Understanding Your Data

G Forces And Steering

G-forces and steering data reveal the physics behind every corner. While speed, throttle, and brake show what the driver did, g-forces show what the car experienced — and the relationship between the two exposes understeer, oversteer, grip limits, and driving efficiency.

Steering and Lateral G

Steering angle directly influences lateral g-force. Turn the wheel and the car generates cornering force. But the relationship is not always proportional, and the telemetry reveals exactly when and where it breaks down.

Reading the Traces Together

When steering input increases and lateral g follows proportionally, the car is responding as expected. The tires have grip to spare. When steering input increases but lateral g plateaus or even decreases, that's understeer — the car is turning less than the driver is asking for. The front tires have exceeded their grip limit.

Smooth vs Jagged Steering

A smooth steering trace — one clean arc of input and release per corner — indicates a driver who is confident and precise. The car follows a predictable path.

A jagged steering trace with frequent corrections — small back-and-forth adjustments through the corner — indicates either an unstable car (poor setup, worn tires, aerodynamic imbalance) or a reactive driving style where the driver is constantly correcting rather than planning. Both cost time because every correction scrubs speed.

Steering Speed

How quickly the driver turns the wheel matters too. Abrupt, fast steering inputs shock-load the front tires and can push them past their grip limit. Smooth, progressive steering inputs gradually build lateral load, giving the tires time to develop grip. The fastest drivers are often the smoothest — not because they're gentle, but because they're precise about how quickly they load the tires.

Longitudinal G

Longitudinal g-force measures acceleration and deceleration along the car's forward axis.

Under Braking

Higher peak longitudinal g under braking means more aggressive deceleration. This is directly related to brake pressure, tire grip, and aerodynamic downforce. At high speed, aero-assisted braking can produce g-forces well above what's possible at low speed.

Compare peak braking g across laps: if it drops over a stint, tire degradation is reducing your braking grip. If it's consistently lower than a reference lap, you may not be braking hard enough initially.

On Acceleration

Longitudinal g on corner exit shows how effectively you're converting throttle input into forward acceleration. In a traction-limited situation, the throttle might be at 100% but longitudinal g is lower than expected — the rear tires are spinning and not all the engine's power is reaching the road.

Compare the throttle trace with the longitudinal g trace on exit. If throttle is full but longitudinal g dips or plateaus, that's wheelspin. A clean exit shows longitudinal g rising smoothly as throttle increases.

The G-G Diagram

If you plot lateral g on one axis and longitudinal g on the other for every data point in a lap, you get what's called a friction circle (or g-g diagram). This is one of the most powerful tools in telemetry analysis.

What It Shows

The outer boundary of the scatter plot represents the maximum combined grip the tires produced during the lap. Points inside that boundary mean grip was available but not being used — the car was coasting, or the driver wasn't pushing to the limit.

The best drivers keep the car near the boundary of the friction circle at all times. They're always using close to the maximum available grip in some combination of braking, cornering, or acceleration. There's no dead time where the car is just rolling.

Reading the Shape

  • Full circle — the driver is using grip in all directions equally. This is rare and usually means the car is well balanced.
  • Flat on top (low acceleration g) — the car is traction-limited on exit. The driver can't use full throttle without wheelspin.
  • Flat on the bottom (low braking g) — the driver isn't braking hard enough or is braking too progressively.
  • Flat on the sides (low lateral g) — the driver isn't carrying enough speed through corners.
  • Asymmetric left vs right — the car has different grip levels turning left vs right, possibly due to setup, camber, or tire condition.

Putting It All Together

Here's how g-forces flow through a single corner, mapped to each phase of the turn:

  1. Brake point — longitudinal g spikes negative as the driver hits the brakes. Peak longitudinal g represents the maximum braking force achieved. This corresponds to the Brake Pressure corner factor.
  2. Trail brake — longitudinal g tapers while lateral g builds. The driver is releasing the brake as they turn in, transferring the tire's effort from braking to cornering. The smoothness of this handoff is captured by the Trail Braking factor.
  3. Minimum speed — lateral g reaches its peak. The car is at maximum cornering force, traveling at the lowest speed. The Minimum Speed and Apex Speed factors correspond to this phase.
  4. Throttle pickup — lateral g begins to decrease as the driver straightens the wheel. Longitudinal g transitions from negative (or zero) to positive as throttle is applied. The Throttle Application factor measures how early and smoothly this transition occurs.
  5. Exit — longitudinal g builds as the car accelerates onto the straight. Exit Speed captures how much velocity you carry out of the corner and onto the following straight.

Each phase connects to the next. A mistake in one phase cascades forward — a poor brake point leads to a rushed trail brake, which leads to a low minimum speed, which delays throttle pickup, which reduces exit speed.

Common Diagnostic Patterns

Understeer

High steering angle but lateral g plateaus or decreases. The front tires have saturated. In the g-g diagram, you'll see the data points cluster below the theoretical maximum on the lateral axis. The driver is asking for more grip than the front tires can provide.

Oversteer Snap

A sudden spike in lateral g followed by a rapid reversal — the rear stepped out and the driver caught it with opposite lock. In the steering trace, you'll see a sharp correction. In the speed trace, there's usually a brief dip as the slide scrubs energy.

Power Oversteer

On corner exit, lateral g suddenly increases despite the driver beginning to unwind the steering. The rear tires have broken traction under throttle, and the car is rotating more than intended. The throttle trace will often show a corresponding lift as the driver backs off to regain control.

Balanced Corner

Smooth transitions between longitudinal and lateral g with no spikes, corrections, or plateaus. The g-g diagram shows the data tracing a smooth arc around the boundary of the friction circle. This is the goal — maximum grip utilization with minimum drama.

See Also