Is this upgrade safe?

[davidsafford]

Hello,
I’ve got a 26" MalTrack blue/black bike. If I clean it up, it should be fine, but I’m thinking about installing a 2000W 52V conversion kit with a 52V 20Ah or 25Ah battery, and I’m not sure which battery size to choose. Would this setup work if I also upgrade to hydraulic brakes? AI told me I’d need torque arms, but I don’t even know what those are. I’m planning to ride at around 50 km/h and want enough power to handle steep roads without struggling — not insanely steep hills, but definitely the kind that would be difficult without a conversion kit.
Does this sound reasonably safe, or is it just a bad idea and not worth doing?

 

[Chargeride]

Its an aluminium frame and I presume youre referring to a large direct drive hub.
You really should fit at least one torque arm, the dropouts will quickly fail and leave you with ripped out motor cabling.
2000w isnt crazy power anymore, hydraulic brakes would be good, but the quality and disc size is more important.

It will easily do 30mph, but its not really a big climber, though the 26 inch wheel size will help.

Of course you are taking a lightweight mtb to its structual limit and need to keep an eye on every bolt and check the frame daily

 

[davidsafford]

Its an aluminium frame and I presume youre referring to a large direct drive hub.
You really should fit at least one torque arm, the dropouts will quickly fail and leave you with ripped out motor cabling.
2000w isnt crazy power anymore, hydraulic brakes would be good, but the quality and disc size is more important.



It will easily do 30mph, but its not really a big climber, though the 26 inch wheel size will help.



Of course you are taking a lightweight mtb to its structual limit and need to keep an eye on every bolt and check the frame daily geometry dash 3d

Thanks for your suggestion.

 

[RunForTheHills]

For long, steep climbs, you would be better off with a mid-drive motor kit rather than more power that can use the gears on the bike. 1000 watts can get you the speed you want. 750 watts can too. Even a DD hub motor will overheat on a long and steep enough hill. You can use the Grin motor simulator to model that.

Keep in mind that 52V X 20A is only 1040 watts. Most people building 2KW+ e-motorcycles are using higher voltage and very big batteries. Bicycle components aren't designed for that kind of power.

 

[RunForTheHills]

Grin Motor Simulator

 

[harryS]

2000W motor in rear? That's mechanically safe. In front, not very safe at all as the forks will break off and you face plant. In the rear, the wheel will just spin if it gets loose, tear out the wires. and might jam the and skid, but you probably won't land on your face. Torque arm is recommended for that kind of power.



My answer to the safety issue is it depends where you are riding, In urban areas, no one will expect a skinny bike to be going 30 mph, 44 feet per second, even if they see you coming. Expect to see a lot of cars making turns in front of you. Not going to be safe at 30 mph. I gave up my motorcycles years ago for that reason, I have no urge to ride ebikes fast in traffic, You can do what you want,

A 52V 20AH battery is rated at 1000Watt-hours. Derate 10-20% for 800-900 WH for real life. At 30 mph, you might get 25 miles is my guess. Wind resistance eats up the watts.

 

[indianajo]

DD motors have no torque until they get over 12 mph. They use massive mounts of watthours climbing any grade over 4%. I abandoned mine in 2020 after 2 unsatisfactory months.
The post about using the gears of a mid-drive to climb hills is a big laugh. You have to have a rear sprocket of 48 or 52 teeth to get significant torque increase. About the size of a dinner plate. Those can only be bought in 10 sprocket or more clusters, so you will be changing the chain every 500-1000 miles. I get 5000 miles out of my 8 speed chain with a geared hub motor on the front. Mountain bikes with such a huge rear sprocket cluster tend to cost $5000. Divide out the ratios. Sprockets sets mostly increase speed, not torque. Many mid-drives have a 46 tooth front cluster. Changing that front sprocket to 42 tooth may void the warranty.
I sailed over a pickup truck bed when I was going pedal powered at 25 mph. The bike went under the wheels. Do that speed only where there are no driveways for any fool to turn left into.
Grin sells torque arms. Unfortunately they are in Canada, so you will pay a tarriff if you get your package at all. Some cables stayed at Memphis ICE warehouse for 9 months while they decided if they contained aluminum (100% tarriff) or not (15% tarriff). Don't expect a worm hose clamp to effectively hold the arm to the bike frame. Lots of photos of those stretched out to 4x normal length, when used on torque arms. I use a 1" band of steel cut out of a dead box fan frame. Use glove cutting sheet metal. I make the torque arm out of 1" steel strap, drilling and filing a flatted side hole to fit the motor shaft. Then I put 13/64" holes in the other end to clear #10 machine screws for the strut band. Use elastic stop nuts on the screws to keep them from coming loose due to vibration.