Kyosho RB7 RC Gearing & Optimization Guide
Optimizing your gear ratio is one of the most effective ways to balance speed, torque, and electronics longevity in your Kyosho Ultima RB7 (2WD Buggy). The relationship between your pinion gear (attached to the motor) and your spur gear (attached to the transmission) dictates how hard your motor has to work — and on a 1/10 2wd racing buggy platform with a 2.6 internal transmission ratio, even a single-tooth pinion change shifts your final drive ratio by 3-5%.
The Kyosho Ultima RB7 is a multi-time IFMAR World Champion 2WD buggy with a 2.6 internal transmission ratio. Kyosho ships the RB7 with a 78T 48-pitch spur, which is slightly smaller than the 81T standard used by Team Associated and TLR; this means an RB7 needs a one-tooth-smaller pinion to achieve the same FDR as a B7 at the same spur position.
🛠️ Essential Tools Required for Gearing Changes
- Hex drivers (1.5mm, 2.0mm, or 2.5mm depending on the Kyosho RB7 variant)
- Paper strip (for setting precise gear mesh)
- Infrared temperature gun (crucial for monitoring motor heat after each run)
- Threadlock (for the pinion gear grub screw)
- Pinion gear puller (recommended when swapping gears on a hot motor shaft)
📋 Comprehensive Gearing & Temperature Guide
1. Understanding Pinion vs. Spur Gear Adjustment
Changing your gears alters your final drive ratio. Installing a larger pinion gear or a smaller spur gear increases top-end speed but increases the load on the motor, causing it to run hotter. Conversely, a smaller pinion or larger spur increases torque and acceleration while lowering top speeds and keeping your motor cool. On the Kyosho RB7, this trade-off is amplified by the fixed 2.6 internal ratio — small external changes have a direct thermal consequence.
2. How to Set a Perfect Gear Mesh
Improper gear mesh will quickly strip your spur gear or bind your drivetrain.
- Loosen the motor mount screws slightly.
- Place a small strip of standard notebook paper between the pinion and spur gear teeth.
- Press the gears tightly together and tighten the motor mount screws.
- Roll the paper out. The paper should have clean, crisp crinkles without ripping.
Recommended Pinion & Spur Chart
All combinations use a 78T 48-pitch spur. FDR is calculated as (spur ÷ pinion) × 2.6 internal ratio.
| Pinion | Spur | FDR | Typical Use |
|---|---|---|---|
| 22T | 78T | 9.22 | Balanced club racing |
| 24T | 78T | 8.45 | Balanced club racing |
| 26T | 78T | 7.8 | Open outdoor / high-speed |
| 28T | 78T | 7.24 | Open outdoor / high-speed |
| 30T | 78T | 6.76 | Wide-open straights / mod motors |
Understanding Pinion & Spur Gears
On the 78T spur, 13.5T motors run 27-30T pinions and 17.5T motors run 24-27T. Kyosho's transmission case has very tight clearance; pinions above 31T may require a longer motor mount bolt or a different spur.
Rollout Targets
Working rollout on the RB7 is 1.70 to 1.90 inches per motor revolution on 2.2 buggy tires. The RB7 SSR mid-motor variant tolerates slightly more rollout on high-bite surfaces.
Motor Temperature Management
Target 160-175F (71-79C) for 13.5T; 170-185F (77-85C) for 17.5T. The RB7 ball-diff drivetrain is efficient but its bearing pack is small, so over-gearing shows up as motor heat faster than on larger transmissions.
⚠️ Critical Safety & Temperature Warning
Always use an infrared thermometer to check your motor and ESC temperatures during a run. RC electric brushless motors should never exceed 160°F (71°C). Exceeding 180°F (82°C) risks permanently demagnetizing your motor rotor and frying your Electronic Speed Controller. If your Kyosho RB7 is running above these thresholds, you must "gear down" by installing a smaller pinion gear immediately, improve airflow with a larger motor fan, and inspect the drivetrain for binding.
Calculate a custom FDR for your Kyosho RB7
Plug different pinion/spur combos into the live calculator on the home page to see top speed, runtime, and FDR estimates for your exact setup.
Open the calculator →