double or single

[CIGARETTEDFL]

here's a subject, I would like some input on from you chassis experts.
I have a back half door car, bracket entry, with ladder bars, car runs 9.70's with low 1.3's 60 ft times. I guess maybe front to rear weight ratio is important so, its 55 percent on the front.
my question is would it be worth changing the rear shocks from a single adjustable Strange coil over to lets say Afco double adjustables?
Presently the shocks must be set at about 80 percent stiff on extension to keep the tire from wadding up.
I really dont mind buying something that helps that I can see on a et slip, but obviously I dont like throwing money away either.
Let me know what your thoughts are
Thanks

[Speedy Goomba]

I put afco double adjustabled on my low 11 second, small tire camaro, everyone told me i was out of my mind.

Not only did i find ET, but i was capable of dialing in my suspension like no single adjustable would allow, it turned a moderately well working car into a car that worked fantastically, and hooks All the time! bald spots, cold tracks, hot tracks!

[CIGARETTEDFL]

Thanks Speedy for your input.
I really dont have any traction issues, the car always hooks and is very consistant. I just dont understand how having a compression adjustment on it can help. maybe there's something I'm missing on the the basics of a double adj. shock. or maybe it's a mind thing

[CIGARETTEDFL]

TTT

[BillyShope]

Personally, I'd remove rear shocks and springs from consideration entirely. What I'm getting at is that, if you adjust your ladder bars so that the car neither squats nor rises, the rear shocks and springs are just going along for the ride. And, you no longer have the rear of the car bobbing up and down as you're trying to get traction.

You can't keep the front of the car from rising, of course, so it's there that you can play some tricks with shocks and springs.

http://home.earthlink.net/~whshope

[Ed-vancedEngines]

As usual Mr Billy and I will slightly disagree.

I do think that one of the better suspension improvements is in going to a good quality double adjustable shock.

I will agree with him that if you are having to use an 80% extension force adjustment that you might look at changing either the front bar pivot position to one hole further down or maybe try just lowering the ride ht, which will in effect be like making a minor bar adjustment. In your case I would favor dropping the front pivot mounting point by one hole, but I do not know how far that could be.

I like the compression forces of a shock in a drag race car to be minimal and enough to not bottom out the suspension. That will give a smoother ride and will also help your tires to stay in contact with pavement.

With any single adjustable you are changing both extension and rebound to be the same amount of stiffness or softness when making adjustments. If you are running at 80% stiff, I can almst bet you that at some point your tires are breaking surface contact.

With any suspension part of both front and rear remember that you are trying to control the car (Sprung weight) and the weight below the shock or springs such as complete rear end, or complete front suspension including tire weight, (Unsprung weight).

I like the Strange Double adjustables. I have no experience with the Afco, but they have a good reputation, and this year the quality control of Koni has seemd to be OUT To LUNCH. I have also heard not good things about the Hal but do not know for fact.

Ed

[CIGARETTEDFL]

Thanks Ed, I thought that single adj shocks, when changing the setting, it only changed the extention and not the compression or at least very little.
I have tried moving the front mount down one hole and it seemed to take most all of the hit out of the lauch, so much that it was lazy leaving, and 60's were not consistant. now if it's true, when adjusting the setting it changes both the rebound and compression equally, I could understand the need for double adjustable shocks.

[Ed-vancedEngines]

After you move the bar down, begin again by taking most of the stiff adjusting from the shocks.

How far apart are the hole centers in your front brackets?

Remember that moving the rear ride ht up or down is like a minor bar adjustment.

Also: Always check and re-adjust pinion angle when you move the bars.

Another thing, Changing tire diameter is also like making a bar adjustment sorta.

Ed

[BillyShope]

You simply cannot have oscillatory loading of the driving wheels and, at the same time, expect maximum tractive effort. If the rear of the car rises on launch, the initial effect is added loading to the rear tires, but, as the rear nears its uppermost position, loading is removed. If the rear of the car squats, the opposite occurs. Unfortunately, the net effect is less than zero. An oscillatory loading is ALWAYS detrimental. The oscillatory loading yields an effect similar to two tires; one loaded at a value higher than the average and the other lower. But, we know that a tire pair yields maximum performance when they are equally loaded. Oscillatory loading...rise or squat, in this case...is to be avoided.

And, if the car neither squats nor rises, the shocks and springs...as stated earlier...are just going along for the ride. They're neither compressed nor extended and, therefore, their performance is inconsequential.

[Ed-vancedEngines]

Guess what Mr Billy,
I am almost agreeing with you this time, but not completely.

Ideally in my opion (?)
The rear tires will see an increased laod at time of hit on launch but will gradually keep seeing a load on them all through the gear until gear change. Then the process starts all over again and a steady force should be exerted on the rear tires, from suspension action at launch and at gear change.

If the rear has an instant, radical upward movement on launch, This is what we used to call chassis separation, I will agree that the suspension action will stop just as abruptly and can result in the rear tire being unloaded.

The trick is to balance the forces so that the car does see an additional load placed on the rear tires, while at the same time, not physically showing a major change in the rear suspension action by looking at the rear fenders vs tire or wheel. here are a lot of variables that also come into play.

If you will watch the really quick cars it looks almost like the rear suspension is not changing much. Things happen faster than the eye can see when those cars are launching but you will not see the rear of the car jumping up 4 or more inches.

I do respect Mr Billy very much and he is very sharp with years of education and experience. We do disagree though from time to time. I am usually dealing with very high horsepower cars.

Ed

[BillyShope]

.
The rear tires will see an increased laod at time of hit on launch but will gradually keep seeing a load on them all through the gear until gear change.

Ed, I'm afraid you're confusing the effects of two inertial forces. The forward thrust provided by the rear tires results in an inertial force in a direction opposite to that of the acceleration. It is this force which provides that which we call "weight transfer." The two horizontal forces...acting at the tire patch and at the height of the center of gravity...produce a couple (torque) which is balanced by two vertical forces; one unloading the front tires and the other loading the rear tires. As long as the car is accelerating forward, the rear tires will experience a load increase.

If the car squats or rises, there are additional inertial forces acting in the vertical direction. Unlike the horizontal inertial force from forward acceleration (which has an effect on rear tire loading as you describe in the sentence I quoted above), these vertical inertial forces are of short time duration and are oscillatory. If the rear of the car rises, it is first accelerated in an upward direction. The inertial force...always acting in a direction opposite to that of the acceleration...increases the loading on the rear tires. But, as the rear of the car approaches its maximum upward position, the acceleration...and the resultant inertial force...reverse direction and unload the rear tires. Since this oscillatory motion is quickly damped, the first effect (the additional loading of the rear tires) would be the greater.

If the rear of the car squats, the first (greater) effect is an unloading of the rear tires. What I'm afraid you're describing as a "hit" occurs as the acceleration direction reverses as the rear of the car approaces its lowest point. This is where our eyes deceive us. We can "see" the loading of the tires during the "hit," , but we cannot "see" the first...and greater...effect when the rear of the car is initially accelerated downward.

So, if one was forced to accept either squat or rise, he'd want rise. But, as I've already explained, tire test data indicates either squat or rise is to be avoided for maximum tire performance.

Summing up, the rear tire loading is increased so long as the car is accelerating forward, but, when it comes to squat or rise, loading is unaffected as soon as the car settles into its final position. (This is avoiding the matter of a very slight increase in CG height with rise.)

[RyonPro1]

Billy, I'm not sure I'm totally understanding what your trying to say. I agree that keeping the car neutral is best. BUT, I don't understand by you saying then the shocks and springs are just going for a ride. I have never seen a run on my D.A. that show the shocks not moving? There will always be movement in the suspension up and down. Is this what you are referring to, or am I missing something?

Shawn

[BillyShope]

Billy, I'm not sure I'm totally understanding what your trying to say. I agree that keeping the car neutral is best. BUT, I don't understand by you saying then the shocks and springs are just going for a ride. I have never seen a run on my D.A. that show the shocks not moving? There will always be movement in the suspension up and down. Is this what you are referring to, or am I missing something?

Shawn

Irregularities in the track surface will always be present and will always result in some deflection of the shock/spring. I was referring to that deflection which results when the suspension instant center is not on the no squat/no rise line (100% anti-squat). If the track surface is at all decent, the small deflections should not seriously affect the tire loadings. So, IF the track surface is perfectly smooth and IF the instant center is on the no squat/no rise line, there would be no deflection of the shock/spring and they would just be "going along for the ride." Sorry about the confusion.

[rooster]

your "flatline" car is fine as long as there is an infinite amount of traction available. Agreed, the goal is to transmit the maximum amount of the rear tires rotational force into a horizontal vector force to efficiently propel the car, albeit within the capabilities of the tires. Temporarily trading some of the horizontal component for a limited vertical component is an effective means to help overcome the maximum inertia. Increasing the downward force on the tires increases traction and allows the application of more power than would otherwise be possible. As inertia is overcome, the vertical force diminishes and the horizontal force is maximized. The shocks are necessary to dampen the rate at which the vector force direction change takes place.

[CIGARETTEDFL]

getting back to the original questions, what advantange would I see in a double adj shock?
Ed you stated that on a single adj shock by tightning the rebound, it has the same effect on the compression is that true?
I have a video of the car lauching on my hard drive, I am trying to figure out how to edit a segment of the video and link it so you guys can determine if any advantages are to be had. so far havent had any luck in doing that.