I understand it's complex, i'm an engineer so i have trouble believing without knowing
The key to this is the vertical load vs lateral force tire characteristic itself.
For real car tires at peak lateral force it is possible to have more lateral force generated than you have vertical force acting on the tire. However, once you get to a certain vertical load the peak lateral force becomes lower than the vertical force. So, after that, the more you load the tire these less lateral force can be generated. This is a proven fact for full size tires.
As an example an F1 tire can have a lateral vs vertical force ratio of well above 1 at light loads.
This is the only opening i can see for those who say more roll and tire load = more grip and i honestly don't know how a Sorex32 loaded at a few hundred grams compares to a Goodyear Eagle loaded at hundreds of kilograms. Full size racing tires operate mostly in the overloaded state and all the literature is written around managing that situation. If RC tires don't spend most of their time overloaded then great, but my tires look pretty shredded after 3-4 rounds on most tracks.
The explanation i have for full size cars on your rollbar question is this:
- if a car is understeering it means the outside front tire is overloaded and is reducing the total front grip, so that the front has less grip than the rear. A stiffer rear rollbar transfers more of the total roll force to the outside rear wheel (overloading it more). So you get the effect that the outside front is loaded less now (becuase the rear outside took more of the load) meaning the total front end has more grip. Additionally, becuase the outside rear is loaded more (and became less efficient than it was before) the total rear grip is less. The net result is more front grip and less rear, but it is a very fine line as to whether the overall grip even changed. (again back to the tire characteristic and the camber effects at each end of the car).
I have 3 very good books on full size cars.
- Chassis Engineering, Herb Adams
- Race Car Vehicle Dynamics, Milliken
- Tire and Vehicle Dynamics, Pacejka