Tested:
Forza Motorsport 7 Brake Bias
So, in Forza games the brake bias settings are a bit weird, I wanted to have a deeper look at this.
Short explanation of what brake bias is and does:
Imagine a car from the side:
The brake forces from the tires act on the center of gravity from below, so it's easy to imagine it as if someone is trying to pull the rug from under you, making you fall over. In our car schematic this falling-over is a (rotational) momentum on the center of gravity that is shifting weight from the back to the front. If the car has a perfect 50:50 weight distribution, it will be heavier at the front under braking, meaning that you will want more brake force at the front for ideal braking.
Now if the brake balance was 50:50 and we would push the brake pedal harder and harder, the rear tires would lock up first and we would lose a lot of grip this way, making us stop slower and send the car spinning at the slightest turning of the steering wheel or from unevenness of the road.
So, not only do we need more brake force for
ideal braking at the front, we need even
more brake force than what is ideal at the front, so that - for safety reasons - the front tires will always lock up first and keep the car going straight (or "understeer" with a turned steering wheel) instead of sending it spinning.
A normal road car has ABS and only needs one hydraulic system, meaning the hydraulic pressure is the same at the front as in the back, but there are other ways to get more brake force to the front:
Note the different sizes of the brake discs and how much bigger the front brake callipers are than the rears.
Many race cars feature two independent hydraulic systems for the front and the rear, making it possible to change the brake bias from the cockpit during a race. But even if that's not the case, often the callipers allow adjustment before a race to set the brake balance.
Why is it weird in Forza?
Even rear engined cars that are heavier at the back need higher front brake force to be safe. In Forza however, the brake bias by default is
always set to 50:50 without sending the player flying off all the time. This
can make sense in a car like our yellow Seat above, if the game means "50:50 brake
pressure" with much larger brake discs at the front (in racing and engineering it's usually the overall brake force distribution, with the different sizes calculated in already). But even in a very low car with 50:50 weight distribution and basically same sized brake discs like a new Mazda MX-5...
Forza still defaults to a 50:50 brake bias. For comparison: Assetto Corsa starts with a realistic and safe OEM brake(-force) bias of 72/28 for the MX-5.
Now, since I
don't lock the rear tires under braking first in Forza all the time, this must mean that the ideal brake bias - for the absolute shortest straight-line stopping distance (even if it's unsafe) - must be further to the rear in Forza's system. It's easy to find the ideal configuration in Forza, since the game shows you calculated and always updated stopping distances on the left side of the tuning menu:
In the car I tried first, I instead found that the stopping distance grew
larger with more rear bias though ...and decreased with more front bias and that you needed to adjust to a lower brake pressure to get ideal results (maybe because the calculation simulation can lock up wheels and needs Forza's bad/slowpoke'ish ABS).
It just didn't make sense.
Now...
The TEST
The car was the
2016 Mazda MX-5 shown above (but not shown in the Forza tuning-menu screenshot, I don't remember which car that was from). The MX-5 was completely stock with only the brake system upgraded to be adjustable.
All distance values are taken from the tuning menu.
Not easy to see, but the values again went up with more rear bias at first, but then quickly decreased like I noticed in the first car.
The shortest stopping distances were found at
100% brake pressure and only
40% front brake bias with 31.1 meters from 60mph to zero and 82.7 meters from 100mph to zero.
[horizontal axis: brake pressure , vertical axis: brake bias , legend colors: stopping distance]
The only way that this makes sense is that
"50:50" means absolutely nothing in Forza and is only signaling the player where the default brake bias was set to by Turn 10... either that, or I am missing something important. Then please tell me.
