while selecting an ebike you must have to check the following things:

Speed:

always keep in mind the speed of the bikes depends on voltage and the power of the motor. If you are making a DIY ebike then you can select the high voltage and power rating of the motor. at various voltage levels, the linear acceleration is different.
you will get an idea about how voltage can affect the speed of the vehicle?

read also “what is the maximum speed achieved in an electric bicycle?”

Range:

it depends on battery capacity. You must decide how many kilometers or mile ranges are needed. However, if you don’t know how much range you will get from ‘X’ amount of battery capacity then use this tool “Range calculator for Ev’s”
this tool can help you to find a battery capacity for the required range.
note: “range calculator” does not include losses of motor, vehicle dynamics, road circumstances so it is best to add an extra 10% capacity to the calculated answer.

Type of battery:

which battery type is used in the ebike is directly related to the weight of the ebike, battery cycle, quality, etc matters a lot. a tip from my side: go for LiFePO4. learn more about Lifepo4. in short, lifepo4 (li-ion) batteries are safe to handle and can sustain inrush current during acceleration.

Motor type:

motors used in ebike are mostly PMDC, BLDC, BLDC hub motors, and mid drives.
tip: it will be better to go for a hub motor. because there are two reasons, first it will give an aesthetic look for your ebike, and second, it doesn’t have any complexity compare to the mid-drive motor.
also, read what is a hub motor?

Loading capacity:

it is essential to have an ebike capable of carrying 180-200 kg.

for example, if you are a teenager (13-19-year-old) go for 24-36V and power of 250-500W, and adults (above 19 years old) – require 48V-60V and power of the 500W-1500W system.

Climbing ability:

check the climbing capability of the ebike. if motor power is around 250w to 500w then better it has “PAS” (pedal assist system). above the power of 500W, there is no need for “PAS”

Features of the controller:

features are very essential for any e-bikes. they are already inbuilt in the controller. in short, more features mean more possibilities.
some of the important features must-have in the controller, like
Pedal assistance, E-brake system, display compatibility, auto-learning wire.

Display Type:

there are two types of displays, analog and digital. analog displays are cheap compare to a digital display. in my opinion, you should buy a digital display.

Warranty:

check which components have warranties and which components need regular maintenance. you should ask do they provide services for the product. for example services like repairing and replacement.

After-sale support:

check the after-sales support. it is essential to have good customer support otherwise you might face trouble when having any technical issues. you can ask your friends for better recommendations.