Locked wheels & ABS

[dumbdave]

Hi all,
I've been wondering, (dangerous thing that)
Often if a driver locks a wheel in a corner brundle will tell us all how that wheel isnt helping the braking.

Does anyone know more in depth about how/why that is the case?

Cheers,
Dave.

[xpensive]

Of coursee it helps, if nothing else you can see the movement-energy being absorbed by the smoke from the friction between the two surfaces.

But less than the unlocked wheel, as the dynamic coefficient of friction (locked wheel)is always less than the static coefficient of friction (unlocked wheel).

[CMSMJ1]

The wheel needs to transfer the braking energy to the car via the brakes and when the brake discs are no longer rotating then they are doing no work.

If the car has unloaded the wheel due to weight transfer then locking it up is not a major issue. Lokcing it when loaded is the killer.

[Scotracer]

What Martin means is that the unloaded wheel isn't helping the car slow down. This is only relevant when the drivers trail-brake (something Hamilton does a lot). Trail braking means continuing to brake (at a reduced rate) after you begn to turn for a corner. As the car rolls across it's chassis (lateral shift) the inside wheel has very little traction therefore it locks. Even if it wasn't locked it couldn't do much braking effort.

[alexbarwell]

Recall Raikonnen locking up badly and heavily flat-spotting in the no-tyre-changes year? How the mishappen tyre progressively broke up then went on to take him off the track in style. A tyre in skid will scrub off a token amount of KE that would ideally be developed as heat in the braking (and recovered energy in KERS now) so less useful braking, but relatively the tyre is ambivalent to the direction of skid and when the front end scrubs out there is a nasty sensation that you are not the one steering any more. So you have to reduce steering input/braking effort/throttle input (or more throttle if the plan is to boot the back end round - not always the right move), all of which could see you getting round the bend slower, or not at all

[ernos5]

If you brake on the absolute limit, you will be braking at 100% capability of the car. When a tyre locks up then it's 30% less effective, so if you braked and locked up, it would take you 30% longer to slow down seeing as you would be braking at 70% of the capability.

Basically,

Threshold braking=100% brake power
Lock-Up braking=70% brake power