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Sonder Frontier [V1] SX Eagle Rigid Rumpus

Quick, lightweight 650b+ modern mountain bike with SRAM SX 1 x 12 groupset, Rigid fork and Love Mud Rumpus wheelset.

£749.00 Was: £799.00

Available on finance, from per month*

Pictures are for illustration and some components and finishing kit of this build may be different. Please refer to the detailed spec sheet before placing an order.

  • Sonder Frontier SX Rigid Rumpus 650b Chilli - Chilli
  • Sonder Frontier SX Rigid Rumpus 650b Stirling Moss - Stirling Moss
    Stirling Moss
  • Sonder Frontier SX Rigid Rumpus 650b Nemo - Nemo

How To Order

All our bikes are built individually to order. If you want to change any part of the spec to suit your needs then get in touch.

  • Frontier Frame [V1]

  • 1. Select Size

    Please select a size. See the fitting guide for size information

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    2. Select Colour

    Please select a colour. If your desired colour is not available, you can request a Stock Alert and you will be emailed when the product is either back in-stock or on pre-order.

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    Stirling Moss
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    Please make sure you have read and understood the terms of a Pre-Order purchase before placing your order. Payment will be taken immediately and your item will be despatched when stock arrives. If you require additional items please place a separate order as it will be held and sent together. More about Pre Orders

Please allow 20 working days for us to build, check, pack and despatch your Sonder.

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Guide to paying with Cycle to Work Schemes

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Alpkit Ltd acts as a credit intermediary and offer credit products provided exclusively by Klarna Bank AB (publ). Klarna Bank AB (publ) is Authorised by the Swedish Financial Services Authority (Finansinspektionen) and is subject to limited regulation by the Financial Conduct Authority. Details about the extent of our regulation by the Financial Conduct Authority are available from us on request. Finance is only available to permanent UK residents aged >18, subject to status, terms and conditions apply. Registered office: Sveavägen 46, 111 34 Stockholm, Sweden. Corporation ID number: 556737-0431.
At a glance
  • For searching out technical terrain
  • 6061 aluminium frame
  • Relaxed riding position for comfort and performance
  • Rigid forks
  • Hydraulic disk brakes
  • QR Boost 141mm rear spacing
  • Rear mudguard and pannier rack mounts
  • 650b+ and 29” wheel size compatible frame

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 and multiple boss mounts on the fork, Frontier is an adaptable off-road explorer.

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

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 100 mm 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. QR Boost 141 mm rear spacing provide 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.

Aluminium frame

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

Internal cable routing

Clean lines and tidy cables thanks to internal 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 2.4 inches.

Boost axle width

The Frontier frame is designed around QR Boost 141 mm rear spacing providing the benefit of stronger, stiffer and more efficient wheels. Seatstay mounted disc brake for clean lines and damage protection.

Pannier ready

Responsive when loaded - Frontier is more than happy to shoulder a pannier.

Frame spec

Frame Weight (kg): S: 1.7; M: 1.8; L: 1.86; XL: 2.0
Rigid Fork Weight - uncut (kg): 1.0
6061 Aluminium frame
Optimised for rigid or 100 mm suspension forks
Internal cable routing
QR Boost 141 rear spacing for wheel strength and optimal chainline
Fork built around QR Boost 110 mm spacing
Threaded 73 mm BSA BB shell for no-creak assembly
Chainstay mounted disc brake for clean lines and damage protection
Adventure cage compatible downtube mount
Full rack mounts and multiple boss mounts on rigid fork
Clearance for 3 inch 650b+ or 2.5 inch 29er tyres
Reverb Stealth port
EN 14766 compliant

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 2 and over
Frame size
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 435 435 435 435
BB - BB drop 50 50 50 50
FO - Fork offset 51 51 51 51
WB - Wheelbase 1089 1127 1147 1174.5
SO - Stand over
RE - Reach 390 420 440 460
SK - Stack
Build SRAM SX Eagle, 1 x 12 Rigid Rumpus 650+ plus
Frame Sonder Frontier Frame
Fork Frontier Fork
Headset Love Mud Rumour, Integrated Sealed Bearing, Tapered
Seat clamp Love Mud Vice, 34.9 mm
Group set
Brake Front SRAM Level
Brake Rear SRAM Level
Rotor Rear Avid Centreline 160 mm
Rotor Front Avid Centreline 180 mm
Rear mech SRAM SX Eagle Rear Derailleur 1x12 Long Cage
Shifter Rear SRAM SX 12sp
Chainset SRAM SX Chainset Powerspline 32T
Bottom Bracket SRAM Powerspline
Chain NX Eagle
Cassette SRAM PG-1210 12sp, 11-50t
Finishing Kit
Stem Love Mud Piskie, 31.8 mm
Seatpost Love Mud Membar, 31.6 mm
Saddle Love Mud Abode
Tape/Grips Love Mud Clutch
Handlebar Love Mud Aspect Riser, 780 mm
Wheels Love Mud Hobo 29er Wheelset
Tyres WTB Trail Boss 2.4 Comp
Tubes WTB Inner Tube Presta 29
Frame S: 1.7 kg; M: 1.8 kg; L: 1.86 kg; XL: 2 kg
Built 12.5 kg; M: 12.7 kg; L: 12.8 kg; XL: 13.3 kg
Pedals not included with full builds

Swapouts and Upgrades

You can interchange Love Mud components on this build at no additional cost. So if you want a different length of stem, a particular saddle or bar then let us know in the notes section in the checkout and we'll get in touch. We also hold big stocks of SRAM, Rockshox, WTB and regular build with Shimano, Hope, Cane Creek. We'll build your Sonder with any part that suits your needs. Give us a call, with the same experienced mechanic helping throughout your build you know who to call if there's anything you want to know.

Click here for more information



Alpine Bond Warranty

We offer a 10 year guarantee on both our handmade titanium and Reynolds steel frames. Our hand welded 6061-T6 alloy triple butted frames and carbon 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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