rear panhard height w/ truck arms

[redss86]

Ok, I need you guys opinions on my setup right now before I weld the frame bracket in completely.

I am setting up a truck arm setup in my 86 Monte Carlo SS and want to know if the phb height I currently have will work good or not. For the front I am going w/ SCandC's Stage 2 setup, for those that are familiar w/ it. I am planning runnig the car 2" lower in the front and approximately 1.5" lower in the rear. The rear will be adjustable by means of screw jacks coming into the trunk, and the phb is adjustable on both ends. I know you want the phb to be level so here are the demensions I currently have:

Rear Axle Height= 13"
Virtual Intersect Point= Approx. 70" in front of axle CL
Virtual Intersect Height= 7"
Arm Angle= 0*
Frame Angle= 2* down in front
Min. PHB Height @0*= 9.5"
Max. PHB Height @0*= 11.5"
Min. PHB Height= 8.75" w/ 4* up on Rt(frame mount)
Max PHB Height= 13.5" w/ 4* up on Rt(frame mount)
9097

9098

9099

9100

Here are some pics of the PHB mounts and rearend setup. The rearend and frame are at ride height. I also included a pic of the truck arm mounts since they too are adjustable. The phb mock up in the first pic is at the lowest possible height.

Any and all help is appreciated
Thanks in advance,
Joe

[sinned]

Looks good Joe. I see no problems with your layout.

[baz67]

It is hard to figure out exactly what you are asking on our opinions. It really depends on how you are going to use your car.

The way it looks to me is you will have some roll understeer getting worse as you go from your lowest PHB level to the highest. I gather that by your forward lateral restraint point at 7" and your rear at 9.5-11.5. In a perfect world you would want those two points at the same height for zero roll steer. However, you have the lesser of two evils with the roll understeer. Your SVSA is about right at 70".

[redss86]

It is hard to figure out exactly what you are asking on our opinions. It really depends on how you are going to use your car.

The way it looks to me is you will have some roll understeer getting worse as you go from your lowest PHB level to the highest. I gather that by your forward lateral restraint point at 7" and your rear at 9.5-11.5. In a perfect world you would want those two points at the same height for zero roll steer. However, you have the lesser of two evils with the roll understeer. Your SVSA is about right at 70".
So, in other words I would have a slight push through cornering, correct? I could make the frame mount lower but I was afraid it would be two low.

https://www.pro-touring.com/forum/showthread.php?t=7840

This is the information I used to setup where it is currently at. As far as what I am wanting on opinions goes, I just want to know how you guys think this setup will handle. I am going to use the car primarily as a street driver, w/ the occasional trip to the track and the strip.

Thanks, Joe

[sinned]

Your good Joe, don't worry about the minor roll under steer. Although zero roll steer is what most shoot for under steer is always better than over steer and nothing is ever perfect in a dynamic environment.

[redss86]

What about having the phb at an angle? Or should I keep it level at ride height?

[baz67]

level at ride height

[Norm Peterson]

You want just enough roll understeer to ensure that bushing and bracket compliances and other effects do not give you a net result of the rear axle rotating into oversteer. Somewhere in the neighborhood of 3% roll U/S should be about right, although another percent or so wouldn't be a deal-breaker (but 7% probably would be). Working that U/S number back from the SVIC to the PHB location would put its elevation in the 9.25" - 9.5" range. That's for the static ride height.

You'll probably want to run a few numbers to see what happens to the roll understeer as ride height varies. Keep in mind that the PHB rises and falls slightly during roll. And under the pitch motion caused by acceleration, the roll U/S % will tend to drop.

Ditto on keeping it level at static ride height, which for the picky, would be with at least the driver on board. That's unless there's some oval-track running envisioned (as an example, the Seekonk track puts on spectator drag races around their smallish oval, so I can see this as being an entirely possible situation), in which case a little tinkering with PHB inclination could help.

Norm

[redss86]

How do you figure the actual roll u/s percentage? If it makes any difference, I am using the arms w/ the monoball setup, and the shock, and phb will have heim joints for mounts. I know I will probably get quite a bit of nvh w/ this setup but I can deal w/ that.

Thanks again,
Joe

[Norm Peterson]

It's the slope as seen in side view of a line drawn between the PHB at the chassis centerline (assuming that the PHB is itself centered) and the virtual intersection of the truckarms. Roll U/S exists when the PHB point is at a higher elevation than the virtual truckarm point.

A 3% slope over the ~75" - 80" between your virtual truckarm intersection and the PHB represents 2.25" - 2.4" that the PHB point should be above the (7") truckarm intersection height.

I think the differences between a monoball and a compliant bushing arrangement boil down to the effective truckarm intersection with bushings lying slightly further forward than the geometric construction suggests. This would tend to reduce the roll U/S % a little, and add in some compliance steer as unequal rear tire longitudinal loads will deform the bushings asymmetrically (read: axle steer). Bottom line is that you should be able to run a little less U/S % with the monoball arrangement than with an otherwise identical compliant bushing setup, though you're relying more heavily on the truckarms' torsional and lateral bending flexibility to accommodate roll.

Norm

[redss86]

I think I am going to make my frame mount a little lower so I can be closer to the 2% u/s at both the lower and upper front mounts. I will still have plenty of movement above and below if needed.

[redss86]

Ok, so I dropped my frame mount down 2". This gives me an adjustment range from 8.25"- 11.75". From my figuring, 2% roll u/s puts the phb at 9.68", which is right in the middle of my adjustability.

This should be a good location, correct?