Viral Bikes founder Steve Domahidy is a big fan of the Pinion gearbox, and you’ll find it his titanium hardtails…and this new full suspension enduro mountain bike, too, which blends two materials with a lot of unique ideas about how to use them.
The Viral Optimist 160 bonds UD carbon fiber tubes between 3D-printed 6/4 titanium lugs made with an advanced, high-power EBM process, with the seatstay lug made to flex. That, plus the Pinion’s single “final drive” gear, allows it to have a very simple single pivot design, but achieve a whopping 160mm of travel with kinematics defined by a linkage.
Starting with the frame, Domahidy says their EBM (Electron Beam Melting) process both sinters and heat treats the titanium as it prints the parts. He says most 3D-printed titanium uses DMLS sintering with a 400-500W laser, possibly up to 1000W. His, however, is 3000W, and it moves magnetically rather than with belts and slides.
This design lets it move faster and heat the material to 700ºC (1,292ºF), which he says is the annealing temperature of titanium, meaning it’s both created and heat treated in a single step. The benefit is that post-production processing is simplified, and because they’re 3D printed, they can customize the geometry, cable routing, and other features based on customer requests.
The bike is a collaborative project with Pinion, utilizing their new electronic SmartShift system. The original Pinion gearboxes, which sit at the crankset, used a dual-cable design with a twist shifter that needed to pull cable in either direction to effect a shift.
The new Pinion SmartShift uses electronic shifting, so there’s a more familiar trigger and no need to run two mechanical cables to it. It’s powered by a self-contained rechargeable battery, with the shifter wire following the brake hose up to the handlebar. Presumably, the 3D-printed BB/Gearbox junction could be made to fit Pinion’s new e-bike motor-with-gearbox unit, too, turning the Optimist into an eMTB (though they’d need a bigger downtube to house the battery, the modular lugged construction should make this easy).
The suspension works by using flex stays, but not where you’d think. Most bikes using a pivot-less rear triangle design the carbon seatstays to flex, but here it’s the titanium lugs near the axle.
The flat section above the axle flexes, and despite appearances, it’s a double wall design with about 2mm of open space inside. Domahidy told us it’s only flexing less than 2º throughout the entire 160mm of travel, so it’s not much.
The other benefit of the 3D printed lugs is that they can print the lower section to fit any shock the customer wants, coil or air, as long as the eye-to-eye and stroke length works with the design. A snap-on cover plate in front of the shock’s trunnion mount lets you access rebound and compression knobs.
The kinematics are designed around a 15% progressivity in leverage ratio, “starting out at a little over 3:1 and ending at 2.44:1, giving amazing small bump compliance and bottom out support.”
Domahidy says the big advantage of the Pinion system is that all of the gears are inside, which means there’s only one chainring and one cog, so the chain’s relationship to the pivot location never changes. This means anti-squat is the same in every gear, so the bike can be fully optimized without having to compromise to work across a huge cassette.
It also takes the weight of a cassette and derailleur off the back, so the suspension can move more freely. Lastly, and especially combined with the Gates Belt Drive, it’s very low maintenance. This bike will get one based on the Pinion C.12, which has 12 speeds and a massive 600% gear range.
It’s a 29er front and rear, with ample clearance for 2.5″ tires (a 2.6″ might fit, depending on tread). It holds one bottle cage on the downtube, and a second mounting point under the top tube fits a 2nd cage or other two-bolt accessories.
While the final geometry and sizes are being finalized, this one is a size medium and has:
- 440mm chainstay length
- 63.5º head tube angle (with a 170mm travel fork)
- 78º seat tube angle
- 485mm reach
Without the Pinion gearbox attached, frame weight is around 5.5lbs (2,490g) with a Rockshox shock as shown. Delivery is expected in early 2024, and pricing is TBA until it’s closer to production.
