[Kevin H]

Originally Posted by lansdownplace

Hi Kevin, I started with my own experience on the relative difference, but as 'why' was asked I thought I should go off and check for myself.

I have now managed to lay my hands on some facts and figures on this
handling issue, which do explain my thesis.

The 412 S1 has 32% more torsional rigidity than the 411 although the beam rigidity is the same, The 412 S2 has the bars at the top of the windows connecting the A and B pillars and other chassis modifications so the torsional rigidity rises to 45% more than the 411 with 25% stiffening in beam rigidity.

Paul, it's always interesting to get more information about our cars, but I'm sure you won't be surprised if I ask where these facts and figures come from?

It's worth pointing out that differences expressed only in percentages are all relational, and the 411 was reckoned to handle very well indeed, and not just by Setright.

There is probably an optimal point for chassis rigidity, and increasing it past that point doesn't necessarily translate into better handling because it also depends upon the suspension (spring rates, damping), roll axis. C of G, wheels and tyres, tyre pressure, anti roll bar, weight distribution and probably one or two other things we haven't thought of!

The other data to hand now is that the center of gravity is 8 mm lower in the 412 than the 411, which I thought sounded small, but the effect is magnified because the center of gravity on a 411 is 80mm above the roll axis, whereas it is 72mm on the 412 ( and lower again on the Beaufighter).That represents a 10% improvement in the roll couple ratio which does make a difference to the balance of the car. In a perfect world the center of gravity would sit on the roll axis, but there you are.

Surely it depends where the roll axis is? This would also induce jacking effect would it not?

I would be keen to know just how the C of G has been lowered, and if the weight distribution differs between the cars.

Some other interesting technical stuff I picked up is that the
Blenheim is three times stiffer than the 411 and the Blenheim had the
highest torsional rigidity of any passenger car up until '98. It is
stiffer than the McLaren F1.

This is quite amazing, if it's true. And if it is true, it clearly demonstrates that chassis stiffness or torsional rigidity does not dictate handling (because a Blenheim does not handle as well as a McLaren F1).

There is another point to consider here. Any figures that come out of BCL refer to original specification cars as they left the factory. There aren't many like that any more, especially when we are talking about 412 or earlier.

For example the 412 S2 had wider, lower profile tyres than the 411, but I now have the same wheels and tyres on my 411, as do many other 411 owners. This in itself lowers the 411 slightly, lowers the roll centres, roll axis and C of G, although it doesn't reduce the roll couple value. But it does makes a very noticeable improvement to how the car handles over the standard steel wheels and tyres. Stick an uprated anti roll bar on it and it improves it further.

Having completely dismantled the front end on my 411 it became clear that what appeared to be a reasonably good and standard condition suspension, was nothing of the sort. And I suspect this is the case with many of the cars that haven't been restored, in which case this all becomes theoretical!