Crankbrothers Synthesis Carbon Gravel wheelset review – super wide and smooth rolling

Crankbrothers latest Synthesis Carbon Gravel wheels have taken the compliance-tuned Synthesis concept that is used in all its mountain bike wheels and brought it to gravel. The theory is the same, adding compliance to the wheel improves grip and comfort however instead of holding lines on rough off-camber trails and absorbing harsh impacts they are carving flat high-speed turns and dampening vibrations on long gravel rides. 

Crankbrothers have aimed the Synthesis Carbon Gravel wheels squarely at the adventurous end of gravel riding where compliance is going to be most appreciated and equipped them with a wide 26.5mm internal rim diameter rim and durable lifetime warranty-backed construction. I have been putting them through their paces to see how they compare to the best gravel bike wheels. 

Design and specifications

It's the shallow 21mm rim profile that is said to allow the Synthesis Carbon Gravel to isolate the rider from vibrations by absorbing and dissipating trail feedback. Crankbrothers says that they have tuned both side-to-side (lateral) and vertical (radial) deflection into the wheel which helps with cornering and vibration absorption.

The internal rim width is one of the widest we have seen on a gravel-specific rim, and as far as I know, only the Zipp 101 XPLR comes in wider. The monstrous 26.5mm inner rim width is said to be optimized to support tires from 40mm to 48mm, although Crankbrothers says they can handle tires from 30mm to 55mm with no problems. The rims themselves use a hookless design, so make sure you are running tubless-specific tires on these wheels.

The new Synthesis Ratchet has middling 10 degrees of engagement which will feel slow if you are used to faster engagement and can come fitted with either XDR or HG freehubs options. The wheels are built up with 28 Sapim D-Light J-bend spokes on each wheel.

The Synthesis Gravel wheels come in both 700c and 650b sizes, there is also an alloy version that features the same dimensions but they weigh a bit more and come with standard Synthesis hubs, rather than Synthesis Ratchet.

Crankbrothers don’t sell the Synthesis wheels as a complete set, instead, they have to be purchased individually. Wheels come neatly taped with valves fitted although you will need to source your own centerlock lock rings. I found tires popped onto the rim with no problems giving the 40mm Halo GXC tires a visibly wider, flatter profile. 

Performance

The compliance of the Crankbrothers Synthesis Carbon Gravel isn't immediately obvious, riding around they still feel tight but hit the trails and the vibe changes. There is a noticeable dulling of impacts and vibrations akin to running three or four PSI less in your tires. I found it to be particularly noticeable on larger impacts where expected shocks through the bars were always less than expected. The lateral tune on the wheels still offers a direct and precise cornering feel, especially with the added sidewall stability offered by the wide rim profile. It's hard to quantify how much extra grip is on offer but the controlled nature gave me confidence to carve hard through corners which often opened gaps to riders trying to hold my wheel.  

Pushing the wheels to the ragged edge of what should be considered sensible on a drop bar bike and your brake fingers will be flinching long before the wheels. Having logged over 1500km on the Crankbrothers Synthesis Carbon Gravel wheelset, they have proven their durability for adventuring. I have hurled them down some properly rugged descents, including the high-speed rock-strewn tracks of the Struggle Borderlands and the wheels are still running straight and true. The hubs still spin smoothly having withstood all manner of unpleasant weather conditions inflicted on them by our so-called Scottish summertime.

The same can’t be said for the tires I used, which are now adorned with the tails of many tubeless repairs. Whether this is caused by the rim profile or simply the wheels encouraging more radical riding is hard to tell. It is something I have experienced with other wide rim and 40mm tire combos though and I suspect it’s caused by the wide inner rim width reducing the height of the tire. Crankbrothers says the rims are optimized for 40mm to 48mm but unless you're running higher pressures to support the sidewalls against impacts or riding on smoother surfaces I would recommend 45mm plus to be safe. Considering the Synthesis Carbon Gravel wheel's adventurous leanings, most riders interested in these wheels will probably be better off on wider tires anyway.

The shallow depth is going to do little for aerodynamics and gravel riders wanting a fast set of wheels would be better looking at a set of FFWD Drift’s or Zipp 303 Firecrest’s. That said the Synthesis Carbon Gravel wheels carry speed very well, especially on rough terrain or twisting sections, and their forgiving nature means you can push a little more air into the tire for faster rolling speeds without being rattled to bits. There isn't much dullness or wallowing under power either allowing them to climb reasonably well, even if the 1555g weight is working against them a little.

Verdict

The combination of big tire compatibility and enough conformity to boost cornering and dampen impacts makes the Crankbrothers Synthesis Carbon Gravel wheelset a dependable adventure/rad gravel wheelset. The compliance characteristics are enough to give them a calm, smooth, confidence-boosting nature on rough gravel trails and are backed up with enough clout to roll out the other side unscathed.

Crankbrothers are up against some stiff competition when it comes to compliant gravel wheel contenders too. At $1500 / £1400 / €1500 for a set, they are right up against Reserve’s 25/GR gravel wheels which are lighter but narrower and only marginally cheaper than the ultra-compliant but heavier Zipp 101 XPLR. 

Tech specs: Crankbrothers Synthesis Carbon Gravel wheelset

• Price: Front wheel $599.99 / £550 / €599,99, Rear wheel $899.99 / £850 / €899.99
• Sizes: 700c / 650b
• Options: XD, HG 
• Weight: Front - 712g / Rear - 843g = 1555g for HG driver version incl valves