Why auto start stop only lasts for 20 seconds?

[SmallWheels]

When I was out in my S yesterday I noted that the start/stop restarted after quite a short time when I had the a/c on. Without the a/c on it remained stopped.

Generally I find the start stop fine in traffic but it's really annoying at junctions when it cuts out at the point where you're mentally getting ready to go just before the foot comes off the brake

[MikeM]

When I was out in my S yesterday I noted that the start/stop restarted after quite a short time when I had the a/c on. Without the a/c on it remained stopped.

Generally I find the start stop fine in traffic but it's really annoying at junctions when it cuts out at the point where you're mentally getting ready to go just before the foot comes off the brake

It restarted because the air con compressor is driven via the engine.

[gmacan]

You're bob-on right there, jaffacake - we certainly didn't buy thes cars for economy but, for me, "stop/start enabled = how much saved?" is just one of those eternally intriguing questions that may or may not be interesting to know the answer of!
You know, the benefits may be marginally there when bimbling around town in 'D' but what of the trade-offs, eg wear-and-tear costs on the components involved (ignition coil, starter motor, clutch/es, etc). Does that inherent wear offset any gains achieved when bimbling around town, in which case generally pointless to use the feature, ultimately.
Bit like the question of which costs less - photo-sensitive on-off-on lights in the evening your house [with the power surge needed to put them back on after they've switched off] or just leave the same lights on all evening??
What conundrums lol

[On-Track]

When I was out in my S yesterday I noted that the start/stop restarted after quite a short time when I had the a/c on. Without the a/c on it remained stopped.

Generally I find the start stop fine in traffic but it's really annoying at junctions when it cuts out at the point where you're mentally getting ready to go just before the foot comes off the brake

Like Paul, I've had the diamond button programmed to turn stop/start on/off on both my Macans. Always turn it off at junctions and roundabouts. Usually leave it on at traffic lights unless on a hill.

On a steep hill, I was stopped at traffic lights in my SD with the engine stopped and "hold" engaged. Lights changed so I moved my foot to the accelerator. This disengaged "hold" and the car started to roll back (only about six inches) before the engine restarted and took up drive. OK, restart is much faster in the GTS but I've no intention of risking that roll-back again.

[SAC1]

On a steep hill, I was stopped at traffic lights in my SD with the engine stopped and "hold" engaged. Lights changed so I moved my foot to the accelerator. This disengaged "hold" and the car started to roll back (only about six inches) before the engine restarted and took up drive. OK, restart is much faster in the GTS but I've no intention of risking that roll-back again.

Ah! not just me then....I had a 'nasty' experience with my SD in a car park with a slight slope. Facing up this slope, I stopped, the engine cut out, HOLD engaged, I put my foot on the accelerator....and it rolled back. So I had to brake PDQ before rolling back into a fence post. I tried again and the same thing happened. Only now the fence was much closer! So I put on the parking and only then was able to drive forward with no roll back.

[Col M]

Personally, have long wondered what the ACTUAL gain in terms of fuel economy is with auto stop/start enabled, therefore inc. coasting, when comparing two absolutely identical journeys. Meaning one with it enabled, the other with it disabled. Assuming optimal condition of battery and weather exactly the same on both occasions. Obviously total saving is entirely dependent on number of stops and amount of coasting but, all things considered,
has anyone done any real-world comparisons and calculations?

It must be pretty negligible, I would imagine, in %age terms, but maybe worthwhile if doing a lot of journeys which involve 'the right' conditions.

[Paul]

Really good find!

Informative, researched and entertaining too! (remarkably articulate for an Aussie)

(and “confirms” what a waste of time stop / start is!)

[jaffacake]

That video is brilliant!

[gmacan]

Brilliant, Col M, big thanks for uploading that - great find, right on point, delivered flawlessly even with some humour, and sooo good to base it on actual research over 10 years and xxx miles .
Thanks again, confirms my gut instinct, and I'll defo be fair and square in the category that saves nowhere near anything from having auto start/stop switched on, that's now confirmed .