:
https://hilltopperbikes.com/product/sprinter-12-mile-24v-electric-bike-kit-copy/

They provide also a torque arm, so maybe it´s recomended even in low power front hub motors?

And at last, that is available in Spain.

Anyway, thank you very much in advance and I hope i don't annoy everybody with my post.

TLDR: you guys know of a lightweight minimal, low power kit with battery for a road donor bike?

He wants some kit for putting on a road donor bike, not very powerful, he says 60km of autonomy, but (I think that´s way too much)....

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That's 40 miles requiring a very large battery pack, something like a a 25 Ah capacity. They are available, but it will be the size of a mail box and weigh almost as much as the donor bike! It's common for newbies to overestimate how much range they need, it's called range anixity. Something around 15 Ah would be more practical to carry.

....he likes Swytch bikes but he doesn't want to wait for it, so it seems he likes the minimalist look.

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It's a good thing you are around to rein your friend in, he's all over the place. He wants to go 40 miles, but a Swytch kit will maybe provide 10 The Swytch kit battery is so small because putting it on the handlebars is about the worst place to put it and any more weight would probably present liability issues.

....in my time LIFEPO4 was one of the safest options, lipo for the bravest... whatever but it´s for someone that is definetely not gonna be tinkerin, so safe and reliable.

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Your time has passed. LiFePo4. while long lasting, is very heavy. And you are lumping all Lithium chemistries together concerning safety. LiPoly (what I use) requires some special handling, but has been subject to a lot fear mongering, but that's besides the point, nobody uses it anymore for ebikes. The battery for him will have Li-Ion round cells and if he wants to be stealthy, it will be in the form of a "water bottle" battery.

I wonder if a bafang mid-drive motor is a good idea

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Hard to say as you have left out the 3 most important critiera;
1)desired speed
2)hills to be encountered
3)how much is he willing to spend.
If he doesn't want to go faster than, say 25 mph, (A gd. pedal along speed), isn't going to be climbing steep hills and would like to save some $$, a sm. hub motor would do the trick w/out to increased cost and maintenance of a mid-drive. Mid-drives have their place, they can extend the system's performance via the bike's gears, but if pushing the parameters isn't in the cards, a hub motor will get the job done w/ more reliablity, and be more stealthy to boot.

A quick search and I saw this:
https://hilltopperbikes.com/product/spr ... -kit-copy/

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That's not too bad a kit, but most experienced builders here would think it's too expensive for what you get and I would venture not many would want a 36 Volt system when a 48 V, or even better, a 52 V system, would provide more range (for a given size of bottle battery) and speed at little or no extra cost.

Rear of front? I remember that rear was better in terms of vibrations in the fork, but is it really a problem with low power systems? also it´s way easier to install, which it seems like a good idea for this user.

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When the power is kept low, a frt. mount can be a gd. option, but care is required to mount (you would have to do it. It has nothing to do with "vibration" (elect. motors don't vibrate), but the torque of the motor. If the motor is not properly mounted the mounting tabs of the fork (drop-outs) can be snapped off. If the forks are steel (something else, along w/ whl. size you have left out), it's piece of cake. The biggest advantage to a frt. mount is the rear whl. and all the shifting stuff is left alone.
Really, the formula for a stealthy, road bike w/ pedal assist is well known here. It would entail a sm. hub motor like the Q100H (Called the Cute) and a water bottle battery around 10 plus Ah. Lot's of builds here, mostly on Big wheel road bikes, with the parts commiong from the Big vendor in China called BMS Battery (bmsbattery.com). Their batteries are very good and they have all the little stuff to complete the build. Figure the freight cost to be about equal to the goods cost. Take a look and while you are at it, you can search here using search words like "road bike", "Q100", "Cute", etc.
But the stuff wouldn't come overnight, If your friend can't wait a couple of weeks, go with the hilltopper kit (or a geared motor kit like it).
If costs are a concern (they do start to add up), some of us are playing around w/ recycled frt. hub motors coming off Jump rental bikes. I have one and it's not too bad. They are a really old design, so they are rather big for stealth and they are a bit noisy, but the price can't be beat;
https://jag35.com/collections/jehus-deals/products/26-bafang-36v-dc-electric-bike-wheel-tire-w-tektro-disk-break
The battery and all the little stuff would have to be sourced somewhere else, of course.

"36 Volt 5.4 Ah Lithium-Ion" .... why do they even bother to include a battery.

Another option is Golden Motor Europe if you do not want to wait for a slow boat from China. However you are going to pay more than the Hilltopper kit because they do not list any flashlight batteries. The quality is excellent.
http://www.devi-motion.com/

In my experience 60km range can be reached with 36V 20Ah battery, as long as some effort is put pedalling and speed kept moderate. On my hardtail mountain bike, Kona Honzo, I have a Bafang G310 geared rear hub motor, which apparently is not even very efficient, something like 80%.

The 10s6p battery is compact enough to easily fit in the frame triangle. Motor assist speed is limited to 30km/h, which is enough for biking in the city, the legal limit for ebikes is 25km/h but that feels too slow for me. Now there's quite a lot of snow and I have spiked tyres with large knobs, and still I get around 70km range, usually I charge the battery after 0-60km though. In the summer with Continental Speed King tyres I expect to get quite a bit more.

I don't know about ready made kits as I got the components separately. But I recommend a small rear hub motor, something that might be rated at 250W but can handle 700-800W at least for a while. And ~600Wh is minimum for the battery. My battery is in a triangle bag, which also has space for the controller and wires. The hub motor is well hidden between the brake disc and cassette, making it not obvious electric bike.

Quick reply, first thank you very much for your answers.

I'll research deeper what you guys are giving me. Talking with him further, he basically wants help starting (stop and go) and actually is OK with the system stopping assisting at 20-25km/h, he could be OK with a single speed. So probably 36v and 10-12ah will be OK. I'll explain him about the batteries handicap... Me knowing his actual use I think he'll be fine. Those cute motors sou d interesting.

Again thank you so much for the help.

EDIT: Is there any kit with at least 48v and 250-350w? Or that is a custom thing.

Pablo_1985 said:

Battery technology? ! I don´t have any idea, in my time LIFEPO4 was one of the safest options, lipo for the bravest... whatever but it´s for someone that is definetely not gonna be tinkerin, so safe and reliable.

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LiFePO4 is still the safest for someone that's definitely not gonna be tinkerin', but doesn't have the economies of scale or availability that LiIon enjoys. LiPo is still enthusiast-class.

Pablo_1985 said:

I wonder if a bafang mid-drive motor is a good idea, but since it´s gonna be a road bike and he likes the clean look, maybe a small hub motor is better (but change my mind if you want), with one of those batteries in a bottle.

Rear of front? I remember that rear was better in terms of vibrations in the fork, but is it really a problem with low power systems? also it´s way easier to install, which it seems like a good idea for this user.

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Rear is always better; Grin has basically eliminated the installation challenge with a single standardized connector to the motor, L1019, which combines all the various motor wires. Very simple.

Pablo_1985 said:

EDIT: Is there any kit with at least 48v and 250-350w? Or that is a custom thing.

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https://ebikes.ca/shop/ready-to-roll-kits/rear-rtr.html?motor_type=136
https://ebikes.ca/shop/ready-to-roll-kits/direct-drive-rtr.html?motor_mount=126

Talking with him further, he basically wants help starting (stop and go)...

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Using the motor system sometimes and pedaling others doesn't work that well. Some guys do it and more claim to, but once the weight of everything is on the bike, pedaling becomes more of a chore. And even a low resistance motor will have a little drag.
The way to use an assist bike is too keep the power level low and "pedal on top of it", adding a mph or two w/ the legs.

...and [he] actually is OK with the system stopping assisting at 20-25km/h

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Wayyyyyy toooo slowww. 15 mph is boring and I'm not sure an ebike is needed to do that. For max efficiency 18 to 20 mph would be gd. To actually get somewhere and have fun doing it, 22 to 24 mph is the sweet spot. Like anything w/ wheels, the more a guy rides/drives it, the faster he will want to go.

he could be OK with a single speed

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Not really, these are called "fixie's, require an adapter and the smallest size they come in is either a 15T or 16T. To pedal along at anything 18 mph and above, a 11T rear is needed. Depending on the bike (BTW, what kind of bike are talking about here?), the largest frt. chain-ring that can be fitted is desirable as well.

probably 36v and 10-12ah will be OK.

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Ok, if he is going to limit the system potential, he wants to make sure he gets a mid-speed motor (usually called a 260, that is 260 rpm no-load @ 36 Volts applied), so he can at least reach 18 to 20 mph.

Is there any kit with at least 48v and 250-350w?

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Those are motor ratings, more of a guide than anything. The motor doesn't care how much Voltage it sees (up to a point). The Wattage rating can easily be doubled, even tripled if big hills are not in the picture.

Once you come to realize a low-power assist road bike should consist of a sm. hub motor and the original shifting gears, you have two big decisions;
1) Where to mount the motor, if it's the rear, there's two more decisions;
a)free-wheel gear-set, in which case a $40 free-wheel will be needed.
b)a cassette type motor where the original cassette can be used. There are a few available, but, depending on the donor bike drop-out's, there could be some fitment issues (due to the overall width).
2)type of controller.
a)There are sine-wave controllers w' displays the provide lot's of info, but require some parameters to be entered.
b)or if you/he just want to put the system on and ride it, a simple LED display square-wave controller will work.
This is the area you should be researching because either way, pick your parts and put together (like from BMS Battery) or buy a "kit", these are the things that tailor an ebike install to the rider's intended usage.
The problem here is your friend isn't sure how he wants to use an ebike, so that's why I'm trying to impress the idea that for a fit cyclist/assist system, the combo should be road bike, sm. geared motor, PAS, water bottle batt., flat resistant tires Otherwise, some time and money could be wasted.

Hi there!

Thank you for your answers.
the donor bike is an old road bike:
https://es.wallapop.com/item/bicicleta-de-carretera-554196273
I´ve contacted bmsbattery, because I think that a kit around the Q100H motor (350W) with a 36V 10AH battery pack for the downtube would be allright.

I keep thinking about going with the motor in the rear, I might change my mind... I like those Grin connectors I also have been thinking about hub motors with the controller inside... again, minimal and simple look is very desirable.

Using the motor system sometimes and pedaling others doesn't work that well. Some guys do it and more claim to, but once the weight of everything is on the bike, pedaling becomes more of a chore. And even a low resistance motor will have a little drag.
The way to use an assist bike is too keep the power level low and "pedal on top of it", adding a mph or two w/ the legs.

Click to expand...

Agree, and that´s what I used to do. But sure enough it helps the whole start and go.

Wayyyyyy toooo slowww. 15 mph is boring and I'm not sure an ebike is needed to do that. For max efficiency 18 to 20 mph would be gd. To actually get somewhere and have fun doing it, 22 to 24 mph is the sweet spot. Like anything w/ wheels, the more a guy rides/drives it, the faster he will want to go.

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You tell me , I had an ebike and I was putting 1750w and love it. But hell, that´s what he wants!

The single speed/fixie comment was more towards explaining that he wants something minimal, not because I think it makes sense, in my 1750w bike sure I didn´t need to change any gears XD, but I don´t expect this for a low power setup.

I know about the motor ratings and so, but we live in different countries and I am not gonna help with the installation, I am looking for somewhere where he can buy a whole easy kit and only one company to talk to in case of any problem (yeah, some sort of customer service is ok ... hahahaha) and not mixing thing so they cannot bounce the problems to any other supplier/user abuse/user wrong choice of componets...

the combo should be road bike, sm. geared motor, PAS, water bottle batt., flat resistant tires Otherwise, some time and money could be wasted.

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"sm. geared motor" what´s "sm"?, PAS is pedal assist?... that´s the plan. Why geared and not a non-geared? for the torque at low speed?

My idea.

350w motor and controller (sinewave desirable for efficiency and noise) with 700c rim (or whatever wattage motor with a 350w controller but with the supplier ok with it).
at least 36v 10ahBattery, or more voltage if offered (48v 7,5AH), for efficiency shake.
Thumb throttle
No display or minimal for selecting power levels.
Pedelec, it´s gonna be used mainly if not only like that

Maybe something like smartpie 5 from Goldenmotor (gosh thay havent´s changed the website at all! XD)

Regards,

Pablo

36V 10Ah battery is only 360Wh which is not that much, unless you plan to primarily pedal. I'd suggest you look for a 36V 15Ah battery so you can at least have 480Wh to ride with. The battery will last longer because you are not draining it every time you use it.

Pablo_1985 said:

Maybe something like smartpie 5 from Goldenmotor (gosh thay havent´s changed the website at all! XD)

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OH it has changed a little. The Vector (series 5) controllers now have a bluetooth option (that they can keep from my perspective).

If that is your father's current ride then I can understand his desire for a minimal system. Take a look at the "weight weenie" bike in my signature. It is currently running a 36 volt 12 Ahr GM rack battery (end of life battery). It ain't fast. It does not go very far but it does get me there and back. If I was starting from scratch on that project I might consider some kind of 'modular' battery system where I could pack 8, 12 or 16 AHr of batteries depending on the trip distance.

GM Smart Pie has the advantage that you can always upgrade from 36 to 48 volts with a battery change and run through GM's software. No need to replace the controller or throttle ... and because I am lazy I like mine on the front end.

One point of not to be overlooked: with a motor your father will tend to ride faster. On the roads in my area high pressure skinny road tires are not a pleasant experience at speed .... and I tend to ride that bike slower.

cheers

OK, now we understand better what he wants. We probably should have started w/ the bike pic., it would have saved some time
It's not the bike I would choose to electrify, but if that's what he wants to do....
Actually, there have been a couple of minimal road bikes like that that have been electrified here on ES.
They went w/ the smallest hub motor available, like the Q75;
https://bmsbattery.com/motor/593-16233-q75-36v-front-driving-hub-motor-ebike-kit.html#/213-rpm-201
BMS Battery used to offer a water bottle battery with an intergrated controller inside, but it looks like one has to buy the parts and put it together.
Mounting a throttle on those drop bars will be a challenge, it probably would be PAS only.
Here is only one thread on electicfying a roadster, but in it are members chas58, and sunder. Search their posts as they are the guys who lead the way.
https://endless-sphere.com/forums/viewtopic.php?t=75991
The irony here is that the smaller (more minimalist), the more complicated things get. Sort of like Quantum Mechanics.
Although the motor is probably a little big, maybe he should go back to the Swytch Kit idea.
Or buy another bike more suitable to ebike usage.

Hi there!

I see you guys are not having problems with the motor in the front, I guess that the low power helps, so I´ll stay with that. BTW, it´s a friend, not my dad, I said at the beginning that when I entered the forum I was a student (joined the forum on Feb 19 2009), but know long time has gone and even a dad of one little girl and boy on the way .
bmsbattery offers battery packs with the controller integrated, which I think it´s awesome for the project:

Option 1:
Battery+controller:
https://bmsbattery.com/ebike-battery/932-17777-36v10ah116ah14ah-new-bottle-battery-pack.html#/138-color-silver/323-controller-s06s_hall_sensor_sine_wave/381-display-lcd5/513-cells_capacity-samsung_29ah_116ah
I don´t understand the display selector, but let´s say LCD5, I would choose the s06P sensorless square wave integrated controller and Samsung 2.9AH for a 11.6AH battery pack.

motor+rim:
https://bmsbattery.com/ebike/581-16212-q75-36v200w-front-v-brake-e-bike-motor-wheel-ebike-kit.html#/213-rpm-201
which I would need to change to s06p controller


Option 2:
Battery+controller:
https://bmsbattery.com/ebike-battery/932-17777-36v10ah116ah14ah-new-bottle-battery-pack.html#/138-color-silver/323-controller-s06s_hall_sensor_sine_wave/381-display-lcd5/513-cells_capacity-samsung_29ah_116ah
I don´t understand the display selector, but let´s say LCD5, I would choose the s06S hall sensor sine wave integrated controller and Samsung 2.9AH for a 11.6AH battery pack.
motor+rim:
NO IDEA
https://bmsbattery.com/31-36v

I would like to see about weights for the hub motors to be able to compare, but they don´t offer that for all, but option 1 is 1,2kg, which seems pretty light. The second option would mean 250w instead of 200w, and a sine wave controller so probably quieter, but I don´t know about weights. ¿Would you guys give me some input about the motor+rim? do they actually mount 700c rims? -and with that I don´t mean just matching the diameter but also the width- and finally would we be missing anything to have a ready to go kit?

Best,

Pablo

Yes, BMS B does offer a water bottle batt. w/ intergrated controller. I just found it helping a guy w/ a kid's build;
https://bmsbattery.com/ebike-battery/1094-18534-36v5ah7ah-haitu-bottle-battery-pack-with-usb-output.html#/510-inner_controller-with/542-cells_capacity-25ah_high_c_rate_5ah
These things had some issues when they came out, but this is a new product and maybe they have been improved. Not familular w/ the brand and there's not much info, it doesn't even say if it's a sine-wave, but I think it must be. Perhaps you can search this or contact BMS B.
Paired with the Q75 or Q85, it could be the system he is looking for.

The Q series motor weights are available, Google or ck greenbikekit.com.
I know the Q100 is 2 Kg.s, and I think the 85 is 1.6Kg. The 75 a little less than that.

I can't say what would be the best approach to the whl.s and tires, I'm an ebike guy, not a bicycle guy Maybe chalo will chime in.

Hi motomech, I saw that one too, but maybe it´s just a a little bit small? that´s why in my options I offered the bigger version which starts at 10ah and goes up to 14ah.

https://bmsbattery.com/ebike-battery/932-17777-36v10ah116ah14ah-new-bottle-battery-pack.html#/138-color-silver/323-controller-s06s_hall_sensor_sine_wave/381-display-lcd5/513-cells_capacity-samsung_29ah_116ah

I think this new BMS B web site is messed up, some things seem hidden.
Yeah, that has a lot of capacity.
I had a SO6S when they first came out, but didn't use it very long, it wouldn't play well w/ the batt chem I use (LiPoly).
There is a ton of stuff here on the SO6S and the earlier and smaller versions of that batt.
Search and you can read for weeks

Sorry, I don´t know why I didn´t think about googling...:
q85= 1,6kg
q100= 2.1kg
q75= 1.2kg (200w)
QSWXK5= 3.283kg
https://bmsbattery.com/ebike/595-16236-q85-36v250w-front-driving-v-brake-e-bike-motor-wheel-ebike-kit.html#/214-rpm-328
So I´ll update options:
Option 1: 200w light
Battery+controller:
5-7AH
https://bmsbattery.com/ebike-battery/1094-18534-36v5ah7ah-haitu-bottle-battery-pack-with-usb-output.html#/510-inner_controller-with/542-cells_capacity-25ah_high_c_rate_5ah
or 10-14AH
https://bmsbattery.com/ebike-battery/932-17777-36v10ah116ah14ah-new-bottle-battery-pack.html#/138-color-silver/323-controller-s06s_hall_sensor_sine_wave/381-display-lcd5/513-cells_capacity-samsung_29ah_116ah

s06P sensorless square wave integrated controller

motor+rim:
https://bmsbattery.com/ebike/581-16212-q75-36v200w-front-v-brake-e-bike-motor-wheel-ebike-kit.html#/213-rpm-201

Option 2: 250w heavier
Battery+controller:
5-7AH
https://bmsbattery.com/ebike-battery/1094-18534-36v5ah7ah-haitu-bottle-battery-pack-with-usb-output.html#/510-inner_controller-with/542-cells_capacity-25ah_high_c_rate_5ah
or 10-14AH
https://bmsbattery.com/ebike-battery/932-17777-36v10ah116ah14ah-new-bottle-battery-pack.html#/138-color-silver/323-controller-s06s_hall_sensor_sine_wave/381-display-lcd5/513-cells_capacity-samsung_29ah_116ah

s06S hall sensor sine wave integrated controller
motor+rim:

https://bmsbattery.com/ebike/595-16236-q85-36v250w-front-driving-v-brake-e-bike-motor-wheel-ebike-kit.html#/214-rpm-328

I would go for option 2, even though is heavier (400g), it´s a little bit more powerfull, and then you can use the sine wave which I havent tried but sounds smooth - It´s tempting to use the q75 motor with a 250w controller, but it goes against all I´ve been talking XD - In terms of the battery I would go with 11,6AH samsung battery, I feel like my friend is anxious about range, so let´s not get crazy with the weight savings, much more if it´s in the downtube, and being Samsung and a bigger capacity a better lifespan should be expected.

I have had Leaf 1500W 35H motor on the front of a fat bike, it was fine. 36V40A also had 52V40A. Different riding technique then rear hub motor but you get used to it and as long as your casually riding its all fine.

I'd do it again!

That kind of power, need two torque arms on a steel rigid fork but some have done it on aluminum fork and suspension forks.

I would highly highly highly suggest that you do not go with 250W, or 350W. At a minimum go with 500W and ideally 750-1kw. Even if your a pedalling fan or wear Lycra.

Damn man, covid times flying by quick, usually have zero plans for weeks on end now all of sudden I gotta rush out the door.

PS Remember that BMSBattery has cheap prices, until you reach the checkout at which time their shipping costs are a tad higher to recoup their product prices. Also, bare hub s/h price is cheaper then laced hub. Laced hubs are usually done with inferior products, like spokes, nipples and rims unless you buy from reputable sellers like Grintech www.ebikes.com or www.em3ev.com or any number of other reputable sellers.

Pablo_1985 said:

Hi guys,

It´s been a long time since my last post, no I am not studying anymore I am a dad and all that... The thing is I have a friend asking me questions and I know that things have easily changed a lot since when I used to be here. So here I come with some newbie questions.

He wants some kit for putting on a road donor bike, not very powerful, he says 60km of autonomy, but (I think that´s way too much), he wants something light, not necessary very powerful, I guess that something around 350w it´s fine (just to fell a little bit more power than most of the things out there), he likes Swytch bikes but he doesn't want to wait for it, so it seems he likes the minimalist look.

Battery technology? ! I don´t have any idea, in my time LIFEPO4 was one of the safest options, lipo for the bravest... whatever but it´s for someone that is definetely not gonna be tinkerin, so safe and reliable.

I wonder if a bafang mid-drive motor is a good idea, but since it´s gonna be a road bike and he likes the clean look, maybe a small hub motor is better (but change my mind if you want), with one of those batteries in a bottle.

Rear of front? I remember that rear was better in terms of vibrations in the fork, but is it really a problem with low power systems? also it´s way easier to install, which it seems like a good idea for this user.

A quick search and I saw this:
https://hilltopperbikes.com/product/sprinter-12-mile-24v-electric-bike-kit-copy/

They provide also a torque arm, so maybe it´s recomended even in low power front hub motors?

And at last, that is available in Spain.

Anyway, thank you very much in advance and I hope i don't annoy everybody with my post.

TLDR: you guys know of a lightweight minimal, low power kit with battery for a road donor bike?

Click to expand...

Pablo...just some thoughts and ideas:

Any kit can be a "low" power kit...just depends on the controller and voltage you use. I'd highly recomend a 14s/52v battery because you will be able to get more capacity which equates to being able to ride more miles under battery power plus you'll have a lot better throttle response than a lower voltage. IMO 14s/52v is becoming the most popular voltage for ebikes and the only reason I'd use anything else is if local laws do not allow you to use the 52v battery. Fully charged the 14s/52v battery is 58.8v...do NOT charge it or any Li Ion battery above 4.2v per cell since the risk of fire and damage to the battery rises dramatically as you exceed 4.2v per cell. For a long life, it is better to not charge above about 4.1v per cell but that is another discussion .

If doing relatively high miles, I'd stay away from a mid-drive and go with either a geared hub motor like a MAC or a Direct Drive (DD) Hub Motor...lots of choices and prices available for a DD motor. Mid drives require the power to go through the chain/sprockets and bicycle parts will wear quickly. Hub motors, both the geared hub and the DD motors transit the power directly to the wheel and not through the bike's drivetrain.

As long as you don't plan to go too high with the amperage a Z910 connector between the motor and the controller can be really convenient and there are a decent number of choices for DD motors with it. If trying to keep the price as low as possible, I'd go with this one: https://www.amazon.com/gp/product/B00Q8JT9H2/ref=ox_sc_saved_title_3?smid=A2V0U2CDI8OSTK&psc=1 It is the kit I am currently considering for my next build.

Batteries...any Li Ion 18650 based battery is going to have the same safety as far as the cells are concerned. LiFePO4 chemistry is better for a battery used for starting a vehicle like a motorcycle where the chemistries that EM3ev.com uses are better for ebikes because they have more capacity. I'd stay away from LiPo unless you need a lot of power and you are ready to deal with a few safety issues. I'd highly recomend EM3ev.com for your battery...they have several redundant safety mechanisms that protect you and the battery.

If you plan to ride below about 30 mph, a MAC has some advantages because it has a 5:1 gear reduction that gives you a lot better acceleration than a DD motor but since EM3ev stopped selling the MAC, they are a little difficult to find now. That means a 12T or a 10T winding...an 8T or winding that has a higher rpm may over heat. The GMAC from Grin Tech is a MAC without a clutch and is capable of regen. Grin sells really good stuff and provides excellent customer support but their prices are a little more than some places...a good example of you get what you pay for :wink: .

Something nobody has mentioned is "tires". The larger the diameter the smoother and easier the bike will roll and the less the rider will feel the bumps/obstacles. Schwalbe Pick-Up and Super Moto-X along with the Maxxis Hookworm are the best road tires I could find.

A suspension seat post is a nice addition that can soften the ride...I like the Diamondback suspension seat post.

Don't know if your frame can use a 1 1/8" steerer fork but if it can the Suntour XCR suspension fork is an economical choice that works pretty good. If the bike has a 1" steerer, you can find the XCR with a 1" steerer several places but you may also need a new headset if going from the old school threaded steerer to the newer designed XCR without threads.

I'd go with a rear mounted motor...I just like the way it handles and rides plus the frame is a stronger attachment point than the fork...although a front mount is feasible in most cases.

Thanks for your comments Bullfrog,

I´ve given my recommendations to my friend, we´ll see where he lands, he also is reading without login...

Best,

Pablo