RadRunner Motor Failing? Here's What's Going Wrong — and How to Fix It
If your Rad Power RadRunner is making grinding noises, losing torque on hills, occasionally cutting out, or just stopped working entirely — you're not alone. We see these symptoms constantly at Temper. Almost all of them trace back to the same handful of failure modes inside the stock 750W geared hub motor.
This post walks through what's actually breaking, why, and the two ways to fix it: a like-for-like replacement, or an upgrade to something stronger that won't break the same way.
Symptoms you're probably seeing
- Grinding, clicking, or rattling under power — often louder uphill or with cargo
- Motor feels weak — assist used to climb your hill, now it doesn't
- Motor cuts out intermittently — works for a few seconds, then nothing
- Burned plastic or hot electrical smell — especially after sustained climbing or heavy loads
- Motor is locked up — won't spin even by hand, or only spins in one direction
- Error codes that won't clear — usually pointing at the motor or controller
These aren't random. Almost every one of them maps to a specific failure inside the hub.
What's actually breaking
The RadRunner's stock 750W motor is a geared hub motor — meaning it uses a small high-RPM motor combined with a planetary gear reduction inside the hub shell. Compact, efficient, decent torque for the size. But geared hubs have a few well-known weak points, and the RadRunner pushes most of them.
1. The nylon planetary gears strip
This is the most common failure we see, by a wide margin. The torque from the motor doesn't go directly to the wheel — it goes through three nylon planetary gears that mesh with a steel ring gear inside the hub shell. Those nylon gears multiply torque, but they're also the weakest part of the system.
Inside a geared hub: the stator (the copper-wound ring) and the planetary gearset. The three white nylon gears are what carry torque to the wheel — and what wears out first.
Sustained heavy load, hills, cargo, or just years of use grinds these gears down. The first sign is usually noise — clicking or grinding under power that wasn't there before. Then loss of torque. Then complete failure, where the motor spins inside the hub but doesn't move the wheel.
2. The stator windings burn out
Geared hub motors are small. They generate a lot of heat for their size, and that heat has nowhere to go. Sustained high current — climbing hills, heavy cargo, hot ambient temperatures — cooks the insulation off the copper windings. Once the insulation fails, the windings short to each other or to the stator core, and the motor stops working or runs intermittently.
The stator face. That orange copper is what carries the current — and what burns out when the motor runs too hot for too long. You can sometimes see the damage: discoloration, melted insulation, or visible breaks in the winding.
Burned windings are usually a death sentence for the motor. They can sometimes be rewound, but it's labor-intensive and the cost is usually close to a new motor.
3. Hall sensors and wiring fail
Three Hall sensors inside the motor tell the controller where the rotor is. If one fails, the motor stutters, won't start, or only works at high speed. Wiring inside the hub can also chafe against the rotating parts and short out. Both are common after a few years of riding.
4. Bearings wear out
Sealed bearings inside the hub take everything — radial load from the rim, axial load from cornering, and the constant churn of gear engagement. When they fail, you get clicking on every wheel rotation, drag when coasting, or play in the axle. Bearings are replaceable but require pulling the whole motor apart.
Why this happens more on the RadRunner
A few reasons RadRunners see more motor failures than your average e-bike:
- Cargo and passenger duty. The RadRunner is designed to haul stuff — that's the whole point. But hauling heavy loads on hills runs the motor at its thermal limit constantly.
- 20-inch wheels. Smaller wheels mean the motor spins faster to maintain the same speed. More rotations = more wear on bearings and gears.
- Fat tires. Higher rolling resistance, especially loaded. The motor compensates by drawing more current. More current = more heat.
- Hills. Geared hubs run hot under sustained climbing. If you live anywhere with real elevation (looking at you, Santa Cruz), the motor takes a beating.
The controller upgrade trap
One of the most common reasons we see premature motor failure on RadRunners: the owner installed an aftermarket controller for more power.
This is an understandable upgrade. The stock RadRunner controller is limited to around 22 amps. A 35-amp aftermarket controller, paired with the same battery, gives you noticeably more torque off the line and faster acceleration. Sounds great.
The problem: the stock 750W motor isn't built for 35 amps. The nylon planetaries weren't sized for that torque. The copper windings can't dissipate that much heat. Within a few months — sometimes a few weeks if you ride aggressively — the motor either strips its gears or cooks its windings.
If you want a stronger controller, you need a stronger motor to match. Otherwise you're just paying for a faster failure.
Your two real options
Option 1: Like-for-like replacement
Drop in another 750W geared hub motor wheel. Cheaper, simpler, you'll be back on the road quickly. You'll also be back in this exact situation in another 1–3 years depending on how hard you ride. Fine if the bike is mostly a casual ride or you want to spend as little as possible.
Option 2: Upgrade to a 1000W Geared Hub
This is what we recommend for most RadRunner owners, especially anyone who's already upgraded the controller or rides loaded regularly. Here's why a stronger motor solves all the failure modes above:
- Stronger gears. The 1000W Bafang G062 uses larger, stronger nylon planetary gears that handle more torque and more miles before wearing out.
- Better copper coiling. Windings designed for higher power with less heat generation. A larger motor body also dissipates heat better — it takes sustained high current without cooking.
- Handles aftermarket controllers cleanly. If you want to run 35A or even 40A through it, the motor can take it.
- Same physical footprint. Same rear dropout width, same connector, same wheel size. No frame modifications, no controller reprogramming — drop it in and ride.
The biggest change is the size. We custom order this motor to match the width of the Rad Power rear dropouts. There are no other suppliers of the Bafang G062 in the 168mm width that fits the RadRunner — that's why off-the-shelf upgrade wheels won't work on this bike, and why we had to source the motor specifically.
The Temper 1000W RadRunner Upgrade
We built our RadRunner 1000W Motor Wheel Upgrade specifically to solve this set of problems. It's a complete drop-in rear wheel for the RadRunner 1 and 2: 20" fat-tire rim, 1000W Bafang G062 in 168mm width, with the same connector as your stock Rad motor. Ready to install.
If you're seeing failure symptoms on your stock motor, or if you've already upgraded the controller and want a motor that won't burn out chasing it — this is the right move.
Free shipping in the contiguous US. We install in-shop in Santa Cruz if you'd rather not do it yourself. Questions about whether it'll fit your specific bike? Send us a message or call (831) 200-3593.