Watts link pivot mounting

[chevy34]

Can any one help me with why its better to mount the watt's link centre pivot off the chassis rather than the axle housing?

I understand roll centres and the afect raising and lowering has on handling I am in the process of building a touring car similar to a V8 Supercar and at this stage have the pivot mounted off the axle housing. I have just got my hands on a V8 supercar watt's link setup that mounts to the chassis and has the screew type adjuster and have been told that this is the prefered option but I cant get a straight answer on why its better to have the piviot on the chassis.

[1200Datto27]

It's much easier to make it adjustable when it's chassis mounted, compared to a diff mounted unit.

[coln72]

Constant roll centre height when mounted to chassis?? Think the roll centre would be constantly moving up and down with the diff the other way making things a bit iffy but I'm no expert

[johnny yuma]

Unsprung weight ?

[chevy34]

The adjustibality reason is the main reson why we are goining to the V8 Supercar watt's link I have read that putting the pivot on the chassis keeps the roll centre constant with the centre of gravity.
Is this the reason why it is better mounted to the chassis if so what effect does it have on the handling?

[coln72]

The roll centre adjustment alters the balance of the car. If the pivot is mounted to the diff, the cars balance will alter with suspension movement.

[Lukin]

It might not be physically possible, but it would probably be an interesting, and perhaps beneficial, characteristic.

Under brakes the rear rises and RRC gets higher and helps the car turn. As you drive off the corner the rear goes into compression, the RRC gets lower and helps the driver.

Perfect!

[coln72]

All I know is that Johnson's "Greens Tuff" Falcon handled like a box until they swapped the mount from the diff to the body.

[chevy34]

Chears guys I was wondering if it was to do with the pitch off the chassis under brakes and drive and the roll centre moving in the direction you would want it to in these situations. And it seams I was on the right train of thought with that one.

[Momus]

Originally Posted by chevy34

Chears guys I was wondering if it was to do with the pitch off the chassis under brakes and drive and the roll centre moving in the direction you would want it to in these situations. And it seams I was on the right train of thought with that one.

I've made and fitted dozens of Watts links over the years, conventionl and Very Low Roll Center assymetric ones.
Most have been with a chassis mounted rocker and I usually don't hear anything negative about the handling change when they are done that way.
When I'm asked the theory and pros and cons I am happy to reply that I am a bit unsure but feel as if the fixed roll center and unsprung weight COG moving to gether are beneficial.
Remember that the lower the Watts rocker's pivot is the lwr the RC will be and the body will move around that center with a different arc, so clearances need to be kept in mind.
RC height is used as in concert with stabiliser bars as a defacto roll stiffness.roll axis tuning tool. A low rear RC will usually give good results provided you have enough bar to keep the body stable.