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The Ultimate Surron XX Rebuild – Part 1

Surron XX Build Stage 1

Today marks the beginning of a new Surron X bike build. This is a bike you may recognize if you’re a regular follower of ECR. This bike started out as the Ultimate Surron XX build, and it’s seen a few variations since that original build in 2020. This latest overhaul will be its most significant yet.

First up, we replaced the motor with a KO RS Motor. The KO RS Motor is an Internal Magnet Motor (IPM) and a direct drop-in replacement for the SurRon Lightbee X, providing superior cooling with it’s super heat sink design, premium magnets, bearings and seals. KO claims that the motor can handle up to 35KW based on the battery you choose, but we plan to run a maximum of 19kW with our current EBMX 72v 42Ah battery, but more on that later.

KO RS Motor for Surron Lightbee X

We paired this KO RS Motor with a KO Pro Series controller. The KO Pro Series controller offers endless tuning capabilities, allowing riders to tune their bikes to hundreds of different configurations and riding styles. Every 500 RPM can change the power level, providing precise power specs. The tuning possibilities with the KO Moto tuning app are so abundant that it can honestly be a bit overwhelming, but it’s an excellent option for those who love tinkering. However, if you prefer plug-and-play options, applying tunes that have already been created for the SurRon X would be ideal. We opted to apply some of GritShift‘s tunes, and we were pleased with the results.

KO Moto Pro Series Controller for Surron Lightbee X

Next, we removed the Fox DHX RC4 Shock added the illustrious EXT Arma E-MX shock. The Arma MX is a direct bolt-on replacement for the Sur Ron Light Bee X and Talaria Sting. The EXT Arma Shock utilizes a Hydraulic Bottom-Out Circuit (HBC, Which EXT claims has been enhanced with a wider range of adjustment, in order to prevent bottom-out issues, while allowing riders to use softer spring rates.

The EXT Arma MX Shock is 4 way adjustable with low speed and high speed compression, low speed rebound and the hydraulic bottom out control we mentioned above. Riders can choose their weight and riding style to utilize the correct spring rate for the shock.

EXT Arma MX Shock for Surron Lightbee X

Lastly, we are waiting for some parts for the Warp 9 linkage and Warp 9 triangle. Once we mount the new EXT Ferro Fork, we will also add the GritShift heavy hitter bar clamp, enabling us to run moto bars. 

These one-off bike builds always throw curveballs, and this one is no exception.

We want to continue to run the 4MF body kit on this build because we love what the kit offers in terms of a seat and shrouds. 

We initially planned to use the a 72v 38Ah battery that CHI Battery custom built for us. Hoping to shorten the battery as much as possible, CHI built us a capless version without the display. Even after trimming the 4MF kit, it was unfortunately still too tall to fit. 

Custom CHI Battery 72v 38Ah for the Surron XX Build

Our solution was to take a long trip to get my EBMX 72v 42Ah battery from the beast build. It too was a tight fit in the 4MF kit, and after gouging the EBMX stickers on the side of the battery, we ended up pulling off the stickers completely.

Mounting the EBMX 72v 42Ah battery into the Ultimate Surron XX Build
EBMX 72v 42Ah Battery

We trimmed every bit of material off the battery lid, pulled all the foam material off the lid, and still trimmed some more. Eventually, we got the lid to close, but there was still a gap that we had to live with. We may use a heat gun later to shape the lid further, but it does fit. 

Trimming the 4MF Kit to fit the EBMX Battery in the Surron X

With the battery in the bike, it was time to test the KO tune that Josh from GritShift had set up for us. We will do more content on the setup procedure and tuning for this KO kit, but basically, Josh and I tested different settings on the street, and I ultimately stuck with Josh’s original tune with a few tweaks to the throttle.

We wanted to test these power settings in the dirt, so we went to Croom to run it in some sand and single track.

Riding the Ultimate Surron XX Rebuild in the dirt

As I hit the dirt, the first thing that struck me was the sheer power of this KO setup. The tune is robust and seemingly endless. I’ll be honest, the bike’s power is almost excessive for this type of riding. Having an abundance of power is better than not, but I do believe it could use some de-tuning for the single track conditions that I’m typically riding.

The EXT shock is another standout feature of this bike. It’s almost too good for the fork I have, causing a slight imbalance in the bike’s feel. The rear shock is incredibly plush right out of the box, and I’m thoroughly impressed with its performance. I’ve ridden the EXT before, but it’s never been set up for me, making it challenging to gauge its true potential. Nonetheless, I’m thoroughly impressed with how it feels on my bike. It’s as smooth as butter. Now we have some work to do in the front to match the performance of the rear EXT shock.

Testing the KO Power on the Ultimate Surron XX Build

While the 19″ front and 16″ rear wheel combo keeps the bike nimble and retains a lot of the stock characteristics of the Surron Lightbee X, I’m just not a fan of how the 19″ front wheel hooks up in corners. Personal preference, for sure, but I am often wanting for a 21″ front wheel. Front end feel is where I’m most sensitive on my bikes and I simply prefer the stability and bite of a 21” front wheel. If I were riding dirt jumps or flow trails, the 19/16 combo would be ideal. However, for me, the 21″ front and 18″ rear wheel combination is the way to go.

Ultimate Surron XX Re-Build - Stage 1

As for the Hayes Dominion A4 Brakes, I’ve ridden with these brakes before on the CZEM Drill One, and they feel fantastic. The adjustability of the levers is a definite plus, and they feel snappy, predictable, and sharp.

Overall, this bike is a whole different animal with its KO setup. It’s almost too powerful for my needs on singletrack. It would be perfect for a motocross track, where the power is necessary.

KO Moto Kit on the Surron XX

We have a bit more work to do to this bike so stay tuned as the SurRon XX ECR bike gets an overhaul. 

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