Cross weight, also known as wedge, is one of the most powerful handling adjustments you can make on a circle track race car. Understanding what it is and how it affects your car's performance is essential for going fast consistently.
What is Cross Weight?
Cross weight is the amount of weight resting on the right front (RF) and left rear (LR) tires combined, expressed as a percentage of the total vehicle weight. It's called "cross" because it involves diagonally opposite corners of the car.
Cross Weight % = (RF weight + LR weight) / Total Weight x 100
For example, if your car weighs 400 lbs total, and the RF weight is 120 lbs while the LR is 100 lbs, the cross weight would be (120+100)/400 = 220/400 = 55%.
Why is Cross Weight Important?
Cross weight affects how the car handles in the center and off the corners. It's a primary tool for adjusting the car's "tightness" or "looseness."
- Higher Cross Weight (more wedge): Increases the car's tendency to be tight (push/understeer) off the corners. The car wants to go straight and resists turning.
- Lower Cross Weight (less wedge): Increases the car's tendency to be loose (oversteer) off the corners. The rear of the car wants to slide around.
Measuring Cross Weight
To measure cross weight, you'll need a set of four scales. Here's the proper procedure:
- Place the car on a level surface.
- Put scales under all four tires.
- The driver should be in the car, in full race gear.
- Fuel should be at race level (full or as raced).
- Bounce the car gently to settle the suspension.
- Record the weight at each corner: Left Front (LF), Right Front (RF), Left Rear (LR), Right Rear (RR).
- Calculate total weight: LF + RF + LR + RR.
- Calculate cross weight: (RF + LR) / Total x 100.
Baseline Cross Weight
For most quarter midgets and karts on oval tracks, a good baseline cross weight is between 50% and 52%. This provides a balanced platform that can be adjusted based on track conditions.
| Track Condition | Recommended Cross Weight | Effect |
|---|---|---|
| Slick, dry track | 48% - 50% | Loosen the car to help it turn on low grip |
| Medium grip | 50% - 52% | Balanced, neutral handling |
| High grip, tacky track | 52% - 55% | Tighten the car to prevent oversteer and use the grip |
How to Adjust Cross Weight
Cross weight is adjusted by changing the length of suspension links, typically the left front or right rear. This changes the preload on the springs at those corners.
To INCREASE Cross Weight (More Tight)
- Shorten the Left Front link (pull the LF down)
- Lengthen the Right Rear link (let the RR up)
This transfers weight to the RF and LR corners.
To DECREASE Cross Weight (More Loose)
- Lengthen the Left Front link (let the LF up)
- Shorten the Right Rear link (pull the RR down)
This transfers weight to the LF and RR corners.
Important: Always make small adjustments (1/4 turn or 1/8" at a time) and re-measure. Also, be aware that changing cross weight will also affect the individual corner weights and ride heights slightly.
Cross Weight vs. Corner Weights
While cross weight is a diagonal measurement, you also want to pay attention to the left side percentage and rear percentage for a complete setup picture.
| Measurement | Formula | Typical Range |
|---|---|---|
| Left Side % | (LF + LR) / Total | 55% - 60% |
| Rear % | (LR + RR) / Total | 65% - 70% |
Common Cross Weight Issues
- Car is tight everywhere: Cross weight may be too high. Try reducing wedge.
- Car is loose everywhere: Cross weight may be too low. Try adding wedge.
- Car is tight in, loose off: Cross weight alone won't fix this; look at springs or shocks.
- Inconsistent handling: Check that all suspension links are snug and not binding. Re-check scales for level surface.
Example Calculation
Let's say you put your car on scales and get these numbers:
- Left Front (LF): 85 lbs
- Right Front (RF): 115 lbs
- Left Rear (LR): 95 lbs
- Right Rear (RR): 105 lbs
- Total: 85+115+95+105 = 400 lbs
Cross Weight: (RF 115 + LR 95) = 210 lbs. 210 / 400 = 0.525 = 52.5%
This is a good baseline for a medium grip track. If the car feels tight, you might want to reduce cross weight to 51% by making a small adjustment.
Summary
Cross weight is a fundamental setup tool. Always start with a known baseline, make small changes, and keep detailed notes. With practice, you'll learn exactly how your car responds to wedge adjustments and be able to dial it in quickly at any track.
For more information on related topics, see our guides on Basic Chassis Set Up and Track Side Chassis Adjustments.