Ariel Square 4 – 1000cc – 1955


The Ariel Square Four 1000cc, often referred to as the “Ariel Square 4,” is one of the most iconic motorcycles produced by Ariel Motorcycles. The 1955 model is especially noteworthy for its engineering innovations and performance. Here’s a detailed overview:


  • Engine: 997cc, four-cylinder, four-stroke, overhead valve (OHV)
  • Configuration: Square Four (two pairs of cylinders arranged in a square)
  • Bore and Stroke: 65mm x 75mm
  • Compression Ratio: 7.2:1
  • Power Output: Approximately 42 horsepower at 5,800 rpm
  • Transmission: Four-speed gearbox with chain final drive
  • Top Speed: Around 100 mph (160 km/h)
  • Frame: Steel tubular frame
  • Suspension:
    • Front: Telescopic forks
    • Rear: Swingarm with dual shock absorbers
  • Brakes:
    • Front: Drum brake
    • Rear: Drum brake
  • Fuel Capacity: 4.5 gallons (20.5 liters)
  • Weight: Approximately 465 pounds (211 kg)

Manufacturer Design:

  • Designer: The Ariel Square Four was designed by Edward Turner, a renowned motorcycle designer who later became the chief designer for Triumph Motorcycles.
  • Aesthetic: The 1955 model features classic British motorcycle styling with a substantial presence, including a teardrop fuel tank, chrome accents, and elegant lines. The distinctive “square” configuration of the engine is a standout feature.
  • Purpose: Designed as a high-performance touring motorcycle, the Square Four was intended to offer a smooth and powerful ride, suitable for long-distance travel.
  • Build Quality: Known for its robust construction and engineering excellence, the Square Four was built to high standards, incorporating advanced materials and manufacturing techniques of the time.


  • Engineering Marvel: The Square Four engine configuration was an innovative design that offered a unique combination of power and smoothness. It helped Ariel establish a reputation for engineering prowess.
  • Iconic Status: The Ariel Square Four is considered one of the most iconic British motorcycles of the mid-20th century, admired for its design and performance.
  • Cultural Impact: The Square Four became a symbol of post-war British engineering and craftsmanship, influencing motorcycle design and culture.
  • Collector’s Item: Today, the Ariel Square Four is highly sought after by collectors and enthusiasts, often fetching high prices at auctions and in the vintage motorcycle market.

Interesting and Important Facts:

  • Unique Engine Design: The Square Four engine design was patented by Edward Turner in 1928. The unique configuration allowed for a compact design while delivering smooth and powerful performance.
  • Heat Management: One of the challenges of the Square Four design was managing heat dissipation from the rear cylinders. Ariel addressed this with improved cooling fins and revised engine placement.
  • Performance and Smoothness: The 1955 model is known for its exceptional smoothness and power delivery, making it a favorite among touring riders of the time.
  • Production Run: The Ariel Square Four was produced from 1931 to 1959, with various improvements and iterations over the years. The 1955 model is part of the Mk II series, which introduced several enhancements.
  • Innovation and Influence: The Square Four’s innovative design influenced other motorcycle manufacturers and demonstrated the potential of multi-cylinder engines in motorcycles.


The Ariel Square Four – 1000cc – 1955 is a landmark motorcycle in the history of British motorcycling. Its unique engine design, combined with classic styling and high performance, make it a standout model from the mid-20th century. The Square Four’s legacy continues to be celebrated by collectors and enthusiasts who appreciate its engineering brilliance and historical significance. Whether admired for its innovative design, cultural impact, or exceptional performance, the Ariel Square Four remains a testament to Ariel Motorcycles’ legacy of excellence.


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