If you’re upgrading a bike’s crankset or replacing a damaged left crank arm, this guide helps you pick the right 170mm crank arm with the correct spindle interface. It highlights options for Diamond Hole and Square Hole interfaces, with clear buyer-focused notes. Ideal for riders seeking durability, compatibility, and straightforward installation. The top picks below cater to road, MTB, e-bike, and folding bike enthusiasts.
| Product | Interface | Length | Best For |
|---|---|---|---|
| Epessa Crank Arm Left 170mm (Diamond/Square Interfaces) | Diamond/Square | 210mm total length; 170mm arm | General replacement, compatible with common 9/16″ pedals |
| Alps2Ocean Crank Arms 170mm Diamond Hole | Diamond | 170mm arm | Sturdy forged aluminum for diverse bike types |
| Epessa Crank Arm Left 170mm (Diamond/Square) | Diamond/Square | 210mm total length; 170mm arm | Versatile compatibility with two hole types |
| WEEROCK Bike Left Crank Arm 170mm | Diamond | 170mm | Steel construction for durability |
| PROWHEEL Left Crank Arm 170mm Square Hole | Square Hole | 170mm | City, folding, MTB, and e-bike applications |
Epessa Crank Arm Left 170mm – Diamond/Square
Features include dual spindle interfaces: Diamond and Square. The 170mm arm has a 210mm total length and fits 9/16 inch pedals. Constructed from high-quality aluminum alloy for light yet durable performance. Best for riders needing flexible compatibility with existing crank setups.
Best for: general replacement and mixed-interface bikes where the left crank must match either Diamond or Square hole orientation. Caution: verify hole type on your crank before purchase to avoid misfit.
Alps2Ocean 170mm Diamond Hole Crank Arm
Made from forged aluminum 6061, this crank arm is designed for strength and durability. Available in 170mm length with Diamond Hole interface. Aimed at riders who want a robust crank with precise hole alignment. Size options include multiple lengths for different riding styles, including e-bike setups.
Best for: e-bike and road riders needing a strong, consistent Diamond Hole crank arm. Caution: confirm hole orientation and length matches your current crank to ensure proper fit.
Epessa 170mm Left Crank Arm (Diamond/Square)
This Epessa crank arm supports both Diamond and Square interfaces with a 170mm arm and 210mm overall length. It accepts 9/16 inch pedals and is crafted from high-quality aluminum alloy for a balanced mix of stiffness and lightness.
Best for: flexible compatibility when upgrading or repairing a multi-bolt crank system. Caution: ensure the port alignment is identical to your original crank port.
WEEROCK Left Crank Arm 170mm, Steel
Steel construction provides enhanced durability for aggressive riding and rough terrain. The 170mm length with Diamond Hole interface makes it compatible with bikes using this standard. Best for riders prioritizing strength and longevity in replacement parts.
Best for: riders needing a rugged, long-lasting left crank arm. Caution: weight is higher than aluminum options, which may affect overall bike balance for some setups.
PROWHEEL Square Hole 170mm Left Crank Arm
Forged aluminum 6061 crank arms in 170mm length with Square Hole interface. Suitable for City, Folding, MTB, E-bike, and Road bikes. Ensures a sturdy connection with 9/16 inch pedals and consistent hole alignment across left-right crank arms.
Best for: versatile use across multiple bike styles where Square Hole is required. Caution: double-check the Square Hole diameter and hole orientation before purchase.
PATHGNAR Square Hole 170mm for Electric Bikes
Square taper crank arm designed for electric bicycles, available in 170mm length with robust forged alloy 6061 construction. Designed specifically for Square Hole orientation and matched pair installation. Great for mid-mounted motor setups in e-bikes.
Best for: e-bike upgrades that require a precise Square Hole interface. Caution: intended for Square taper configurations; confirm motor and crank compatibility before purchase.
Alps2Ocean Square Hole 170mm Crank Arm
Forged alloy 6061 crank arms in 170mm length with Square Hole interface. The design emphasizes high strength and resistance to deformation, suitable for a range of bikes including e-bikes and mid-mounted motors. Availability in ten sizes helps with precise fitment.
Best for: riders needing a reliable Square Hole option across multiple frame types. Caution: verify Square Hole diameter matches your crank spindle to avoid misalignment.
Buying Guide
What should you check before buying a crank arm?
- Spindle interface: Diamond Hole vs Square Hole. Confirm which interface your crankset uses and ensure both left and right arms match the hole type.
- Arm length: Common lengths are 89mm to 175mm. A 170mm length is popular for balanced power and stroke, but check your leg reach and crankset clearance.
- Pedal compatibility: Most 9/16 inch pedals fit standard crank arms, but verify your pedal threading and crank arm compatibility.
- Material and weight: Aluminum alloys offer lightness with good stiffness; steel provides extra durability but adds weight.
- Intended use: Road, MTB, e-bike, or folding bikes may favor specific arm designs or hole orientations. Choose accordingly.
Frequently Asked Questions
- What is the difference between Diamond Hole and Square Hole crank arms? Diamond Hole uses a circular/diamond-shaped interface, while Square Hole uses a square taper interface; fitment requires matching the crank spindle orientation.
- Can I mix left and right crank arms from different brands? It’s best to use the same interface type and compatible dimensions on both sides to avoid misalignment.
- Is 170mm crank length suitable for all riders? Not always. Taller riders or off-road riders may prefer longer or shorter lengths based on pedaling stroke and knee clearance.
- Should I replace both crank arms at the same time? Replacing both arms ensures consistent chainline, stiffness, and aesthetics, especially on older drivetrains.
- Are forged aluminum crank arms stronger than steel? Forged aluminum is lighter and stiff, while steel offers greater durability and impact resistance; choose based on riding style and weight considerations.
- How do I verify compatibility for an e-bike crank? Check that the selected arm matches your e-bike’s motor mounting and hole orientation, and ensure correct length for pedal clearance and motor spacing.