Crankbrothers Synthesis I9 Alloy Wheelset Pairs Uniquely-Tuned Front and Rear Wheels [Review]

Collaboration is essential in the trail-toy industry. Every component company has to create things that work well with parts from another brands. In the case of wheels, there are often multiple manufacturers involved in the production of the spokes, nipples, rims, hub shells, bearings, seals, tubeless tape, valves, freehub, spacers, and axle. The list of cooks in the kitchen can fill a spacious dining hall.

Like several other wheel brands, Crankbrothers has partnered with Industry Nine to create their innovative alloy and carbon mountain bike wheels. While you can pick up an affordable set of Synthesis Alloy wheels with Crankbrothers hubs for €/$598, the Industry Nine 1/1 hubs tighten up the freehub’s engagement from 17° to 4° for more immediate power transfer, and they weigh a little less. The 29″ Boost Synthesis I9 Alloy wheels tested here retail for €/$798 total and hit the scale just a hair under the brand’s stated 1913g total weight. The front and rear wheels are sold separately, so savvy buyers could purchase the Industry Nine equipped rear and Crankbrothers front wheel, receiving most of the same benefits at a lower cost of €/$738.

Crankbrothers sells the Synthesis wheels separately because they are designed to function separately. The front rim is 31.5mm wide to offer a slightly broader traction patch than the 29.5mm rear rim. A narrower rear rim out back is thought to create a better biting tire profile for improved grip. The rear wheel also has four additional spokes that are of a heavier gauge than the 28 laced in the front hub. Those 32 rear spokes add strength and stiffness to the rear wheel so it can better manage the power we put into it and to absorb impacts from the earth. The more compliant front-wheel tune is said to improve grip where it counts.

Australian engineer, Mello Bouwmeester, developed the new Synthesis alloy and carbon models for Crankbrothers at their testing lab in Utah. Mello was the first wheel engineer to develop a solid, single-wall carbon rim back in the day, similar to what SRAM is using in their 3Zero Moto rims, alongside several of his other innovations that are in use today. He says that they tested a heap of competitors’ wheels to start the design process for the carbon Synthesis.

“It’s kind of two schools of thought with wheels. Stiffness is better or compliance is better. Then we did blind testing, no matter what the combination was of stiff front and compliant rear [rim], or [the opposite], or stiff and stiff or compliant and compliant, the result always came back that compliant front and stiff rear were your favorite. Regardless of your initial preference. So we sorta knew we were onto a good thing there.”

“Then once we’d done the carbon done we were like, ‘can this apply to aluminum?’ You do want a little more stiffness in the rear because that’s where the majority of the loads are pushed through the bike. Whereas the front you want a little more compliant to basically manage those loads but not deflect you off the line. So we went through the same process with alloy. Obviously the spoke pattern and choice had a lot to do with that. The difference between carbon and aluminum is that you get a little more design freedom with carbon. Because you get to control the ride characteristics of the rim dependent on the layup. When you move to alloy you have a material that basically has the same properties in all directions. So the profile will dictate how the rim performs. So there’s a little more meat in the rear than the front. We tried to keep the front as light as we could.”

The wheels arrive taped, with a quality set of tubeless valves. The tape is a little thicker than some, and I didn’t manage to puncture it with the tire lever while dismounting tight tires. The shape of the inner rim makes for a happy pairing with any tire bead I’ve tried, and tubeless rubber snaps into place as expected. Tire profiles with these two widths seem just right to give the tread maximum ground contact while not stretching too wide and creating problems. I’m stoked to see internal rim widths staying between 27 and 33mm these days, as wider rims didn’t play so well with 2.3-2.4″ tires and the older narrow rim options created a great deal of tire squirm.

On the trail, the performance characteristics that Crankbrothers laid out before these wheels hold true. The rear circle feels almost as stiff as some carbon fiber rimmed wheels, while it tracks well and has managed to hold true over several months of hard riding. The spoke tension still feels even and surprisingly the wheels don’t need to be straightened out quite yet. It’s a rare set of alloy wheels that doesn’t have to be trued once it’s time to write a review, indicating that this system was well built from the start.

The more compliant front wheel is where this set really shines. With additional room to flex and adapt to the trail thanks to its lower spoke count, the Synthesis I9 Alloy front wheel tracks dirt predictably. It’s not so compliant that riders will need to think about it while riding or change fork settings. Instead, this bit of flex is the sort of nuance that makes the ride better without calling attention to itself. I tested a few different tires on these rims, all in the 2.35 to 2.4″ range that I’m most comfortable on, and I was surprised on multiple occasions when I managed to roll across damp root mats that I typically slide and dance across with the same tires. The tire carcass feels notably well supported by the 31.5mm wide rim, and when it’s time to ride light across slippery features this wheelset offers a confident foundation.

Over the summer I tested a carbon-rimmed wheelset that was truly too stiff for my taste, and it was a helpful reminder of how important a well-tuned wheel is. A wheel needs to be strong enough to hold its shape, while compliant enough to give a little for the sake of traction, with some measure of malleability and rebound built into the system to allow for mistakes and harder hits. Not every alloy wheelset includes all of those key ingredients, and it’s clear that the cooks took a little extra time with this one.

Looking inward, the Industry Nine 1/1 hubs have performed exquisitely, as expected. The bearings are still rolling smoothly, and the 4° of engagement seems plenty tight for my needs. I like to play around on technical climbs to see how far I can get up things that are meant to be ridden down, and the tighter 1/1 freehub engagement feels nearly immediate. I’m genuinely pleased to see the new industry standard for high-quality hubs come in this practical and relatively affordable package. The simplicity of the classic J-bend flanges will make life easier for folks who spend time deep in the mountains and may need to source a spoke while adventuring.

The only thing I would swap on these hubs is the rotor mount, as center lock mounts make swapping rotors a far faster process. If you use the same wheel set on two different bikes with different braking systems, center lock mounts are a welcomed feature. Also, it would be rad to see Industry Nine offer the 1/1 hubs in different colors. I’m sure it makes some sense to keep the color options for the top Hydra model, but I would happily pay a little extra for a colorful 1/1 in the middle of my wheel.

Crankbrothers has a wide variety of wheels available, from the €/$598 alloy set with their hubs to the Synthesis Enduro 11 Carbon wheelset with I9 Hydra hubs at €/$2,399, and several in between. If you’re on the hunt for a wheel system that’s been run through all of the ringers and came out with some of the best parts in the business, these hoops are certainly worth closer consideration.

⭐️ Find the Crankbrothers Synthesis Enduro wheels at JensonUSA.