Understanding How Weight Distribution Affects Your Race Car (2023)

Understanding How Weight Distribution Affects Your Race Car (1)



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Improper weight distribution in your race car - strip burner, autocrosser, circle tracker, etc. - can make your car dive like a dump truck or a block of wood on ice. Get it right and your car launches down the corner, hits that hard hairpin just right and holds the corner at full throttle. We’re going to take a quick look at what several sanctioning bodies say about weight and how it is to be distributed throughout the car. We’ll then talk about static weight distribution and cross-weight percentage and how they affect how your race car handles.

Image courtesy Wikimedia Commons

Weight is strictly enforced in all NHRA competition classes, with weight requirements and limits varying from class to class. The hard and fast rules that stay the same across all classes are:
• any weight added, ballast, may not extend over the front or rear of the car’s body or tires, and
• must be permanently attached to the vehicle, and
• there may be a maximum of 500 lbs ballast with a maximum of 100 lbs of that being removable.
NOTE: This information is from an NHRA Rule Book 2019 Addendum. The full rule book is only available to current members/racers.

The sanctioning body for most off road racing events (like Baja) is SCORE International. Each class has a minimum and maximum weight limit. Roll bar/cage requirements also vary based upon vehicle weight. On top of this, SCORE has one rule regarding weight that applies to all classes:
• Any ballast used must be installed as an integral part of the vehicle’s structure.

Image by Enilda Aguilar

Like other bodies, the SCCA sets a minimum weight requirement for all classes. As an example, all cars in the TA2/Trans Am 2 class cars must weigh at least 2830 pounds and any ballast used to meet this minimum must be mounted securely. SCCA also mandates that no more than 52% of the vehicle’s weight may be over the rear wheels and fuel may be removed during tech/weigh-in to meet that requirement. One difference with the SCCA is that they require that the car be in race trim, including the driver.

Image courtesy pxhere

Static weight distribution is the weight of the car on each wheel at rest set up and prepared for the race, including the driver. The easiest way to explain static weight is to have you step on a scale. Your weight on the scale is your static weight. Race cars can be weighed either by placing wheel scales under each wheel and combining the values from the four scales or by driving on a four wheel scale. When measuring static weight, you need to unload the suspension before taking your weight reading if you don’t have skid pads/turn plates on your scale pads, because not doing so can skew your cross-weight percentage, which we’ll talk about below.

Image by Enilda Aguilar

Cross-weight percentage is the percentage of vehicle weight on diagonally opposite corners. Most everyone is familiar with front-rear weight distribution - how much of your vehicle’s weight is on the front and rear axles. Let’s take the SCCA example of 2830 pounds from above. No more than 1,471.6 pounds of that weight, 52%, may be over the rear axle/wheels, leaving 1.358.4 pounds for the front wheels.

Image by Enilda Aguilar

Let’s say that the weight over the two axles is divided equally side-to-side. This means there are 735.8 pounds on each rear wheel and 679.2 on each front. To determine cross-weight we add the weight of the right front and left rear wheels and divide that sum by the total weight of the car. Our sample car has a cross-weight of 50, meaning it’s neutral. If the percentage was over 50 we’d have “positive wedge,” and negative/reverse wedge for a number below 50.

NOTE: It’s the rare vehicle whose weight is evenly distributed side-to-side, especially with a driver in the cockpit.

Above, you can see the result of improper weight distribution- a spin out.
Image courtesy Wikipedia

If your car has positive wedge, it’s most likely going to understeer, or “push,” through left corners. Reverse wedge means you’ll experience oversteer. Positive wedge loads the LR tire in a left corner, giving you better drive-off than if your car is loose (oversteering). This is helpful for circle track racers, but not so much for anyone who also has to make right turns in a race. Excess cross-weight for those who like to turn left and right while racing will cause excessive weight/load transfer when switching from hard left to hard right, which can cause things to “get interesting” for the driver trying to drive on the edge and maintain control.

If you don’t get cross-weight and front-rear distribution correct you’re going to have a very trying experience on race day. It’s a balancing act. Imagine yourself on a pair of shoes with a ridge down the sole. Now try and run as fast as you can without falling. You can if you get your weight distribution right. If not, road rash happens.

Image courtesy US Air Force

Static weight distribution can only be changed by adding or removing weight where needed, usually by adding or removing ballast from the front or rear centerline of the vehicle. If the class in which you’re racing allows it, you can also adjust weight distribution by moving components such as the battery and fuel cell or fire bottle. If you have to adjust your static weight, make sure you do so in a manner that fits in the rules.

When you need to adjust static weight distribution, make sure the ballast/weight you’re moving around is as far to the side or corner needing adjustment as possible. For example, if you need to increase the vehicle’s rear weight, place that weight as close to the bumper as you can and still mount/secure it firmly. Not getting that ballast as far into the corner or out over the edge as possible allows part of that weight to be felt on the other side. You don’t want the weight you’re adding to the left front to also add weight to the right front or either rear wheel.

Image by Enilda Aguilar

Adjusting cross weight percentage isn’t done by adding or subtracting weight in the vehicle. Cross weight is adjusted by raising or lowering one or more corners of the vehicle. For example, if your cross weight percentage is 52 and you want to get it down to 50, you need to lower the right front or right rear and/or raise the left front or right rear. Ideally, you want to raise or lower one side to get half of the desired adjustment and then move to the opposite side and lower or raise (opposite what you did on the first corner adjustment) an amount equal to the adjustment on the other corner.

In the example above of a 52 percent distribution, you can lower the right front or left rear an increment or two, then raise the left front or right rear an equal increment. The idea here is to get the ideal cross weight percentage while not changing ride height very much. Tire stagger, tire pressure and firmer springs will also change cross weight percentage measurements, as they modify ride height and cross weight distribution is a function mostly of ride height.

Load transfer in drag racing mostly deals with the transfer of weight from front to rear at launch.
Image by Enilda Aguilar

Up to now we’ve been talking about static weights - the car is sitting in a garage on a scale. That’s all fine and dandy for the garage, but the track is a completely different monster, my friends. Load transfer is why we don’t want a 50-50 front-rear or cross weight; we want something a bit different. Exactly what you want will depend on the type of racing you do.

The above photo shows examples of cornering loads NASCAR vehicles experience at tracks like Charlotte.
Image from NSF lecture

What is load transfer, though? It is how the weight or load of the vehicle moves around while you’re driving. Pay close attention at the drag strip this weekend. Watch the rear of the cars as they leave. You’ll see the rear squat, the front lift, and the torque will also cause the vehicle to twist and put more weight, or load, on the right rear. This can cause you to leave your lane or hit the wall. Not good.

Image by Enilda Aguilar

It’s the same with any type of racing. Take a look at the picture above of a NASCAR vehicle on the short track at New Hampshire. Notice the left front lifting? That’s load transfer. That’s lost grip. You need to eliminate as much of that as possible, preferably by weighting and lowering that corner.

As you can see, improper weight distribution and chassis setup can turn your enjoyable day at the track into sheer hell. Get it right and you’ll be celebrating in victory lane. Get it wrong and you may be going home on a wrecker. See ya at the track!

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Understanding How Weight Distribution Affects Your Race Car (19)

Mike's love of cars began in the early 1970's when his father started taking him to his Chevron service station. He's done pretty much everything in the automotive aftermarket from gas station island attendant, parts counter, mechanic, and new and used sales. Mike also has experience in the amateur ranks of many of racing's sanctioning bodies.

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Understanding How Weight Distribution Affects Your Race Car? ›

A road race car's left/right weight distribution usually falls between 50 and 52 percent (either side depending if the track has more left or right turns). It's a fairly cut-and-dry issue: If the road course has more right-hand turns, then the weight is biased to the right side of the car.

Does weight distribution affect the performance of a race car? ›

Weight distribution will have a drastic effect on how the car handles at high speed, and so whether the car is front, rear, four- or all-wheel drive is also important to consider. Careful tuning of the car's weight distribution and brake bias is key to maximizing performance.

How does weight distribution affect performance? ›

If a vehicle has a 40/60 weight distribution to the rear, it can brake later and harder into a corner. This is because weight moves towards the front of the vehicle as braking takes place. This gives the vehicle close to 50/50 distribution and means all tyres now have equal grip on the ground and can brake evenly.

How does weight affect a cars performance? ›

The heavier the vehicle, the more energy it needs to get moving. Extra weight also increases a vehicle's rolling resistance, which is a force that resists forward motion produced as the wheels roll over the road. This means that reducing weight is a very effective way to lower a vehicle's fuel consumption.

How does weight affect drag race cars? ›

Drag Race Weight Transfer - YouTube

What is the best weight distribution for a race car? ›

A road race car's left/right weight distribution usually falls between 50 and 52 percent (either side depending if the track has more left or right turns).

What is the best weight distribution for drag racing? ›

Typical values for front-engine, rear-drive cars are 55-51 percent front/ 45-49 percent rear.

What is a 50/50 weight distribution? ›

What is 50/50 Weight Distribution? Every car on the road uses its front tires to carry some percentage of its weight, and the rear tires carry the rest of the weight. However, in a car with 50/50 weight distribution, the front and the back wheels bear the same amount of weight.

What happens if I put too much weight in my car? ›

When you overload a vehicle it puts tons of strain on it. The tires can wear out quickly as well as overheat. This leads to expensive tire failure and the possibility of a dangerous blowout. Extra strain means the engine is also working harder to make the vehicle move.

How does cross weight affect handling? ›

On oval track cars, cross-weight is usually used in conjunction with stagger (where the right rear tire is larger in circumference than the left rear tire) to balance handling. More stagger usually loosens the handling in left turns, so more cross-weight is used to tighten it up.

Do heavier cars go faster? ›

Adding extra weight to your car will slow acceleration, but won't reduce its top speed. In determining a car's top speed, its engine battles two main forces: rolling resistance and aerodynamic drag.

Does weight matter Racing? ›

While reducing your weight may help your run, it could be to the detriment of your swim and bike. For swimming you need muscle to be strong and fast, plus a little fat to help with buoyancy. For cycling, it's all about power and endurance which can have very little to do with weight.

Why is a lighter car faster? ›

One logical solution is to make the car lighter. The amount of energy it takes to move a car from one point to another is highly dependent on the mass, so the lighter the vehicle, the less energy it takes to move it from one place to another. A lighter car is also a faster car.

Does driver weight matter in drag racing? ›

The heavier the car is, the more weight the engine has power forward. This means that it is vital to reduce any excess weight on the car, affecting the car's lap time.

Where do you want the weight on a drag car? ›

Weight Placement Drag Racing NoPrep and Prep - YouTube

Does weight affect aerodynamics of a car? ›

Four forces affect aerodynamic properties of a car: lift, weight, thrust and drag. These make a car move up, down, faster or slower. The amount of each force changes how a car moves through the air.

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