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Sonder Vir Fortis Go full fat. Carbon fat bike for wilder, wider adventures to places no other bike can venture

Sonder Vir Fortis frame and fork

With geometry inspired for the trail, a lightweight carbon fat bike frame and fork bundle for a bike that is as wide as your dreams

Sonder Vir Fortis GX Eagle

Carbon fat bike with SRAM GX Eagle

Go full fat and go where no other bike can. A full carbon fat bike with slack geometry for a fun characterful trail friendly ride. Float over surfaces, or blast local trails on big 4.8” tyres.

Built for exploring and Iditarod capable, Vir Fortis isn't your regular faceless hero.

Hand laid T700 carbon fat bike for rides (and riders) that don't conform to the norm. Guaranteed for 5 years the frame weighs in at 1380g and fork at 650g.

Vir Fortis frame and fork at £850; complete bikes from £1899.

Arrange a demo at one of our stores or test ride over a weekend for £39 a day plus £30 delivery and return shipping.

Compatible with 4.8” tyres, Vir Fortis is set up to get you over the most adventurous terrain. Vir Fortis might not be the bike you ride everyday, but it will be the bike you want to ride everyday!

Geometry with a trail riding pedigree, Vir Fortis positively encourages you to explore the outer limits of your trail and cross country riding. The ultimate expression of this is finding terrain which used to be a no go area for bikes - like snow or sand.

The only thing wider than the grin on your face will be your tyres - and that’s as it should be. Go nice places regular bikes can’t go. Bigger tyres equals bigger adventures.

Trail bike inspired geometry

The Vir Fortis take fun to the next level by slackening the bike out a bit, giving it a more relaxed, playful character. With natural air suspension from the enormous tyre volume Vir Fortis is ready to roll over all terrains.

Internally tapered head tube

Who would choose to be a head tube? You might as well step into the ring with Mike Tyson. It is a critical junction point where forces are distributed around the frame and steering precision is won or lost. Vir Fortis uses a fully integrated internal headset and a fork with a tapered carbon steerer tube to make sure you hold your line over broken ground.

Disk brake compatible

​Once rolling you will be surprised by how you can carry your momentum which is why you are going to be thankful for the stopping power of disc brakes. The Vir Fortis carbon frame is fully compatible with disc brakes.

High spec builds

If you’ve a dream build in mind, please get in touch and we’ll do our best to source the parts you want.

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Frame spec

Carbon is the most versatile material for building a bike frame, not only can you mold it to look exactly how you want, you can also layer it up differently to affect the ride characteristics. This allows us to build frames that are stiff in the areas they need to be and have the right amount of compliance in others making for an incredibly lively but comfortable ride.

Key Features

Toray T700 carbon fibre

Headset: IS42/28.6 | IS52/40

Seat post: 31.6 mm

Seat tube OD: 34.9 mm

100mm BSA BB shell

Frame Weight: S: 1475 g; M: 1550 g; L: 1595 g

Fork Weight: 650 g


It is important to get the right size bike, if the bike fits it will be faster, more comfortable and easier to handle. You can also take into consideration the standover height to ensure you pick a bike that will be a good fit. If you measure your inside leg and ensure there is a minimum of an inch from the toptube to your crotch this will give you enough seatpost adjustment to find your optimum saddle height.

Generally we recommend:

Riders between 5ft 2in and 5ft 7in

Riders between 5ft 6in and 5ft 10in

Riders between 5ft 9in and 6ft 2in

Size Small Medium Large
ST - Seat tube 406 457 505
TT - Top tube 580 605 625
HT - Head tube 100 110 130
HA - Head angle 68.5 68.5 68.5
SA - Seat angle 73.5 73 73
CS - Chainstay 445 445 445
BB - BB drop 60 60 60
FO - Fork offset 45 45 45
WB - Wheelbase 1103 1123 1145
SO - Stand over
RE - Reach 406 423 437
SK - Stack 586 595 614

Build Options

All our bikes are built in-house, checked and signed off by Cytech trained mechanics before being despatched to you in a custom-made bike box.

Alpine Bond Warranty

Our titanium frames are handmade and come with a 10 year frame warranty. Our hand welded 6061-T6 alloy triple butted frames come with a 5 year manufacturing defect warranty. All our bikes are built, checked and signed off by Cytech trained mechanics before being despatched to you in a custom-made bike box.


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