T-bars vs Stored energy

All IRS cars squat like that on the starting line. With no rigid axle tubes, the torque reaction at the axles tries to push the hubs up into the car. Gravity fills the void and the car squats.
Squatting the tire is different. Cars with little or no suspension rely on a hard initial hit which stretches the tire front-to-back. This leads to a longer footprint and thus compensates to the lack of actual weight over the rear.
As a rule, lower horsepower cars (under 6-700 horsepower) use an active suspension and physical weight transfer to gain traction. Higher horsepower use little to no suspension and focus all of the energies toward working the tire into the ground while the physical weight of the car is used to counterbalance the force of the pinion trying to climb the ring gear.