Key Takeaways

• The pinion gear meshes with the spur gear to transfer power from the motor to the wheels
• Choosing the right pinion size involves balancing speed vs torque
• Smaller pinions provide more torque and acceleration, larger pinions provide more top speed
• Pinion size, spur gear size, tire size, and motor Kv all factor into final drive ratio
• Online gear ratio calculators can help select pinion size once other variables are known
• Real-world testing is needed to finalize the ideal gearing for conditions

Introduction

The pinion gear is a key component in RC vehicles that meshes with the spur gear to transfer power from the motor to the wheels. Selecting the proper pinion size for your vehicle and motor setup impacts important performance characteristics like speed, acceleration, torque, and drivetrain efficiency. The needs of your driving style and track conditions should drive pinion selection.

This article will provide an overview of how pinion sizing works, what factors impact pinion choice, and how to use gear ratio calculators to narrow down options. We’ll also look at real-world testing procedures to validate your gearing. Properly sizing and pairing the pinion with the spur gear delivers the best drivetrain performance.

Pinion Gear Basics

Before jumping into size selection, let’s quickly cover some pinion gear basics for context:

• Made of metal or plastic and mounts to the motor output shaft
• Meshes with larger spur gear to transfer power to wheels
• Comes in range of different tooth counts
• Common sizes range from 10T to 50T for many RC applications
• Sold as replaceable parts for tuning gear ratios

The number of teeth determine the size – more teeth equals a physically larger pinion. As the motor spins the pinion, it turns the spur gear which then rotates the wheels. The relative sizes between these two meshed gears determine the final drive ratio and speed.

Pinions are consumable parts that wear over time and need periodic replacement, especially plastic ones. Regular inspection of the gear teeth is recommended to check for damage that could impact performance.

Pinion Size Impact on Speed vs Torque

The main tradeoff to evaluate when selecting your pinion size is speed versus torque. The pinion size along with the paired spur gear determine the overall gear reduction ratio between the motor and wheels. This gearing ratio impacts whether your vehicle favors acceleration or top speed.

Smaller Pinion Size – A smaller pinion with fewer teeth creates a higher gear reduction. This increases torque at the wheels allowing more acceleration and climbing power. However, the vehicle’s overall top speed potential will be lower.

Larger Pinion Size – A larger pinion decreases the gear reduction. This reduces torque but increases potential top speed. Acceleration and low-end power are traded off for higher speed when using a bigger pinion.

So if your priority is getting up to speed quickly, smaller pinions are preferable. If you want to maximize outright top speed on long stretches, larger pinions are better. Gearing for balanced performance involves finding the right compromise between the two extremes.

Factors Influencing Pinion Selection

Pinion sizing depends on multiple parts working together in your drivetrain. Consider these factors:

Motor Kv – The motor’s Kv rating impacts RPM and torque. Higher Kv motors need smaller pinions to avoid excess speed. Lower Kv motors can use bigger pinions.

Spur Gear Size – The spur gear pairs with the pinion so its size impacts the ratio. Bigger spur gears allow bigger pinions.

Tire Size – Larger tire diameter increases effective gearing at the wheels. Smaller tires may need bigger pinions to compensate.

Vehicle Type – Different RC models have gearing preferences. Stadium trucks need more torque, buggies need balanced ratios.

Track Conditions – Tight, technical tracks need more low-end torque. Loose or slippery surfaces need lower gearing too.

Driving Style – Aggressive racers may want quicker acceleration. High-speed runs need bigger pinions.

Considering all these factors will help narrow down ideal pinion sizes to experiment with when testing.

Using Gear Ratio Calculators

The relationship between the spur gear and pinion sizes can be represented as a numeric gear ratio. Online gear ratio calculators are handy tools to input your parts and determine the final drive ratio for a given pinion size.

Plugging in variables like motor Kv, spur size, tire diameter, and a trial pinion size allows you to model different scenarios digitally before wrenching on your vehicle. The calculators will show you the effect a particular pinion choice will have on torque, top speed, and other factors.

Here are some tips for using these tools effectively:

• Fix your known variables – Set your existing hardware specs so you can tweak just the pinion size
• Try a range of pinions – Test low, medium and high options to see tradeoffs
• Note torque and speed changes – Look for sweet spot between torque loss and speed gain
• Check max RPM – Make sure not too high to avoid motor damage
• Model real conditions – Factor in traction and slip losses for realistic numbers

Using a calculator to identify a suitable pinion range provides a starting point for real-world testing.

Real-world Testing

Ultimately, determining the best pinion comes down to physically testing a few sizes with your actual vehicle and motor. Gears that may seem ideal on paper could behave very differently on the track or trail.

Here are some tips for pinion testing:

• Start with existing pinion – Get a baseline rather than blindly changing size
• Only change pinion – Keep other parts the same to isolate effects
• Test in small increments – Try 2-3 tooth jumps to hone in
• Check torque and speed – Accelerate, climb, top speed, braking etc.
• Watch temps – Heat indicates potential issues
• Consider longevity – Larger pinions wear faster
• Fine tune with spur – Can also tweak ratio with spur gear
• Keep data – Note results to optimize and adjust further

Dedicate testing sessions to pinion trials. Swap sizes, perform runs, record data, and tweak based on real observations. Gradually zero in on your motor system’s sweet spot.

Maintaining Proper Gear Mesh

When changing pinion gears, be sure to properly set the mesh by adjusting gear slippage and backlash. Poor mesh can lead to premature wear, noise, and power loss.

Follow your manufacturer’s instructions to set gear mesh clearance typically around .010″ – .020″. Shims, spacers, and motor screws allow fine adjustment of the meshed gears.

Proper break-in of new gears is also important to avoid damage at first. Consult your user manual for break-in procedures specific to your vehicle.

Conclusion

Choosing the ideal pinion size involves balancing speed and torque by testing different gear ratios. Consider motor Kv, spur size, tires, and conditions when selecting initial pinions to try. Use a gear calculator to model ratios digitally first. Then conduct real-world testing and gear mesh adjustment to finalize the best pinion for your vehicle and motors. With some thoughtful testing and tuning, you can achieve your ideal drivetrain setup.

FAQ

How do I calculate the gear ratio for a given pinion size?

Use the spur gear teeth divided by the pinion gear teeth. For example, a 20 tooth pinion and 80 tooth spur equates to an 80/20 = 4.0 ratio. Higher ratios provide more torque, lower ratios provide more speed.

If I go up in pinion size, do I need to change the spur gear too?

Not necessarily. You can run different sized pinions with the same spur gear to change the ratio. Going up in pinion size alone will reduce torque and increase speed.

How much does pinion size affect acceleration and speed?

It has a large impact. A low 15T pinion may accelerate 60% quicker but have 50% less top speed than a 25T pinion on the same vehicle. Exact differences depend on the gear ratio change.

Should I gear more conservatively for brushless vs brushed motors?

Yes, brushless setups can use slightly taller gears than brushed systems. The higher RPM capacity of brushless provides extra headroom to take advantage of bigger pinions. But follow manufacturer guidance.

How can I check if my pinion size is too big or too small?

Signs of undersized pinions include sluggish acceleration and motor/ESC overheating. Oversized pinions may have poor torque and lack top speed due to excess slippage. Gear accordingly to minimize these issues.

What pinion material lasts longer, metal or plastic?

Metal pinion gears (steel, aluminum) have greater durability and life than plastic ones. However, metal can damage the spur gear prematurely if not properly broken-in. Use care when running metal pinion and spur combinations.

Should I switch pinion sizes for different driving conditions?

Potentially. On high-traction surfaces you may opt for larger pinions. On low-grip or dusty conditions, dropping down in pinion size helps regain lost torque. Tune as needed for your environment.

Besides pinions, what other ways can I experiment with gearing?

Swapping the spur gear itself allows more drastic ratio changes. Some vehicles also allow gearing changes in the transmission or different motor mounting positions. Refer to your model’s tuning options.

How much does tire size influence my gearing decisions?

Tire diameter changes gearing effect at the wheels. With larger tires, you may need to compensate with smaller pinions to achieve the desired torque and speed. There is no direct formula, so testing is required.