Cratus Crankarms
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Performance Benefit
Tested savings of 0.001–0.002 m² CdA per 10 mm Q-factor reduction, depending on rider.
What It Is
Adjustable-length crankarms designed for compatibility with leading spider-based power meters.
Best For
Riders seeking Cratus fit optimisation while retaining their preferred power meter system.
Compatibility
Compatible with a range of leading spider-based power meters and drivetrain configurations. Find our fit calculator HERE.
Why Cratus?
Brings the fit flexibility of the Cratus platform to existing power meter ecosystems.
Product Information
Cratus Crankarms bring the aerodynamic and fit benefits of the Cratus platform to a range of market-leading spider-based power meter systems. Featuring a CFD-optimised crankarm profile, adjustable crank lengths and reduced Q-factors, they allow riders to optimise both aerodynamics and biomechanics while retaining their preferred power measurement solution.
Available in both Short and Long versions, crank length can be adjusted in 2.5 mm increments across ranges of 145–160 mm and 160–175 mm respectively using interchangeable pedal inserts.
Each crankarm set is supplied with a DUB spindle (Narrow or Standard, depending on the selected configuration). Only your existing spider or direct mount chainring is retained. Depending on the crankarm and spindle combination selected, Q-factor ranges from 129 mm to 141 mm, providing reductions of up to 21 mm compared to many stock cranksets.
Manufactured from 7075-T6 aluminium, anodised black and finished with subtle laser-etched WattShop branding.
Please refer to the Fit Calculator for detailed information regarding supported power meters, spindle selection, bottom bracket requirements and Q-factor options.
Spider and/or direct mount chainring is not included.
Technical Specifications
COMPATIBILITY
- SRAM AXS/Quarq (8-bolt)
- Rotor INspider
- SRM Origin
- FSA Powerbox
- Power2Max Open Source (via adapter)
Compatibility with after market spider manufacturers such as XCadey can not be guaranteed.
BOTTOM BRACKET REQUIREMENTS
- Existing DUB users typically require no BB changes.
- 30 mm BB users require DUB conversion adapters or a DUB BB.
- 24 mm BB users require a DUB BB.
FITMENT CONSIDERATIONS
There are two main aspects which need to be considered. Crankarm to chainstay clearance and chainstrike. The latter is between the chain and crankarm when in the smallest sprocket of your cassette.
Please refer to our fit calculator. The dimensions provided will help provide crankarm position relative to the frame centreline; from this, you can work out chainstay clearance.
Secondly, the fit calculator also provides a chainstrike clearance estimate. This is based on your input parameters.
2x COMPATIBILITY
If you plan to use the crankarms in a 2x setup. We can not guarantee 2x compatibility. The straight crankarms are not compatible. Whereas the compatibility of the +3mm crankarms is model-dependent and can not be guaranteed. From 1x chainline to the inside face of the crankarm, the dimensions are as follows:
SRAM (+3) = 9.43mm
SRM Origin (+3) = 13.20mm
FSA (+3) = 9.31mm
Rotor (+3) = 10.86mm
When doing your compatibility calculations for clearance, please consider:
- A 2x outer chainring chainline is 3.5-4.5mm further outboard than a 1x chainline.
- The dimension from the outside face of the chainring to the outside face of the front derailleur.
- Ensure that you account for any "over shift" whereby the front derailleur shifts excessively outboard before returning to its normal position.
WEIGHT
- 160-175mm crankarms = 402g
- 145-160mm crankarms = 382g
- DUB Spindle (narrow) = 73g
- DUB Spindle (standard) = 77g
- Pedal Inserts (inc plates) = 35g/pair
Crankarm weight may vary depending on the DS model.
CRANKARM UPDATES INCLUDE
Cratus crankarm updates build upon the original platform with several key improvements:
- Reduced overall system weight.
- New +3 mm crankarm option for increased compatibility and clearance.
- Transition to the DUB spindle standard.
Common non-drive side crankarms and spindles across the Cratus range for simplified configuration and future upgrades.
What's Included
A full crankset comprises of the following.
1x pair of crankarms (DS and NDS)
1x DUB spindle (ultra narrow, narrow or standard)
2x retention bolts (DS + NDS)
1x DS retention bolts (DS + NDS)
1x pair of pedal inserts and plates
1x spider lockring (spider model dependent)
Optional Items:
Pedal puller
30mm-to-DUB adapters
All required mounting hardware, included.
More information can be found on each components page; spindles, pedal inserts, pedal puller and 30mm-to-DUB adapters.
Install Guides & Resources
Why we created Cratus Crankarms
Cratus crankarms were created to give riders access to the fit and biomechanical benefits of the Cratus platform while retaining compatibility with market-leading spider-based power meters. Adjustable crank lengths allow riders to refine their position as their fit evolves, without compromising their preferred power measurement solution.
Compatible Power Meters
Optimise crank length and rider fit while retaining compatibility with leading spider-based power meters.
Crankarm Lengths
The Short Armed model is optimised for riders seeking shorter crank lengths and supports adjustment from 145 mm to 160 mm. Interchangeable pedal inserts allow crank length to be fine-tuned within the available range.
The Long Armed model is optimised for riders seeking longer crank lengths and supports adjustment from 160 mm to 175 mm. Interchangeable pedal inserts allow crank length to be fine-tuned within the available range.
Straight vs +3 mm Offset Crankarms
The Cratus Mk2 system is available with either straight or +3 mm offset crankarms. The +3 mm option increases pedal stance width by 3 mm per side (6 mm total), providing additional chainstay and heel clearance while allowing riders to optimise Q-factor for their individual fit requirements.
Spindle Lengths
Cratus Mk2 is available with three spindle lengths to accommodate different frame standards, bottom bracket widths and Q-factor requirements. Selecting the correct spindle ensures optimal fit, chainline and crankarm clearance for your bike.
Aerodynamic gains through Q-factor optimisation
A 10 mm reduction in Q-factor has been shown to deliver rider-dependent aerodynamic savings of approximately 0.001–0.002 m² CdA. While the exact benefit varies depending on rider morphology, position and wider bike setup, narrowing stance width can reduce the frontal area and improve airflow interaction between the rider’s legs and the bike.
Using a standard air density of 1.225 kg/m³, this equates to approximately:
- 1.2–2.4 W saved at 45 kph
- 2.2–4.4 W saved at 55 kph
For riders targeting maximum performance, these are meaningful gains from a single fit-related adjustment — particularly when combined with crank length, position and drivetrain optimisation.