adjustable panhard rods and roll centers

[Celica RA45]

on panhard rods that are std on ta23 celicas and sponters and ke70 corollas as they are level on these cars ,i now thats the roll center height ,but if you dropped the panhard down with new brackets say 150mm lower than std height will this now be the roll center

[mrshin]

This is a good question... It works on cars with a watts link (e.g. old Alfa's), but being well past my bedtime I can't quite my head around it all enough to work out if it would work with a panhard bar.

[gianttomato]

It should do Glenn.

But I thought the ideal was to keep the Panhard rod level. This keeps the Panhard rod moving through the "flattest" portion of its arc, thereby locating the diff more evenly thru the usual range of suspension movement (ie less sideways movement).

[Celica RA45]

its still level but 150mm lower have welded new bracket s to both ends

[JustenGT8]

Nope, panard rod geometry is very very simple and roll center stays at the axle line in terms of height no matter where the panard rod sits. I'm 90% sure that's the same with a watts linkage as well. These two are just means to keep the diff laterally fixed, with the watts a better design as the diff stays central thru suspension movement wheras the panard rod causes the diff to 'walk' slightly.

The only way i know of to lower roll center on a live axle is with a Wob link and that's not a practical way to go on a street car as to get any worthwhile gains you loose too much ground clearance.

Just lower your centre of gravity by lowering the car and use RCAs on the front to keep the front/rear roll centre matched. Best you'll do and more than enough for a street/casual track car.

[takai]

Ah, welcome to the forums Justen, and you are very right, both the Watts linkage and Panhard rod setups will still result in the rollcenter being along the axle line.

The Wob link will lower the roll center somewhat, but im not entirely sure how much though, some tricky maths could figure it out im sure.

Oh yeah, and Glenns (CelicaRA45) car is no street/casual track car. Needless to say i think he is probably already thinking abou ta Wob link now.

[Norbie]

Hey Justen, you got any info on the Wob link? I tried Google without much joy.

[Celica RA45]

so you guys are saying that by moving it down say 150mm lower than the diff ,it wont make any difference to the roll center at all ,you sure about this

[takai]

Yes, because, as i understand it, the main suspension pickup points (i.e. your pivot links) are still mounted to the diff, and the rollcenter is a spline between these points.
The panhard rod is only used to laterally locate the diff. So the roll center may change laterally a few mm or so with the panhard rod lowered, but not what you want.

[gianttomato]

I have gone back to my basic book, "How to make your car handle" by Fred Punh, just to be sure. Here is an image scanned from said book.



For all intents and purposes this is very similar (if not identical) to a 40 series Celica. I can't remember if the RA45 has two upper trailing arms or just the one. The roll centre is, in part, determined by the height of the panhard rod at the midline (ie point A). If the whole Panhard rod is lower, point A will be lower. Seeing as the roll centre is determined as the point where a line from point A to point B crosses the vertical plane of the axle centreline, the roll centre can only be lower if point A is lower.

Or have I got it horribly wrong?

[Hen]

Just from reading GTs scanning above, it seems like lowering the entire panhard rod will lower the roll centre significantly.

Hen

[AE86slut]

Hey Justen, you got any info on the Wob link? I tried Google without much joy.

Stands for James Watt (surprise surprise), Maurice Olley, and Donald Bastow




These are great for checking out the different types of designs in detail

http://www.susprog.com/susptype.htm

http://www.bevenyoung.com.au/config.html


For the ultimate in craziness, check out the 'Mumford' link

[AE86slut]

May be a dumb question, but with a rear and that has parallel trailing arms, how do you determine the intersection point (B)???

*waits to crawl under rock after hearing obvious answer*

[LeeRoy]

I'm a little confused as to what the main point of this thread is but this is how i am understanding it. Obviously we are talking about lowering a car and this now changing the rear geometry including the roll center - which i think is meaning the panhard rod's pivoting point. Ive got a little drawing i made up that may make it easier in understanding what i'm trying to say.

In this the blue lines are panhard rods with the two black rectangles resembling tyres. Ive put the circle in there to show travelling path of the rod.
Now the image on the left is one of a car with a panhard rod level with the diff (or close to it) and the image on the right is of a panhard rod thet isn't level with the diff which can be achieved by lowering the chassis mount or lowering the car making the diff closer to the chassis.
The smaller images below are zoomed to show the path of travel respectively.
A is the up and down suspension travel with the curved line being its path, and B is the lateral or side to side movement.
Now assuming the same travel on the A axis occurs in both scenarios, the length of lateral travel or B is the difference.
Now by making the parhard rod more parallel to the diff, the axis which it moves on becomes closer to the diff, and then the amound of lateral movement or B can be reduced.
In conclusion, a pivoting point closer to the diff lowers lateral (or side to side) diff movement.

Btw i'm not too great with the drawing software
- LeeRoy

[AE86slut]

Nice one LeeRoy. It couldn't be explained any easier I don't think!