Our site works best with JavaScript enabled.

Sonder Vir Fortis Full carbon fat bike for wilder, wider adventures

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 SRAM GX1

Carbon mountain bike with SRAM GX1. With a SRAM 1x groupset

Designed for exploring and Iditarod capable, Vir Fortis isn't your regular faceless hero, its slackened off geometry gives a characterful ride. It just floats over soft surfaces with big wheels and even bigger 4.8" tyres for free rolling all conditions.

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.

If you want to style your own Vir Fortis pick it up in its raw beauty as a frame and fork for just £849, or let our Sonder guru Neil build you up one of his SRAM GX1 builds for £1849.

Arrange a demo at our Nottingham factory store 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

Check out the specs on the individual product pages. They are built to order and are fully customizable – if you want a different stem length, saddle, wheelset, bar or gear ratio then let us know. If you’ve a dream build in mind then please get in touch and we’ll do our best to source the parts you want.

Hide features

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 (g): S: 1474, M: 1884, L: 1947, XL: 2006

Fork weight (g): 650


It is important to get the right size bike, if the bike fits you well 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.

Riders between 5ft to 5ft 7in

Riders between 5ft 7in to 5ft 10in

Riders between 5ft 10in to 6ft 4in

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.


Dsc 0053-890x600
Single track Review Sonder

Singletrack came by Sonder at the London Bike Show

Read on Singletrack

Pink Bike Checks Out Sonder

PinkBike visit us at the London Bike Show

Read on Pinkbike

Explore other content related to Sonder Adventure Bikes on our site.

09 03 2017 - Daring Deeds

Life on the Broken Road Part 2
More bike travel in NZ

03 03 2017 - Daring Deeds

Life on the Broken Road Part 1
adventure through New Zealand by bike

14 02 2017 - Daring Deeds

Offa leads me home
Continuing to chase Offa's adventure

10 02 2017 - Daring Deeds

Offa’s Dyke Leads Home
An Unremarkable Adventure Chasing Offa

26 01 2017 - Spotlight

Long Mynd delights
bikepacking around Shropshire

24 01 2017 - Develop

2 new Sonder bikes
2 new bikes set to join Sonder

Sneedham basquetrip 026
30 11 2016 - Daring Deeds

Pyrenees Traverse – Mules, Munitions and Million Star Hotels.
6 days in the mountains

10 09 2016 - Daring Deeds

Pips Tour De France
Cycle touring through France on a tandem

Screen shot 2016-07-15 at 11.02.55
15 07 2016 - News

Northern Grip Mountain Bike Festival
Celebrating all things mountain bike in Ramsbottom

Mycamino 14
06 07 2016 - Daring Deeds

The Camino Report - part 3
reviewing the Sonder Camino

Mycamino 6
28 06 2016 - Daring Deeds

The Camino Report - part 2
riding home to Norway

Mycamino 1
14 06 2016 - Daring Deeds

The Camino Report - Part 1
first impressions on the Sonder Camino