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I'm confused, as always thought any sort of braking while cornering will cause understeer, because it uses up part of the grip that would have been used to turn.
But then I have read and also watched a video that talks about braking to move weight forwards and reduce understeer
the hard cornering anyway contributes a decelerating effect, increasing the front contact force and reducing the rear contact force
ie in cornering balance this is a contribution in the direction of oversteer
with road car cornering balance (mandated) the oversteer contribution will be less than the mandated understeer
with race car cornering balance the oversteer contribution will be dominant
braking increases the deceleration effect contributed
if the brake balance is matched to this situation the brake force will rob front and rear cornering capability equally
but road car brake balance is usually fixed and so may rob the front cornering capability more than the rear, ie give understeer
(iirc ABS is arranged to support this)
I guess F1 does roughly this as the balance won't be ideally manipulable for this purpose (in the absence of any ABS)
imo the F1 driver can recover the situation by jumping on the brake eg Mr J Villeneuve seemed to do this later in his F1 career
trail braking will be the most tracktime-efficient use of the tyre's grip in corners of decreasing radius
but there's a big difference between trail braking with road car cornering balance and tb with cornering balance set for the track
The first fundamental is that the more vertical loading on a tyre, the more grip that it can potentially generate, up to its threshold. Adding more load (weight on the tyre past this point doesn't offer more grip. F1 experienced this phenomenom during the last year of the Bridgestone control tyre era.........
Braking while turning in (trail braking) can reduce understeer, as braking transfers weight forward, increasing the vertical load on the front tyres, up to the tyre's limit of adhesion. This is a given in all forms of motor racing.
However, if the tyre's full grip potential is mostly used resisting cornering (lateral) loads, then applying the brakes, and asking the tyre to resist the added longitudinal deceleration, tips the tyre over its grip limit, either understeering, or worst case scenario locking up that wheel.
To counteract, the driver must either ease brake pedal pressure, or open the steering angle, until the tyre re establishes its grip level.
As a note, some tyres are stronger in longitudinal loading than lateral loading, and vice versa. Chassis and aero setup should be sympathetic to the relative strengths, and needs of the tyres, as they are all forces act through them. Sometimes this is forgotten in all the complexity that we add to this game called motor racing...
There was a noted motorsport writer that described it all, calling it "The Friction Circle". Google it, easiest method I've read to explain it all.
