My son wants this conversion kit for his mountain bike.
Posted by damnyankee26@reddit | ebikes | View on Reddit | 31 comments
Does anyone have any thoughts on this brand or how safe this kit would be for a 14 year old? My concern isnt necessarily top speed as we will monitor that remotely but I am concerned with torque and acceleration.
MaxTrixLe@reddit
That's likely a 72V20ah UPP style battery (450-500$) and a generic 3kw motor (150-250$), the rest of the kit is anywhere from 50-150$ so you're paying twice the cost through a drop shipper
RichTrifle1785@reddit
this is way overkill and not really safe for a 14 year old. if you're choosing this kit because your son recommended you this and you don't know what other options you have, i'd look into the 36-48v conversion kits that do 750w-1000w peak
damnyankee26@reddit (OP)
Yes, he sent me this and I dont know much about ebikes. From what I gathered, this was going to be too powerful but wasnt sure.
RichTrifle1785@reddit
it's a lot more powerful than you'd expect, especially on a skinny mtb frame not built to withstand highway speeds.
since you don't seem to know where to go from here, i'd maybe go on amazon and look for some conversion kits sold by varstrom. i haven't used a conversion kit yet, i've just heard good things about the varstrom ones specifically.
and since your kid tried tricking you into building him an overpowered bike, i'd buy a 500w kit that tops out at maybe 20mph or not build a bike at all. god knows what your son was planning to do
SwiftUnban@reddit
Honestly I agree, I have a 4KW kit on my bike and it’s zippy as fuck.
Me and my sister did a side by side race from a stop in her ford escape, I was pulling ahead until I hit my top speed of about 40mph.
1kw is still plenty, hell, I was shocked at how powerful my 250w was coming from a normal bike.
If OPs intentions are for it to be used like a bike at speeds of a bike 3kw is way too much.
Gold_Area5109@reddit
First off...
Legally the most you can use one the road without a motorcycle license is:
750 watt, 20mph by throttle or 28 mph with pedal assist
If your son wants an off road dirt bike it could be fine if you're alright with him going 50 to 60 mph.
What your son picked out is a dirt bike power on a mountain bike frame... Which typically isn't designed to handle that much power. Which raises more questions about safety.
Old_Cockroach_2993@reddit
If you don't like your son this is the gift.
weefees@reddit
A 3000w is roughly the same output as a 50cc two stroke motor. Do not allow.
atlasraven@reddit
It's a very fast kit. Something in the 750-1000w range would be more appropriate.
damnyankee26@reddit (OP)
Thanks for the quick response. Are there and particular brands that are decent? I want to stay around $1,000.
cutsnek@reddit
Please be mindful this is a trend at the moment especially with young boys to get these cheap and powerful kits or the cheap powerful fat tyre style e-bikes that are more like motor bikes than bicycles.
These can be extremely dangerous and are starting to get outlawed where I live due to the number of injuries / deaths associated with them, especially with young boys.
Kids are trying to convince their parents these are safe, they for the most part do not meet basic safety requirements.
atlasraven@reddit
It's all my china. Pick something quality. Bafang is well known.
geoffpz1@reddit
I did this. I am an old guy. 1000/48 will get you to 30, easy. Bike parts will explode and you will crash(I did, broke my face when the rear brake failed and I went over the front, full face helmet and new bike now). Bottom line is that at 14, I would have absolutely done this if I had the tech available, but my parents would have said hell no. So, be a parent and pay attention. Kids will mess with the electronics to make it go as fast as possible and it is not hard with youtube. They will kill you and cars do not expect you. This = dead if you are playing in traffic. If you do this, make him build it and make him test it. Great learning opportunity with the right boundaries IMHO.
Erik0xff0000@reddit
Look at the fatality rates for motorcycles and consider whether you should give a 14 year old a motorcycle.
Repulsive_Aside_4122@reddit
IMO, For a hub motor kit, I would suggest a 48 volt kit with a 20AH 52 volt battery. 72v is overpowered for a hub motor, you can expect a lot of broken spokes as well as braking & cornering 'mishaps' 48 volt hub motor with a 20AH 52 v battery gives acceptable performance and range
oldfrancis@reddit
Get a 750 watt mid drive kit from Bafang.
The other kit is not appropriate.
Full-Part2427@reddit
I'm skeptical about the quality of the bike to begin with.
oldfrancis@reddit
That is not an unfair concern.
I chose a vintage bike. It's a steel framed 1985 Schwinn Cimarron. It doesn't have disc brakes (which many people think are we requirement for e-bikes) but, My kit doesn't drive my bike faster than 30 miles an hour and 30 miles an hour is bicycle speeds. The cantilever breaks on my bike can lock up both wheels on dry pavement at will and I have no problem controlling my speed on descents.
Taiyoryu@reddit
Check your local regulations. Your son may be too young to legally ride an ebike on public throughways regardless of power. Many jurisdictions require a rider to be 16. Otherwise your son will be limited to private property where he has consent to ride.
Full-Part2427@reddit
The only thing this is good for is being a gd menace. A 3000watt hub motor is garbage on the trails, is too heavy and still struggles climbing hills in a safe way.
It's only good for blasting through town at 45mph.
GreenAccident3004@reddit
3000 watt 72V ? You by that for a 14 year old, get some life insurance & a restful plot.
mdjak1@reddit
How fast do you want him to go? My 750 watt Lectric XP4 will do 28 mph.
classaceairspace@reddit
That's a crazy amount of power for a bike, especially so for a 14 year old, this is solidly in meat crayon territory.
Realistic_Mix3652@reddit
Your son has more than enough energy in his yong legs to get himself in trouble (but not too much trouble). Adding a motor to his bike is NOT a good idea.
Ok_Incident8962@reddit
This is really one of those times you just ask yourself how cool you are with your son do wheelies at 60 mph in front of the middle school on something designed to do 15 phone safely. Send it!
bradland@reddit
Heh. He's going straight for the killshot.
E-bike kits come in a few varieties. Let's look at two criteria: battery voltage and motor type.
E-bike batteries come in a handful of common voltages: 36V, 48V/52V, 60V, and 72V. Think of voltage like pressure in the electrical system. Higher voltages allow the battery to do more work for a given current. So 72V 20A will do a lot more work than 48V 20A (A means amps). Generally speaking, the only reason to use a 72V system is if you want to to very fast (+30 mph) for an e-bike.
Motors come in three types: mid-drive, geared hub, and direct drive hub. The kit your son has spec'd is a direct drive hub. Speaking in broad generalities here (there are definitely exceptions) DD hub motors are designed for speed, not acceleration. The motor's "windings" will determine its top speed, but with a 72V kit, that bike is likely to top 40 MPH.
If you're not getting the picture already, your son has spec'd out a kit that is very high performance. It is not at all suitable for a 14 year old. It is also going to be very hard on the bicycle frame. Hub motors drive the rear wheels by twisting on the axle. There's a great explanation here:
https://ebikes.ca/catalog/category/view/s/torque-arms/id/13/
Your son's kit appears to come with torque arms, but they won't be enough for a 72V 3kW drive on most bicycle frames. Your son is young, so he has no idea what he's getting into. The dropouts on bicycle frames will get loose and the frame will crack if you run a kit like the one he's picked.
Do yourself a favor and head over to https://www.leafbike.com and find a 48V kit that is wound for <40 MPH top speed. Motors are most efficient when running at around 80% of top speed, so if a kit is wound for 37 MPH, top speed will be right around 30 MPH, which is just above class 3 speeds (28 MPH). A kit wound for 25 MPH will hit right around 20 MPH, which is class 2 speed. IMO, class 2 is far more suitable for someone his age.
mickeyaaaa@reddit
This is approximately 50 mph kit meaning essentially turning a bicycle into a motorcycle by most measures.
It will end badly if you allow us. Almost guaranteed. Either by injury, death or impound.
Relative-Display-676@reddit
your son will be the next ghost rider with this kit. those are rebranded UPP batteries that had a recall on them from CPSP
BWWFC@reddit
what's the necessary torque/acceleration "concern"?
are the brakes/suspension adequate, and will the torque destroy the frame even in the hand of a mature and experienced rider???
Brian43ny@reddit
Would also say these kits require some mechanical skill and they require a fair amount of tweaking.
BassesNBikes@reddit
A 3kW direct drive hub will ruin his mountain bike with 20+ lb of unsprung weight in the rear wheel while also rendering it an unregistered motorized vehicle. You'd be much better off with a legal, 750W mid-drive kit from Bafang or TongSheng.