carbon onone fatbike sarto in jig

What you see here, certainly looks like and is labeled as, a forthcoming carbon fatbike that looks to be a collaboration between On-One and Sarto bicycles who are known for their carbon road bikes. If it comes true, this would be the carbon sibling to On-One’s aluminum Fatty. The pictures are gleaned from ShedFire’s website who happens to be the designer for On-One, Titus, and Planet X, so it seems highly probable.

What can we tell about the Carbon Fatty from the photos? Read on to find out.

From the looks of things, the carbon Fatty will continue the use of a 100mm bottom bracket, we’re guessing it would be threaded which means bonded inserts, but at this point it is anyone’s guess. Also, at the crux of the chainstays it looks to be just over 4 inches wide. Plenty wide for most fat bike tires, but certainly not Moonlander territory.

on-one fatty carbon fat bike

Just like the aluminum Fatty, the carbon version looks like it may have a similar split top tube design. It will be interesting to see how they bond the seat tube and top tube junction together as it currently looks to be just jigged in place. Clearly, the seat tube is one continuous piece all the way to where the seat would be. Could this be a carbon Fatty with a seat mast? Or will the tube just be cut down once completed? Also, from the first image more than this one, you can see that it looks like the Carbon Fatty will be built with a 1 1/8 to 1.5″ tapered head tube. There aren’t a lot of tapered Fatbike forks on the market, but it seems like they’re slowly coming.

We’ve reached out to ShedFire for more info, but until then start dreaming of your carbon Fatty build…

Update: After reaching out to Brant last night, he quickly got back to us with this reply –

We’ve been working with Sarto for a while, we have a mini-production run bike done for Planet X called the Mondo, and we’re about to launch a full custom project with them, handled via us at Planet X, with full bikefitting and custom frame service at an amazingly good price. I went over to visit them last week, got to see exactly how they do some aspects of their production, and so the Fatty Carbon came about because I wanted to see how flexible their manufacturing systems were. If they could make a custom Fatty for us, I know they can cope with anything.

The frame’s as you see it now, and is dimensionally similar to our Fatty alloy frame, but with a 600mm top tube to give that custom thing I wanted. I’m hoping to be able to race it in the Rovaniemi 150 race in mid February. 

The details you’ve noted on the pictures are representative of the model we’re making there. The seat tube will be cut at the white line about eight inches from the top. There’s going to be a reinforcing strut to the top tube “somehow”. The chainstays give the same internal clearance as our current bike, but there’s no reason we couldn’t go wider, but we’re just sticking to what dims we know work, due to our short lead time requirement. 

They didn’t let me see all their production methods. The carbon wrapping process is hidden behind closed doors so there’s stuff I really don’t know, but I’m 100% confident in their construction. They’ve even made 20in trials bikes for people in the past!

I would hope the frame could retail for around £2500 (USD$3250).

We’ll bring you more detail when we have it..


  1. So, unless they have no idea how to set up a digital camera, this was in the jig over a year ago?

    The bike looks interesting enough, though. Kinda like they cut a normal frame in half and are patching it down the middle… Interesting take on building a new frame, said no one ever.

  2. Does seem a bit pricey considering their brand’s mantra, but still good that Brant is back with On-One and helping them doing cool schnit again. On-One is not-much without B.

What do you think?