How to Install Sur-Ron Ultra Bee Brakes on a Super73 (Rear Only)

by Kesar Long

Why Upgrade to a Sur-Ron Ultra Bee Rear Brake?

The Sur-Ron Ultra Bee rear brake conversion has become a popular upgrade for modified Super73, Macfox, Ridstar, and other high-performance e-bike builds.

Compared with typical stock bicycle-style brake systems, the Ultra Bee setup gives you a much larger, more substantial braking system designed for a heavier and more powerful machine. Paired with the included 220mm rotor, it provides stronger braking performance and improved heat capacity for higher-powered builds.

For riders looking to upgrade the rear brake without replacing the entire front and rear braking system, the rear-only Ultra Bee conversion is a great option.

👉 Shop the Pre-Bled Ultra Bee Rear Brake Kit for Super73, Macfox, Ridstar & Other E-Bikes at K. Mods

Important: This Kit Uses a 220mm Rotor

The K. Mods Ultra Bee rear brake conversion is designed to be used with the included 220mm rotor.

Do not attempt to install the Ultra Bee caliper using the stock 180mm Super73 rear rotor. The conversion bracket and caliper position are designed around the 220mm rotor supplied with the kit.

The good news is that the 220mm rotor is already included, so you don’t need to source one separately.

The brake assembly also arrives pre-bled, making installation much easier. In most cases, you can install the brake and have a firm lever without performing a full bleed.

Compatibility

Super73 S2, RX, R, ZX and compatible models:
Uses the 220mm rotor and rear Ultra Bee conversion bracket included with the kit. Always confirm your exact model and mounting configuration before installation.

Macfox, Ridstar and similar e-bikes:
Some models require an additional 180mm upper/post-mount adapter between the bike’s existing brake mount and the Ultra Bee conversion bracket.

If your setup requires the 180mm upper adapter, you’ll find the recommended adapter link in the K. Mods product description.

What You’ll Need

  • K. Mods Pre-Bled Ultra Bee Rear Brake Kit
  • Included 220mm rear rotor
  • Included Ultra Bee conversion bracket and mounting hardware
  • 180mm upper/post-mount adapter for applicable Macfox/Ridstar setups
  • 5mm hex key
  • Torx T25
  • Torque wrench
  • Isopropyl alcohol
  • Clean, lint-free cloth
  • Nitrile gloves

Step 1: Remove the Stock Rear Brake and Rotor

Remove the bolts securing the stock rear caliper and move the brake assembly out of the way.

Next, remove the stock rear rotor by loosening its six rotor bolts in an alternating or star pattern.

Keep the wheel and rotor mounting surface clean during installation.

Step 2: Install the Included 220mm Rotor

Position the included 220mm rotor on the rear hub.

Install the six rotor bolts by hand first, then tighten them gradually in a star pattern so the rotor seats evenly against the hub.

Torque the rotor bolts according to the rotor/hub manufacturer’s specification.

Once installed, clean the braking surface with isopropyl alcohol and a clean lint-free cloth.

Avoid touching the braking surface with your bare hands. Oils from your skin can contaminate the rotor and reduce braking performance.

Step 3: Install the Ultra Bee Conversion Bracket

Install the supplied K. Mods Ultra Bee conversion bracket onto the bike’s rear brake mount using the supplied hardware.

The bracket positions the larger Ultra Bee caliper correctly over the 220mm rotor.

Macfox & Ridstar Riders

Certain Macfox, Ridstar and similar frames require an additional 180mm upper/post-mount adapter before the Ultra Bee conversion bracket can be installed in the correct position.

If your bike requires this adapter, install the 180mm adapter first, followed by the Ultra Bee conversion bracket.

Do not force the bracket into position or stack random washers/spacers to compensate for incorrect alignment.

Step 4: Mount the Ultra Bee Caliper

Position the Ultra Bee caliper over the 220mm rotor.

Loosely install the caliper mounting bolts so the caliper can still move slightly from side to side.

Before tightening anything completely, verify that the rotor is properly positioned between the brake pads and that the caliper and rotor have adequate clearance.

Step 5: Center the Caliper

With the caliper mounting bolts still slightly loose, firmly squeeze and hold the rear brake lever.

While holding the lever, gradually tighten the caliper mounting bolts.

Release the lever and spin the rear wheel.

The rotor should pass cleanly through the caliper without significant rubbing.

If the rotor rubs, loosen the mounting bolts slightly and manually fine-tune the caliper position until the rotor runs centered between the pads.

Step 6: Check Lever Feel

The K. Mods Ultra Bee rear brake assembly arrives pre-bled, so the lever should feel firm after installation.

If the lever feels unusually soft or spongy after shipping or installation, inspect the brake system for trapped air or leaks before riding.

IMPORTANT: Ultra Bee Brakes Use DOT 4 Brake Fluid

If bleeding or servicing the brake becomes necessary, use DOT 4 brake fluid.

DO NOT use mineral oil.

The Sur-Ron Ultra Bee braking system is designed for DOT 4 fluid. Mixing mineral oil with a DOT-based brake system can damage seals and other internal brake components.

DOT brake fluid can also damage painted or certain plastic surfaces, so immediately clean up any spills and protect surrounding components when servicing the brake.

If you’re unfamiliar with bleeding DOT brake systems, have the brake serviced by an experienced technician.

Step 7: Bed In the New Pads and Rotor

New brake pads and rotors need to be properly bedded together before they reach full braking performance.

In a safe, traffic-free area:

  1. Accelerate to approximately 15–20 mph.
  2. Apply firm, controlled rear brake pressure and slow the bike to approximately 5 mph.
  3. Release the brake and accelerate again.
  4. Repeat approximately 8–10 times.

Avoid coming to a complete stop while holding the brake during the bedding process when possible.

You should notice braking power becoming progressively stronger and more consistent as the pads transfer material onto the rotor.

Final Installation Tips

Re-check all mounting hardware after your first few rides.

Keep DOT 4 brake fluid, lubricants, cleaners and other contaminants away from the brake pads and rotor braking surface.

Always verify that the wheel spins freely and the rotor is centered before riding.

For Macfox, Ridstar and similar builds, confirm whether your bike requires the additional 180mm upper/post-mount adapter before installation.

Remember: the K. Mods Ultra Bee conversion is designed around the included 220mm rear rotor. Do not substitute the stock 180mm rotor.

After installation, test the brake at low speed before riding normally.

Ready to Upgrade?

Grab the K. Mods Pre-Bled Ultra Bee Rear Brake Kit for your Super73, Macfox, Ridstar or compatible e-bike.

The kit includes the 220mm rotor, Ultra Bee rear brake assembly, conversion bracket and mounting hardware, with the brake pre-bled and ready for installation.

Built for riders who need more brake for more bike.

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