Jochem's Mosaic RT-1
The start of a dream project
It had been on my wishlist for a long time: building a fully custom titanium road bike. Not just picking something from a catalog, but creating something that fits me from A to Z. After years of riding my Mosaic GT-1 i45 gravel bike with great joy and seeing plenty of envy-inducing custom builds pass by, the itch got stronger.
And then Mosaic released a limited edition in Ultraviolet, of which only five would be made. The color, the collaboration with Chris King… everything clicked. I thought: I just have to go for it!
Color and finish
Let’s start with the color. Mosaic offers nearly anything you can imagine: from raw titanium to fully painted frames, and everything in between. They also have fixed layouts and so-called artist series, where you give them creative freedom. That’s what I did.
Ultraviolet wouldn’t normally be my first choice, far from it, but this version looked amazing at first glance. It stuck with me.
What makes it even more special: this limited edition was developed in collaboration with Chris King. All Ultraviolet parts: headset, bottom bracket and hubs were selected to complete the whole package. A strong concept, and a great excuse to build a truly complete bike.
About Mosaic
At Mosaic, you choose between two frame types:
- Level 2: standard geometry, in a limited number of options. Faster delivery and a lower price are the advantages.
- Level 1 (Modules): fully custom. Everything is configurable: geometry, paint, mounts, cable routing, derailleur hangers, seatpost diameter.
For this build, I chose a Level 1 frame. You first sit down with the dealer and determine everything—from seat tube angle to top tube shape. Then Mosaic starts building.
It starts with some titanium tubes, a few sketches, and a lot of craftsmanship and ends in a bike that’s truly built for you. Everything is welded, painted, and finished in-house.
The production process
If you choose Level 1, the journey begins with yourself or rather, your body. A bike fitting is essential. That way the frame won’t be a standard size like 54 or 56, but is tailored to your body and riding style. It essentially has no size anymore. That means: perfect position, and often: no spacers needed.
Next, you (or a specialist) go through all the details. The choices are endless, so precision matters. Road bike? Gravel? In between? Do you want mounts for bags? Racks? Fenders? Internal or external cable routing?
Once everything is decided, the order goes to Mosaic. The frame is hand-cut and welded. Even the paint, often overlooked, is done completely in-house. Pretty cool, right?
My frame and geometry
I knew one thing for sure: it had to be a true, sporty road bike. A classic machine with sharp lines, direct handling, and enough comfort for long rides.
The geometry is compact: short wheelbase, low stack, and an almost horizontal top tube, for both looks and function. Only bottle cage bolts are mounted; the rest of the frame remains as clean as possible.
Since I wanted to use Shimano Di2, the cable routing was integrated from the start. And despite the sporty geometry, there’s clearance for 35 mm tires, a modern touch that adds versatility.
Drivetrain
I went with Shimano Dura-Ace Di2. Clean, proven, reliable, and visually well-balanced with the frame. I chose 52/36 in front and 11-34 in back on purpose: 52 for flat rides, 36/34 for climbing. No need to swap parts.
Crank length: 172.5 mm. A conservative choice and honestly, it fits this bike well.
Wheelset
The Chris King ARD44 wheelset came standard with this frame. It wouldn’t have been my first choice, but it just worked here.
The rims are 44 mm deep, a great middle ground and wide enough for 32 mm tires, which I really wanted to try. The carbon rim is US-made, just like the frame. The Chris King Ultraviolet hubs complete the aesthetic.
Handling is surprisingly direct, and the wider tires give just that bit of extra confidence, even on rough tarmac or light gravel.
Finishing & details
The frame, groupset, and wheels form the base. But it’s the details that make a bike personal.
The Chris King headset, bottom bracket, and hubs came with the frame. No choice there, but I wouldn't have it any other way. All in Ultraviolet, all spot-on.
ENVE provides the fork, stem, and seatpost as standard. These are painted to match the frame, no clashing parts, just one clean unit. The stem is 100 mm, the handlebar is an ENVE SES AR in 380 mm, my favorite, both for road and gravel.
The saddle is the 3D version of the Prologo Nago R4. I’m familiar with the regular one and liked it, so I’m curious what this extra layer brings, literally and figuratively.
As for the tires: I was set on trying 32 mm. I ended up with the Panaracer Agilest TLR. Good reputation, reasonable weight, and visually a great match.
To top it off, I chose a 3D-printed Silca/ENVE computer mount. A subtle touch, but if you want to get it right… you get it. And bottle cages? I usually go with Arundel Mandible, but this time I found titanium ones by Silca in a matching color. Perfect match!
Ride feel
Now that everything’s mounted, it’s time for the best part: riding. I’m really curious how titanium compares to carbon. Softer? More lively? Less stiff? Or exactly what I’m looking for?
The first real test will be serious right away: the Strade Bianche Gran Fondo in Siena. Lots of gravel, climbing, and variation. If the bike proves itself there, I’ll know it’s a winner.
But honestly: I’m just excited. Excited to ride, to feel what I’ve put together, and to find out whether this frame, this build, and this material truly bring something special. More to follow in a ride update!
Jochem
