Brakes

This defines the normal brakes. (Foot brakes) Tells the game how fast the car will reduce its speed.

0.50 = Very slow braking. The car has to be very heavy if you use this...
0.70 = I guess this a good one for trucks. (At least I use this)
0.85 = This could be the average value.
1.00 = Sports car brakes.
2.00 = Just for fun.

Braking strength multiplier

This is an odd one, but I'll give it a try.

0.0 = You might think that now the car can't slow down, but it does, so nothing special here.
1.0 = I'm not sure, but I think this is the default value.
750.0 = Farewell to ABS-brakes! This will lock the wheels when you use the brakes. (foot brake or handbrake) Steering will become harder now during braking.