35 Chain vs 420: Which Chain Size Is Right for Your Dirt Bike?

When it comes to upgrading or replacing the drivetrain on your dirt bike, the 35 chain vs 420 debate is one of the most common dilemmas riders face. The chain is the vital link between your engine’s power and your rear wheel’s traction. Choosing the wrong size can lead to poor performance, rapid wear, or even a dangerous breakage while riding. This guide dives deep into the mechanical differences, performance implications, and specific use cases for both the 35 and 420 chains, helping you make a data-driven decision for your machine.

Understanding Chain Dimensions: Breaking Down the Numbers

Before we compare performance, it is critical to understand what the numbers “35” and “420” actually mean. In the motorcycle industry, chain sizes are standardized using pitch and roller width. The first digit(s) represent the pitch in eighths of an inch, while the last digit(s) represent the roller width in eighths of an inch. For the #35 chain, the pitch is 3/8 of an inch, and the width is 3/8 of an inch. This makes it a compact, lightweight option often seen on mini bikes and pit bikes. On the other hand, a #420 chain has a 4/8 (or 1/2) inch pitch and a 2/8 (or 1/4) inch width. This subtle difference in geometry translates to a significant shift in strength and application.

Weight and Rotational Mass: The Hidden Performance Factor

One of the most immediate differences between these two chains is their physical weight. A standard 420 chain is noticeably heavier and bulkier than a 35 chain. In the 35 chain vs 420 comparison, reducing rotational mass (the weight of the chain and sprockets) is critical for quick throttle response. A lighter 35 chain allows the engine to rev up faster and spool the rear wheel with less inertia. This makes the 35 chain a favorite for competitive pit bike racing or youth classes where rider weight is minimal and explosive acceleration is paramount. However, this weight reduction comes at the cost of tensile strength, which we will address next.

Strength and Durability: Which Chain Handles the Torque?

The primary reason many larger dirt bikes use a 420 chain is simple: tensile strength. The thicker side plates and larger pins of a 420 chain provide a much higher breaking load compared to a 35 chain. If you are riding a 150cc or larger pit bike, or a small-displacement motocross bike, the torque from the engine can stress a 35 chain to its limit. In the 35 chain vs 420 durability test, the 420 chain offers superior resistance to stretching and snapping. For aggressive riders who routinely “pin it” out of corners or navigate rocky trails, the safety buffer of a 420 chain is essential. A snapped chain at high speed can destroy your engine case, so please do not underestimate the importance of this structural integrity.

Top Speed and Gear Ratio Calculations: The Science of Sprockets

Many riders assume that a larger chain means higher speed, but that is a misconception. The chain itself does not determine speed—the sprocket size does. However, the chain size dictates the minimum sprocket size you can use. A 35 chain allows for a smaller front sprocket (often 11 or 12 teeth