Indeed!
Brings to mind the great hunks of weight hung off the back of transmissions of cars like Vegas and certain Datsuns, and the massively counterweighted front bumpers of convertible TR7s, about which I inadvertently discovered when I removed one whilst sitting underneath it and thought I would just pull it off and catch it on my chest…
I was the (very junior) engineer on the impact tests for that bumper system. We had genuine concerns for the impactor.
GM (and likely others) in the '60’s placed largish cylindrical damper cans (aka “cocktail shakers”) in the corners of some of their convertibles (Corvair and Camaro that I know of for sure) to help manage chassis twist/shake. Very inelegant. 
I finally got around to measuring the ride frequencies on my car. I loaded a acceleration frequency analysis app called resonance on my phone. I taped the phone to the flat back of the bumper overider. I dialed my GAZ shocks to full soft. Then lightly bounced the car and recorded accelerations for 10 sec. Repeating steps for the rear.
I got 1.4 hz in the front and 1.5 hz rear. No occupants and 3/8 tank of fuel.
(Sorry I didn’t mean to submit the first sentence without the rest)
If they’re true dynamic absorbers - tuned mass attached by a compliant mount - and not just chunks of metal, the theory is quite elegant although reality can be ugly. The absorber’s natural frequency interacts with that of the “target” component and reduces its severity, while adding a pair of lower intensity vibrations either side of the original. One practical drawback is the amount of mass that’s typically required. They work best where the problem frequency is distinct and consistent, such as TR7 convertible where the problem related to a specific structural condition.
I don’t know if the same theory applies to harmonic balancers found on engines, I imagine the wide range of engine speeds poses a different set of problems.
Excellent, thanks. Good information to work with.
A bit of suspense is always a good way to start a Saturday.
That sounds fairly aggressive, higher than I expected relative to the Jaguar image (although it will obviously go lower with people on board), reasonable front / rear balance?
It will be interesting to see how the front / rear damping compares.
IIRC, some SS cars used weights at the ends of their bumpers: @Rob_Reilly can probably illuminate that point.
I had another look at the effect of the rear suspension mounts, using data for similar V-shaped Metalastik mounts with a bench rate of 1500-2000 N/mm (depending on rubber compound) for a pair in parallel. Plotting that in series with the springs and a tyre suggests the suspension mounts don’t play a significant part in the overall system stiffness. (from 1500N/mm the blue curve blends with the red curve, for tyre and springs only).
In practice I think the difference will be smaller because the static load on the suspension will preload the system further into the V, increasing the effective rate.
Thanks for the suggestion, good to remember next time
Hi Clive…im probably like most here with little knowledge of suspension geometry and interpreting graphs. …but are you sayin that the rubber mounted irs unit will have little effect on ride and handleing?..Steve
Hi Steve - no, I certainly wouldn’t make that general statement. I intended to say only that the rubber mounting of the suspension and drive assembly to the body structure would not significantly alter the vertical wheel rate, ie the vertical stiffness of the suspension in the frequency range relating to ride and roll motions. In other words, it doesn’t need to be considered in a discussion of spring rates. No more than that. I’m sure it has a profound effect in the higher frequency range where road noise and harshness are encountered.
I’m equally sure that horizontal motions of the irs mounts are important components of the ride and handling, resolving drive, cornering and ride inputs loads. I had no intention of suggesting otherwise.
On reflection the graph was a bit obscure.
All discussion related to the vertical plane, for ride motion. Ignore the green line.
I was trying to show how stiff the diff mounts would have to be to have no effect on ride stiffness. Because they are effectively springs in series, they are added as (1/each stiffness) +…+…so any value which is significantly higher than the others ceases to have an effect. That happens here - as the diff mounts reach 1500N/mm, the total (blue) curve merges with the red one, which ignores the diff mounts.
The final step is that the data suggests the diff mounts are in that higher region, so I concluded we don’t need to consider them in ride calculations.
Hope this is more clear.
Interesting, thanks for that David. Ironic that modern cars routinely use the engine and mounts as a mass-damper system to reduce front end structural vibration.
Well I did some figures, working back from Tom’s numbers to an estimate of rear axle weight. From there to the front axle load, then through the frequency to an estimate of front spring rate, side stepping the actual torsion bar.
I could just deliver the numbers but I really think a matter of such gravity deserves a chart. Nothing earth shattering, but maybe some mild interest to those of us who consider a day wasted without a chart. Tomorrow will not be wasted.
Without one of your daily charts, I feel like an unloved child.
There’s another more involved article on the site which I was unable to find.
A straight eight: how cool THAT woulda been!
Wonder if the car was ever unburied?
OK, let’s just close this thread. The answer if rather simple. Just get Jenson Button to drive your car 
I’d be interested in any more detail that might appear, I have a sad fascination with vehicle structures and vibrations.
Turns out Faculty Head Mr. Crouch was right all along, I do wish I’d paid more attention in class.
Thanks.