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  #1 (permalink)  
Old 11-05-2005, 07:40 PM
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mustang rear coil overs

on a pretty fast mustang(1985) is it worth the money and time top install rear coil overs, i already installed a complete tubulr front k-member and tubklar a-arms with coil overs up front

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Old 11-06-2005, 02:46 AM
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I assume you're dragracing it. You really can't do much with the rear springs in a dragrace car. I realize this probably isn't the case with your car, but, for instance, if a car is set up with 100% anti-squat, the rear springs are just going along for the ride. They don't even know when the car is being launched.

What about preloading? Yes, you could preload with the adjustable rear coilovers, but you already have adjustable coilovers at the front, meaning that you already have the ability to load the right rear by cranking in some force at the left front.

But, with what you have at the front, there is a much better "fix" than a static preload. Instead of fooling with the rear springs, I'd invest a few bucks for a higher rate right front spring. If your right front spring has a rate about 50% higher than the left front, you're pretty close to a perfect cancellation of driveshaft torque at the rear. In other words, for any value of driveshaft torque, your rear tires will be loaded fairly equally. It is important that you borrow some wheel scales and adjust for equal static rear tire loading.
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Old 11-07-2005, 01:02 AM
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Quote:
Originally Posted by 347mustang
on a pretty fast mustang(1985) is it worth the money and time top install rear coil overs, i already installed a complete tubulr front k-member and tubklar a-arms with coil overs up front
What set up did you use? I have been researching double A-arms for foxes.
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Old 11-08-2005, 06:51 AM
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i use the stuff from qa1, i love the front end set up now, it clears up some serious room and weights about 100lbs less
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Old 11-08-2005, 11:43 PM
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Quote:
Originally Posted by 347mustang
i use the stuff from qa1, i love the front end set up now, it clears up some serious room and weights about 100lbs less

347 // 100 pounds off the front !!!!!!!... Cool, I will look into it.

BillyShope // I forgot to comment about Billy's input. He has some good stuff there. For all the chassis stuff I have done, I guess I always knew that but I never really considered it in the terms he used. That is correct. During acceleration at 100 % anti-squat the springs don't even need to be there.... But most of us don't have 100%..... or even close. Thanks Billy!!!
(of course until we hit the gas, something has to hold up the car, lol)
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Old 11-08-2005, 11:51 PM
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Quote:
Originally Posted by BillyShope
I assume you're dragracing it. You really can't do much with the rear springs in a dragrace car. I realize this probably isn't the case with your car, but, for instance, if a car is set up with 100% anti-squat, the rear springs are just going along for the ride. They don't even know when the car is being launched.

What about preloading? Yes, you could preload with the adjustable rear coilovers, but you already have adjustable coilovers at the front, meaning that you already have the ability to load the right rear by cranking in some force at the left front.

But, with what you have at the front, there is a much better "fix" than a static preload. Instead of fooling with the rear springs, I'd invest a few bucks for a higher rate right front spring. If your right front spring has a rate about 50% higher than the left front, you're pretty close to a perfect cancellation of driveshaft torque at the rear. In other words, for any value of driveshaft torque, your rear tires will be loaded fairly equally. It is important that you borrow some wheel scales and adjust for equal static rear tire loading.

Question.

Doesn't drive shaft torque manifest itself as lifting the right rear tire off the ground????

For drag racing, considering body roll by torque, wouldn't it be better to adjust up or stiffen the right rear coil over than to adjust up the left front???

Upping the left front jacks cross weight but aggravates torque roll to the right. Upping the right rear loads the right rear AND reduces body torque roll thereby planting the right rear tire. Remember when we used an air bag at the right rear with the existing spring?
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Old 11-10-2005, 05:40 AM
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The reaction to the driveshaft torque is taken at the engine/transmission mounts, where it is distributed, front-to-rear, in proportion to the relative roll stiffness. If all of the roll stiffness were at the rear, all of the reaction torque would go back to the rear and there would be no tendency to unload the right rear. This is why many dragracers add a hefty rear anti-sway bar. (Unfortunately, they often leave the front bar in place, which is defeating the purpose.) Since there will always be some roll stiffness at the front, it is impossible to totally cancel the tendency to unload the right rear.

With this understanding, it's evident that static preloading, whether it's done by jacking the LF or the RR spring, produces the same results as far as wheel loading is concerned. But, if you're serious about elimination of that unloading of the right rear, static preloading is the difficult way to go.

Some sort of dynamic loading is to be preferred. In other words, you want the forces, naturally available during launch, to work for you in that cancellation. One answer is an asymmetric rear suspension. You have forces acting through the links which are proportional to driveshaft torque, so it is possible to arrange those links asymmetrically to achieve full cancellation with any value of driveshaft torque. (I won't go into specific designs here.)

I mentioned another answer in my previous post. The sum of the loads carried by the right side tires must remain constant. If this were not the case, the car would be rolling over. So, when a higher rate right front spring is installed, the result is that, during launch, weight comes off the right front "quicker" than off the left front, meaning that most of the weight transfer is coming off the right front, meaning that...since the sum of the right side loads must remain constant...the majority of the weight transfer is going to the right rear tire. Again, the forces inherent to the launch are being used to cancel the tendency to unload the right rear.
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Old 11-12-2005, 06:37 PM
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Quote:
Originally Posted by BillyShope

I mentioned another answer in my previous post. The sum of the loads carried by the right side tires must remain constant. If this were not the case, the car would be rolling over. So, when a higher rate right front spring is installed, the result is that, during launch, weight comes off the right front "quicker" than off the left front, meaning that most of the weight transfer is coming off the right front, meaning that...since the sum of the right side loads must remain constant...the majority of the weight transfer is going to the right rear tire. Again, the forces inherent to the launch are being used to cancel the tendency to unload the right rear.
This is a drag car launching, not a circle track car...

I guess I am missing something......

If the right front spring is stouter, it does not pitch up as quickly and as much as the left side, limiting the suspension extension on the right front and therefore unloading the right front tire quicker, transferring that right front weight to the right rear of the body NOT the right rear tire (total remains constant).....which to me makes the right side of the car pitch down even more..... (it is true the body is trying to push down on the spring,,, but)

If no changes are made to the rear suspension, the right rear wheel still lifts from torque compressing the right rear spring....

this incombination with the reduced suspension action on the right front and its subsequent weight transfer to the right rear of the body causes the body to roll even more to the right.......

It seems to me.......
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Old 11-13-2005, 04:21 AM
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Step back and look at the big picture. Consider a "car" with only 2 wheels, one on the left side and one on the right. Looking at it from the rear, let's suppose that everything's symmetrical. That is, the CG is in the middle of the track, so the force pushing up on that single left side tire is exactly equal to that pushing up on the right side tire.

Okay, let's get ridiculous and add 99 more axles. Now, we've got 100 wheels on the left side and 100 on the right. The sum of the forces pushing up on the 100 right side wheels must equal the force pushing up on that single right side wheel with which we began.

Returning to reality, we have a car with 2 axles and 4 wheels. Nah, reality's no fun! Let's return to the absurd. We'll put a coil spring from a railroad car at the right front and, at the left front, we'll use a watch spring with a free length of five miles. So, both the railroad spring and the watch spring are working together to hold up the front of the car. On launch, the left front spring would have to extend 10 feet to change the left front wheel loading by a pound, but the right front spring would only have to extend by a couple of thousandths of an inch to do the same. So, essentially all of the weight transfer is coming off the right front. Since the left front wheel loading isn't changing, neither is the left rear. But, the right front wheel loading is decreasing by the amount of weight transfer and the right rear wheel loading is increasing by the same amount.

Hope this helps. Please don't be offended by my absurd examples. It's just that I feel that the effects of small changes are often made more evident if you take them to extremes. Once you see the effect of the extreme change, you can then scale it back to reality.
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Old 11-13-2005, 10:15 AM
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Your scenerio is NOT going to prevent the right rear tire from lifting itself up towards the body. The "torque" is still applying "up pressure" to the right rear spring and "down pressure" to the left spring rotating the entire rear axle assembly under the body.

This "engine/driveline rotational torque" is independent in its action and has nothing to do with front suspension. It will do it with the car frame sitting on jacks.

Haven't you ever seen a "wheels-up" launch with the entire car rolling to the right????? How is the front spring going to prevent that if the front wheels are off the ground???????

Let's go back to post # 6.

Last edited by xntrik; 11-13-2005 at 10:24 AM.
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Old 11-13-2005, 01:57 PM
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I'm sorry. I'm afraid I didn't do a very good job of completing the picture. In my last post, I showed that, with a high rate right front spring, a majority of the weight transfer could be directed toward the right rear tire. But, why would anyonw want to do this? It's because, as you just pointed out, the driveshaft torque is trying to unload that right rear. Now, the weight transfer is proportional to the driveshaft torque, so, if you have the right proportion of left and right front spring rates (not the railroad car and watch springs I used in my fanciful description), it's possible to end up with equal rear tire loading during launch. (And, incidentally, the driveshaft reaction torque causes the front tire loading to also be equal.)

Again, I apologize for omitting the final step in the explanation.

(It's possible to calculate the proper spring rate ratio for a given car, but, as I think I indicated in an earlier post, a right front rate half again as large as the left front will get you pretty close, in most cases.)
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Old 11-13-2005, 06:03 PM
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Please read reply # 10 again carefully.

Like I asked......

How is a front spring going to prevent the body torque roll if the front wheels are off the ground....?????

If you have a logical simple answer I would like to hear it.

thanks
x
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Old 11-13-2005, 09:46 PM
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Logical and very simple: It can't.

But, if the car has been set up to provide equal rear tire loading up to the point that the fronts lift, who cares? Some have said that, once the fronts lift, you automatically have equal rear loading. Well, that's right up to a point. Certainly, with nothing for the rears to react against, the loading will eventually become equal, but it's that "eventually" which causes trouble. If the rears are unequally loaded as the fronts lift, the loading will bounce back and forth like a barefoot boy on a hot sidewalk. There's very little damping within the tire, itself. So, the goal in setting up a drag car is to provide equal rear tire loading with any value of driveshaft torque, which will prevent the "hot sidewalk" syndrome. And, yes, I've seen the pictures. A car with the front spring setup I've described will not do this, however, for the front tires will be equally loaded until the instant they lift.

I'm editing this to correct that last statement, which is definitely in error. While the front tire loading will remain equal, the chassis will certainly not remain on an even keel. The left front fender will be higher as the fronts lift and, indeed, this "twisting" of the chassis will be accentuated...not minimized...when springs of different rates are used. (Of course, the chassis is not actually twisting. The effect is only visual and would exist even if the chassis was infinitely stiff in torsion.)

Last edited by BillyShope; 11-14-2005 at 04:37 AM.
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