72V Razor Motor Kit Fitment Guide

Before you commit to an electric dirt bike motor kit, the real question is whether the hardware will sit in your frame, line up with your chain and talk to a battery you already own or plan to buy. This guide works through the KR5V V2 — a 72V 5000W brushless motor paired with an NS18 Fardriver 100A Bluetooth controller — chassis by chassis, so a Razor MX650 motor upgrade is planned around measurements and hardware checks rather than a marketplace headline. You will find what ships in the box, what is deliberately left out, how the three sprocket options change the result, and which points to confirm on your own bike before ordering.

View the KR5V V2 Kit Contact Us

Kunray KR5V Electric BLDC Motor 72V 5000W Upgrade Electric Motor For Razor, Electric Motorcycle, Go Kart Brushless DC Motor Mid Motor

Fitment Check: Pick Your Chassis

Select your bike to see what the kit documentation states, and the four points that decide whether the order goes smoothly.

Razor MX650 Razor MX500 Razor SX500 Indian650 Razor RSF650

Compatibility is stated for the frames listed on the product page. Model year and previous modifications fall outside that statement.

Listed as a direct mount

Razor MX650

The product page states that this motor mounts directly into the Razor MX650 chassis without modification. Treat that as the starting point, not the finish line.

Confirm your model year — the mounting statement does not publish a year range.
Confirm the bike has no previous motor, mount or swingarm modification.
Confirm your rear chain type before choosing #35 9T, #35 11T or 420-10T.
Plan a 72V battery, because the kit ships without one.

What Ships, What Does Not

Four items arrive in the box. One critical item deliberately does not — and it is the one that decides how the build performs.

KR5V V2 72V 5000W motor kit layout with controller, throttle and sprocket — KR5V V2 kit: motor, NS18 Fardriver controller, throttle choice and chain/sprocket set. Packing follows the selected SKU.

Included in the kit

KR5V V2 72V 5000W brushless motor with reinforced shaft and updated housing
NS18 Fardriver controller — 100A rated, Bluetooth built in
LED throttle with voltage display — pedal or 3-speed half-handlebar style
Chain, tooth and sprocket set (#35 9T, #35 11T or 420-10T)

Not included: the battery. No pack, BMS, cabling or fuse ships with this kit. A 72V battery is a separate purchase and a separate design decision for every build. If you cannot name the pack you are fitting, this is the first thing to settle.

Choose your sprocket and throttle at checkout

Because the September 2025 case update changed the shaft size, the sprocket diameter is now larger and the sprockets are described as stronger. Sprocket availability therefore follows the current version, not older builds you may have seen online.

KR5V V2 motor

Rated voltage72V

Rated / peak power5000W / 10KW

Rated / peak speed5000 RPM / 8000 RPM

Rated / peak current60A / 80–100A

Torque / peak torque8.5 N·m / 35 N·m

Poles5 pair / 10 pcs

SensorsHall + KTY84-130

Insulation classF (155°C)

IP ratingIP54, air cooled

Phase wire8mm²

NS18 Fardriver controller

Rated power3000–5000W

Rated voltage48–72V

Rated current100A

Protect phase current300A

Waterproof gradeIP67

BluetoothBuilt in, Android & iOS

Net weight1.9 kg

CompatibilityKR5V, QS Motor, most BLDC

Control typeSine wave, self-learning

Chassis Fitment Matrix

Five frames are named on the product page. Everything beyond that statement depends on the individual bike, so the last column lists what to verify before you order.

Chassis	Mounting statement	Sprocket options	Rotation / wiring	Verify before ordering
Razor MX650	Direct mount, no frame modification stated	#35 9T / #35 11T / 420-10T	Left side, counter-clockwise	Model year, previous motor or mount work, rear chain size
Razor MX500	Direct mount, no frame modification stated	#35 9T / #35 11T / 420-10T	Left side, counter-clockwise	Model year, earlier wiring changes, rear chain size
Razor SX500	Direct mount, no frame modification stated	#35 9T / #35 11T / 420-10T	Left side, counter-clockwise	Model year, case clearance after a test fit, rear chain size
Indian650	Direct mount, no frame modification stated	#35 9T / #35 11T / 420-10T	Left side, counter-clockwise	Model year, motor mount bolt pattern, rear chain size
Razor RSF650	Direct mount, no frame modification stated	#35 9T / #35 11T / 420-10T	Left side, counter-clockwise	Model year, swingarm clearance, rear chain size

The verify column is not a claim of fitment — it is the short list of things that vary between individual bikes and that no listing can settle for you. Measure, photograph your mounts, and confirm the chain standard before you choose a sprocket.

KR5V 72V 5000W brushless motor and Fardriver controller side view — Check motor case clearance and sprocket alignment on your frame before wiring anything.

Why the shaft change matters

The current version uses a revised motor shaft and a larger sprocket diameter than earlier builds. That is good news for strength, but it means an old sprocket from a previous kit may not be the right reference point for your alignment measurements.

What “direct mount” actually covers

The statement covers the frame and mount points named by the manufacturer. It does not cover battery tray space, brake hardware, tyre choice or controller programming. Those remain your build decisions, and the modules below deal with them one at a time.

Planning a build you have not measured yet? Send photos of your motor mounts and rear sprocket to the support team and ask for a fitment opinion before you pay.

Power-System Dependency Map

A 100A controller does not upgrade your battery — it exposes it. Here is the chain of parts that has to agree before the motor can deliver what it is rated for.

72V battery pack Not included

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Battery BMS Continuous discharge rating

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Fuse, breaker and cabling Build responsibility

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NS18 Fardriver controller 48–72V, 100A rated

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KR5V V2 motor 72V, 5000W rated

LED throttle Pedal or 3-speed, included

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Bluetooth app Android / iOS tuning

NS18 Fardriver 100A Bluetooth controller supplied with the KR5V V2 motor kit — The NS18 controller is rated 100A with a 300A protect phase current figure, and is IP67 rated.

Gearing & Speed Reality Check

The headline number is real, but it comes with conditions written on the same page. Read them before you build your expectations.

KR5V Kunray 72V 5000W upgrade motor for Razor, electric motorcycle and go-kart — The motor is rated for a 100–200 kg load range; rider and chassis weight belong in your speed planning.

The kit page states 60 mph at a 6.0 gear ratio, with a full battery on 72 volts and 100 line amps. It also states that results vary with rider weight, wheel size, chain size, tyre size and drivetrain. Treat 60 mph as a reference point achieved on a specific build, not a guaranteed outcome of yours.

What actually moves the number

Gear ratio between the motor sprocket and the rear wheel
Rider plus chassis weight against the stated 100–200 kg load range
Wheel and tyre diameter, which changes the effective final drive
Chain size and condition, and the current limit you set in the app

Sprocket trade-offs at a glance

Option	Chain standard	Practical effect
#35 9T	#35	Smallest drive sprocket of the three — more torque multiplication, lower theoretical top speed
#35 11T	#35	Larger than the 9T on the same chain — higher theoretical top speed, softer low-end multiplication
420-10T	420	For bikes already running 420 chain — never mix this with a #35 rear setup

Match Your Build to the Specification

Four common starting points, and the specification decision each one forces.

Sprocket: #35 9T / #35 11T

Stock Razor still on #35 chain

Stay inside the #35 family and pick the tooth count that suits your riding. The 9T leans toward acceleration and the 11T leans toward top speed. Whichever you choose, inspect the rear sprocket and chain for wear first — a new motor against a worn chain will not stay aligned.

Sprocket: 420-10T

Bike already converted to 420 chain

If a previous build moved the rear wheel to a 420 setup, the 420-10T is the only one of the three options that matches it. Chain standard is a hard constraint — it outranks any preference about tooth count.

Load range: 100–200 kg

Adult rider, hills and stop-start use

The stated load range is about 100–200 kg, so add rider and chassis weight honestly. Above the comfortable end of that range, and on gradients, favour the option that multiplies torque rather than the one chasing top speed.

Throttle: pedal or twist

Foot-operated frame versus twist-bar frame

The kit lets you choose one of three throttles: a pedal kit, a half twist throttle kit or a blue throttle kit. Match the control to the riding position of your frame, because a twist throttle on a foot-forward chassis is an ergonomic compromise you will feel on every ride.

Building More Than One Bike?

Shops, teams and small manufacturers order these kits in multiples and often need a different sprocket combination or throttle configuration than the standard SKU. Tell the team what you are building and they can confirm the configuration before you commit.

Listed at $399.99, down from $449.99, with a 4.9 rating across 23 reviews and 176 units sold. Ships from the US or CN, and the listing states free shipping with no tax for the US, Australia and some EU countries.

Check Options & Stock

KR5V V2 motor kit configuration for bulk and custom orders

Frequently Asked Questions

what information is shown for this product?

review the product details, images, and specifications presented on the official product page.

where can i check the intended application?

use the application and use-case information published on the official product page.

which specifications should i confirm before ordering?

confirm the specifications and options listed for the exact product variant before placing an order.

where can i check available options?

check the official product page or ask the supplier about options shown for the selected product.

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use the official contact or inquiry path provided on the site.

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72V Razor Motor Kit Fitment Guide