Mosaic GT-1 45 review: Plush, custom, titanium gravel goodness

It’s hard to refrain from unloading a barrage of praise on Mosaic’s GT-1 45. It’s an exceptionally plush, tough, and well-balanced gravel bike. The sculpted, butted titanium is beautifully finished both in terms of the welding and the painting done in-house at Mosaic’s shop in Boulder, Colorado. It’s agile enough to play on swoopy singletrack, but calm enough to scream down loose and steep gravel descents without flinching. Being titanium, flying rocks kicked up by the front wheel or other riders don’t faze it.

Mosaic will build the GT-1 45 to your specifications, not only in terms of geometry and paint, but how the tubing is tuned for your preferences or body weight.

Also, it costs a small fortune.

I tested this bike on The Spirit World 100 course, the ’Rad Dirt Fest course, and on various gravel roads and trails. I even carried it up the backside of Mount Lemmon for good measure.

Gravel + titanium = happy days

Titanium is not a new material for bicycles. At one point, it was the hot material for road bikes, with the Tennessee brand Litespeed notably making waves at the Tour de France under Lotto-Adecco in 2002. It was (and is) lighter than steel and far more compliant and comfortable than aluminum. Then a little thing called carbon fiber came along.

While small boutique brands like Moots kept working away with the material, I honestly had mentally left it behind. Then in 2018 I tested a Litespeed Cherohala and had an ah-ha moment: while clearly heavier than carbon on the road, titanium is so forgiving and so strong it’s dang near the ideal material for gravel. When rocks get kicked up and bang off a carbon frame, I wince. More brands are adding rubber down tube protectors to their carbon frames, which is cool. Titanium looks at this and laughs — the metal is its own armor.

Anyhow, titanium. It’s expensive. It’s not light. And it may well be the perfect material for a gravel bike you want to have for years and years and years.

GT-1 45 frameset details versus the GT-1 AR

Mosaic has two GT-1 models. Both use an Enve gravel fork on a frame that is custom cut and built with T3A/2.5V double-butted titanium. The GT-1 AR is a steeper, shorter-wheelbase bike with less tire clearance — thus the ‘all-road’ moniker. And the GT-1 45 is a slightly lower, slacker, and longer machine that can take up to, you guessed it, 45mm tires.

This 56cm frame has a 56.5cm top tube with a 71.5 head tube. With 62mm of trail, it lives in the middle ground for gravel bikes: calmer than a Specialized Diverge or Cervélo Aspero with 58mm of trail, but livelier than a Salsa Warbird or Giant Revolt, which both have 71mm of trail.

I tested this stock demo bike, which has a 15.5cmm head tube, so there is still plenty of handlebar drop.

Aside from the beautiful welds, nice small touches included internal routing for both Shimano Di2 and brake hosing with internal tubes to prevent any rattling. And of course the threaded bottom bracket, like the frameset itself, is built for long-haul durability and serviceability.

GT-1 45 component details

Mosaic will build up the bike to your specifications, but this luxury demo had Shimano GRX Di2 and Shimano’s Pro components, including the carbon Discover bar and Offroad Stealth saddle, plus Enve G23 wheels and WTB Raddler 44 tubeless tires rounding out the package.

You can also get an Enve cockpit or a Mosaic titanium cockpit.

I realize the double-ring GRX isn’t as fashionable as a single-ring setup, but I certainly appreciate the range of gearing and the ability to quickly make big gears jumps at the tops and bottoms of hills. A front derailleur is still a beautiful thing, in my book. And here you can have it with a 45mm tire, too.

I like the GRX Di2 levers. They have a slightly longer hood reach than the mechanical option (and Shimano’s road options), which lets you better wrap your fingers underneath. Then the hook at the end of the hood keeps you feeling locked in. Lastly, the little button just above the thumb can be programmed to control your Garmin, so you can change pages without taking your hands off the bars. Oh, and they shift and brake pretty darn well, too.

The Pro components are well suited for gravel. I was initially a little turned off by their appearance, with the Discover bar having a super-shallow drop and a fair amount of backsweep. But darned if it wasn’t a comfortable perch for long days on bumpy roads. The same goes for the well-padded Offroad Stealth saddle.

Enve’s G23 wheels are hard to complain about. At 1,316g with Chris King hubs, they are crazy light and durable. I raced these at the DK 200/Unbound, and appreciated both of those factors. They aren’t the widest internal gravel wheels (at 23mm), but they serve as a perfectly solid foundation for 44mm tires. Speaking of, WTB is doing great work hitting that double sweet spot of fast-rolling but still grippy in corners, and supple but still tough against punctures. The Raddler is a slightly toothier version of the Riddler. Both have big knobs on the shoulders and smaller ones in the center.

Bottom line: A durable gem, and a serious investment

In building custom titanium frames, Mosaic exists in some seriously rarified air, with only a few other brands like Seven, Firefly, Dean, and Zinn doing such work. The frameset alone will run you $6,900, and complete builds just take off from there. Some of the big brands are selling stock carbon bikes in the $14,000 range now, but there are no two ways about such a machine being a serious investment.

But how does it ride? The Mosaic GT-1 45 is easily among the best gravel bikes I have ever ridden, striking a balance of playful but plush in a configuration that allows for a road-like posture with titanium’s all-day, rough-road comfort. Beyond the custom geometry, Mosaic’s gorgeous paint options are incredible. Even if you’ll never ride a Mosaic, surfing through the brand’s Instagram account to ogle the designs is a fun ride on its own.