Ever lengthening cruise control gaps

[slothinker]

I was initially under the impression that each 'bar' shown in the Taycan Cruise Control dash widget indicated an average car length or maybe two. Over time it seems to me that this gap has widened. Initially I used 4 bars when doing highway driving which kept my car at a reasonable distance from the car in front.

Now I'm down to 2 bars which keeps my can an estimated 3.5 car lengths behind at highway speed. I'm wondering if these changes are the result of software updates or perhaps something else has changed in my vehicle specifically?

Sponsored

 

[ovonrein]

Varies with speed.

 

[2P168S]

Yes, varies with speed and more closely correlates to following time gap than following distance gap

 

[anonymouse]

Now I'm down to 2 bars which keeps my can an estimated 3.5 car lengths behind at highway speed.

3.5 car lengths is not a safe distance at 65mph (US highway speed) is it?

in the UK, driving instructors recommend 3-second minimum gap in dry conditions, 4-5 in wet conditions. The UK highway code says (for 70mph):
- thinking distance 21m
- plus braking distance 75m
- equals total stopping distance 96m
- this is roughly 24 car lengths.

You might not keep 24 car lengths but 3.5 is a long way off that target.

Even the "2-second rule" which some countries recommend, would place you 12-13 car lengths behind at 65mph.

In other words, Innodrive/ALK is correctly extending the distance to keep better safety.

 

[slothinker]

3.5 car lengths is not a safe distance at 65mph (US highway speed) is it?

in the UK, driving instructors recommend 3-second minimum gap in dry conditions, 4-5 in wet conditions. The UK highway code says (for 70mph):
- thinking distance 21m
- plus braking distance 75m
- equals total stopping distance 96m
- this is roughly 24 car lengths.

You might not keep 24 car lengths but 3.5 is a long way off that target.

Even the "2-second rule" which some countries recommend, would place you 12-13 car lengths behind at 65mph.

In other words, Innodrive/ALK is correctly extending the distance to keep better safety.

I don't think the changes I've noticed over time relate to driving conditions.

Regarding maintaining 24 car lengths ...wouldn't happen on a major U.S. highway because cars would be pulling in front of your constantly. Might make sense for a road with only two lanes.

 

[ovonrein]

wouldn't happen on a major U.S. highway because cars would be pulling in front of your constantly.

Happens in Europe too. First time I tried an ACC (on a hire car) I was leaving Lux on a Friday night. I left the ACC to do its thing on the motorway. My car was almost going backwards. People were constantly jumping into the gaps and my car was always backing off. It was comical.

Also, ACC is creating havoc on German motorways. The way it used to be is that a faster car would run up the rear of a fast car. The fast car would calculate the arrival of the faster car in the rear mirror and eye a short gap to their right to briefly jump out of the way to let the faster car pass unimpeded (before immediately jumping back into the fast lane to avoid crashing into the back of the car in the slow lane).

With ACC, the faster car backs off before the fast car even perceives them as faster and people no longer move out of the fast lane to make room. (There isn't enough room in the slow lane to allow the faster car to accelerate past. The fast car cannot hence afford to be curteous.)

The fallback used to be that the faster car would flash the fast car to alert them to their imminent approach and of their desire to quickly overtake. But when I last did this to roll up a fast lane in Germany, drivers in faster cars than mine (who appeared to me as just bumbling along in the fast lane) were getting really upset. When they then later overtook me after *I* had cleared the lane for them, the penny dropped - they had all their ACC engaged which was politely keeping distances...

There are many many very strange quirks to these ACC systems. You will get used to them. Basically, they work well on motorways. Also in stationary town traffic. But in European town centers, they are a nightmare. My Taycan will slam the brakes in town for no apparent reasons. It will also attempt to kill me every time I slip off the motorway.

But these things are not unique to Porsche. My wife nearly hit the dash on a test drive with a Mini when the car performed an emergency halt because some pedestrian was standing by the roadside...

 

[Solid]

It is follow time not distance, and they have changed what each bar means over the years in response to drivability concerns. You can see the follow time in the manual and they are calibrated to use average human reaction time + a margin of error. If you look on say a 2015 Macan S you'll see in the manual that the closest ACC follow distance equates to ~1.3 seconds. The average reaction time from incident to perception to reaction for a driver paying attention is ~ 0.75 seconds. Making it 1.3 nearly doubled the margin of error and of course all of us overconfident hairless beach apes would constantly cut into that excessive gap, and then the car tries to recover its margin of error by slowing down. The closer in front of you someone cuts in, the more aggressively it slows to recover the follow time (from basically coasting down to braking hard). The Taycan has a significantly shorter follow time on the closest setting that better balances safety and human behavior. With up to date software in the modules it will also remember the setting between driving sessions (which it did not when new and it would default back to the middle of its range). No one pays attention anymore because of phones, and driver aids tend to make us pay even less attention, so they need to budget over that 0.75 seconds for you to look up from your phone or come out of your daydream.

 

[jdirik]

Yes, varies with speed and more closely correlates to following time gap than following distance gap

Definitely makes sense!

Sponsored