Selecting the right road bike crank arm can influence pedaling efficiency, crank alignment, and overall ride comfort. When replacing a left crank arm, it’s crucial to match hole orientation (Diamond Hole vs Square Hole), pedal thread (typically 9/16 inch), and the correct arm length to your leg extension and bike geometry. The five products below represent common, compatible options for road, city, and hybrid builds, spanning forged aluminum and steel variants with multiple length choices. Use the quick reference table to compare key specs, then review each option in detail to determine the best fit for your setup.
| Product | Brand | Length (mm) | Hole Type(s) | Notes |
|---|---|---|---|---|
| ZUKKA Left Arm | ZUKKA | 152 / 165 / 170 | Diamond Hole | Left arm; 9/16″ pedals; aluminum |
| BLLREMIPSUR Left Crank | BLLREMIPSUR | 170 | Diamond Hole (+ round hole) | Two left cranks included; steel |
| Alps2Ocean Left Crank Arm | Alps2Ocean | 152 / 160 / 165 / 170 / 175 | Diamond Hole and Square Hole | Forged alloy 6061; multiple sizes |
| THALOUS Diamond Hole Crank Arm | THALOUS | 170 | Diamond Hole | 6061-T6 forged aluminum; 9/16″ pedal |
| Rhinenet Left Crank Arm | Rhinenet | 170 | Diamond Hole | Aluminium alloy; left arm, horizontal |
ZUKKA Left Crank Arm For Road Use
The ZUKKA crank arm is an aluminum alloy piece designed for left-side replacement in road, mountain, city, folding, and even E-bike setups. It lists a hole spacing of 152mm and a total length of 185mm, with compatibility for 9/16 inch pedals. The spindle interface is Diamond Hole, so verify your current crank orientation before purchasing. Built for durability and high hardness, this arm aims to resist deformation under typical riding stresses, making it a practical option for riders seeking a dependable, lighter-weight upgrade or replacement.
BLLREMIPSUR Left Crank Arm Replacement
The BLLREMIPSUR offering includes two left crank arms at 170mm, designed specifically for a left-side upgrade. The product highlights a center-to-center length of 170mm and distinguishes a round left hole at 2 cm in front and a diamond hole at 1.6 cm at the rear, signaling the need to match a diamond-hole orientation on your crankset. Constructed from solid steel, this set emphasizes high strength, durability, and resistance to warping, indicating long-term reliability for riders who frequently replace or upgrade components on heavier riding rigs.
Alps2Ocean Left Crank Arm 152–175mm
The Alps2Ocean universal left crank arm comes in five sizes (152/160/165/170/175mm) and is forged from 6061 aluminum for strength and durability. It supports a 9/16 inch pedal interface and is available with Diamond Hole or Square Hole orientation, though buyers should confirm which hole type matches their crank. This versatility makes it a practical upgrade for city bikes, folding bikes, MTB, E-bikes, road bikes, and exercise bikes, enabling a broad cross-section of riders to find a compatible match.
THALOUS Diamond Hole 170mm Left Crank Arm
The THALOUS crank arm is a 170mm left arm crafted from forged aluminum alloy 6061-T6, offering high strength, light weight, and durability. It is specified for Diamond Hole orientation, with a caveat that Square Hole variants do not fit this left arm. Compatible with 9/16 inch pedals, this arm is positioned as a robust upgrade for riders seeking a stiff, corrosion-resistant component that holds up under regular road and urban riding conditions. Installation and fit should align with your existing drivetrain’s hole orientation to ensure proper operation.
Rhinenet Left 170mm Crank Arm
The Rhinenet left crank arm is an aluminium alloy component designed specifically for a left-arm replacement at 170mm. It’s described as suitable for electric, folding, hybrid, mountain, and road bikes, highlighting its versatility across a range of bike styles. The product emphasizes high-quality materials, sturdiness, and easy installation, with a focus on a left-arm configuration and a Diamond Hole interface. Prospective buyers should verify hole orientation on their current crank to ensure a proper fit and avoid compatibility issues during installation.
Buying Guide
- Crank arm length: Common road bike options range from 152mm to 175mm. The right length depends on your leg length, riding style, and crankset geometry. If in doubt, consult a bike-fitting guide or a professional shop to determine the optimal length for your cadence and knee comfort.
- Hole orientation: Diamond Hole vs Square Hole is a critical compatibility factor. Check your existing crank’s spindle interface to avoid buying an arm that won’t fit. Some arms support both hole types, while others are dedicated to one orientation; swapping requires matching both arms’ orientations for a secure fit.
- Material and durability: Aluminum alloys (like 6061-T6) offer a strong, lightweight option with good fatigue resistance. Steel variants provide durability and different stiffness characteristics but can add weight. Consider your riding conditions (city commuting vs long road rides) when choosing material.
- Left-arm only vs set: Some products are sold as left-arm replacements, while others come as a left-right pair or include multiple left arms. If your drivetrain requires a specific two-arm arrangement, verify whether a kit or single arm best fits your needs.
- Pedal compatibility: Most road bikes use standard 9/16 inch pedal threads, but some smaller or retro bikes may use 1/2 inch. Confirm pedal threading on your existing pedals and crank arms to ensure seamless installation and removal during maintenance.
- Installation considerations: Replacement may require a crank puller or specific wrenches (often 8mm or 14mm). After installation, check chainline and crank alignment to ensure smooth shifting and no pedal-to-chainring interference.
- Cost vs value: While not listing prices here, evaluate whether a single or paired solution offers better long-term value, especially if you ride frequently or modify bikes for different uses (commuting, racing, or touring).
- Compatibility with cranksets: Some arms specify compatibility with 9/16 inch spindles and may assume a standard square or diamond hole orientation. If you use a non-standard crankset, confirm compatibility before purchasing to avoid a mismatch that requires additional adapters.
- Maintenance and care: Aluminum and steel arms should be inspected for signs of deformation, corrosion, or excessive wear at the spindle interface. Regular torque checks and cleaning help extend the life of replacement arms.
- Avoiding counterfeit parts: Stick to reputable brands and verify product dimensions (length, hole type, and pedal fit) against your bike’s specifications to avoid mismatches or subpar components.