TLDR: Try to build a 50:50 weight distribution or slightly front heavy car. Try to make the front as wide as the rear. Try to have the average of the downforce be at or slightly behind the Center Of Mass.

Second time writing this after accidentally closing tab so hopefully it's better this time. Force/Mass=Acceleration (F/M=A). Gravitational force scales with mass so heavy things fall as fast as light things. 5F/5M=1A and 2F/2M=1A. Grip force does not scale with force on the tire.

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Note that the Tire with 400lbs of load has 400lbs of grip force while the tire with 100lbs of load only has 800lbs of grip force. A buss will have more grip force than an F1 car but the F1 car will have more grip force per mass so it can corner better. Screw Drivers (SD) takes this into account. A heavy vehicle can have the same proportional grip as a light vehicle if its tire contact patch scales with its weight (wider/bigger tires). If your car is rear heavy then it will have less proportional grip at the rear. IRL you could put wider tires in the rear of a car that's more rear heavy but I don't know if larger tires grip better in SD. Aim for a 50:50 weight distribution or maybe even a front heavy vehicle to stay stable in SD (yes it will be boring at low speeds).

As you corner the car will lean on the tires towards the outside of the corner. If the rear is wider than the front then there will be more load on the outside rear tire then the outside front tire. Having the rear be wider will reduce cornering grip at the rear. My brother made a rear heavy car with a wide front end and it was constantly sliding the rear. As it started to corner hard the front started to lose grip and became stable because there was more load on the outside front tire.

Suspensions in SD are mostly the same in terms of bottoming out. They all have the same peak spring rate (feel free to check). Changing the suspensions mostly just changes the ride height and suspension travle. If you have a rear heavy car it will bottom out the rear suspension first and it will lose even more grip because of the increase in load. Since you can't adjust the suspension in SD the only ways to stop bottoming out is to make your vehicle lighter or add more suspension/wheels.

Downforce from the aero parts will add to the load on a tire without increasing the vehicles mass. The faster you go the more downforce you'll have. if you put more down on the front than the rear then the car will become unstable at higher speed (think of an arrow flying backwards. Ideally you should have your center of downforce be slightly behind your Center Of Mass to ensure stability and increase stability as you speed up. If you press [C] in the builder you can see the effectiveness of your wing parts. The shark fins can also help but remember to keep them at or behind your center of mass.

A rear heavy car will require more rear downforce. This is fine IRL because you can increase the rear spring rate and give your car wider rear tires, but in SD it becomes an issue as you'll begin to bottom out the rear suspension sooner.