Project 911 Goes to a Weight Clinic
There’s more speed in the chassis than there is in the motor. If that doesn’t make immediate sense remember that the only thing a motor does is push the car down the road. If you want your car to go down the road faster there are two ways to do it. First, you can increase the amount of power that propels the car. The second (and perhaps more effective) way to make your car faster is to make it roll down the road with less effort.
The first place to begin a proper alignment is ride height adjustment. Every Sunday when we watch the Sprint Cup cars on TV we hear about the mechanics adjusting the ride height of the cars. When the NASCAR folks adjust ride height they call it “putting a little wedge in”. The crew member that shoves the wrench in the back window of Dale Earnhardt’s car is actually adjusting the ride height of the car in an attempt to improve the car’s handling.
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| You can use your cell phone screen if you purchase the wireless scales. |
With Project 911 we didn’t need any “wedge” in the chassis; but we did want all four tires to apply equal pressures to the ground. Why? Think about how hard it is to sit on a chair where on leg is shorter than the other three. This is how the average Porsche goes down the road.
Since most of us, unlike Rusty Wallace, want out cars to turn both left and right; we also want them to react the same way in both directions. This is called balanced handling. We get this by putting an equal load on all four tires.
The way we get this equal loading of all four wheels is by carefully measuring the weight at each corner. In the bad old days we used grain scales and levers with little two-inch dial that read to 800 lb. These old system were accurate to about 100 lbs. Not good enough.
Now, there’s a high-tech solution. We talked the folks at Speedway Motors into loaning us a set of the latest computerized scales, designed to make a tough job a bit easier. Plus, if these scales were what the big boys use should we use anything less for Project 911? The computer does all the math calculations for us. Technology is wonderful, especially when you have no patience for tedious calculations.
The scales consist of four electronic pads that are wired into a handy laptop console. When you get the system all set up you simply sit in the car and read the display on the console. It’s the only system I know of where one person can do all the work. There’s no need to promise your friends extra beer and chances to drive the car in order to get the job done. This alone might save you enough money to pay for the Longacre scales. Better yet, get together with fellow club members or racers and pool your bucks for the purchase.
The first step is to make sure that the tops of the four scale platforms are absolutely level. The best way to do this is to use a carpenter’s water level. This is one of the nicest little devices around. It consists of two graduated glasses connected by ten feet of vinyl tubing. Since water always seeks it own level, you simply raise (or lower) each scale platform until the water levels on all four platforms are all at the same height.
You can’t imagine how much of a slope even the finest garage floor has until you actually use this water level. An eighth of an inch in ten feet is no big deal but just try to get the four pads level. When you finally get the first three level, then the fourth platform is totally out of whack. Just keep going.
The good part is that you should only have to do this once. Draw little yellow squares on the floor and keep a record of the height adjustments. Next time you can put the platforms back to a level position with a minimum of fuss and bother.
Now that we know the four scales are level, and the actual calculations accurate, let’s return to the theory of what we want out of Project 911. The left side of the car should have the same weight distribution as the total weight of the car. For instance, if the total weight of the car is distributed 40 percent on the front and 60 percent on the rear then the weight of the left side should be 40/60 as well. Likewise with the right side. Remember, in anything but a formula car the weight will never be equal side to side. The weight of the driver on the left will always make one side of the car heavier than the other.
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This was where we ended up. |
If we get the weight distribution correct the sum of the left front corner and the right rear corner will be exactly the same as one-half the weight of the car. The other half will be balanced on the right front and left rear tires. This is a balanced car. The actual weight will not be the same front to rear but the ratios will be.
Before you do anything with the scales make sure that you disconnect the sway bars. The sway bars shouldn’t change the weight but they just might. A pre-load, or a twist, in the say bars could give you some very funny weights. What happens is that a sway bar with a preload acts as a spring, pushing the wheel on one side down and raising the other side.
Project 911 weighs 2588 lbs. with a driver in the seat and with the gas tank half full. When we placed the car on the scales we were able to calculate that we had 1552 on the rear of the car and 1035 on the front wheels. That meant that the cross weights were a real mess. We certainly didn’t have a balanced car.
The left rear wheel of Project 911 was way too heavy and left front tire was far too light. Now comes the fun. Getting them right. With the wisdom that comes from having botched too many projects we had already installed the Sway-A-Way adjustable spring plates. This meant that I could adjust the rear ride height of the Project 911 just as easily as you normally adjust the front ride heights.
When you have an error in the weight balance the amount of the error will be the same for each tire. If two tires are too heavy then two tires will be light. Remember, the weight of the car doesn’t change; only the way the car is balanced on the four tires changes.
Back to our calculations. If we want to increase the weight of one wheel we rais the ride height on that wheel. If we want to lower he weight on that corner then we loser the ride height. Just to keep things interesting any change you make on one wheel will change the weight on the other three wheels. Remember, we’re not adding or subtracting weight from the car, we’re just moving it around.
With Project 911 the right front tire was way too light so we lowered the ride height of that corner with the torsion bar adjuster. The left front tire was way too heavy so we raised that corner of the car. The amazing thing was that we got the weight just right on the left rear ties on the first try. The other corners were a real mess though. Back to the adjuster screws.
This is a lengthy process. I have a friend who points out that to balance the weight and align the wheels can take as much as six hours. Believe him. It involves a lot of crawling around on the floor and getting in and out of the car. Each time you make an adjustment you get back in the car and punch buttons on the console to wee what you actually did.
When you finally get the weights all set to the proper numbers, you can attach the missing sway bar link. Then check the weight once again. The weight should not have changed. If it did then you have a problem with a bent sway bar. You should adjust the links so that the weight does not change with the attachment of the sway bar.
The final step is to have the car aligned. All the effort we put into getting the weight balanced moved the alignment settings out of place. Lowering the ride height on one corner means that we’ve changed the camber, which means we also changed the toe setting, and so on and so forth. The part that makes this so much fun is that ride height, camber, caster and toe are all related. Change any one of them and you’ve changed all of them. The net result of all this effort is that Project 911 handles better than it did before we started the process. Considering the price of the scales they’re a wise investment. A set of computerized scales is just slightly more than a Recaro seat, and less than the price of the new valve guides that we so desperately need. The bottom line it that setting the cross weights can make more of a difference than either of those items.
Originally Published in European Car
December 1992
Note: The original images are long gone. In 1992 we were using film and part of the contract required that the magazine be given all the original negatives. Magazines such as European Car have been bought and sold several times since the early nineties All of the old images were lost in the many transitions.
Here's the car that we used in the article. I still own it today.
Here's the car that we used in the article. I still own it today.