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Cornerweighting a race car, part 1
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This will be a 2-part series on how to cornerweight a car.
A poorly balanced car could give you a lot of unwanted thrills if you are racing when competing in high speed events such as Drag Racing, Tim Trials or Road Racing. Downshifting and hard braking at 100+mph will exaggerate any weight imbalance your car may have, even though you may not have noticed it at slower speeds. In fact, you may not notice any real balance issues unless you are driving your Neon at its liimit. Trail braking and heel/toe downshifting can help smooth over an unstable chassis, but a properly balanced car will react in a much more predictable fashion, allowing the driver to push the limits of tire adhesion without excessive twitch and roll.
So, what does it take to engineer a well-balanced machine? For many vehicles, all it takes is access to accurate scales, help from a friend, and about an hour of your time. You need to have the ability to raise and lower each corner of the car, however, to make this work. That will require an aftermarket, fully adjustable suspension. Actually, any car that you intend to race seriously should have adjustable spring perches, if competition rules permit.
So grab a buddy, get a note pad and pen (to record changes from inside the cockpit while your friend reads the weights), and push your Neon onto a set of electronic scales. Make sure that you have the car in racing trim. I recently helped my friend cornerweight his 1985 Toyota MR2. After going through a few cycles of raising and lowering the corners, he realized that he had his 40 lb. Easy-Up pit tent in the trunk of his car. It was funny for a few seconds, but then we realized that we had to start all over.
So to to help you avoid a similar incident, let’s take you through a sample cornerweighting session. These are the actual results of the first time we put the Speednation.com 1996 Turbo Neon on the scales. By the way, even though this car was a National Championship Solo II car in the competent hands of Mark Daddio, there was no way in the world I was going to drive it at 120+ MPH up a 1 1/2 lane wide mountain road until it was as perfectly balanced as possible. Good balance = predictability.
A few notes about the Speednation.com Turbo Neon. It has two lightweight racing seats, a complete interior in the forward cockpit, but is completely gutted behind the driver’s and front passenger seat (SCCA Street Modified rules). A full, SCCA legal roll cage was added to the way Daddio had prepared the car for autocrossing.
Before pushing the car onto the scales, make sure that they have been leveled, and once the car is on the scales, rock it a little to settle the suspension. The first thing to write down is the dry, or curb weight of the car. These numbers won’t be of much use unless you’re planning to pilot it by remote control. The heaviest weight you will ever add to your car is YOU, so YOU should be in the driver’s seat when the car is on the scales. So, therefore, the next step is for you to get into the car, and then take a look at the scale readings. Where do you suppose the majority of the weight went when I got into the car? Surprise, nearly 60% of the weight ended up in the left (driver’s) rear corner! 62 lbs. was added to the LF (left front), 56 lbs. went to the RF (right front), 106 lbs. went to the LR, and only 5 lbs. went to the RR. Worse yet, the LF/RR diagonal gained only 67 lbs. while the RF/LR gained a whopping 162 lbs. To compensate for that, the first change we made was to lower the RR (right rear) and raise the LR (left rear). Two principles are at work here. The first is that vehicle weight is not balanced from one side to another, but on a diagonal. For instance, if your Neon is relatively well-balanced, except for the LR which is too light, you can’t just add some weight to that corner and expect to solve your problem. If you do, prepare for a shock. Sure, some of the weight will go to the LR, but the RF (right front) will also increase substantially.
The second principle is that raising a corner will make it heavier. That, however, doesn’t seem to make sense to a lot of people. If you think about it in terms of what is happening to the wheel, you will understand more clearly. You’re not so much raising a corner of the car as you are pushing the wheel down towards the ground. We found a very easy way to remember this very important principle: Lower = Lighter.
For more information, check out my books. Next week - the conclusion of this article.
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