Brake performance wrong in GT4 prologue!?

Discussion in 'Gran Turismo 4: Prologue' started by Buggy Boy, Jun 5, 2004.

  1. Greyout


    Just a news flash for everyone - the size of the brake caliper and rotor have very little to do with the stopping distance. The size of the brakes allow for repeated agressive stopping, because the pads wear less, and the rotor & caliper can disipate heat better if they are larger.

    However, Even the brakes on my old 1984 celica, which consisted of drums in the back and what looked like tea cup saucers in the front, could lock up all four tires when traveling at highway speeds.

    Modern brakes on just about any car in production have the ability to overcome the traction of the tires. Its not about the size of the brakes. Braking distance is most strongly influenced by:

    Tire compound and size: The rubber meeting the road is the only place where the slowing down actually happens, so obviously the tires grip is a primary factor in stopping distance.

    Front / Rear weight distribution: Like mentioned before, traction does not increase at the same rate that weight increases. Anything other then a perfect 50/50 split in DYNAMIC weight distribution produces less traction then an even split. This does not mean a 50/50 split when the car is parked, but a 50/50 split under braking - meaning a car that had a 50/50 dynamic balance under threshhold braking would have a rediculously aft weight bias... I would guess such a car probably does not exist (at least not a production car), but I could be wrong.

    Height of center of gravity: The higher the center of gravity, the more foward weight shift occurs under threshhold braking. see above as to what that means.

    ABS software: The tuning of the ABS software detirmines how well the car will stop under full brake pedal effort. Race-worthy ABS is much more fine-tuned then your regular street ABS.

    Suspension tuning:
    Suspension tuning detirmines how well the tires will stay in contact with the pavement over irregularities as you try and stop. A suspension that is too stiff will "skip" over bumps, and between the bumps the tire will not be in contact with the ground. A suspension that is too soft will cause excessive suspension deflection,(big changes in dynamic alignment), could loose contact with the ground at the top of bumps, and could even result in the front suspension bottoming out on the bumpstops if the car is low enough, thus causing the rear to have a severe drop in traction. The body could also bottom out, which is a weight transfer and aerodynamic disaster.

    Suspension geometry: The deflection of the suspension causes the alignment to change. Generally, as the suspension travels upward, the camber increases, causing the tires to increasingly ride on the inside edge. The toe also changes with suspension travel. This all results in a tire that is not firmly planted to the ground.

    Aerodynamics: The downforce created at whatever angle the car is at when under full deceleration affects traction. Its possible for a spoiler to be mounted at an angle that provides maximum downforce, but then "stalls" if the nose of the car drops enough.

    Weight: Self explanitory. Its the stuff you are trying to stop :). traction increases with weight, but not at the same rate.
  2. rx7guy


    Mazda3 and 911 turbo (996)

    Tire compound and size: Mazda has bridgestone potenza 205/50 R17 while turbo has 295/30 R18 pirelli p-zero rossa

    Front / Rear weight distribution: Mazda3 61.3%/38.7% front/rear. porsche is 38.8%/61.2%

    Height of center of gravity: Nt sure of centre but mazda3 is 1465 mm high porsche is 1305mm , which would suggest porsche has lower centre of gravity.

    ABS software, Suspension tuning: I have no idea bt porsche are a performance car...

    Aerodynamics: Drag co-efficent of turbo .31 , mazda3 .35

    Weight: Mazda weighs 1288kg which is lighter than turbo at 1560

    u would think as a $305,000 (NZ) car the porsche would be significantly better than a $35,995 car

    Mazda3 has breaking distance of 100-0km/h of 32.94 metres while porsche 911 turbo is 34.50 meters as recorded by nz autocar.
  3. Scaff

    Scaff Staff Emeritus

    United Kingdom
    Sorry to bring this thread back from the dead, but you guys should read these

    Its from a series of articles regarding the physics of racing and explains (in great detail) how the total mass of a car is unrelated to its brakeing ability.

    Mainly due to maximum brakes force being principaly a factor of the tyres maximum grip level.

    It assumes that maximum braking force is applied without locking the wheels and exceeding the tyres maximum grip level.