Tires are the only part of your car that actually touches the racetrack. Even then very little of the tire is actually in contact with the pavement at any given time. Everything you do on the track requires contact between the surface of the track and your tires. Because so little rubber is in contact with the track you need to maximize the tire’s footprint. Since all four tires to have to contribute to this traction the first step is to make sure all four tires are equally loaded. Remember that the tire with the least traction is going to set your cornering limit.
An unbalanced car feels unpredictable and unstable to the driver. When you drive hard into a corner you need to have confidence that you’ll come out of that corner with no surprises. Since we turn both right and left we want the car to react the same way regardless of which way we’re turning.
This means we need to measure how much weight is on each of our four tires. In the bad old days we weighed our cars with four huge grain scales. Some of us even used bathroom scales. With these old systems we could get to about fifty pounds of accuracy. Today we can get to within a couple of pounds..
These modern systems consist of four electronic pads that are connected to a console. This console does all of the calculations for us. It’ll then save all the calculations to memory. The newest scale systems even use a wireless connection between the scale pads and the console, or indicator panel.
The Theory
You’re never going to have equal weights on all four wheels. That just won’t happen. Blame it on physics. Blame it on the fact you have a rather heavy engine on one end of the car. The goal is to have the left side of the car have the same weight distribution as the whole car. In other words if the total weight of the car is such that 60 per cent of the weight of the car is on the rear tires you’ll want 60 per cent of the left side weight on the left rear wheel. In anything other than a formula car you’re never going to have equal left and right side weights. That’s because the driver sits on one side of the car – not in the middle.
If you do this correctly you’re going to end up with the sum of the left front and the right rear being equal to the right front and the left rear. This is called the cross weight. In road racing we want these cross weights to be equal. You should be able to get the two sums within a few pounds of each other. At least that should be your goal.
You get a weight shift by adjusting the ride height of your car. If you raise the left front corner of the car then more weight is going to be placed on the right rear tire. How easy it’s going to be to make this adjustment depends on your car. If you have coilovers at all four corners a ride height adjustment is going to be really easy. You simply adjust the spring perches on the shocks until the car balances out. Adjustability is a big reason coilovers are so popular on racecars.
If you have torsion bars at all four corners the task is reasonably pleasant. You just adjust the torsion bars until the car is balanced out. Now if you have an MGA your job just got a lot harder. Cars that use coil springs up front and leaf springs on the rear are not much fun. It usually involves shims for the front and leaf spring shims for the rear.
You probably won’t be able to hit the correct cross weights by just adjusting the ride height of your car. You’ve probably already noticed that some of the cars in the paddock area have a big steel weight bolted to the floor of the car. This weight was added to get the corner weights correct. Yes you can make your car faster by adding weight. The idea is to place this extra weight in such a way that the corner weights of the car are balanced.
The Weight Thing
Most vintage groups don’t weigh cars. That's like an undated hall pass in junior high school. Even if your sanctioning group actually weighs cars not much changes for you. You always want to make your car as light as possible. You then add weight to bring it back up to the legal specification. You don’t just add weight randomly. You want to carefully add the weight to places where it will help the handling of your car. Add the weight while you have the car on the scales. Some teams have found so many lightweight (and very expensive) techniques that their cars are carrying more than 400 pounds of ballast. That’s a good thing if you add the weight to improve the cross balance.
I’ve seen just about every sort of weight possible used for corner balancing. Lead ingots and weights from a barbell set are the most common. You can even purchase sheets of lead for use in this process. You need to make sure that all of this weight is bolted securely to your car. You certainly don’t need a lead ingot flying around your car in the event of a crash.
The Actual Process
The first thing you need to do is make sure your car is ready to be weighed. This means that all the fluids are filled to operating capacity. Disconnect the front and rear sway bars. Some people even disconnect the shock absorbers. In addition have the tire pressure set to your normal cold pressures. You should have the alignment set to an approximation of normal. This is a little complicated since changing the ride height of you car will change the alignment and changing the alignment will change the ride height. I’ll return to this in a little bit.
You always want to have the weight of the car the same as when it goes out on the track. That means with the driver in the car. There are two ways to do this. One way is to have the driver in the seat while the cross balancing procedures are carried out. The other way is to put an amount of weight into the driver’s seat that’s equivalent to what he or she weighs.
Let’s assume that you’ve purchased the necessary scales and you’re going to do this in your own garage. First your garage isn’t very level. At least it’s not level enough for weighing a racecar. I use a water level to set my scale pads. I place the pads in the correct location and then use the water level, or a really long bubble level, to make sure the four scale pads are all level with one another. You might have to make some small shims from ¼-inch Masonite for gross adjustments. Most scale pads have adjuster screws in the bottom of the pads for minor corrections. You should mark all of this on your garage floor so you can replicate the set up.
Once you have the car on the scales you’ll know where you are. You want to know the sums of the cross weights. In other words you add the left front and right rear together. In a perfect world this number will be the same as the right front and left rear. Your world is not perfect so you’ll need to think about which corner of the car to attack first.
Since different cars need different techniques I’m not going to get into anything detailed here. Just think logically and it’ll be simple. Frustrating but simple. If I raise the left front corner of my car I’m going to be placing more of the total weight on the right rear of the car. I’m not going to change the weight of the car but I am going to change the way that weight is distributed on the four tires.
If I raise the left rear corner more of the car’s total weight will be placed on the right front tire. Got it? The key thing here is to think about all of this before you start making adjustment to the ride height. When you look at the indicator panel you’ll see which tire needs more weight. Now you need to adjust the car’s ride height to get it there.
You’ll never do this is one easy adjustment. It’s going to take a series of adjustments. Each adjustment though should be smaller than the ones you did earlier. You have to sneak up on it. Now add in the factor that when you adjust the alignment of the car the weight balance will shift again. After you make that adjustment the alignment will be off ever so much. You just need to keep making a series of adjustments.
The first time you do this you might plan on taking four to six hours. If you have a shop do this for you be prepared for a bill that might approach four figures. The good part is that once you get the weights balanced and the alignment correct everything will stay the same. Until you take the car apart. In which case you can start all over again.
What’s This Going to Cost?
There are two basic ways of doing this. You can pay someone or you can buy all the necessary equipment and do it yourself. Corner balancing a racecar takes a lot of experience. Even with all of the digital readouts there’s still a lot of art involved. There’s nothing wrong with having it done by an experienced shop.
You need to find a shop that has both the equipment and the skill to do this. The cost of having a race shop do this may be a little intimidating. You need to add up what a set of scales and roll-on roll-off ramps are going to cost you and then make the comparison. There’s no really cheap way around this.
Scales aren’t cheap. While you can get started with a set of used scales for less than $1,000 you can easily spend over $10,000 if you want all the little extras. The roll off ramps are what’s expensive.
These are aluminum ramps that fit between the front and rear scales. They allow you roll the car back as you make adjustments Then you simply roll the car forward onto the four scale pads when you complete the adjustment. If you do all of this work at home these ramps can be as simple as wooden ramps that elevate your car to the height of the scale pads.
Most shops charge an hourly rate for weight balancing a car. It’s almost impossible to put a time on this task. The only thing you can be sure of is that the first time you have it done will be the most expensive. You need to inquire as to what most people spend the first time. Also keep in mind that corner balancing will include the cost of an alignment. You really can’t adjust the weight of a car without messing up the alignment.
If all you want is to have your car checked then an hour of shop time should be more than sufficient. If your car needs corrective measures then the time (and cost) will increase. It’ll increase geometrically. Remember that the alignment and the corner weights of your car are two side of one coin. Most of the time you’re going to be working with the corner balance and the alignment of the car at the same time.
Alignment is also one of the reasons you might want to have a shop do all this work for you. A well-equipped shop can do the corner balancing and the alignment at the same time. If you do the corner balancing at home you’re going to have to take the car out to be aligned. Then you’ll have to check the corner weights again. Any ride height adjustment will mess up that perfect alignment.
The one solution is to learn how to do a string alignment in your home garage. You’ll notice in the pictures of the professional cars that the teams are aligning and weight balancing their cars at the same time. This is really common at the major events. String alignments though are a subject for another issue.
This is the easy part. You need to check the corner balance after every race. I learned that from Danny Kellermyer at DJ Race. (djrace.com). When Danny’s cars come out of the trailer they right to the scales. The corner weights give him an indication as to whether the alignment on the car has changed. If the camber setting on the left front has changed he’ll see this as a change in the corner weights. If the corner weights are the same as when he left for the track life is simple. If the weights have changed he looks for a reason for this change took place.
I know any number of people who do a complete cross balance and alignment at the beginning of the season and then simply do a weight check as the season goes along. If you keep track of your tire temperatures you’ll know how good your alignment really is. Once you get everything correct just leave things alone. Does anyone actually do that? Have you ever seen a paddock where no one is working on a car?
