Weight Distribution

Old 09-12-2008, 05:49 AM
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ssym
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Default Weight Distribution

I have a question about left to right weight distribution:

1966 Nova, Chassis Works Front End, Chassis Engineering 4 Link.

Left Front = 872 pounds Right Front = 902 pounds

Left Rear = 852 pounds Right Rear = 734 pounds

These weights are with my 220 pound as# in the drivers seat.

Is the left to right difference important? Can it be adjusted with spring adjustment?

Have not had it on the track yet...Moroso is down until October.

Thanks for the time,

Steve
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Old 09-12-2008, 06:16 PM
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gearhead1011
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I think 118 lbs. difference from side to side is too much. Depending on your car you will want to be within 50 lbs. My car likes about 50 lbs extra on the left but some cars will work better heavy on the right. When you scale and adjust your car do it with the driver weight in the car and the top right 4 link bar disconnected. If you have an anti roll bar disconnect one of the drop links on it also. Once you have the weight where you want it hook the 4 link bar and the drop link back up and set them both neutral. When you're adjusting the corner weights you might want to crank up the left front to put more weight on the right rear. This will help keep the car level from left to right.
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Old 09-13-2008, 03:15 AM
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ssym
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Default re:

I did not have the top right bar disconnected when we weighed the car.

Should I re-weigh?

Is there a set method one what spring to adjust to shift weight? I have them set equal left to right right now.

Could be chassis since I welded it up, but I didn't use that much wire!
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Old 09-13-2008, 10:49 AM
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gearhead1011
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Default Re: re:

Scaling the chassis and setting the corner weights is all part of the initial chassis set up. It doesn't reflect on the quality of the build although the better the it's built the easier it will be to set up. Usually you will try to start with the rear weight close to even and make passes with the car to find out what it needs. If it goes to the right you need to add weight to the right rear.

It would be better to use scales to do this. The reason I suggest disconecting the 4 link bar is because it will preload the chassis and that will affect corner weights. You want to try to set things up where the rear weights are close to even and you don't have to worry about the front corners, it won't make any difference with how the car leaves. If you want to increase the weight on the right rear (and it looks like you should) you can either adjust the left rear down or the left front up. I have found to offset the driver weight and set the rear even usually adjusting the left front up is the way to go. If the front is higher than what you want you can drop the right front to have the same effect. The weight will change diagonally.
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Old 09-14-2008, 02:14 AM
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ssym
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Thanks Chuck.

That gives me a good point to go back to the scales with. Makes good sense.

Steve
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Old 09-16-2008, 04:09 AM
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We know that the driveshaft torque tends to unload the right rear. It follows, then, that, if your suspension is symmetrical and your rear weights are equal when you're sitting in the pits, those rear weights are going to be very unequal during launch.

So, you have two choices: One is to put some asymmetry into your suspension (which I strongly recommend) or to statically preload the right rear.

If you're going to statically preload, weighing the car with suspension links disconnected is of no value. Think about it: When are you going to run the car with a link disconnected? Or, looking at it another way, why would you want the rears equally loaded statically, when you know that, as soon as you launch, the loadings are going to change?

But, weighing the car with it set up exactly as it will be at the strip is also of no value UNLESS you know how much preload you need.

Right about now, you might be wishing you had the money you spent on scales back in your pocket. Actually, those scales, when properly used, can give you an edge over most of your competition.

If you simulate...in your shop and without even starting the engine...the launch loads on your car, you can use those scales to determine the rear tire loading during launch. This is true whether you statically preload or use some form of asymmetry. You do this with what I call a "traction dyno." Its configuration and use is described at my site.
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Old 09-16-2008, 06:53 AM
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Steve check this website out its really informative. http://forums.racingjunk.com/viewtopic.php?t=2363
His user name is edvancedengines. Im sure he wont mind if you PM him. You don't have to have a traction dyno to get your car close. Drag racing isn't rocket science, just alittle common sense goes a long way. Keep it as simple as possible. Im sure hes going to get you to get those weights from side to side closer to the same.
good luck let us know what happens,
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Old 09-16-2008, 08:58 AM
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gearhead1011
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I suggested disconnecting the 4 link bar only to do the basic ride height/corner weight set up. You know if the 4 link isn't neutral that it can keep the spring adjustments from making any changes in the car's height. I usually keep adjusting the bar to neutral while I adjust the spriongs but I thought it would be easier to explain this method.

I know a lot of guys will move static weight in a car to correct the way a car leaves. Others will adjust the corner weights and others still will adjust the four link. The latter is what I assume you mean by "put some asymmetry into your suspension". That is what I will do at the track if the car is not going straight but I still think you need to be close with the initial setup. Not everyone, especially a bracket racer on a budget, has access to a chassis dyno.

Of course I know Who Billy Shope is and I respect what he has to say.
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Old 09-16-2008, 12:49 PM
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Originally Posted by gearhead1011
The latter is what I assume you mean by "put some asymmetry into your suspension".
The driveshaft torque provides an asymmetry. In other words, if you start with a perfectly symmetrical car, one with equal left and right loads at the front and equal left and right loads at the rear, everything becomes asymmetrical as soon as you launch. The right rear suddenly becomes lighter than the left rear and the left front suddenly becomes lighter than the right front.

But, if you design in an asymmetry which acts in the opposite sense, you can counteract and cancel the effects of driveshaft torque. For instance, if you have more anti-squat adjusted into the links on the right side of your 4link than you have on the left side, the link loads will place more of the weight transfer on the right rear than on the left rear. And, since those link loads are proportional to driveshaft torque, it is possible for this built in asymmetry to exactly cancel the driveshaft torque's tendency to unload the right rear.

It is important to note that such an arrangement requires no static preload.

There are many other ways to achieve this same sort of asymmetric cancellation, some of which I discuss at my site.
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Old 09-16-2008, 02:32 PM
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ssym
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Man I appreciate all the info. I have studied Ed's post at the top and have Beckel's book.

I am an Aircraft Mech and have acces to calibrated airplane scales, so that is a plus. Just finished the car last month and trying to get ready for the track in October.

I was surprised at the left to right weight difference. I am curious if you think I should do anything now or wait until I get a couple launches under the wheels?

Steve
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