XRacer - Mark's IFS has a dirty great big strap between the two sides so it effectively behaves as the single beam. We'll see if he keeps it in place when he reports back. Stu's car does without that adornment.
Reactive castor works by giving the car an easier entry to the corner, stands the kingpin up a bit to gain mid-corner grip and then returns to more castor to help the car complete the turn. It certainly works on LMP cars.
When setting up the GT, the castor at rest is as important a setting as the ride height. Too much castor makes the car lazy on entry - a right pain for changing direction in chicanes - and loses grip mid-corner, so the first setting to sort out is that. Most cars set up around 3.5 to 4deg static castor (chassis complete and ready to race) and then set ride height as required whilst retaining that setting.
The amount of reactive change is not that much. With 4mm ground clearance and the chassis coming off clean (not decking out) the most movement you'll get is around 2.5mm. Push the car down that amount and the castor goes to about 2.5deg to 3deg depending on the springs fitted.
(Note - push the car down on the outside of the LiPo, not across the front axle. Pushing across the front axle effective doubles the spring rate and gives you a false impression. Pushing on the outside of the LiPo weights the outside wheel and unweights the inside wheel, closer to what actually happens.)
The amount of movement depends mostly on the springs used. Next, the amount of steering depends on the amount of stiffness of the front suspension in roll. If the suspension is too soft it will un-weight the inside wheel more and you lose traction. More weight goes on to the outside wheel while the inside one is unweighted more. Also, the increased roll from a disconnected front end will make the kingpin camber reduce more and give less tyre contact on the outside wheel. That tends to generate understeer. Depending on your driving style, this works for some and not others.
Load induced flex is common to all the cars. None of the front ends can be infinitely stiff (if they were they would break under load!) as they need resilience to absorb static and dynamic loads. It doesn't take much to flex the front ends of any of the cars, even slightly, but that is a function of good design using resilient materials that don't snap the instant we clip a barrier!
In reality the amount the kingpin leans out in roll hugely exceeds any flex so the flex is negligible. All the cars theoretically generate more camber because as the wheels turn they describe an arc that presents more of the inside of the tyre to the track. That's just the geometry - there's no way to avoid that. However that is not changing static camber in roll relative to the chassis, it is a function of the geometry of the front axle and kingpin with their camber and castor angles in play. In that respect the GT can generate more than most because you can get it up to 5 or 6deg static castor - but then it gets lazy in the turns...!
It's all a compromise as so many have said on here. The reality is that the roll centres front (theoretically on the floor) and rear (theoretically at the centre of the pivot ball) play a more important role than the front suspension geometry in the handling. That's why the GT now has a revised rear roll centre!
Looking forward to the weekend and our last GT National of the season. I'll keep an eye on Mark's progress - if IFS is really that good he'll beat me for the first time since SYR in January!
