4 Link System - Step by Step

[Mike Peters]

I'll move up the rear pivot of the lower bar, reduce the IC for the almost 55...60% (against the 85% of my car)

Not sure if that's the right move in your case my friend. Since you don't have the huge massive amounts of torque to use to transfer weight to the rear of the car, your best approach might be to increase the anti-squat percentage to leverage the tires into the track for more traction. Does that make sense? A short I/C that is actually behind the anti-squat line might work very well for your car and those street tires. This geometry will try to raise the rear of the car as well as push the rear end housing into the track so, the good shocks will help you in controlling the rate of body/tire separation. Also, increasing the "bar spreads" or distance between the upper and lower mounting points can be used to strike the tires harder. Read Patrick Budd's article very carefully to understand the effects of bar spreads. Further away strikes the tires harder but, you lose leverage of pulling on the chassis as the car starts rolling. Once again, since you don't have massive amounts of torque, the wider bar spreads might give the instant strike to hook your street tires. Lower bar angle may not be as crucial in your car due to, once again, low engine torque. You may not experience the "roll steer" the higher horsepower cars do when the rear end housing wants to drive over or under the chassi mounting point of the lower link.

Now, the question is: How about the assimetrical bars spread for my case?

Once again, not sure how well the asymmetrical set-up would work for you. I've been thinking about this and am not sure this would be a good approach for you since you have upper and lower suspension links of different lengths. This could cause binding as the housing goes through it's arc of travel. If you did ever decide to try this approach, remove the shocks and test the housing movement while the car is suspended off the ground.

[Bruce69Camaro]

Hey Jeff,

Got an idea for you, just promise Mike some fried green beans and ranch dressing and get him a plane ticket, and I"m sure he'll be happy to fly down to give you a hand setting things up....

One thing I was told to ask you, you do have a copy of the Doorslammers book don't you?

Stay warm my friend.

Bruce

[Jeff 4100]

Hey Jeff,

Got an idea for you, just promise Mike some fried green beans and ranch dressing and get him a plane ticket, and I"m sure he'll be happy to fly down to give you a hand setting things up....

Owwww Bruce...I forgot to ask Mike about it...

One thing I was told to ask you, you do have a copy of the Doorslammers book don't you?

Yes, I do!! Dave autographed a book for me!!! I bought the DVD's too...Now I'm starting the 2nd DVD...

But, would be fine if I will be able to join the Yellow Dot personally with Dave...I'd like to go in the end of this year...Its my Dream that I promised to myself for 2010!!!

Stay warm my friend.

[/quote]
I try to be fine everyday...but since I knew the Dragstuff Friends I can not sleep normally anymore...

Thanks

[Jeff 4100]

Since you don't have the huge massive amounts of torque to use to transfer weight to the rear of the car, your best approach might be to increase the anti-squat percentage to leverage the tires into the track for more traction..

Mike,
We had the race on this weekend. I couldn't go there, but my friend (the 2nd car that I build last year) ran there. He called me by the phone to say that his car was with the tires slipping a lot. His 60 feet time was horrible. In addition to, the track was not good too...The car's handling was just over the pedal...the car was not hooking down the track...

His bar spread is different than mine. Look below.
Second the Budd's article, I think the lower bar position helps to the car body to separate from the axle centerline because its flatter position...it compromised hook.
Its a thing that I think that could be improved...
What could be done to keep the tires loaded for a more time??
How about the upper bars??
Thanks,

[Mike Peters]

He called me by the phone to say that his car was with the tires slipping a lot. His 60 feet time was horrible. In addition to, the track was not good too...

If the track is not good, it will be very hard for you to learn anything.

His bar spread is different than mine. Look below.

That geometry looks wrong. If you want to see the effects of loading the tires harder, move the rear of the lower bar down to the bottom hole and raise the rear of the upper bar to the top hole.

Second the Budd's article, I think the lower bar position helps to the car body to separate from the axle centerline because its flatter position...it compromised hook.

Yes, the lower bar position does influence the ability of the body and axle centerline to separate. If the bar is lower in the rear, that would move the I/C towards the rear of the car and separate easier. The reason Patrick wants the lower bar level is because the high horsepower cars can have handling problems. I don't think you're making enough horsepower to experience this problem so, I think you could move the lower bar down on the housing.

What could be done to keep the tires loaded for a more time??

The shorter I/C I'm describing should load the tires more. Plus, have you guys moved all the weight of the car towards the rear that you can? Have you made the front end of the car as light as you can?

How about the upper bars??

Raise the rear of the upper bars to the top hole on the housing. Again, this will shorten your I/C and will create more separation of the body and axle centerline therefore creating more leverage to drive the tires into the track. Keep weight in the rear of the car so resistance is created to prevent only the body from moving upward.

[Jeff 4100]

If you want to see the effects of loading the tires harder, move the rear of the lower bar down to the bottom hole and raise the rear of the upper bar to the top hole.

Thanks Mike!!
Here we'll go!!!

[BillyShope]

Looks good, Jeff. Very close to 100% antisquat. There's another combination, though, at about 65 inches forward, which will give you the same performance and be affected less by ride height changes. You might consider it.
http://www.racetec.cc/shope

[BillyShope]

Jeff, I suppose there's some distortion when I print the picture you posted, but it looks like that forward point would involve placing the fronts of both upper and lower links in the top hole, the rear of the upper link in the bottom hole, and the rear of the lower link in the second hole from the top.

Try those settings in your 4link software and see what you get for antisquat. Also, lower the front points 1 inch and run the program again to see how much the antisquat is affected by ride height. Then, do the same for the link locations you posted. If the software won't allow you to do that, use Page 13 at my site.
http://www.racetec.cc/shope

[Jeff 4100]

Jeff, I suppose there's some distortion when I print the picture you posted, but it looks like that forward point would involve placing the fronts of both upper and lower links in the top hole, the rear of the upper link in the bottom hole, and the rear of the lower link in the second hole from the top.

Bill, check if If understood you...

Try those settings in your 4link software and see what you get for antisquat. Also, lower the front points 1 inch and run the program again to see how much the antisquat is affected by ride height. Then, do the same for the link locations you posted. If the software won't allow you to do that, use Page 13 at my site.
http://www.racetec.cc/shope

Check it 1 inch lower.


Considering the Mike's suggestion 1 inch lower.

And then?

[BillyShope]

I was trying to hit that cross just to the left. It's closer to 100% antisquat. Looks like the rear pivot for the bottom link needs to be in the bottom hole and the front pivot for the same link needs to be in the middle hole.

But, the important thing I wanted to show you is still there. That 1 inch ride height difference made more of a difference in antisquat with the instant center closer to the rear axle. Yes, it's only a slight difference. It would have been much greater if we could have hit that other cross.
http://www.racetec.cc/shope

[BillyShope]

Here's a post of mine from another forum. Thought it might clear up the questions some of you have:

I'm tired of waiting. Let's bust some more myths! Specifically, these 3:

* Lower link angle is, in itself, significant.
* 4link spread affects weight transfer.
* Instant center distance forward is, in itself, significant.


Consider a competition 4link. To simplify the calculations, rear pivot points will always be directly above or below the axle centerline.

"Out" will always be the horizontal distance forward from the axle centerline and "up" will always be the vertical distance from the strip surface.

The lower link is 6 inches up and is horizontal.

The rear pivot for the upper link is 20 inches up.

The instant center is 50 inches out, which means that, since the lower link is horizontal, it is 6 inches up.

The thrust (horizontal force) at the rear tire patch is 3000 pounds.

The lower link would be in compression and the upper link in tension.

The slope of the upper link is 6 minus 20 over 50 or minus 0.28 . This means that the vertical force component, acting in the upper link, would be 0.28 times the horizontal force component. Since the lower link is horizontal, this would be the only vertical force acting against the vertical force at the tire patch. In other words, this would be the total weight transfer carried through the links.

For a horizontal force balance, the horizontal force carried through the lower link, less the horizontal force in the upper link, must equal 3000 pounds. For a moment balance, 6 times the lower link horizontal force must equal 20 times the upper link horizontal force. This gives us 2 equations and 2 unknowns. Solving, we get an upper horizontal force of 1286 pounds tension and a lower horizontal force of 4286 pounds compression.

So, the weight transfer carried through the links is 0.28 times 1286 or 360 pounds.

Now, we'll discard that lower link and install a new link above the upper link. In other words, what was the upper link is now the lower link. This new link has a rear pivot which is 100 inches up. No, it can't be built, but it CAN be calculated and the results will be interesting. Since the instant center is still 50 inches out and 6 inches up, the slope of this new link will be 6 minus 100 over 50 or minus 1.88 .

Total vertical forces will now be 1.88 times the upper link horizontal force downward less 0.28 times the lower link horizontal force upward.

The horizontal force balance remains the same, but the moment balance is now 20 times the lower link horizontal force less 100 times the upper link horizontal force. Solving, we get an upper horizontal force of 750 pounds and a lower horizontal force of 3750 pounds.

So, the weight transfer carried through the links is 1.88 times 750 minus 0.28 times 3750 or 360 pounds. That number sounds familiar, doesn't it?

But, we're not finished. A line through the tire patch and the instant center is a line of constant percent antisquat. So, let's move the instant center out along that line. We'll move it to 500 inches out, which would mean that it would be 60 inches up. We'll return to the original link arrangement: A lower lower link with a rear pivot 6 inches up and an upper link with a rear pivot 20 inches up.

But, for the link lines to intersect at the new instant center, the slopes have greatly changed. The slope of the upper link is 60 minus 20 over 500 or 0.08 . The slope of the lower link is 60 minus 6 over 500 or 0.108 .

Total vertical forces will now be 0.108 times the lower link horizontal force downward less 0.08 times the upper link horizontal force upward.

The moment balance is as it was for the first case: 6 times the lower link horizontal force must equal 20 times the upper link horizontal force. Not surprisingly, the horizontal forces are the same as in the first case: 1286 pounds tension in the upper link and 4286 pounds compression in the lower link.

So, the vertical force is 0.108 times 4286 pounds downward less 0.08 times 1286 pounds upward or 360 (there's that number again!) downward.

So, the weight transfer carried through the links is the same regardless of extreme changes in lower link angle, 4link spread, or distance out to the instant center SO LONG AS the antisquat percentage remains unchanged.
http://www.racetec.cc/shope

[Jeff 4100]

That geometry looks wrong. If you want to see the effects of loading the tires harder, move the rear of the lower bar down to the bottom hole and raise the rear of the upper bar to the top hole.

My Buddy,

I came back to the GM Opala Project because we will have a race on this weekend...My friend will run on it and I changed the 4 link setup based what you said above.

But the question now is: Our Buddy Dave Morgan said on his article on the Dragzine about the correct angle for the powertrain.

But on our car the engine is on 7° and the driveshaft is on 0°. What would be the best position for the rear housing??

The engine angle is too higher...I don't know If I can apply that concept on it...

Thanks!

[Mike Peters]

Jeff,

Pinion angle is always a topic that many disagree on. Here is a link to the method I think is correct -

http://www.rosslertrans.com/Pinion%20angle.htm

[bracketracer]

Jeff, I may be wrong (I don't think it will be the first time ) but I would try and set the rear so when it's under power the shaft and pinion angle are straight or close to it...

Can you drop the engine in the frame??? Even if you can get it down some like an inch or two should help some..

Can you get some pic's from the side that shows the tailshaft/rear pinion??

[Jeff 4100]

Jeff,

Pinion angle is always a topic that many disagree on. Here is a link to the method I think is correct -

http://www.rosslertrans.com/Pinion%20angle.htm

Thanks Mike!


Considering this method, I can't do this...

The best way for me would be to change the engine angle...but the rules do not allow us it...
For now, the chance will be to test the new bars spread...tomorrow the race begins.

Good luck for us!!!