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Author Topic:   the rear weight placement debate
Roadhzrd
Member
posted December 30, 1999 07:43 PM
when the track gets slick, I usually put my 40 lb chunk of lead on my mod bumper. Some people like to put it above the rear axle, but if you do that you need to use more weight to get the same rw% where is the trade off for having a lighter car vs. more lead above the axle?


jammin
Administrator
posted December 30, 1999 08:29 PM
Road, the primary reason that you need the weight over the rear is for front weight. When you distribute weight that far back, you actually take weight off of the front tires. This see-saw effect will cause the car to feel tighter than it actually is. It may cause the front to wash out also. But if you put it over the rear or forward, you only (majorly) affect the portion of the car you are putting the weight on. If you keep the front weight, then you can run a tighter car and still steer the thing. Tighter is faster. Hope this helps.


M GLICK
unregistered
posted January 01, 2000 06:09 PM           
Down here in Texas the tracks usually go dry slick. But we don't add any lead. We do tighten the car considerably though. Our car have about 61%rear with out lead. and weigh about 2300 lbs with 32 gallons of fuel. The lead can hurt more than help if placed in the wrong spot. Like Dave said on the rear bumper it will have a pedulum effect making it extremly loose in the middle of the turn.


dlm
unregistered
posted January 01, 2000 09:34 PM           
Also when you feel that adding weight to your car to make it handle ,always try to keep it in front of the rear axle but as low as possible.The higher the weight is the more swing it will give to the car in the middle of the corner and coming off. I have found over the years that there is usually a spring/shock compo that will work at a given track for a night like your seeing. Esspecially if it's your regular track. good luck


turmoil
Member
posted January 03, 2000 09:34 PM
What about bolting the weight to the rearend itself. I've seen it done but don't know how good it works.


jammin
Administrator
posted January 04, 2000 09:15 AM
bolting the weight to the rear end increases unsprung weight. That is a big no-no. If you do this, it takes longer for your suspension to react to bumps and contours of the racing surface. Compression and rebound of the suspension will be slower.


turmoil
Member
posted January 04, 2000 02:47 PM
Basically what I'm guessing you guys are saying instead of bolting 40 lbs to the bumper I should put 150 lbs (to get the same rw%) above and slighty behind the rear and make my 2400 lb car a 2510 lb car. I'm not afraid to try anything, but I never have experianced the pendulum effect. I am concerned about making the car that much heavier though. Also I have my fuel cell mounted about four inches from the back bumper and am considering moving it fwd about five inches. I run a high bank track and fly in the high groove which is ussualy the prefered groove but I would like to run the low line a little better.


jammin
Administrator
posted January 05, 2000 03:43 PM
Road, Dave is right in that the weight of the car is actually going to help you on the tires. Since we usually do run smaller tires than everyone else, it will help. Our actual pound per square inch on the tire patch has to be thought about. If you have a late model that has a larger tire patch, the cars can hook up easier with less weight (fewer psi on more patch). Think about when this patch is grown smaller, what happens. The actual psi on the patch has to increase with the smaller patch to keep the same traction(with the same HP). So the smaller you get(with the same horsepower) basically the more weight that is going to be required to keep it on the ground. I think this is the way to look at this debate. It is true, you have less weight to move to get it down the stretch, but where is the line drawn, there has to be one with the motors that we run. I am going to be digging, trying to find some formulas for this. It can be done mathematically, just have to find out what the formulas are. We will see what we can do. This is a question that plagues many, many racers.


modman
Administrator
posted February 12, 2000 07:43 AM
There are so many variables.


krazy 76
unregistered
posted February 15, 2000 06:52 PM           
If you're going to add lead to your car there are some things you have to consider. When you place the lead in the car do it the first time on a set of scales. It is amazing what happens to the diagonal or lr weights when ballast is added. Record your current set-up (baseline). Add the weight and see the change to the ride heights and the wedge.Turn the screws to get the ride heights back to the initial settings and double check the %'s. Write down every turn needed for each screw and save it for when you do add the weight at the track. If this sounds like alot of grief for just adding lead then don't add the lead. Figure out another way to go on the slick.

How about changing the ratio of the throttle pedal?

Roadhzrd
Member
posted February 16, 2000 11:06 PM
All these points are very good, thanks for responding. This discussion brings up another point I often try to visualize. A tire loses traction when there isn't enough weight on it, but it also loses traction when it's overloaded so all these mods running with 60% rw have to be pushing the edge. It would make you have to drive your car with the rearend. It seems if you already have all your weight on your rear end you're not going to have much weight to transfer from the front. what do ya think?


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