Since going to Padova for the 2014 "Auto e moto d'epoca" I have been thinking about how the Giulietta would put up for a roll center test. The reason for this is that at the italian event I spoke quite a lot with Tommy Kjehr, who has been racing classic cars successfully for a decade or more; first he ruled in his dark blue Alfa Romeo 2000 GTAm replica and for the last couple of years he has been winning in a Ford Escort RS 1600 BDA - quite convincingly!
He told me about the broom-stick method and about the dynamics of roll-centers. The broom-stick is a virtual line that connects the rear and front roll-centers - and the dynamics is the way the broom-stick wiggles under the car when I go through braking and cornering. I got the first part - but totally forgot about the latter part; the dynamics.
It was a cumbersome work to get all the measurements and the weights on all four wheels, but once I had the values, I could sit down with a pencil and a ruler and draw the roll-centers. Only after buying a program from the internet called "Roll Center Calculator" (see www.performancetrends.com) I remembered what Tommy had said about the dynamics: Turn-in is influenced by roll-center movement! And it makes perfectly sense; anybody who has driven cars on the limit, knows that the exact time when you transfer from straight-line driving to turning is crucial - especially if you are not quite finished braking yet.
Magazine road tests from the mid-1950's mentions the pronounced roll of the Giuliettas. But they also say that the driver doesn't feel it as something that prevents rapid progress on twisty roads, and that they were surprised to see photographs of their driving.
With both 101- and 105-series Alfa Romeos you have to turn in with determination and show enough courage while negotiating a bend, if you really want to go fast. It is hugely satisfying, but at first it takes a bit of conviction to go at it for real. It's at the core of the Alfa Romeo driving character, and I am certain that the cars have been deliberately designed this way.
By having the front roll-center as low a in the Giulietta, Alfa Romeo has created this "downhill skiing" emotion. It is partly because the long pendulum arm of the car mass (center-of-gravity, CoG) around the roll center, but also because the roll-center moves a lot when the car leans and the suspension settles either left or right.
The rear end of the Giulietta (and equally for the 105-series cars) would hardly roll on it's own, because the roll center is 40 cm up - on top of the differential. The rear end only rolls because it is an integral part of the car - and the front end has most of the mass. You could say that the rear end is always firmly planted, especially with soft rear spring, and with no rear anti-roll bar at all. The broom-stick is firmly attached to the rear roll-center and it "sweeps" around under the car up-and-down and left-to-right, quite violently.
But first of all I cannot change my suspension because of the homologation rules, secondly it probably wouldn't be safe ... but most importantly: I don't want to change it. I don't want my Alfa Romeo Giulietta Sprint Veloce to drive like a Ford Escort BDA.
Know what I mean?