Back to Bike FinderYears: 1953 · 1952 · 1951 · 1950 · 1949
Ariel 4G Square Four Mark I
1951Allround

Ariel 4G Square Four Mark I

Key specifications

Engine
995 cc
Power
35 HP
Weight
197 kg
Fuel type
petrol
Fuel capacity
4.2 L
Transmission
4-speed
Front brakes
Expanding brake (drum brake)
Rear brakes
Expanding brake (drum brake)

Overview

Introducing the 1951 Ariel 4G Square Four Mark I The 1951 Ariel 4G Square Four Mark I, affectionately nicknamed the "Squariel," stands as a testament to British engineering and design brilliance. Positioned in the all-round category, this motorcycle appeals to enthusiasts seeking a blend of power, style, and nostalgia. Designed by the legendary Edward Turner, the Square Four is instantly recognizable for its unique square four-cylinder engine configuration, which not only distinguishes it visually but also sets it apart in performance. As the motorcycle market burgeoned in the post-war era, the Ariel 4G emerged as a versatile option for riders craving both daily commuting efficiency and weekend adventure. Engine Performance and Riding Characteristics At the heart of the Ariel 4G lies a robust 995 cc square four-cylinder engine that produces an exhilarating 35 HP at 5,500 RPM, making it capable of reaching a top speed of 144.8 km/h (90.0 mph). This power, coupled with a 6.0:1 compression ratio, ensures a spirited ride whether navigating city streets or cruising on open highways. The engine's smooth torque delivery enhances the riding experience, while the 4-speed gearbox offers seamless shifts that cater to both relaxed rides and spirited acceleration. The air-cooled setup, along with the SU MC2 carburettor, provides reliability and ease of maintenance—a crucial factor for riders who appreciate the charm of vintage mechanics. Key Features and Technology The Ariel 4G Square Four Mark I doesn't just rest on its laurels with impressive engine specs; it also boasts an innovative tubular single-loop frame for improved rigidity and handling. The oil-damped telescopic front fork and plunger-link rear suspension work in tandem to deliver a comfortable and stable ride, even on uneven terrains. The braking system, featuring drum brakes with generous diameters of 203 mm at the front and 178 mm at the rear, provides ample stopping power. A fuel capacity of 16 liters (4.23 gallons) ensures that riders can enjoy extended journeys without frequent stops. The classic red and chrome color options further accentuate its vintage appeal, making it a head-turner in any setting. **

Pros

    Cons

    • Unique Square Four engine design offers distinctive performance and character.
    • Comfortable riding experience due to advanced suspension technology for its time.
    • Reliable and easy-to-maintain components, making it suitable for both enthusiasts and daily riders.
    • Weighty at 197 kg (434.3 pounds), which may affect maneuverability for some riders.
    • Drum brakes, while adequate, may not provide the stopping power expected by modern standards.
    • Limited aftermarket support compared to more mainstream brands, potentially making parts harder to source.

    Technical details

    Source specification data

    Make
    Ariel
    Model
    4G Square Four Mark I
    Category
    Allround
    Light
    30 Watt headlamp.
    Starter
    Kick
    Comments
    Also
    called ´
    Squariel
    ´.
    Designed
    by
    Edward Turner
    .
    Electrical
    6 Volt battery.
    Color Options
    Red/chrome
    Power
    35.00 HP (25.5 kW)) @ 5500 RPM
    Gearbox
    4-speed
    Top Speed
    144.8 km/h (90.0 mph)
    Engine Type
    Double twin cylinder arranged as a square.
    Fuel System
    Carburettor. SU MC2 carburettor
    Bore X Stroke
    65.0 x 78.0 mm (2.6 x 3.1 inches)
    Compression
    6.0:1
    Displacement
    995.00 ccm (60.71 cubic inches)
    Cooling System
    Air
    Engine Details
    Square four cylinder
    Exhaust System
    Dual two-into-one
    Lubrication System
    Dry sump with dual oil pump.
    Valves Per Cylinder
    2
    Transmission Type Final Drive
    Chain
    Dry Weight
    197.0 kg (434.3 pounds)
    Fuel Capacity
    16.00 litres (4.23 gallons)
    Overall Length
    2,083 mm (82.0 inches)
    Power Weight Ratio
    0.1777 HP/kg
    Seat
    Solo seat
    Wheels
    Wire spoked
    Rear Tyre
    4.00-18
    Frame Type
    Tubular single loop
    Front Tyre
    3.25-19
    Rear Brakes
    Expanding brake (drum brake)
    Front Brakes
    Expanding brake (drum brake)
    Rear Suspension
    Plunger-link spring
    Front Suspension
    Oil damped telescopic fork
    Rear Brakes Diameter
    178 mm (7.0 inches)
    Front Brakes Diameter
    203 mm (8.0 inches)

    Available colors

    Red/chrome