My take on roll centres and suspesion stiffness.
Roll centres is one of those adjustments that no-one ever seems to agree on - there never seems to be a definitive answer.
Raising the suspension mounts off the chassis = higher roll centre.
In theory the car will be stiffer, therefore less body roll, and less grip.
I have found it to be the complete opposite, when it comes to the "less grip" part. I find a car that rolls too much to be very easy to drive, but simply too slow through the corners.
Whenever I make an adjustment that makes the car stiffer (either raising the roll centre or stiffer springs etc) I find my car becomes noticeably quicker thru the corners - I can simply maintain a higher corner speed when the car has less roll.
Most people believe that the more roll you have, the more grip.
All of the info I have researched tells me that this is wrong - and that body roll gives an overall net LOSS of grip.
The reason is that the increased grip of the outside "loaded" wheel is not in proportion to the decreased grip of the inside "unloaded" wheel.
As an example: When the car starts to roll, the outside tyre may gain 10% traction, but the inside tyre will lose 15% traction - so overall there is a net loss.
Obviously, when the car is softer, it is easier to drive, so it feels like it has more grip, but in reality it is an illusion.
When the car is stiffer, it seems like less grip because the car feels "twitchy" or "edgy" - the reality is the car feels like this because the tyres are being pressed onto the track surface harder, and both the rear AND front tyres are responding quicker.
Last weekend, we had our first major meeting, the Summer Cup, run on low grip asphalt with rubber tyres. My car (19T class) was initially ok, running a fairly stiff setup (18pound springs front, 16 rear).
I went to a softer spring combo (16 front, 14 rear) and the car went slower - but it was much easier to drive. By the time we started the finals I was back on my original spring combo. Qualified 5th.
Finished 3rd and 4th in the first 2 A-Finals, and for the 3rd final I raised
the roll centre. The car was harder
to drive - but much quicker
through the corners - and I won the last A-Final
What was most noticeable was that though I made a few mistakes getting used to the car, I was able to catch the leader each time and finally make the pass. The car simply out-cornered the opposition in this race.
It was my best time of the day and substantially quicker than my qualifying time.
As I said this was on fairly low-grip dusty asphalt, but I have found the same thing on very-low grip, bumpy concrete (my local track) - when the car is stiffer, it's harder to drive, but it's MUCH quicker.