Hi Guys:

I Currently have a '55 Chevy Bel Air hardtop with a modified rear suspension that has QA1 coilovers and ladder bars that are mounted on the outside of the stock frame. They are mounted to a Ford 9" rear end with the upper bar about the middle of the axle and the lower bar 5.5 inches lower. My problem is that I don't like the ride I get, and the car does not handle, nor can I put any power to the ground. In light of the fact that I have just over 300 HP and a 2.73/1 rear end ratio this should not be the case. It may not have been set up, or tuned correctly, but I still want to switch to a Parallel 4 Bar suspension system. I have read that in order to get the Anti Squat correct that I should angle the Bars upward at the forward end. Because of body clearance the maximum I can get is about 1 1/4' up. If anyone has comments, questions, or sugggestions I sure would welcome them.

Chevy Guy

Ladder bars suck unlesss you have alot of HP.

With a parallel 4 bar the anti squat is neutral. So angling them up does little, if anything for traction.

A 4 link is what you want, if you want to tune your bars for more/less anti squat. The multiple mounting points let you adjust your instant center where ever you want..,and yes, the closer you get to the CG height of your car, the more anti squat you have. but remember, what you gain in acceleration traction, you lose in braking traction, and a car with alot of anti squat, will lift the rear wheels in heavy braking.

If you want the best of all worlds, for street use a 4 bar is fine. I just put a Jim Meyer 4 bar under a customers 56 chevy, with a zz4 motor and a set of 3.50 gears/ limited slip 9" ford rear, 2200 stall speed TQ, it hooked up really good.

I didn't try doing anything like them big time dragrace guys do, like powerbraking to the stall speed ...but in a slow rolling start, nail it and you get only a couple of tire chirps, the car squatted only slightly and got all it's power down to the pavement..

The customer was EXTREMELY pleased with the way the car handled and worked.

As you can see in the pics, the Jim Meyer setup has th eability to be set up as either a 4 bar or 4 link, merely by changing the forward mounting position of the bars.

in case you are wondering, the customer wanted the car to sit at the stock height when it was done. So that's why it isn't all low, like most of the folks want it done.. Meyer has an option to set it up high. There are several other mfgs making 4 bar kits as well as 4 link, and triangulated 4 bar sets for those cars.

Hope this helps, mikey

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Thanks for your reply; It was very appropriate as my car has a Jim Meyer suspension, brakes, etc all around. I had them install it in Lincoln City at their
plant. I had ordered a 4 Bar rear suspension, but they talked me into ladder
bars and installed them outside the frame because they didn't want to mess
with my exhaust system. I didn't mention that my car is only driven on the street and will never see the "Strip." I just want it to handle well and get the
power to the ground. JIM MEYER has said he will sell me some ladder bars and
make a pair of front brackets to weld on the outsice of the frame. My car has a rake to it and is about 4" higher in the rear than the front. The front cross
member is only about 4 3/4" off the ground.

Chevy Guy

The exhaust system was no easy task with the 4 bar, but it can be done and exit out the back.




Didyou mean four bars? I thought you said you already have the ladder bars.

If you can mount a set of four bars outside the rails , that'd work too. and you are already halfway there .


I liked Jim Meyer company...they guys I dealt with were very accomodating of all of the stuff we wanted to do and change around.


later, mikey

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You're right--I should have said Jim Meyer will sell me a 4 Bar set up with a pair of front brackets to weld onto the frame.

I take it by your answers that if I mount the Parallel Bars close to Parallel with the ground that my handling and hook up should be pretty good.

I was considering getting the top Bars made with right and left threads on the ends so I could make adjustments in other than 180 degree turns. Is that necessary, or is it ok to just have one end adjustable?

When they talk about the set up for the pinion angle being about 3 degrees upward is that from parallel to the ground or to the frame. My frame is NOT
parallel to the ground.

Thanks, Mert

The 4 bars all seem to work pretty good being close to parallel with the ground, within a few inches at the end up or down.

It would be easier to adjust with opposed threads on either end, but not totally necessary.

I take any recommendation for a static pinion angle with caution,, and instead set the angle up so that it aligns with the trans output shaft, and allow the correct additional angle for the suspension type .They don't know how the motor is set in, and a static 3* angle will only work if the motor is set in on 3 1/2*

(1/2 degree for "wrap up" is what I allow for urethane bushings and a 4 bar.)


Later, mikey

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That is slick, nice job!
I would like to see that set up under my Dakota.

Yes, you can adjust percent anti-squat with the 4bar suspension. With the 4bar, the percent anti-squat is determined by the angle. The 100% anti-squat line has a tangent (slope) equal to the center of gravity height divided by the wheelbase. Since parallel lines meet at infinity, you will have 100% anti-squat if the 4bar is set at that angle. If you want the rear end to rise on launch, the angle must be larger; to squat, smaller.

Further, the 4bar can be adjusted to provide perfect dynamic cancellation of the unloading of the right rear caused by the driveshaft torque. See page 19 of my site for an explanation and a spreadsheet.

The 4bar, in other words, can do everything that the 4link can do. I would only caution you, if you're buying a kit, to make certain that the components are beefy enough for your application.

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

I did not realize that a 4 bar can be set to provide anti squat like a 4 link, by angling the links upward.

From a few numbers plugged into your calculator, it does seem like you'd need a fairly steep angle to get high percent of anti squat from a 4 bar. It would seem that you'd need to do some cutting on the floorpan to get your front mounts in a position to achieve a good amount of anti squat in a lowered car. I notice that a 4 link can get the IC closer towards the CG , while still keeping the forward mounts in a somewhat low position.

If I understand your page correctly,(down a ways on the "getting started " section), it says that angling the 4 bars up can also increase roll oversteer, which may be undesirable for some drivers in street use.. Does the 4 link do this also?

Thanks, Mikey

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Thanks for your comments.

When you caution that I should be sure that the 4 Bar components are beefy enough for the job, how about 18" bars of 1" high strength seamless
tubing with 0.156 inch wall?

I would like to see if I could get the angle set for 100% anti squat, but I don't know how high my center of gravity is. My wheel base is 115" and my center of gravity is about 2 1/2" below stock. I have not been able to find the center of gravity of the stock '55 Chevy. I do know that the front of my
car weighs 2000 lbs and the rear is 1850 lbs.

Any Sugestions?

Mert Beebe

Billy's website has a cool calculator on page 31.

You do need some scales and a way of tilting the car up.

Mikey

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First, I appreciate your reaction to my post. I was afraid you'd be offended.

The instant center height affects the steering characteristics when cornering. If a line connecting the axle centerline to the IC is angled upwards from the rear, something called "roll oversteer" occurs. In addition, the shorter the suspension links, the more severe the roll oversteer. It's easy to visualize what's happening. As you turn left, the left side angle becomes more severe, pulling the left side of the axle housing forward. Meanwhile, the right side angle decreases, pushing the right side of the axle housing rearward. The result is that the axle tends to steer the rear of the car toward the outside of the turn. This is the same effect that might be encountered with a tail heavy car, hence the name "roll oversteer."

But, while the steering effect might be the same as with a tail heavy car, the dynamics are not the same. Roll oversteer doesn't produce any of the nasty stability problems. So, as long as the "different" steering inputs can be tolerated by the driver, there need be no fear of a "critical speed" or anything like that.

Yes, both 4link and 4bar can produce roll oversteer. Ladder bars, too.

There's a notion that the IC location relative to the center of gravity is of importance. I can understand, from an intuitive viewpoint, why it might be thought that an IC forward of the CG would help to raise the front of the car. Unfortunately, this is another of those cases where intuition fails us. If this were the case, a 4bar, which has the IC an infinite distance forward of the CG, would provide a violent blowover. Rather than IC location, the percent anti-squat is what's important. And, I believe all suspension software provides this information. Certainly, it's available with the spreadsheet at my site.

So, we can see that the advantage of the 4link is that it can provide high values of percent anti-squat while keeping the IC height low.

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

I like the wall, but not the diameter. If I were fabbing, I wouldn't go below 2 inch. But, I'm the cautious type and I don't believe this is an area where it's worthwhile to try and save a few ounces.



As has been pointed out, there is a method to determine CG height and I have a spreadsheet to help, but, quite frankly, I don't feel it necessary to pursue the matter to that extent. If you can estimate it within plus or minus 2 inches, that's probably good enough. You can play with the spreadsheet and I think you'll find out that you can be a bit off on CG height and it doesn't change suspension settings all that much.

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

No, Billy, I'm not offended at all, I am just trying to keep the bigger picture all together, and learn something from you.
Merton B had said in his initial post that the foward bar mounting position was limited by his body panels,(floor pan, I assume), but that he could go up with those mounts 1 1/2".

This is the case in many of these installations, as most guys don't want to cut thier floor pans. Many folks are concerned with installation costs and losing part of thier backseat is disturbing.
I believe that his installation would behave differently than a level car, as his car is raked 4" from front to back, which would put the CG height ,(and anti squat line), lower in relation to the rear axle.




I always understood that a 4 bar acted neutrally, possibly because when a company designs a frame with 4 bars or offers a 4 bar "kit", the front mounts are positioned so a guy does not have to cut into his floor pan. Obviously this restriction usually puts the bars fairly close to level with the ground, even with the upper bar mount centered on the front of the axle tube. So when the bars are installed in that fashion, don't they act neutrally?

On the spreadsheet you have on page 19 it shows the bar angles required to get them parallel with the 100% anti squat line, , but also it shows a different angle setup from side to side to cancel driveshaft torque. Is the average of those 2 angles what you'd want on a car with the same setting from side to side?

I did estimate that the CGH was about 20" when I entered the numbers I thought would be close, and got approximatly 13* on 1 side and 7* on the other.

I used 44" as the lateral width, because Merton said he was mounting the bars on the outside of the frame.

Thanks, Mikey

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my signature lines...not really directed at anyone in particular..

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I don't understand your meaning of "neutrally." If the 4bar is mounted horizontally, you'd have 0% anti-squat, meaning that the car would squat horribly on launch. For a street car, there's really nothing wrong with this, but it certainly wouldn't be desired for optimum dragstrip performance.

I appreciate the sheet metal clearance problem at the front and I might have included that as another advantage for the 4link. However, if the rear of the 4bar is mounted as low as possible (and practical), I think the higher percentage anti-squat values would be available without too much butchering. Unfortunately, the available kits might require a lot of rework.



If what you'd want is 100% anti-squat, yes. But, again, IF you can accommodate that large angle on the right side, the asymmetrical arrangement would be far better for dragracing.

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