How is a vehicle's stiffness measured?

[framedetective]

Is there any information out there that serves as a guide / criteria to follow to measure a vehicle's stiffness?

I mean, I have no clue from where or how it's measured and I haven't seen any relevant information on the net.

Cheers!

[MagicRat]

I have read of two different criteria being used.
One is a measure of torsional rigidity; that is, how much force (newtons, for example) is required to deflect the chassis a certain amount (degrees) from its unloaded position.

Another measure of stiffness is in terms of vibration harmonics. Chassis will vibrate at a certain rate (hertz). Often it is not practical to eliminate all vibration, so the vibration can be 'tuned' to cancel itself out and/or raised or lowered to lessen its intrusion into the passenger compartment.

A good example of tuned vibration was in the 1961 - 67 Lincoln convertibles. These were unit body 4 door cars, initially designed as a sedan.

When the design had its roof removed (to make the convertible model) the entire structure was dependent on the sheet steel floor pan and door sill 'torque boxes'. This structure was somewhat flexible, so the trick was to make it as solid-feeling as the regular model with the steel roof.

The company added about 250 lbs or floor bracing to control the torsional flexing, but found the car still shook or vibrated too much. The vibration could be tamed through another 400 lbs of bracing, but this would make the car too heavy.

Instead, the added 4 tuning weights, placed at each corner just behind the bumpers. These weights essentially vibrated in opposition to the chassis vibration, thus damping them and creating the illusion of a solid, smooth feeling for the passengers.

[sad-lumina-owner]

Originally Posted by framedetective

Is there any information out there that serves as a guide / criteria to follow to measure a vehicle's stiffness?

I mean, I have no clue from where or how it's measured and I haven't seen any relevant information on the net.

Cheers!

In order to detect the vehicle's stiffness yourself, your garage must be a snug fit. You can tighten the fit by slipping a plastic dust-cover over the car.

Now as you drive in and out of the garage, the ribbed pattern on the dust-cover should vibrate the garage warmly, and you should be able to feel this through the steering wheel.

If the car is too flaccid, rubbing against the garage door frame will be ineffective in sustaining the required sensation. You can enhance the effect by having the engine idle very low, almost stalling, during the session.

Blue under-dash lights are a nice addition, but candles are a fire hazard.

[534BC]

I just can't say which answer I am more impressed with.

[sad-lumina-owner]

Originally Posted by 534BC

I just can't say which answer I am more impressed with.

This educational video about corrective lenses might help:

http://www.youtube.com/watch?v=FvQqHd50NAA&NR=1