@snakebite it makes sense on thesurface, but you’re ignoring that the front has more grip than the rear, under trail braking.
Also as a one-time tyre engineer I call BS on you saying the rotating tyre doesn’t slow the car further.
Scientifically speaking, whenever a car is accelerating (in whatever direction – remember acceleration is a vector quantity) the tyre is never fully “gripping” the road. There is always, at an almost microscopic level, a level of slip. When talking about forwards/backwards (along the tyre’s rotational axis) then we talk of slip ratio, and when talking about cornering and lateral acceleration, then we talk of slip angles.
You can disregard the numbers here as different tyres have different numbers, but what you need to pay attention to here is the general shape of the curve.
This is a graph which plots slip ratio, against the traction force – ie the further to the right, that means a greater difference between road speed and the tyre’s rotational speed. If a car has its tyres at 0 rotational – ie a locked tyre – then the slip ratio is at its greatest (car speed vs 0kph)
Because each tyre is basically slipping at every accelerative force that goes through it, there is actually no thing as “grip” in the everyday conversational sense. There is always some slide in the car. Each amount of slide, however, brings along a different level of grip. As with the graph (which is from FSAE) the tyres hit an optimum “sweet spot” at a certain slip ratio, before there is less grip on either side of it. A locked tyre, which will tend towards the far right end of the graph – will have severely reduced grip.
Back to the trail braking debate, all of this is a transient condition, and it’s over so quickly that the driver being comfortable with the setup under braking will probably gain more time than the theoretical loss of a slightly worse off brake bias.