72V: Stock Settings, Tuning, and Upgrades

If you’re looking to upgrade your ONYX RCR 72V, understand the stock bike first. Bookmark this post if you’re planning a build. I’ll keep updating it with build plans, parts lists, and costs. We’ll start with the RCR as it originally came from the factory, with its ONYX 23 Ah battery and Kelly controller. Once you understand how that bike pulls in Sport, it’s easier to decide what you can get from a tune and when it makes sense to change parts.

Some RCR owners still riding on their original ONYX 23 Ah batteries are finding that their bikes top out around 45 mph in Sport. These packs go back to 2020, and as they age, their voltage can drop more under load.

This post is long overdue. I’ve spent seven years racing and modifying these bikes, and ONYX Motors has eight years of experience with them. Some of the best builds I’ve seen came from ONYX itself and from riders who build and race their own RCRs. I’ll explain which changes have proven themselves, what they do for the bike, and which ones are worth considering for your build.

When I talk about the ONYX RCR, I talk about racing because that’s how I approach the platform. You might ride yours to work every day, but you’re still riding the same platform. Whether you’re maintaining it as it came from the factory or building it with aftermarket parts, treat it like a race bike. The battery, controller, motor, brakes, and tires all have to work together.

The table shows the battery-side DC current ranges this guide covers for each pack.

I’ll start with what you can do with the factory Kelly, then build out two more paths: upgrading the battery while keeping the Kelly, and moving to an aftermarket controller. Each plan will cover the parts you need, the short list of suppliers I trust, what it costs to do it yourself or hire someone, and what to ask an installer to check before you get the bike back. Some of those topics will get posts of their own as the series expands to the CTY2 and then the RCR 80V.

How the Stock ONYX RCR 72V Pulls in Sport

Twist the throttle all the way open on a stock RCR 72V in Sport and you can feel the pull build. Two settings on the factory Kelly KLS7230S help explain that feeling. Forward Throttle Map, set to 30, shapes how much torque you ask for as you turn the grip. Acceleration Time, set to 5, gives that request about half a second to build from zero to full.

The original 23 Ah battery starts at 84 volts fully charged. Under hard acceleration, the voltage drops. That’s voltage sag. The stock 8 AWG discharge leads and SB50 connector add a little voltage drop of their own and turn some power into heat. We’ll use 50 amps DC as the baseline for the original SB50 setup. Using 79 volts at the Kelly’s input for this example, the controller takes in 3,950 watts. That voltage already accounts for the drop through the leads and connector. Allow 5% for losses inside the Kelly and about 3,750 watts reaches the motor.

At low speed, the Kelly can deliver more amps to the motor than it draws from the battery by using a lower motor voltage. That extra motor current helps produce the pull you feel in Sport. In a simplified three-phase example, 125 amps RMS through each motor lead at 10 volts RMS from phase to neutral gives 1,250 watts per phase, or 3,750 watts total, when the phases are balanced and voltage and current are in step. In that example, the voltage between two motor leads would be 17.3 volts RMS.

The factory settings also give us an estimate of the Kelly’s battery current ceiling. Current Percent, set to 50, gives an estimated 150 phase amps from the controller’s 300-amp peak rating. If Battery Current Limit, set to 55, applies 55% to that figure, the ceiling works out to about 83 amps DC. That’s the estimated controller limit. The original 23 Ah pack has its own discharge limits.

What Changes When You Put a QS8 on the ONYX 23 Ah Battery?

Back in 2020, we were already swapping the SB50 for a QS8 on the original ONYX 23 Ah battery. The QS8 gives the battery connection more room to carry current. To see what higher battery current could mean, compare a 50 A SB50 example with a 75 A QS8 example. At the same contact resistance, 75 amps generates 2.25 times as much heat as 50 amps. That shows how quickly heat can build as current rises. The actual heat depends on the connector and crimps.

Both columns use the original ONYX 23 Ah battery and the factory Kelly tune in Sport. For the math, we use 79 volts at the Kelly, allow 5% for controller losses, and hold motor current at 125 amps RMS per lead. The AC calculation assumes balanced phases with voltage and current in step.

Holding motor current steady in the example shows where the extra power goes. At 75 battery amps, the Kelly has more power available, and in this comparison that shows up as higher AC voltage at the motor. On the bike, both motor voltage and phase current change as you accelerate.

The Three ONYX RCR 72V Batteries

Here we’re comparing all three batteries in Sport on the same factory Kelly tune. The Ah rating tells you how much charge the pack stores. The cells, battery management system, discharge leads, and connector help determine how much current the pack can supply and for how long.

ONYX 23 Ah. This is how the original RCR came from the factory. The SB50 example uses 50 amps. With the QS8, I’ve seen the pack briefly reach about 70 amps, and the table above works through the math at 75 amps. As the original pack ages, extra voltage sag under load can soften the pull and make it harder to maintain speed in Sport.

ONYX 41 Ah. This pack stores more energy. A healthy one can also hold its voltage better under load than an aging 23 Ah pack, so the bike may hold its pull better as you accelerate. The original SB50 and the QS8 upgrade are two ways of connecting the pack. The QS8 gives the connection more room to handle current and heat. The pack still has its own discharge limits.

ONYX 45 Ah. This pack came with a QS8 from the factory and has the most capacity and discharge headroom of the three. A healthy 45 Ah pack can help the bike hold voltage under load and give you more range. The 180 A figure is the pack’s published peak. In Sport, the factory Kelly settings give us a separate estimate of about 83 A DC for the controller’s ceiling. A larger pack can make the pull more consistent while the controller settings stay the same.

If the bike loses power under hard throttle, where you measure voltage matters. A large drop at the battery under load points you toward the pack. A much lower reading at the Kelly under the same load points you toward the leads, crimps, and connector between them.

What the Factory Kelly Can Tune

So far, we’ve looked at how the RCR behaves in Sport with the factory Kelly settings. Before we get into changing those settings, it helps to know what each one controls. SICKO Mode is a tune for the factory Kelly, and I’ll cover it in a future update and link to the step-by-step guide here.

The distinction to remember is that changing how quickly the pull comes on is different from raising the current limits. A sharper throttle response can make the bike feel more immediate with the same limits. Raising those limits asks more of the battery, wiring, or motor. Understanding that difference now will make it easier to follow what changes when we get to SICKO Mode.