Whats going on at the mo is rear inside wheel lift is occurring and the owner rather it didn't, at the same time he wishes to have good travel to absorb bumps/dips but without the body roll.
I've spent a couple of days with Paul (
@pollyp) where he was still getting inside wheel lift, but a very consistent and strong road holding capability. Every drivers different but to generalise the setup, stiffer damping rear, and higher rear tyre pressures are a good baseline
I've been doing some reading and trying to understand suspension dynamics better, in particular roll centres and how this effects balance.
Anyway the prospect of raising the roll centre to a similar height to the centre of mass thereby reducing the roll couple or the leverage around the roll centre (and therefore roll) always comes up when explaining roll centres. The reason that this wasn't done was given as this would increase 'jacking' without explaining much what jacking was or how a raised roll centre resulted in more jacking.
Usually attaching a scary picture like this (which caused me to go Argh! what the $%(! you're right I don't want that....
):
Jacking was explained as due to a high roll centre not a particular suspension design or due to the positive camber in the picture (it'd be negative if the suspension was going the right way!).
I eventually (I think) got an idea what jacking was and what causes it.
In the above picture say (for arguments sake) we got the centre of mass and roll centre in exactly the same spot so the car didn't roll at all, or all cornering force was being directed sideways through the roll centre with no rotational component.
If you follow the dotted line in the above picture from the roll centre to the tyre contact patch there is a slope downwards this means there is a sideways component (the majority) and a vertical component(minor) which isn't causing the suspension to compress but weirdly to extend.
So rather than compress the suspension on the outside wheel it's extending, if the centre of mass was above the roll centre body roll would be combating/balancing this extension and we might corner flat.
Looking at say this picture (picked at random
):
Overall the car seems to have some roll but viewed in isolation the rear doesn't seem to have any roll (what would it look like if both wheels were on the ground?).
The wheel on the inside is either compressed or neutral, when we'd expect it to be extended, but it is connected to the outside wheel via the beam axle IF the outside wheel were being extended and twisted by jacking this force could hold the inside wheel up via the beam (think of it as a pivot around the roll centre which is approximately the beam axle centre). The rear of the car is also higher than the front, which may be because of braking dive but could also be caused by the same jacking force, lifting the rear as in the first photo above.
So this led me to wonder what you could do about it...
One thing appears to be like mentioned above we could induce more body roll to combat the jacking, but that seems to be robbing peter to pay paul.
The ideal seemed to be to try to lower the roll centre and therefore minimize the vertical component between the roll centre and the tyre contact patch(middle picture), but as this roughly (very roughly) centred around the middle of the beam without changing suspension design this seemed impossible... until I thought what determines the height of the beam? well the wheels and tyres, so what if we went for the smallest diameter wheels and tyres we could fit we could effectively lower the roll centre and probably not be breaking any racing class rules either
OK it might look a bit different but this is a race car right? results are more important!
Anyway is there a hole in my thinking? it could be a relatively cheap experiment I'd think, but interesting to think that large rims could also be making the problem worse!
For those with wide and large rims fitted to gain a wider contact patch and more grip the front tyres are the ones likely to need this rather than the rears, keep the fronts and change the rears?