Do you find that sometimes when you brake, the amount of brake pedal travel is different? For example, sometimes I brake and it's instantly firm, starts braking with just a little touch of the brake pedal. But most of the time, it requires a little more travel of the pedal, slightly softer overall. It feels like it's related to a computer thing... almost as if the car is priming the brakes in anticipation for you to hit them.

also, i had an interesting experience when i was using the auto cruise control the other day and traffic slowed quickly and the car braked VERY hard to try and stop and I could even hear my tires skid briefly. good to know the system is there... although this particularly case the car probably didn't have to brake as hard as it did automatically... so I quickly took over.

 

That is EXACTLY what the truck is doing. You should read up on the Porsche Stability Management (PSM) system.

Excerpt from Porsche on PSM definition:

"Enhanced Porsche Stability Management (PSM) is fitted as standard. This system automatically maintains stability even at the limits of dynamic driving performance. Sensors continuously monitor the speed, yaw velocity and lateral acceleration of the car. Using this information, PSM is able to calculate the actual direction of travel at any given moment. If the car begins to oversteer or understeer, PSM applies selective braking on individual wheels in order to restore stability.

Under acceleration on wet or low-grip road surfaces, PSM improves traction – as well as agility and safety – using the automatic brake differential (ABD) and antislip regulation (ASR). Integrated ABS is designed to minimise braking distances.

If you prefer an ever sportier drive, PSM can be switched off. For your safety, however, PSM remains set to intervene if the vehicle is braked and ABS assistance is required. ABS and ABD remain switched on at all times. Also included with PSM are engine drag torque control (EDC), precharging of the brake system and brake assist. If you suddenly release the accelerator pedal, PSM automatically prepares for your next action: the braking system is precharged so that the brake pads are already in light contact with the brake discs. Maximum braking power is therefore achieved much sooner. Brake assist detects a panic braking situation and generates the brake pressure required for maximum deceleration."

 

For even more interesting information on the PSM system (good read), download attachment on this post

 

thank you both for these replies. very interesting and i also read the full article on the linked page. i understand all of this. however, I'm not sure it's what i'm feeling in reference to my post... because sometimes it does this "feeling" even when straight on the highway. sometimes the brake pedal is its normal "squishy" and other times it's much firmer from the initial push.

also, these articles about PSM talk about the car braking individual wheels which I don't think would adjust how the brake pedal itself feels, no?

anyhow, i find it interesting to think about these things and think about how the car / computers are operating... so appreciate the thoughts. thanks!

 

It has to do with the ACC.
Even if you do not have cruise active, it is still reading the car ahead.
It will intervene if need be. Also primes the breaks for power breaaking.

For instance if driving at 50 mph if you remove your foot from the gas slowly and apply whatever breaks the car will break normally.

If driving at that same speed, and you release gas abruptly, by the time your foot gets to the break it has not only started to apply breaks, but the pedal feel is even that more sensitive.

With ceramics this feeling is even more noticeable.

 

Good explanation Jace....Thanks

 

Jase's answer is the closest to be the right one, however is not (no offence ). If I wouldn't have read the manual that would definitely concern me as well.

What makes the break have a different feeling is the actual breaking system and not the ACC. On sudden and hard breaking, the breaking system replaces the air spaces in the lines with break fluid for faster breaking response. For speeds over 85mph, the systems replaces the air spaces at all times. Just do the test by yourself... Drive with 30mph and brake sudden and hard... Then drive with 85mph and touch the brake... same feeling right? Feels stiff (hard) and it breaks right away!

Then drive with 40mph and be smooth and nice... Feels soft and smooth right?

Thank you

 

I wasn't referencing the "different feeling" so much as I was the applying the breaks for you when you get the car icon in the display, meaning you are following too closely, or when the car in front brakes and yours does before you actually apply the breaks.

the pedal feel is correct in previous explanation but the pressue/braking on it's own, it the explanation I was trying to lend, all which is related to ACC.