bored!

Lets start a thread about kingpins.....

Adrian,
according to these folk, excessive chassis flex isn't a good idea...
< http://www.infrastructure.gov.au/roads/ ... eb2006.pdf >

Although aimed at modified vehicles, there's a mention of a minimum acceptable torsional stiffness for our UK equivalent of a 'one-off' vehicle.

Sticking to facts and not opinions, fatigue failure and low torsional stiffness are inextricably linked.
Although breaking a piece of metal by repeatedly bending it to and fro is not quite the same thing, since the metal is taken beyond its elastic limit in that instance, the fatigue limit can be exceeded by many more repetitions at a lower stress level.

Viking, that Aussie document bears out your earlier comment about poor quality repairs to chassis, since the real problem there is the abrupt change in structural properties at the edges of the 'reinforcements', acting as stress risers.

Here's hoping we may get there soon, instead of going round in circles...

ken.

<scratches chin>

The whole concept of chassis stress analysis is vast and open to allsorts of interpretations, although the basics that any chassis should be above a minimum strength and as strong (between the axles) as poss everyone seems to agree with. Minimizing concentrations of stress also desirable - traditionally British car makers made up with their lack of slide rules with extra metal, effectively 'dead weight'. Some people love the idea of such a 'solid, strong' car, others prefer cars to be properly engineered more along the lines of an aircraft.

I go by the seat of the pants feeling, so a bit of scuttle shake present on cars with some ladder frame chassis which isn't there on those with Cit chassis is not good in my book. Neat turn-in followed with unpeturbability in corners where the suspension is dealing with ripples and bumps is desirable. All this assumes everything else being the same and correct, such as dampers, ride height, springbox pre-loadings, corner weights, tyres etc, before spanners mentions all the variables again.

Interesting that an original is stiffer and lighter than aftermarket ones, wouldn't ya say? SLC makes a lot of sense for everyday vehicles, where roadsalt and confused MoT testers fail to affect them...

Wow, this is some thread. I think mine is on a Dyane chassis, whatever that means.

oolong,
even more interesting is that the very thing which enables an OE chassis to be both stiffer and lighter also happens to be its Achilles heel...

Because an OE chassis is a 'stressed skin' structure, its characteristics are totally dependent on its various components, including the internal diaphragms as well as the skin, being unaffected by corrosion or accidental damage, which could trigger buckling of the diaphragms or the skin.
Once either of these occurs, there is a dramatic reduction in its stability, to the point where large deflections can and will occur without any increase in load.
( Anyone else had the experience of removing a bodyshell during a chassis change, only to see the chassis sink onto the floor?
Up until the bodyshell was removed, the steering column was often the only (structural!) item preventing the chassis from folding.)

In contrast, ladder frame chassis are not affected as dramatically, because their structural elements are not as susceptible to localised damage.

ken.

ken is a Dyane chassis 'OE'? Mine has a flat underside, even the engine has a skid plate. I drove another 2CV a couple of years ago - I was thnking of buying it because it was smarter and had a galvanised chassis, but on the road it wasn't a patch on mine. It vibrated on poorer roads, didn't corner well and potholes felt about 10 times bigger than they were, even though it had been refurbished only a year previously, new shockers, chassis, floors, sills and so on.

Tim,
the vast majority of UK Dyanes were fitted with P.O. chassis, which was the export version of the standard OE (original equipment) chassis.
They had reinforcements fitted to the chassis webs (sides in layman's terms ;o) ) immediately behind the front axle mounting point, which made them much more resistant to 'chassis collapso' and most probably also made them slightly stiffer.
In addition, the engine bay undertray was larger then the welded-in version on the standard chassis and was bolted on.

There may have been other internal differences, but I've never cut one apart to investigate.
Maybe when the one on my 1970 Dyane decides it's had enough neglect during the 15 years I've owned it?

ken.

( p.s. P.O. = Pays Outre-mer = Overseas countries? )

The only real difference between a "Dyane chassis" and a "2cv chassis" is that a Dyane chassis has the bolt-on undertray for engine & box, whilst a 2cv had a smaller, welded-on one. Most of the replacement chassis sold (or fitted under rust warranty) by Citroen were "Dyane chassis", and I think to PO spec - strengthened, for raid use, as seen in the Citroen publication "Ici Commence l'Aventure"

Don't forget that there's an original Ami Chassis sitting in Bullwinkle's garage near Horncastle, Lincs if anybody would like the guy's details?