How Does Race Car Ballast Placement Affect Handling?
Different Types of Ballast for Race Cars
Even in the early days of motorsports, it was clear that moving weight around had a profound effect on the car’s handling and performance. Some enterprising racers began to add extra weight in places they thought might aid traction or weight transfer and give them an edge. We’ve all heard tales of gassers with tube rear bumpers packed full of lead shot and stock cars with trunks full of old flywheels chained together.
As race car construction has evolved over the years, so has the science of adding race car ballast. Instead of repurposing scrap iron, it’s possible to purchase materials with a high weight density that were designed specifically to be used as ballast. Weight density is the amount of mass contained within a unit of volume. We care about this science because materials with higher weight density allow for more weight to be added in the often tight confines of a race car chassis. There are three materials most commonly used for race car ballast:
Lead is a very popular material for ballast. Lead weights for a race car are releatively inexpensive and have a high weight density (11.3 grams per cubic centimeter) but lead is toxic, so proper handling and containment are essential.
Steel has the lowest weight density of the three most popular materials (7.8 grams per cubic centimeter) but it’s inexpensive and very easy to come by. We’ve seen race cars with steel barbell weights bolted down for ballast.
Tungsten has an incredibly high weight density (19.3 grams per cubic centimeter) which allows for more weight in a smaller package, but it’s far more expensive than steel or lead.
What is the Best Material for Race Car Ballast?
Lead is the most practical and widely available material for race car ballast weights. Speedway Motors carries a variety of lead race car ballast. Lead is incredibly dense as well as being soft, easy to work with, and relatively inexpensive. The downside to lead is the obvious toxic nature of the material. You’ve heard of lead poisoning? Wear your PPE when cutting or drilling lead weights and be responsible when disposing of chips created by working with the material.
As for the other common options, tungsten race car ballast is 150% the density of lead and is non-toxic, but it is harder to work and significantly more expensive than lead or steel. What steel lacks in weight density, it makes up for in availability. But remember, it will take significantly more steel to add up to the same weight as the denser materials.
How Does Ballast Placement Affect Race Car Handling?
As we discussed in our guide to Race Car Weight Distribution & How to Corner Balance, the only way to change a car’s static weight distribution is to move weight around in the chassis. If your class rules allow for it, the best practice is to mount heavy components like the engine, transmission, driver’s seat, and fuel tank in ideal locations for whatever the optimal static weight distribution is for your race type. It is not possible to make substantial changes to the car’s front/rear and left/right weight percentages by jacking weight at the corners. Once the main components are in place, the only way to really change these numbers is by adding ballast.
One key principle to keep in mind is the relationship of ballast placement relative to the car’s center of gravity. This is where the car’s dynamic state beyond the static weight that’s measured on the scales becomes a factor. This is a complicated physics problem, but there are a couple key things to consider.
First, mounting weight higher in the chassis increases the leverage that weight has to act on the chassis. As the weight is moved up, the additional leverage causes more of the mass to be transferred to the side of the car on the outside of the turn. This weight transfer has a significant effect on the car’s handling in the corners and its ability to transition quickly.
Second is the concept that mounting weight as compactly as possible and as close to the car’s center of gravity as possible can be desirable for many cars. The best way to illustrate this is the oft-quoted seesaw principle. Imagine a seesaw with a few hundred pounds of weight on the ends where the riders would normally sit. It will be difficult to set the seesaw in motion, and once it’s moving it will be extremely difficult to stop. Now imagine the weight moved to the center, over the fulcrum. It will not only be easier to set the machine in motion, it will also be easier to control and ultimately stop it. By this logic, your race car’s suspension will be better able to control the added mass if it is in the center of the chassis, not rocking around on the perimeter.
Weight Management
Regardless of the type of race car you’re building, the best practice is almost always to make the car as light as possible, then strategically add ballast to get up to class weight minimums. This allows you to put the weight where you want it. Weight and inertia are always enemies of a fast car, so apply best practices when putting a car together.
It’s easy to understand the benefits of weight savings on large parts like replacing heavy steel hoods with fiberglass or carbon fiber, running aluminum heads and engine blocks, and using lightweight alloy wheels instead of steel. It’s also important to remember that when building a race car, every ounce matters. Think about weight with every decision you make when putting a car together, from tubing size and wall thickness down to fastener material. All of these small decisions will add up when the car is complete.
It’s worth pointing out here that you should never compromise strength or safety to lighten a car. We’ve all heard stories from the early days of racing where cars were built out of exhaust tubing or holes were crudely torched into frames to cut weight. The resulting cars were sketchy death traps and most modern rulebooks ban such silliness. Safety first, always.
Race Car Ballast Mounting Types
It’s very important to mount race car lead ballast safely. A heavy weight coming loose can make for a very dangerous situation for you as well as other drivers. Obviously, your weights need to stay put under the hard acceleration and cornering forces that your car will see on the track. But it’s also important to consider what might happen in case of a crash.
That weight will have incredible g-forces acting on it and trying to break it free from its mounts if you experience an impact. Don’t just mount your ballast for normal forces. Instead, anticipate the extreme g-forces that will be trying to break your weights loose and turn them into projectiles in the case of an impact.
Speedway Motors offers a variety of ballast mounting solutions. The most common are clamps that attach to the round tubing on your chassis or cage and use a stud for mounting the weight. Some weights are designed to clamp directly to the chassis tubing, and some use race car ballast boxes to contain the weight. Use best practices when choosing the fasteners to mount your weights. Locking nuts will keep the weight from vibrating loose and large flat washers will help distribute forces acting on the weights. Many sanctioning bodies have rules governing how ballast is to be mounted, so pay attention to the rulebook for your class.
Ballast Placement Guide
Generally speaking, every chassis design and racing type will respond differently as weight is moved around in the chassis. Depending on the racer ballast locations will vary widely. As discussed above, the relationship of added mass to the car’s center of gravity is tremendously impactful. Also, we’ve been considering ballast added as “sprung” weight to the car itself. Ballast added to the suspension or axle as “unsprung” weight will have an entirely different effect on the car. Beyond these big picture principles, here are some common scenarios by race type and thoughts to consider as you look to add weight to your race car.
Circle track: The center of gravity and ballast mounting height have a huge impact on a circle track car’s behavior through the corners. Since it’s critical for the car to handle predictably and maintain inertia from corner entry to corner exit, weight transfer in the corners is a critical tuning tool. Adding weight to the left side will typically tighten the car, and its height will affect how that weight is transferred. Moving the weight up increases the lever arm acting on the chassis on corner entry and can help the car hook, but may adversely affect the car’s behavior through the rest of the corner. A good crew chief or driver will keep a detailed setup log that includes ballast location and adjustments necessary as track conditions change.
Road racing/Autocross: As we discussed in our corner balancing guide, cars turning both directions generally benefit from a neutral weight distribution with minimal cross weight. In these cars, ballast is often used to add static weight to balance the car side to side or change front to rear weight bias.
In our experience, these cars benefit greatly from a low center of gravity. They are often making extremely fast transitions from hard left to hard right, then visa-versa. That lever arm that we discussed above will make those fast transfers more difficult. Think about running in a zig-zag pattern while holding a heavy rock over your head. Now run the same pattern with the rock held close to your chest. The second scenario will be much easier. Your race car feels the same way.
Drag racing: In the old days, drag cars often sat high in the air, with weight mounted high in the chassis on a short wheelbase to maximize weight transfer to the rear of the car. With the advent of tube chassis cars and significant advances in tire and suspension technology, this is no longer the prevailing logic. Drag racing weight ballast can be used to control the transfer of weight to the rear tires under launch or add weight to the front to mitigate wheelstands. Simply hanging weight out as far rearward as possible is not always the right answer. Depending on suspension and chassis design, adding drag car ballast at very rear of the car can have an adverse effect, actually causing slower reaction times or leading to wheelstands. The location of the points at which the rear suspension’s locating links (think front pivot of 4-bar links) connect to the chassis is related to car’s center of gravity and has a profound effect on the launching characteristics of a drag car. The placement of any ballast must be complimentary to the suspension’s ability to plant the slicks and unload the front suspension without causing an undesirable behavior.
We’ve heard it said that a race car is a puzzle. It’s up to the driver or mechanic to put the puzzle together, and you can’t do it with someone else’s puzzle pieces. In other words, every car and every driver are different. As with all aspects of race car tuning, where and how you apply ballast to your car will be different from how your friends and competitors are doing it. Build adjustability (and safety) into your mounting system and keep detailed records of how changes to the car’s weight affect its performance on the track. In the end, there’s no one size fits all solution and the only way you’ll truly determine what works best for you is through testing.
