Performance Trends 4 Link Calculator

Measure links, brackets, and ride height with clear geometry feedback. Compare instant center movement clearly. Plan suspension changes before race day setup choices accurately.

Calculator Inputs

Vehicle And Target Data

in
Distance from rear axle center to front axle center.
in
Estimated height from ground to vehicle center of gravity.
lb
Race weight with driver and fuel.
%
Common baseline is near 100 percent.
in
Distance between rear tire contact centerlines.
in
Desired rear roll center height from ground.
in
Bracket height change used in the trend table.
deg
Negative value usually points pinion downward.
deg
Measure with the same sign convention as pinion angle.

Side View Lower Link Points

in
Rear lower axle bracket X from rear axle centerline.
in
Rear lower axle bracket height from ground.
in
Front lower chassis bracket X forward from rear axle.
in
Front lower chassis bracket height from ground.

Side View Upper Link Points

in
Rear upper axle bracket X from rear axle centerline.
in
Rear upper axle bracket height from ground.
in
Front upper chassis bracket X forward from rear axle.
in
Front upper chassis bracket height from ground.

Rear View Lower Link Points

in
Lateral distance from vehicle centerline to lower axle point.
in
Rear view lower axle bracket height.
in
Lateral distance from centerline to lower frame point.
in
Rear view lower frame bracket height.

Rear View Upper Link Points

in
Lateral distance from centerline to upper axle point.
in
Rear view upper axle bracket height.
in
Lateral distance from centerline to upper frame point.
in
Rear view upper frame bracket height.
Reset

Example Data Table

Setup Type Wheelbase CG Height Upper Front Height Lower Front Height Expected Behavior
Baseline drag setup 110 in 20 in 24 in 10 in Balanced hit with useful anti squat range.
Higher hit setup 108 in 22 in 26 in 9 in Shorter instant center and stronger tire application.
Softer track setup 112 in 19 in 22 in 11 in Lower anti squat with smoother rear movement.

Formula Used

Line intersection: Each link is treated as a straight line. The lower and upper link extensions meet at the side view instant center.

Anti squat: Anti Squat % = [(IC Height ÷ IC X) ÷ (CG Height ÷ Wheelbase)] × 100.

Roll center: Rear view link intersection is connected to the tire contact patch. The height at vehicle centerline is the estimated roll center.

Load transfer: Load Transfer Per G = Vehicle Weight × CG Height ÷ Wheelbase.

Anti squat load proxy: Load Transfer Per G × Anti Squat % ÷ 100. This is a comparison value, not a measured tire force.

How To Use This Calculator

  1. Measure all points from the same rear axle centerline.
  2. Use ground height for every vertical input.
  3. Enter side view link points for instant center and anti squat.
  4. Enter rear view link points for roll center estimate.
  5. Press calculate and review the result section above the form.
  6. Use the trend table before moving brackets on the car.
  7. Download CSV or PDF for setup records.

Understanding Four Link Setup

A four link suspension changes how a car plants the tire. Small bracket moves can create large traction changes. This calculator gives a structured way to compare those moves. It estimates instant center, anti squat, link angle, roll center, and basic setup balance. The goal is not to replace track testing. The goal is to make each test more controlled.

Why Geometry Matters

The side view instant center shows where the upper and lower bars meet when extended. A short and high instant center usually hits the tire harder. A long and low instant center usually applies load more slowly. Anti squat compares that force line with the center of gravity line. Values near one hundred percent often feel neutral. Higher values can separate the rear and plant harder. Lower values can let the car squat more.

Rear View Behavior

The rear view inputs estimate the lateral instant center and roll center. This helps show how the axle reacts during body roll. A very high roll center can feel quick but harsh. A very low roll center can feel lazy. The best number depends on tire, surface, power, and vehicle weight. Use the result as a tuning map, not an absolute rule.

Using Trend Results

The trend table changes the upper front bracket height by your chosen step. This shows whether a small bracket move raises or lowers anti squat. It also reveals instant center travel. When the trend changes quickly, make smaller physical changes. When the trend changes slowly, larger bracket moves may be needed. Record every pass, track condition, launch rpm, and tire pressure. Good notes make the calculator far more useful.

Practical Setup Tips

Start with accurate measurements. Measure from the rear axle centerline and from the ground. Keep left and right sides equal unless you have a clear reason. Check rod end bind through full travel. Recheck pinion angle after ride height changes. Use safe stands before measuring under a vehicle. A clean baseline prevents confusion. After one adjustment, test again. One change at a time gives clearer answers. Compare results with video, because suspension travel often explains confusing timeslip changes clearly.

FAQs

What does this calculator measure?

It estimates four link instant center, anti squat, roll center, link angles, driveline angle, and setup trend changes from entered suspension points.

Is this a replacement for track testing?

No. It helps plan changes and compare geometry. Real traction still depends on tire, power, shock settings, surface, and driver input.

What is a good anti squat value?

Many setups start near 100 percent. More can hit the tire harder. Less can soften the hit. The best value depends on the car.

Why is instant center important?

Instant center shows where link force paths meet. Its position affects how quickly the rear suspension separates, squats, or plants the tire.

How should I measure X values?

Use the rear axle centerline as zero. Measure forward as positive. Keep the same reference point for every side view bracket.

How should I measure height values?

Measure vertical distance from level ground to the center of each rod end, bracket hole, axle point, or frame point.

What does the trend table show?

It raises and lowers the upper front bracket by your chosen step. This shows how anti squat and instant center react.

Can I use metric measurements?

Yes, but keep every length unit consistent. If you use millimeters, all length values must use millimeters for meaningful results.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.