The plus (+) and minus (-) signs on an automatic car's gear selector or steering wheel paddles activate the manual shift mode. This feature allows you to override the automatic transmission to upshift for better fuel economy or downshift for immediate power and engine braking. It's a tool for gaining more control in specific driving situations, not for daily commuting.
Modern automatic transmissions with manual modes, often labeled as "M," "+/-," or accompanied by paddle shifters, are designed to give drivers selective control without the complexity of a manual clutch. According to industry analysis from sources like Hagerty and Consumer Reports, using this feature appropriately can influence vehicle dynamics, safety, and even long-term maintenance costs.
The primary functions are straightforward:
- Plus (+): Command an upshift to a higher gear. This reduces engine RPM (revolutions per minute) for quieter, more fuel-efficient cruising.
- Minus (-): Command a downshift to a lower gear. This increases engine RPM, providing more power for acceleration or using engine drag to slow the vehicle.
Key practical applications and data-supported rationales include:
Engine Braking on Descents: Downshifting before a long downhill grade uses engine compression to control speed. This can reduce brake use by an estimated 30-50% on sustained descents, preventing brake fade and excessive wear. Relying solely on brakes can overheat them, temporarily reducing effectiveness—a significant safety consideration in mountainous regions.
Optimized Overtaking and Acceleration: A downshift via the minus (-) paddle before passing provides near-instantaneous torque increase. For many modern turbocharged engines, this can mean accessing peak torque 1-2 seconds faster than waiting for the automatic transmission's kick-down response, making maneuvers quicker and safer.
Enhanced Traction in Low-Grip Conditions: Starting manually in 2nd gear on snow or ice reduces torque to the drive wheels, minimizing wheel spin. Data from cold-weather testing by automotive organizations shows this can improve initial traction by a measurable margin compared to standard "Drive" mode on slick surfaces.
Towing and Heavy Load Management: When towing or climbing steep grades, manually locking the transmission in a lower gear (e.g., 3rd or 4th) prevents unwanted, frequent upshifts that strain the engine. This maintains a consistent power band and helps keep transmission temperatures within a safer operating range.
How to Use the Manual Mode:
- Activate: Shift the gear lever from "D" (Drive) to the separate gate marked "M" or "+/-." In some cars, simply tapping a paddle shifter temporarily engages manual control.
- Shift: Use the lever (push forward for +, pull back for -) or the steering wheel paddles (right for +, left for -).
- Safety Overrides: The transmission computer will intervene to prevent damaging shifts. It may refuse an upshift if RPM is too low or automatically downshift/upshift to protect the engine if you ignore redline or stall warnings.
| Use Case | Recommended Action | Primary Benefit |
|---|
| Long Downhill Drive | Downshift 1-2 gears with (-) | Preserves brake performance & prevents overheating |
| Highway Overtaking | Downshift 1 gear with (-) before accelerating | Faster acceleration for safer passing |
| Slippery Start (Snow/Mud) | Start from stop in 2nd gear (using +) | Reduces wheel spin, improves traction |
| Towing a Trailer Uphill | Manually select and hold a lower gear (e.g., 3rd) | Prevents gear "hunting," provides steady power |
While not used constantly, understanding the plus/minus functions transforms your automatic car into a more versatile tool, offering greater command for safety and performance when conditions demand it.
