What is the difference between front and rear roll center?
The difference between front and rear roll centers primarily concerns their relative height, which is often designed differently based on a car's drivetrain layout (front-wheel drive or rear-wheel drive).
Every vehicle has a front roll center and a rear roll center. The roll center is a virtual point in the suspension geometry around which the car's body rolls when cornering or encountering uneven surfaces. While the general concept is the same for both the front and rear, their specific location (especially height) and interaction significantly affect a car's handling balance.
Based on vehicle design principles, especially concerning power delivery and grip:
- Front-Wheel Drive (FWD) Cars: For a front-wheel drive car, the front roll center will generally be lower down than the rear roll center.
- Rear-Wheel Drive (RWD) Cars: For a rear-wheel drive car, the rear roll center will often be lower than the front roll center.
Why the Height Difference Matters
This difference in relative height is intentional and linked to how the vehicle puts power down and maintains grip through corners. As noted, a key purpose of having the driven axle's roll center lower is to influence body roll and tire grip:
- A lower roll center on an axle allows for more body roll on that specific end of the car.
- Increased body roll can potentially provide the driven wheels (the ones responsible for propelling the car and managing power during cornering) with more grip through the corner. This helps the car accelerate out of turns more effectively or manage cornering forces better on the powered wheels.
In essence, the difference isn't just about having two separate points, but how their relative positions, particularly vertical height, are strategically designed to optimize the vehicle's handling characteristics, especially grip distribution related to the drivetrain.
Summary of Relative Heights (Based on Drivetrain)
| Car Type | Front Roll Center Relative Height | Rear Roll Center Relative Height |
|---|---|---|
| Front-Wheel Drive | Generally Lower than Rear | Generally Higher than Front |
| Rear-Wheel Drive | Often Higher than Rear | Often Lower than Front |
This difference contributes significantly to the overall roll axis (the imaginary line connecting the front and rear roll centers), which dictates how the vehicle body rotates during cornering.
