72V ONYX Brake System Guide

This post is a complete breakdown of how braking works on the 72V ONYX RCR and how to maintain and upgrade the system properly.

It covers:

• How the stock front + rear + regenerative braking system behaves
• Safe brake bias for downhill, rain, traffic, and uphill riding
• How to fix the factory weak brake light
• Choosing the right brake pads
• DOT brake fluid types and compatibility
• Front brake inspection, cleaning, and common fixes

It starts with simple riding fundamentals, then moves into hardware choices and advanced maintenance.

TLDR - Braking Essentials

• Front brake provides most stopping power
• Rear brake + regen are mainly for stability
• Avoid regen when battery is above ~82V downhill
• Fix the weak brake light using the buck-boost 12V source
• Organic pads = quiet street riding
• Sintered pads = aggressive riding
• DOT 4 or DOT 5.1 brake fluid recommended
• Inspect front brakes every ~2,000 miles

Stock ONYX Brake Design (Simple Overview)

The ONYX RCR uses:

• Large front brake (primary stopping power)
• Small rear brake (stability)
• Regenerative braking via the left rear lever

This design prevents rear wheel lock-up from the heavy hub motor and keeps the bike stable under hard braking.

Two Rear Brakes Explained

The left rear brake lever controls two systems:

• Regenerative braking (electric)
• Rear brake caliper (mechanical)

Light pull (~1 inch):

• Regen only

Hard pull:

• Regen + rear brake pads

To reduce rear pad wear:

• Use regen only for most slowing
• Avoid squeezing past the first inch unless needed

Regenerative Braking Behavior

Regen is effectively an on / off switch inside the lever.

How to use it:

• Squeeze about 1 inch
• Hold steady
• Release to disengage

Practice on quiet streets until it becomes muscle memory.

Downhill + Full Battery Warning

If battery voltage is above ~82V:

• Avoid regen braking downhill

Why:

• Regen sends energy back into the battery
• A full battery has nowhere to store it
• The BMS may shut down to protect itself

Use mechanical brakes instead until voltage drops.

Brake Bias Fundamentals

Brake bias = how braking force is split front vs rear.

When braking:

• Weight shifts forward
• Front tire gains grip
• Rear tire becomes lighter

Too much rear brake:

• Fishtail

Too much front brake:

• Front wheel lock

Correct bias = smooth, predictable stops.

Recommended Brake Bias by Scenario

Downhill Riding

• Front 90% / Rear 10%

Tips:

• Use front brake smoothly
• Light rear brake only for balance
• Avoid regen if battery is full
• Never grab the front brake suddenly

Rain Riding

• Front 60% / Rear 40% (or 50/50)

Tips:

• Brake earlier
• Increase rear brake use
• Avoid braking mid-turn
• Look for dry pavement patches

Heavy Traffic

• Front 70% / Rear 30%

Low speed:

• 50/50 for smoothness

Tips:

• Cover both brakes
• Maintain distance
• Avoid sudden grabs

Uphill Riding

• Front 60% / Rear 40%

Why:

• More rear traction
• Less forward weight transfer

Tips:

• Use rear brake to prevent rollback
• Smooth front brake input

Weak Brake Light Overview

Many ONYX RCR bikes ship with a dim brake light because it is powered by the controller’s weak 12V line (~10V) instead of the dedicated buck-boost converter.

Symptoms:

• Brake light much dimmer than DRL
• Low measured voltage

Brake Light Wiring Fix

The brake switch should receive 12V from the buck-boost converter.

Fix summary:

• Locate brake switch connector
• Remove green wire (controller 12V)
• Replace with 12V from buck-boost converter

Results:

• Bright brake light
• Proper voltage
• Better visibility

Some newer wiring harnesses already include this fix.

Brake Pad Types (Quick Guide)

Brake Pad Materials

Organic (Resin)

Pros:

• Quiet
• Rotor friendly
• Strong initial bite

Cons:

• Short life
• Heat fade
• Poor wet performance

Semi-Metallic

Pros:

• Durable
• Good heat tolerance

Cons:

• Noisier
• More rotor wear

Sintered (Metallic)

Pros:

• Best in heat & abuse
• Works wet or dry
• Long lifespan

Cons:

• Noisy
• Rotor wear
• Longer bed-in

Ceramic

Pros:

• Very quiet
• Low dust
• Long life

Cons:

• Expensive
• Less aggressive bite

Bedding In Brake Pads

• Moderate speed
• Smooth repeated stops
• No panic braking
• Continue until bite improves

DOT Brake Fluid Overview

ONYX ships with DOT 3, but upgrades are safe.

Brake Fluid Comparison

⚠️ Never mix DOT 5 with other fluids.

Recommended Brake Fluid

• Daily riding: DOT 4
• Performance riding: DOT 5.1

Front Brake Maintenance Overview

Inspect every ~2,000 miles:

• Pad thickness
• Rotor condition
• Fluid level
• Hose routing
• Caliper movement

Checking Brake Fluid Level

• Bike upright
• Front wheel straight
• Check reservoir window
• Half full = ideal

Front Brake Pad Inspection

Replace if:

• Thin
• Contaminated
• Cracked or glazed

Fixing Front Brake Squeak

Tools:

• 300-500 grit sandpaper
• 3000-5000 grit sandpaper
• Brake parts cleaner

Process:

• Sand disc edges
• Finish with fine grit
• Clean thoroughly

Stuck Front Brake Piston

Fix:

• Crack bleed valve
• Push piston flush
• Close valve

Brake Disc Glazing

Symptoms:

• Vibration
• Weak braking
• Noise
• Lever pulsing

Fix:

• Light pad sanding
• Replace pads if severe

Caliper Pad Clips

Ensure proper alignment.

Front Brake Pad Cleaning

Every 2,000 miles:

• Light sanding
• Brake cleaner
• No oils

Brake Cleaner Rules

• Use outdoors
• Avoid paint/plastics
• Don’t touch pads after cleaning
• No WD-40

Front Fork Brake Line Clip

Prevents tire contact.

• Inspect often
• Add stainless locking tie for Shinko 241/244 tires

Removing Front Brake Pads

Final Advice

Front brake for stopping. Rear brake and regen for stability.

Fix the brake light, choose quality pads and fluid, and maintain the system regularly to keep your ONYX fast, safe, and predictable.