Sonder Frontier SX Eagle

Sonder Frontier SX Eagle

Hardtail mountain bike


Quick, lightweight 27.5+ modern mountain bike with SRAM SX Eagle 1x12 groupset, Rockshox Recon fork and Sonder Nova wheelset.

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Frontier is our multi-activity hardtail mountain bike. Ride hard at the trail centre, load it up for a midweek bikepacking trip, pocket your passport and continue around the world. With full rack mounts at the back, Frontier is an adaptable off-road explorer.

The geometry is for long day comfort but it’s no slouch.

At a glance
  • 6061 aluminium frame
  • Set up as an XC for speed or relaxed for comfort and performance
  • Rockshox Recon RL Silver / 100mm / 29 suspension forks
  • SRAM SX Eagle Groupset / 1 x 12 / 11-50
  • SRAM Level Hydraulic disc brakes
  • Bolt through boost 148mm rear spacing
  • Rear mudguard and pannier rack mounts
  • Sonder Nova 27.5+ Wheelset / Shimano
  • 27.5+ and 29” wheel size compatible frame

The 6061 aluminium frame provides a durable and stiff chassis giving a responsive kick as you demand power when the slope steepens or enjoy feedback and precision through the corners.

Available as a fully rigid or with 100mm suspension fork. Set it up for XC race speed or for all day big mile comfort.


Tyre clearance gives you the choice of 27.5+ or 29in wheelsets. Bolt through 148mm boost rear spacing provides the benefit of stronger, stiffer and more efficient wheels.

Why SX Eagle?

SRAM Eagle drivetrains are designed, engineered and manufactured to work as complete drivetrain systems. Its 1x drivetrain is built to be lightweight, strong and intuitive, with the gear range to ride on any terrain.


SX Eagle provides the same Eagle performance benefits as NX Eagle, but at a lower price point. The main differences stem from the choice of materials and finish options, but functionally SX is fully compatible with SRAMs Eagle groupset.

A First Look at the Sonder Frontier

It is a bike that will likely tick many boxes for anyone planning multi-day rides, without first returning home for their tea.

Read the full review here.

Author: Bearbonesnorm
Active Traveller Review the Sonder Frontier

This cracking value and rock solid machine from Sonder is just crying out to be loaded up and taken to the horizon.

Read the full review here.

Author: Andy McCandlish
CyclingLife Review the Sonder Frontier

Giving several centimeters of squish, their suspension-like characteristics help the Frontier float over rough terrain. With big handlebars, an upright position, and loads of stand-over, the Frontier is great for roistering about on, and could certainly serve as a regular mountain bike.

Read the full review here.

Author: CyclingLife
Frontier Makes Red Bulls List of Best Bikepacking Bikes 2020

Arguably one of the best value bikes in this selection, Sonder’s Frontier Rigid is a 27.5” (or 29” compatible) mountain bike, armed with a wide-ranging SRAM SX Eagle 12-speed chainset. You’ll find plenty of mounting points for bottles, cages, racks and guards, including mounts on the rigid forks.

See the full list here.

Author: Katherine Moore
Frontier - Tried and Tested

The Frontier might be considered a Jack of all trades but the clever bit is, it's able to master most of them.

Read the full review here.

Author: Bearbonesnorm
Geometry and Sizing


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. Generally we recommend:
Riders between 5ft 2in and 5ft 7in
Riders between 5ft 6in and 5ft 10in
Riders between 5ft 9in and 6ft 2in
Riders 6ft 2in and over
Size Small Medium Large X-Large
ST - Seat tube 380 430 480 520
TT - Top tube 566 602 622 647
HT - Head tube 110 130 130 150
HA - Head angle 68 68 68 68
SA - Seat angle 73 73 73 73
CS - Chainstay 445 445 445 445
BB - BB drop 50 50 50 50
FO - Fork offset 51 51 51 51
WB - Wheelbase 1089 1127 1147 1174.5
SO - Stand over 764 793 825 853
RE - Reach 390 420 440 460
SK - Stack 566 580 594 613
Build Spec
BuildFrontier SX Eagle Recon 27.5+
Frame:Sonder Frontier Frame
Fork:Rockshox Recon RL Silver / 100mm / 29
Headset:FSA Orbit C-40-ACB Headset / 7.8mm Spacer
Seat Clamp:Love Mud Silent Partner / 34.9mm
Group Set
Brake Front:SRAM Level / Direct / 850mm
Brake Rear:SRAM Level / Direct / 1800mm
Rotor Front:Avid Centreline Rotor / 180mm
Rotor Rear:Avid Centreline Rotor / 160mm
Rear Mech:SRAM SX Eagle Rear Derailleur / 12 / Long
Rear Shifter:SRAM SX Eagle Trigger Shifter
Chainset:SRAM SX Eagle Crankset / Powerspline / 170mm / 32
Bottom Bracket:SRAM Powerspline Bottom Bracket / 73mm / 118mm
Chain:SRAM NX Eagle Chain / 118 Links
Cassette:SRAM PG1210 Cassette / 12 / 11-50
Finishing Kit
Stem:Love Mud Piskie Stem / 31.8mm / 55mm
Seatpost:Love Mud Membar / 31.6mm / 400mm
Saddle:Love Mud Abode / Black
Tape/Grips:Love Mud Clutch / Black
Handlebar:Love Mud Aspect Riser
Wheels:Sonder Nova 27.5+ Wheelset / Shimano
Front Tyre:WTB Ranger / Comp / 27.5 / 2.8
Rear Tyre:WTB Ranger / Comp / 27.5 / 2.8
Tubes:WTB Inner Tube / 27.5 / 2.5
Frame:S: 1.84kg; M: 1.9kg; L: 1.98kg; XL: 2.03kg
Built:S: TBC; M: TBC; L: TBC; XL: TBC
Pedals not included with full builds
Frame Spec
Frame Weight: S: 1.84kg; M: 1.9kg; L: 1.98kg; XL: 2.03kg
Rigid Fork Weight - uncut: 1kg
6061 Aluminium frame
Optimised for rigid or 100mm suspension forks
Internal cable routing through downtube
Bolt Through Boost 148mm rear spacing for wheel strength and optimal chainline
Fork built around Bolt Through Boost 110mm spacing
Threaded 73mm BSA BB shell for no-creak assembly
Chainstay mounted disc brake for clean lines and damage protection
Triple bottle cage mount on downtube
Use a seat clamp with integrated mounts for pannier rack compatibility
Clearance for 3 inch 27.5+ or 2.5 inch 29er tyres
Reverb Stealth port
EN 14766 compliant

Aluminium Frame

The 6061 aluminium tubing is durable, light, low maintenance and stiff.

Internal Cable Routing

Clean lines and tidy cables thanks to internal downtube routing. Frontier also incorporates routing for a dropper seat post.

Wide Tyre Clearance

Extra width between the chainstays gives you the choice of running 27.5+ tyres up to 3 inches or 29 inch tyres up to 2.5 inches.

Boost Axle Width

The Frontier frame is designed around bolt through Boost 148mm rear spacing providing the benefit of stronger, stiffer and more efficient wheels. Seatstay mounted disc brake for clean lines and damage protection.

Triple Bottle Cage Mounts

Fit 2 bottles in their standard location or run your downtube bottle cage a little lower to clear a bikepacking frame bag. Plus there’s an extra bottle cage mount under the downtube.

Pannier Rack Mount

​Seat clamp mounted pannier attachment points make fitting a rack easier and keep pannier rack rails free from twisting and warping.