adjustable panhard rods and roll centers

[Rodger]

As I understand it:

A new old Celica (that is back when they came from the factory), say a TA-22 or RA-23, had the Panhard bar angeling down from the drivers side to the centre of the diff housing on the passenger side. In other words not paraleel to the diff housing by design.

Most old Celicas springs have sagged and may result in a parallel panhard bar. This is indeed the beter set up. So lowering to this height is the desirable outcome by choice of spring.

If the whole bar is lowered at both ends below the diff centreline then indeed the roll centre is effected. A drop of 150mm would have a great effect on the roll center.

Regards

Rodger

[gixer]

Over the years I have spent alot of time researching roll centres with regards to panhard rods and watts links, basically with a watts link where it pivots on the diff housing will be the rear roll centre, with a panhard rod, where the rod cross the intersection of the axle centreline will be the roll centre, thus if you lower the panhard rod the roll centre will drop. The panhard on my ae86 has different mounting locations and a change in height alters the handling significantly as the roll centre is moved away or closer to the centre of gravity. If you change the distance from the roll centre to the centre of gravity(away from one another) this has the effect of softening the spring rate due to a longer leverage effect.

[gixer]

If you look at the pictures GIANTTOMATO posted up it's quite obvious that a change of panhard rod will change the rollcentre. Point A will be at a different height which then affects the height of the roll centre as it intersect the axle centre line.

[Rodger]

A quote from Heb Adams, book "Chassis Engineering" HP Books

Chapter 9 Live Axle Rear Suspension design:

"The roll centre of a rear suspension that uses a Panhard bar is at the height where the bar attaches to the axle. A lower roll centre at the rear makes a car handle more consistantly, so I recommend mounting the bar as low as possible."page 62

Herb also describes a Watt's Linkage. The roll centre height is at the main pivot point.

Most V8 Supercars and racing sedans run an adjustable Watt's Linkage rear. Rear roll centre adjustments in the V8s for example, can be made by the pit crew by turning an external adjusting nut/rod during pit stops, moving the main pivot point up or down.

I plan to run a Watt's Linkage in the rear of my Celica and make it on a mount which will allow me to adjust the roll centre by selecting the bolt hole on the mount to set the height.

Regards

Rodger

[Celica RA45]

to begin with the car has been lowered and the panhard was level before i decided to lower it more and the car is more of a race car than daily driver as it has only club rego or ch plates .daves pics are handy but they show the trailing arms going into each other ,which isnt what a ra45 celica is same as a 40 series so it would be interesting to see the tangent lines crossing into each other then working it all out ,im going to the island in 2 weeks so i will drop it down 1 size at a time to see how the car handles ,hopefully it will stop braking traction on accelerating through honda and out of mg corner ,thanks for all the replys

[Cool1]

Here you go ladies, some of Glens pictures

[RobertoX]

^^ top work! Does this get rid of that horrible 'jacking' you sometimes get? like when the outside wheel feels like it is trying to push the rear end up... this is one thing that really shits me about sprinters and corollas that i've pushed.

by the way how rigid is the new mount on the axle? its a little hard to see but does the sheet with the bolt holes that is closest to the diff have a box section behind it?

[Celica RA45]

the 1 on the left is welded onto the bango with a gusset to give it strength under the original pick up so i can still use it . the 1 on the right bolts through the existing hole and we have drilled higher up onto the left of the original hole and put in a peace of pipe and new long bolt so it wont move and its very strong and it can come out if i dont wont it there

[Celica RA45]

actually you see some pics of the car at winton that i was running with my mate steve in the ke25 corolla go to www.holdenclub.com/ then move down to see the 1st round at winton click on the pics scroll down you wont miss it steve beat me on the day as i was trying different things mainly trying to find the right diff ratio and rear bar changes as well as wheels

[RobertoX]

is it the white ra40 with the meridian motorsport sticker?

[gianttomato]

Glenn Celica, Steve KE25.

Nice low panhard rod dude.

[RobertoX]

^^thanks,
the one with the 'beams' 3sge eh? looks awesome!
also nice looking brake setup with bias bar

[Wezelton]

I must say very impressive work, how low do the new brackets sit towards the ground ? looks metal low hey. I would be keen to look into this but im starting with new sway bars all round.

Is it rose jointed at only one end ? I was thinking a adjustable panhard rod would do enough but reading this is making me more curious. Greats pics too!

Wes.

[JustenGT8]

I guess there's the text book case and then what you can do in reality. From the numbers i crunched playing around with the 3SGTE TA22 there was no gain in lower roll centre i could get from moving the panard rod that didn't stuff up something else. The roll center would end up in bizzare places, sometime outside of the body line of the car. The only 'real' way i could get a benefit was with a wob link and that just wasn't practical for a street car.

Getting the panard rod parallel has benefits and get an adjustable one so you can recentre the diff but that's as much effort as i would go to.

[RobertoX]

Justen, just out of interest, how did you crunch the numbers? Did you use a software package, speradsheet, matlab or code in some other language?
Did you use a kinematic model or equations found in text books?

Cheers rob