Stop start - rough restart issue

[Markp]

Er, guys, doesn’t the standard auto handbrake - if switched on - apply automatically whenever stationary, and disengage automatically when you apply throttle? Doesn’t matter whether on flat, uphill or downhill. Why would you need any “extra”facility for a hill or when in a queue?
On second thoughts, ignore me. I don’t care

[Surrey Sam]

R.E - naming of the Hold/Hill Hold Assist function. I think it has officially been called both.

From looking at my RS4 brochure sat here in my desk drawer; the option there is called Audi Hill Hold Assist. But if you go back to the Audi workshop self-study documents, its call Audi Hold Assist. I certainly wouldn't name the EPB (Electromechanical Parking Brake - aka 'handbrake') Hill Hold though.

The Audi Hold Assist function is controlled by the ESP system and maintains braking force to all four wheels, once the vehicle has stopped, and your foot lifted from the brake pedal. The EPB is a different and secondary circuit, controlled by another separate module. This will only activate spindles which drive the rear brake calliper pistons inwards, to maintain brake pressure on the rear axle only.

Coming back to the original thread point - Rough/jolting restart, which can overcome the Audi Hold Assist.

It'd be worth testing the following to see if it makes a difference - When coming to a stop, we naturally ease up on the brake pedal to stop the car smoothly. So the ESP systems holding pressure is quite low, hence why it is noticeably smoother taking off again, rather driving through the alternative handbrake function. So next time, when coming to a holt. Try depressing the brake pedal further down, before lifting your foot from the pedal. My theory is that the ESP system builds more pressure to hold the vehicle firmer, and doesn't then get overcome by the engine torque in the Start/Stop cycle.

[Daveperc]

Related question - does the Electromechanical Parking Brake - aka 'handbrake' - work on all for wheels (via the gearbox), or just the rear wheels (like in the old days??)

Could definitely affect my winter driving approach!!

Dave

[Surrey Sam]

The EPB works only on the rear wheels.

Putting the car into P (Park) will then engage the parking lock on the gearbox, thus locking the transmission. However the front wheels are still able to rotate.

If you were engaging the EPB (and hold) while moving, then the speed in which you are travelling will dictate how the system reacts. Below 8km/h the EPB will brake the rear wheels only at a maximum de-acceleration rate of 8m/s, but as I understand, they will NOT lock up. As the system monitors wheels speed and will decrease line pressure. Over 8km/h pulling the EPB (and holding) will engage the dynamic emergency brake function and the ESP system will take over and brake all 4 wheels.

[Daveperc]

Ah - all the clever electronics!!

So how do I brake just the rear wheels momentarily to induce oversteer when driving on ice/snow at above 8Km/hr?? It was so easy when a quick snatch at the handbrake would do it!!

Dave

[Surrey Sam]

In theory - you can't, but I've never tried on a low grip surface to find out for sure.

Might have to brush up on your scandinavian flick technique instead.

[harrier]

Sam's right. I can fully recommend Audi's Ice Driving in Sweden as the place to practice it. They had us fully turning off the traction control (ESP), before flicking the cars (B8 S4's) on the 7.5K circuit on the frozen lake, up near Arvidsjaur, at every opportunity - huge fun.