Colorado-based custom frame builder Mosaic has unveiled the new RT-Zero, a bike intended to take the brand’s titanium craftsmanship to a whole new level.

Mosaic’s expertise is something I’ve had first-hand experience of, having had a custom Mosaic RT1 1TR built last year. The new RT-Zero takes all of Mosaic’s engineering, fabrication and design knowledge and elevates it to a new level.

Mosaic claims the new RT-Zero frameset is its most ambitious R&D initiative to date.

It’s a design that has become a proving ground for advanced titanium construction and integration, with the aim of taking Mosaic’s refined aesthetics to a new, higher standard.

The RT-Zero sets the standard for the future of Mosaic’s bike design and is the result of a three-year design project.

• Best titanium road bikes in 2025 for smooth and luxurious riding, as reviewed by BikeRadar
  

The Zero Ops project

The Zero Ops project took the brand’s most popular model, the RT-1, as its template. The design team, led by Mosaic founder Aaron Barcheck, were then let loose in a ground-up refinement of every element, without constraints.

Barcheck explains: “With the RT-Zero, we wanted to experiment with new ideas and new product designs that could eventually lead to improved performance characteristics in our existing product line.

“This Zero Ops project, as we’re calling it, is a great way to bring new ideas to one of our existing frame models, the RT-1, while at the same time pushing our own design boundaries without having to immediately focus on the commercial viability of the product.”

New ideas with traditional fabrication

The RT-Zero’s standout feature is the new fully integrated carbon seat mast with a custom D-shaped profile.

Mosaic claims that not only does this enhance the look of the RT-Zero, but it has performance benefits, too. It says the carbon mast brings added tuneability, enabling it to customise the ride characteristics more than with traditional titanium tubing.

The carbon seat tube/mast also brings significant weight savings.

Mosaic also says it would have been relatively easy to use 3D-printing technology to create the new pieces required for the integration of the seat mast, not to mention the dropouts, head tube and bottom bracket shell.

Instead, it backed the in-house quality of its CNC-machining and proven fabrication techniques.

3D printing has become a buzzword for titanium bikes and we’ve seen many of Mosaic’s rivals utilising additive printing technology.

Barcheck has strong opinions on the validity of 3D printing for a brand that produces full-custom geometry as the norm.

“Honestly, I’ve just not been turned on by any of the 3D printing stuff out there,” he says. “So, I really wanted to do this project without 3D printing anything and instead stick to using more traditional bike-making methods.”

That means all the pieces that enable the carbon mast to join with the titanium frame – even if they look as though they were 3D printed – were made using CNC machining and combined with TIG welding.

Barcheck continues: “With 3D printing, you have to ask yourself, what is it really doing for what we’ve found is essentially the same cost?

“And if it’s not more cost-effective or transformationally different, then it’s not something we want to pursue just because it’s the latest hot trend. That’s especially true since doing it the way we’ve always done things allows us to continue to deliver made-to-order custom geometry without long turn times.

“Plus, anything that can be done in-house allows you to have a higher level of quality control, which translates to a better product.”

A fine-looking machine

The results are stunning, with certain elements of the bike looking as if they were 3D printed.

Take the carbon seat mast integration or the new one-piece titanium CNC dropouts that integrate with the flat-mount.

The new oversized head tube junction allows for full internal cable routing, as seen on the RT1 ITR, and the refinement of the design on the RT-Zero should see it trickle down to the standard RT1 within the next year.

The RT-Zero’s new bottom bracket shell adopts the increasingly popular T47 threaded standard.

The tubing used in the RT-Zero is Mosaic’s Ultra-Butted titanium; it’s based on Mosaic’s signature double-butted tubesets but pushed out to even thinner walls. Mosaic claims this will retain the celebrated Mosaic ride feel while reducing the overall weight.

Very limited edition

The RT-Zero’s groundbreaking design is going into production, although initially, the Zero Ops project bikes will be limited to only 25 framesets. Mosaic has stated that the innovations seen on this halo project will influence the future of the company’s core road models, such as the RT-1.

The framesets will be offered in a multitude of minimal paint finishes to showcase the natural titanium, combined with precision anodising and hand-polished elements.

Barcheck justifies the limited run and high price of the RT-Zero because “This is the most premium product Mosaic has made to date”.

He adds: “Maybe we only sell 25 of these ever. But selling $11,000 framesets is not the primary end goal. We’re not planning to become that company.

“We do these types of projects and the R&D that comes with them as a means to improve our other bikes. What will make sense to bring from the RT-Zero to the RT-1 remains to be seen, but it’s safe to assume it will continue to drive aesthetic enhancements and increased tunability and performance.”

Pricing

Frameset pricing will be set at $11,000 and will include the frame, fork, ENVE one-piece bar/stem, carbon seat mast, and Mosaic Carbon Topper and RT-Zero finish.

Complete bikes will be offered with component brand partners for wheels, accessories and groupsets. Based on component selection, complete RT-Zero bikes will be available for in the range of $20,000 to $24,000.

Polish company 7Anna, which owns Rondo, Creme Cycles, NS Bikes and Octane One, has officially filed for bankruptcy. 

In a statement released on behalf of 7Anna, the brand’s founder Szymon Kobyliński explained the last two to three years have been “incredibly difficult”.

“[T]he entire team has put in a superhuman effort to fight and navigate such a brutal environment. The problems began a year and a half ago when our largest client, who sold our bikes in Western Europe, went bankrupt. This left a huge hole, but we kept going. The following season, we had problems with our bank, which withheld funding from partners for several months. As a result, our bikes were not released until after the season,” wrote Kobyliński.

This was followed by the bankruptcy of one of 7Anna’s largest suppliers, which meant it was left without “top-of-the-line bikes”. Then, Kobyliński says, hackers stole “a huge sum by redirecting a transfer from our client to a fake account in Portugal”.

“Literally two weeks later, our largest client received a large shipment of bikes but didn’t pay for it and simultaneously cancelled the contract for subsequent deliveries. All of this coincided with the deadline for repaying our bank loan. We couldn’t take so many blows at once and needed help and time to reorganize,” Kobyliński added.

Founded in 2001 by Kobyliński and his wife Anna, 7Anna created several brands. NS Bikes launched in 2004, followed by Octane One in 2008 and Creme Cycles in 2017. 

7Anna launched Rondo in 2017, which has become known for its unusual road and gravel bike designs, such as the Rondo Ruut.  

Rondo’s marketing manager, Aneta Romanik, wrote on LinkedIn: “The past few years have been an enormous challenge for 7ANNA Group Sp. z o.o. and our team, but we’re still fighting for the future of our brands – Rondo, NS Bikes, and Creme. 

“Filing for bankruptcy is a formal step – it does not mean the end of our operations, but rather gives us space for reorganization and talks with investors.”

Kobyliński’s statement also echoed Romanik: “We’re not giving up. We’re still operating, servicing our bikes, supporting you, our customers, and paying attention to every detail. For now, nothing changes – stores, service, and warranties are operating as usual. We’re not disappearing – we’re continuing the history of brands that have often inspired the industry. Every bike that left our company carried with it passion and uniqueness.

“This is certainly not a bed of roses – we know that many of our trading partners are feeling anxious, but we assure you that we are doing everything in our power to ensure that our brands survive and continue to inspire. We believe that the capital we have built – as one of the few Polish brands recognized globally in its segment – will be appreciated.” 

7Anna is not the only cycling company to endure extreme financial difficulty in recent years, with many brands facing similar turmoil.

In October 2023, Wiggle and Chain Reaction were put into administration. In 2024, Orange called in administrators, while GT has reduced the size of its workforce.

This year, Brompton’s profits crashed and YT Industries entered self-administration, citing “a brutal discount war for survival”.

The new Insta360 Go Ultra might be the action camera that gets me excited about video capture again.

I’m not a connoisseur of action cameras. I used the first few GoPro generations, but was never bowled over by the less-than-user-friendly experience. I also tried Garmin’s long-forgotten Virb, which was easier to use but had less than optimal recording quality capabilities.

After those less-than-satisfactory experiments, I haven’t been impressed enough to step back into the ride-recording fray.

My camera tech experience since then has been limited to having various cameras strapped to me or my bike by our videographer experts over on Bike Radar’s YouTube channel.

• Read more: What are cycling cameras and why should you own one?

Insta360’s new Go Ultra has got me excited about action cameras again. Not just for its clever camera design, but also because of its excellent app with built-in, easy-to-use editing capabilities.

The Go’s super-compact dimensions set it apart from the X series cameras Insta360 is known for.

The Go Ultra camera looks at first glance to have similar dimensions to a GoPro; the clever part is that the camera can be unclipped from its magnetic locator in the base unit, which Insta 360 calls the Action Pod.

The camera is no bigger than an average-sized wristwatch and weighs only 53g.

What’s new with the Go Ultra?

The new super-compact camera comes with a 1/1.28-inch sensor, 220% larger than the previous Go camera. It also gets a new 5nm AI chip, the most advanced yet for a Go camera. Insta360 claims it can deliver “ultra-smooth, ultra-crisp 4K 60fps video”.

This is combined with Insta360’s PureVideo feature, which uses AI algorithms to reduce visual noise and enhance low-light brightness.

The base unit, or Action Pod, connects to the tiny camera via Bluetooth, enabling you to monitor and control recording from a distance on the 2.5in flip touchscreen.

Like the previous Go 3S, the tiny camera element has a magnetic base, although here the magnet is larger and more powerful.

Included with the camera is a magnetic pendant that the camera locks into, meaning on-bike POV video is easier than ever to capture.

Also included is a hat clip with a magnetic base built into a clip that can be attached to a helmet peak, giving another option for POV video.

Action cam mount adaptors are also included in the package.

Plenty of add-ons

Lots of accessories are available at launch, too, with a flexi-strap mount (£13.99 / $14.99) giving lots of bike-mount options and a new angle-adjust cycle mount on the way.

The accessory I find most useful is the new Ring remote (£41.99 / $44.99), a tiny single-button Bluetooth remote that’s attached to a small Velcro strap. Insta360 intends it to be worn like a ring to remotely operate the record function on the camera.

For on-bike users, it’s the perfect size to strap to a handlebar so you can activate the camera while riding, without having to take a hand off the bar.

The Standalone Camera has a claimed run time of 70 minutes on a single charge, and 200 minutes when combined with the Action Pod.

I haven’t managed to get close to 70 minutes, but I’ve only tried the camera on full-fat 4k at 60fps with all the AI stability controls maxed out. So, I’d suggest those claims are for lower resolutions and fewer AI aids in motion.

However, when you do run the tiny camera out, you can simply lock it into the Action Pod and it’ll recharge to 80% after 12 minutes in the base unit.

While the Action Pod isn’t waterproof, the camera is rated to IPX8, so it can be fully submerged down to 10 metres underwater, so it should cope easily on a soggy bike ride.

The Go Ultra also makes the switch to microSD storage; the previous Go 3S only had internal storage. This gives the Ultra Go up to a potential 2TB of storage.

Smart connection and a smart app

The camera connects to the free Insta360 phone app (available on iOS and Android), via a private Wi-Fi connection. The app’s editing software brings multiple cuts, transitions, a wealth of other effects, music and the ability to overlay cycling data from a Strava account in real time.

The user-friendliness of the Go Ultra has impressed me so far, and it could very well be the gateway to getting me excited about action cameras again.

Pricing details

The Insta360 Go Ultra is available now. The standard bundle includes the camera and Action Pod, along with a quick-release safety cord, magnetic easy clip, magnet pendant, USB-C charge cable and a lens guard.

The standard bundle is priced at £389 / $449.99 / €429.

There is also a Creator bundle package, which includes the standard bundle plus a mini two-in-one tripod, quick-release mount and a Pivot stand, priced at £429 / $499.99 / €479.

Key specifications

• Aperture: F2.85
• 35mm equivalent focal length: 14.27mm
• Weight: camera 53g, Action Pod 109g
• Size: camera 46×45.7×18.3mm (1.8×1.8×0.7in), with lens guard: 46×45.7×22.4mm (1.8×1.8×0.9in),
  Action Pod (touchscreen closed): 70.4×48.8×33.3mm (2.8×1.9×1.3in)
• Photo resolution, 50MP: 8192×6144 (4:3), 37MP: 8192×4608 (16:9), 12MP: 4096×3072 (4:3), 9MP: 4096×2304 (16:9)
• Video resolution, highest video quality: 4K60fps, highest video frame rate: 1080p@240fps
• ISO range: 100–6400
• Shutter speed, photo: 1/8000–120s, Video: 1/8000 – to the limit of frames per second
• Battery capacity, camera: 500mAh, Action Pod: 1450mAh

With a number of factors influencing what size tyres you should have on your bike, working out what tyres will fit can be difficult.

Bikes these days come in an array of different wheel-size diameters, from 700c found commonly on road bikes to 27.5in found on mountain bikes.

Width has also changed a lot, with wider tyre sizes on all types of bikes proving more popular thanks to their bump-absorbing nature.

Of course, you can always replace like with like, but if you want to try running a different tyre, or maybe just the same tyre in a different width, there are a few things to consider.

In this guide, we’ll run through everything you need to know about bike tyre sizes and delve into the unique size specifications of road bike tyres, mountain bike tyres, gravel tyres and commuter bike tyres.

How do I find the size of my current tyres?

The size of a tyre should be printed on its sidewall.

The definitive tyre size is the ETRTO number, which will be embossed on the sidewall of all tyres.

It consists of a tyre width measurement in millimetres, a dash and then the tyre bead diameter, also in millimetres. For example, 25-622 means the tyre is 25mm wide and will fit a 700c wheel, while 65-584 means the tyre is 65mm wide and will fit a 650b wheel.

Because ETRTO numbers are not commonly understood, most tyres will have a metric size such as 700c x 25mm, or an imperial size such as 27.5 x 2.60in embossed on them too, sometimes both.

A tyre’s size may be printed in black, and quite tricky to read, so outdoors or under a bright light is the easiest place to pick it out

What defines the size of a bike tyre?

There are two parameters that define bike tyre size:

• Tyre diameter
• Tyre width

The tyre diameter, or to be more specific the tyre bead diameter, is defined by the size of the wheel that it has to fit on. We’ll cover this in more detail.

Tyre width is also a factor to consider. There are more options here, as well as some variability in the width the tyre ends up when it’s mounted on your wheel rim. We’ll come on to this.

Tyre and wheel diameter

Confusingly, there are multiple ways in which tyre and wheel sizes are designated.

Road bike tyres are typically sized using the traditional European measurement system. Usually, a road bike will have 700c rims and fit 700c tyres.

Mountain bikes, on the other hand, usually have tyre and wheel sizes designated in inches, reflecting the US roots of the sport.

Typical mountain bike wheel sizes and tyre sizes are 29in, 27.5in and, historically, 26in.

29in wheels and tyres have the same bead diameter as 700c; 27.5in is the same diameter as 650b.

The 26in wheels that dominated mountain bikes for years are now more-or-less obsolete.

Like road bikes, gravel bikes have metric-sized wheels, but they tend to be either 700c or 650b.

What about ETRTO tyre sizing?

It gets even more complex, because there’s also an ETRTO sizing that’s typically printed on the sidewalls of tyres, defined by the European Tyre and Rim Technical Organisation.

This is controlled by an ISO international standard and ensures that any tyre of a designated diameter should fit on any rim of the same designated diameter.

The ETRTO number is expressed in millimetres:

• For a 700c or a 29in wheel and tyre, the ETRTO diameter is 622mm
• For a 650b or a 27.5in wheel, the ETRTO diameter is 584mm
• For a 26in wheel, the ETRTO diameter is 559mm

With this in mind, there are actually a limited number of wheel and tyre diameters readily commercially available. A tyre of a specified diameter should fit a rim of the same diameter, although, as we’ll come on to, the width of the tyre and rim are also significant factors to consider.

When it comes to tyre size, the wheel/tyre diameter will be combined with the tyre width to give you the full ETRTO number. For example, a 25-622 tyre will have a nominal width of 25mm and a diameter of 622mm (to fit a 700c wheel).

Despite the ETRTO standards outlined above, manufacturing tolerances mean the fit between the tyre and rim can be tighter or looser than expected.

If you need to change a bike tyre fitted with an inner tube, that may just mean the difference between an easy job mounting a tyre and sore thumbs from prising an over-tight tyre onto a rim or off again.

For tubeless tyres, it’s more critical there’s a close fit between the tyre and the rim, particularly for road bike tubeless tyres, where tyre pressures are higher and there’s more risk of a blow-out than with an MTB or gravel bike tyre.

Manufacturers are now making the best tubeless road tyres to much closer tolerances than a few years ago to ensure safety, particularly on the latest hookless rims.

Makers of road bike wheels with hookless rims will often publish a list of tyres recommended for use with their wheels, and it’s best to consult these lists to avoid any mishaps out on the road.

Tyre width

Although there are a limited number of tyre bead diameters to fit discrete wheel sizes, there’s a lot more variation in tyre width.

To start with, mountain bike tyres are a lot wider than road bike tyres. This is one reason why you’ll likely be unable to fit a mountain bike tyre in a road bike frame, although you can in principle fit a mountain bike tyre on a road bike rim.

Road bike and hybrid tyres are typically sized in millimetres, when it comes to width.

Most gravel bike tyres are also sized in millimetres, although super-wide gravel tyres – akin to mountain bike tyres – may be sized in inches.

Mountain bike tyres are typically sized in inches too.

Road bike tyre sizes explained

When it comes to choosing the best road bike tyres for you, width is the key factor to consider.

Almost all road bike wheels are 700c (with a beam diameter of 622mm), although some bike brands fit 650b wheels (with a bead diameter of 584mm) to some of their smaller-sized bikes, so they can maintain a similar road bike geometry to larger frame sizes.

In the past, 23mm was the typical width for most road tyres, and some tyres came in a 20mm width or narrower.

Now, 25mm is the narrowest tyre that typically comes fitted to road bikes and many bikes have 28mm tyres, with clearance on some of the latest bikes for 32mm rubber and beyond.

Wider tyres can offer improvements in grip, comfort and rolling resistance. However, you should check the clearance offered by your frame before committing to a wider tyre.

One final point – while millimetres are often used to measure or refer to the width of a road bike tyre, its actual width when inflated will depend on manufacturing tolerances, the rim width and tyre pressure.

As a result, you may see the width referred to in ‘c’. For example, 25c instead of 25mm.

Common road bike tyre sizes

Here’s an overview of common road bike tyre sizes.

Mountain bike tyre sizes explained

Mountain bikes are now split between 27.5in and 29in wheels. Some mountain bikes have a 29in wheel at the front and a 27.5in wheel at the rear. These bikes are often referred to as mullet bikes, and it’s a popular setup on trail bikes and enduro bikes.

Wide rubber rules the day with the best mountain bike tyres. Typical widths range from 2in up to 2.6in, depending on the type of riding the tyre is designed for. Increasingly, wider tyres are also available.

Common mountain bike tyre sizes

Here’s an overview of common mountain bike tyre sizes, across 26in, 27.5in and 29in wheel sizes.

Gravel bike tyre sizes

Choosing the best gravel bike tyres for your bike often means weighing up wheel size, tyre width and tread pattern, to find an option that suits your riding style and the terrain you’ll be taking on.

Gravel bikes come with either 700c or 650b wheels and you’ll need to choose a tyre that will fit the wheel size you have on your bike.

700c gravel bike tyres start off at around 32mm wide, although most frames can take wider rubber and many riders now opt for 40mm or 45mm tyres. Gravel tyres can reach around 50mm if they fit in the frame.

Switch to 650b wheels and tyres are usually wider, to add extra air volume and comfort. 650b gravel bike tyres typically start at around 40mm wide and travel up towards 60mm, by which point, inches may be used to express the width.

A 650b wheel with a wider (and hence deeper) tyre will have a similar rolling circumference to a narrower tyre on a 700c rim, so many gravel bike frames can take either wheel size.

While gravel tyres may appear to share much in common with cyclocross tyres, UCI regulations for cyclocross racing dictate that CX tyres must be 33mm or narrower for competition.

Common gravel bike tyre sizes

Here’s an overview of common gravel bike tyre sizes for 700c wheels.

Commuting bike tyre sizes

Commuter hybrid bikes have 700c, 650b or 26in wheel sizes, with 700c being the most popular.

Although hybrid bikes tend to have the same-size wheels as road bikes, robustness and comfort are prioritised over speed, so they typically have significantly wider tyres that are heavier and incorporate a more pronounced tread pattern.

Hybrid bike tyres typically start at 30-plus millimetres wide and go up into the high 40s. If you go much wider than this, increased rolling resistance can make for slow progress.

Common hybrid bike tyre sizes

Here’s an overview of common hybrid bike tyre sizes for 700c wheels.

How does rim width affect tyre size?

Although we’ve talked a lot about tyre width, this is only the tyre’s nominal width (i.e. what the manufacturer has stated, rather than the actual width when measured).

A tyre’s actual width will be different when mounted on a wheel. There are two reasons for this:

• First, when inflated, a tyre may plump up wider than its stated width, due to variations in manufacturing tolerances
• Second, the tyre represents only around three-quarters of the circumference of the wheel/tyre combination, the rest is determined by the rim bed

Wheel rims are getting wider both for road bikes and mountain bikes. So, whereas 17mm used to be a fairly standard road bike rim width, many modern road bike wheels have rims with internal widths of well over 20mm.

The Zipp 303 Firecrest wheel, for example, has an internal rim width of 25mm. That adds significantly to the width of the mounted tyre, so a nominally 28mm Michelin Power tyre measured up at 30.9mm wide in our test of the wheelset.

Among the advantages of wider rims, the extra volume of the tyre means it can be run at lower pressure for a more comfortable and possibly faster ride, without any weight penalty. On the downside, you may have clearance issues in your bike frame if a tyre measures up significantly more than the stated width.