How to use the corner weight and cross weight calculator
- Weigh each corner of the car on level scales and enter the four readings in any one unit, such as pounds or kilograms.
- Optionally open the advanced options and enter the cross weight percentage you want to reach.
- Read the total, the front, rear, left and right shares, and the cross weight.
- Read how much weight has to move onto or off the cross diagonal to reach your target, and copy or download the table.
Formula
front share = (LF + RF) / total; left share = (LF + LR) / total
cross weight = (LF + RR) / total
weight to move = target % x total - (LF + RR)
LF, RF, LR and RR are the left front, right front, left rear and right rear readings. Cross weight, also called wedge, is the share carried by the diagonal from the left front to the right rear. Moving weight between diagonals leaves the total the same.
A car on four scales
Readings of 842, 801, 748 and 809 give a total of 3,200. The front share is 1,643 / 3,200 = 51.34% and the left share is 1,590 / 3,200 = 49.69%. The diagonal LF + RR is 842 + 809 = 1,651, a cross weight of 51.59%.
To reach 50% the diagonal must carry 1,600, so 51 must come off it. In practice this is done by adjusting the ride height or spring pre-load at one corner, which moves weight between the diagonals.
Why these percentages matter
Race and track cars are often set up so the weight is balanced from side to side and the cross weight is near a chosen value. This tends to make left and right turns feel alike. The front and rear shares are set by where the heavy parts sit and cannot be changed by adjustments at the corners, which only move weight between the diagonals.
The numbers do not tell you the best setup. That depends on the car, the track and the class rules, and any change affects handling, so go in small steps. Power compared with weight is in the Power to Weight Ratio Calculator, tire pressures in the Tire Pressure Temperature Adjustment Calculator, and loads when towing in the Towing Weight Limits Calculator.
Taking good readings
Weigh with the driver or equivalent ballast in the seat, a normal fuel load, tires at working pressure, and the car on a flat surface. Roll the car on and off the scales and let the suspension settle before reading. Scales that are not level or are not set to the same zero make the percentages wrong.
Assumptions and limits
- The four readings are in the same unit and all are above zero.
- The cross weight target defaults to 50%, an example, and is yours to change.
- The weight to move is the change in the diagonal LF + RR, taken from or given to the other diagonal.
- Percentages are shown to two decimals, rounded half up.
- The page does not know your suspension, so it cannot say which adjustment moves how much weight.
Frequently asked questions
What is cross weight?
It is the share of the car's weight on the diagonal that runs from the left front to the right rear, as a percentage of the total.
Does the total change when I adjust cross weight?
No. Adjusting a corner moves weight between corners, so the total stays the same.
Is 50% the right cross weight?
Not always. It is a common starting target for cars that turn both ways, but the best value depends on the car, the track and the class.
Why can I not change the front share with the corner adjusters?
Front and rear shares depend on where the mass sits along the car. Corner adjusters move weight between diagonals, which changes the cross weight, not the front share.