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Old 04-22-2007, 09:34 PM
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Too much wheelstand

I need a little help, but first a little background. I have a superpro 77 Olds Starfire. I run a destroked 400(377) smallblock with a powerglide. It has 538 gears and has ladder bars with coilovers. My problem began when I went to the 377 from a 358. The launch is a little too much. The wheel stand is way too much. It hits the wheelie bars hard. It always had a tendency to stand but now it is about out of control on the launch. Does anybody out there have any good ideas. I usually launch at 3800 with a 5500 stall converter.

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Old 04-23-2007, 05:11 AM
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I'm sure you already know the answer: You have to rebalance the car. Could you fab a battery box ahead of the radiator, for instance? Ideally, of course, you'd like to leave 100 pounds or so on the track up front. That's less than 5% of your total and you'll never miss it.
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Old 04-23-2007, 07:07 AM
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IIRC, if you adjust your bars to move the instant center rearward, you will decrease the tendency to lift the front end.
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Old 04-23-2007, 09:59 AM
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I'm afraid weight transfer is a function of only acceleration, center of gravity position, and wheelbase. (Actually, including "wheelbase" is just another way of saying "center of gravity position.") So, your only options are to reduce acceleration (which you're not likely to consider) or to change the position of the center of gravity. You might "fix" the situation by a change in suspension geometry, but what you've really done is decrease the acceleration. Another way of stating your choices is to either accept an increase in 60 foot times or start shifting weight.
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Old 04-23-2007, 04:47 PM
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wheelstand

Thanks for the info. Is there a chance that moving the ladder bar pivot up on the front will help? I have one hole below where it is now and 4 above. Is this what you are referring to when you said geometry.
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Old 04-23-2007, 05:38 PM
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Billy is not quite right. It's more than just dead weight.
The ladder bar position does help determine the instant center that redsdad mentioned. I know changeing the position affects the IC I just don't know the details.

I would do a google on instant center ladder bar, here I did and I got pages of info
Like this page http://www.raceglides.com.au/TechInfo.htm

look at this picture, it's looks like it's saying to raise the IC ( ladder bar mount)to reduce squat which is the same as wheelstand in your case I believe

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Old 04-23-2007, 07:19 PM
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The "pushing on the refrigerator" analogy is not a good one. In all 3 cases, the refrigerator push is at floor level and the weight transfer is unchanged.

Again, you can play with the suspension all you want, but the only way you're going to reduce the wheelstands is to either decrease the acceleration or move the CG.

The forward thrust is at the tire patches. This results in an equal but opposite inertial force acting through the CG. This moment (thrust times CG height) results in an equal but opposite moment, consisting of the weight transfer times the wheelbase.

Squat and rise are not directly related to the activity at the front of the car. With a RWD car, the front will always rise on launch. Adding a lot of squat would lower the CG a bit, but it wouldn't be enough and that's a poor fix, anyway. The proper solution is to move the weight forward and down.

For a much more detailed explanation, look at pages 4 and 11:

http://home.earthlink.net/~whshope
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Old 04-23-2007, 10:18 PM
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wheel stand

My question remains. If I raise the front connection of my ladder bars will it cause the wheel standing to lesson?
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Old 04-23-2007, 10:29 PM
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If it were my car, I would move the front mounts up one hole. Test the launch to see if it calms it down. Check your 60 foot times and let us know. I am making the assumption that you don't have it set correctly now. Of course, I also assumed you had a 4 link.

Don't forget to reset your pinion angle before you try out your launches.
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Old 04-24-2007, 07:14 AM
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Quote:
Originally Posted by mthall
My question remains. If I raise the front connection of my ladder bars will it cause the wheel standing to lesson?
What you're suggesting is equivalent to that shown in the bottom picture by "427v8." Note that the rear of the car goes up. This would raise the CG and make the wheelstand problem worse, not better.
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Old 04-24-2007, 07:29 AM
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It does raise the center of gravity on launch. But it raises the point where the force is applied in the chassis from the rear end (the instant center) more. This reduces the moment arm length between the CG and IC and therefore reduces the wheelstand tendency.
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Old 04-24-2007, 07:45 AM
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Quote:
Originally Posted by BillyShope

Again, you can play with the suspension all you want, but the only way you're going to reduce the wheelstands is to either decrease the acceleration or move the CG.

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So how do you explain those cars at the wheelstand contest that one day are lifting the wheels about 6 inches and the next are dragging the bumpers?
Bags of sand in the trunk???
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Old 04-24-2007, 09:03 AM
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you need to get a alot more info...
holy double posts..batman!
kurt

Last edited by seriousracer; 04-24-2007 at 09:08 AM.
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Old 04-24-2007, 09:07 AM
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you need to get a alot more info...
springs corner wieghts pinion angle,ladder bar length,shocks,,need more info before you move wieght or change suspesion.
stock control arms?
modified with mono balls or hiem joints??
lots of questions . not much info..

also why are you running such a loose converter and leaving so low. you flashing the converter on your launch and actually launching harder . just my .02

kurt
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Old 04-24-2007, 11:03 AM
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Quote:
Originally Posted by redsdad
It does raise the center of gravity on launch. But it raises the point where the force is applied in the chassis from the rear end (the instant center) more. This reduces the moment arm length between the CG and IC and therefore reduces the wheelstand tendency.
A wheelstand occurs when the product of static front end weight and the wheelbase is less than the product of forward thrust (at the rear tire patches) and the CG height. It doesn't matter whether you're considering an actual car or a concrete model, those are the only forces involved. Changing the suspension geometry is no more effective than changing the spring force on the cigarette lighter. The only choice is a decrease in acceleration or a shift in CG location.
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