Rotobox Carbon Wheels | SR Tested

A new entry into the rather exclusive carbon wheel market is Rotobox. Manufactured in Slovenia, the Rotobox wheels not only boast a very unique look that separates them from other wheels (never mind other carbon wheels), but their design and manufacturing technique are different as well.

According to company reps, the Rotobox wheels are made using “dry carbon technology”, although their description of the manufacturing method sounds more like a process known in the carbon manufacturing industry as “vacuum resin transfer molding.” This is done by laying the dry fabric over a specially built mold that can tightly control the shape and thickness, plus have an airtight seal; then the resin is injected into the mold with high vacuum pressure to ensure no microscopic bubbles or voids are present.

The Rotobox wheel design is unique in that the massive spokes are actually hollow and contribute to the total air volume of the tire when inflated. The company claims that the “rotary box” design prevents the spokes from separating from the hub, as well as offering the lowest moment of inertia (the amount of work needed to spin the wheel).

We ordered up a set to fit our 2012 Kawasaki ZX-10R test bike, and while we couldn’t substantiate the structural integrity of the wheel (Rotobox claims the wheels pass the JASO — the Japanese Automotive Standards Organization — T203-85 standard for light alloy wheels for motorcycles, which subjects the wheels to various vertical, lateral, and torsional stress), the wheels definitely have a robust build quality, with 7075 aluminum alloy hub components for the bearing and brake disc attachment points. There’s no doubt that the Rotobox carbon wheels shed some critical weight, too; with all parts installed (brake rotors, bearings, rear sprocket carrier, etc.) except tires, the front Rotobox assembly drops 3.46 pounds from the stock wheel, while the rear sheds 5.94 pounds of unsprung weight (note: custom sprockets are required). That’s a huge amount of unsprung mass to cut, and we were anxious to see how much of a difference it would make out on the track.

But first we wanted to see how much of an improvement these wheels would make in acceleration with their lesser moment of inertia compared to the stock aluminum wheels. In order to keep the test results consistent and comparable, we started the acceleration test with the bike already rolling at 20 mph in order to take the launch variable out of the equation. The results were dramatic; at 100 mph, the Rotobox wheels already had nearly two-tenths of a second advantage, and at 120 mph, almost three-tenths of a second. Three-tenths of a second at 120 mph is an eternity in acceleration numbers — it’s basically like adding 10-15 horsepower to the engine.

Overall handling effects were as we expected, with easier turn initiation into corners becoming more noticeable the faster you went. While the wheels didn’t exactly make the ZX-10R flick through Buttonwillow’s ess-turns like a 600, the decreased amount of steering effort needed to bank into the faster turns was a welcome advantage after numerous laps wrestling the big Kawasaki around the track. And there were no stability problems with the lighter Rotobox wheels as well.

But one niggling problem that kept on cropping up during our racetrack laps was a distinct feeling as if the front wheel was almost flexing at the apex of corners when the front end was heavily loaded. We also noticed that the front end moved around a lot more in the faster, bumpier turns on the track, with Bradley even complaining that “it felt like the front end was going to push or fold; you definitely have to ride the wheels with some reservation there.” No amount of chassis fiddling could quell the problem, and it zapped enough confidence that lap times were basically the same as stock.

Could this have been an anomaly with our particular set of wheels? Maybe, but at $4100 per set, that's an awfully expensive chance to take. SR

Rotobox carbon fiber wheels
Retail: $4100/set

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