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Ok I recently sold my c8 but have always been curious about this. Tell me if my summarization is wrong…A while back I think Jerry U who is pretty knowledgeable let the “cat out of the bag” on my interpretation:
The cars brake by wire, ABS system is designed to stop the car at a certain distance. Due to the skidding issue for amateurs in a mid engine car- the system has been “dumbed down”. My interpretation is that if you have z51, non z51 or some aftermarket pad the stopping will be about the same. Only tires make a slight difference. To truly modify system you would have to go deep into cars computerized brake system. I am not sure what the word bite means in reference to brakes. Also I am not talking about prolonged high speed braking and track use. Please explain to me if my layman’s interpretation is not correct!
Is there a specific reason you chose to do this in PTM: Wet? It will engage ABS much sooner in that mode by design. You should reproduce this in Race mode. Tire size and brand would be helpful as well. That all said, engaging ABS on the OEM 245s is not an impressive feat, IMO; they are extremely easy to lock up.
ABS for stopping is designed to engage ANYTIME the tires lose traction under decel. This is for safety. ABS as a function of ESC and TC are mitigated through drive modes.
It's a good question of why I use pct wet. I use it on the streets because I have ptm on my z button and it's the only mode that allows the suspension to be in sport instead of track. This way I can use the scroll wheel to change ptm modes instead of drive modes. I never change drive modes. I use z mode 100%
With the mode in track ABS actually activates probably a millisecond or so sooner because of less weight transfer and brakes in track mode are set to "track" sensitivity which is just a harder pedal feel. In wet it's the lighter touring pedal feel.
But here's another cold run in race 2...no nannies...
Ok I recently sold my c8 but have always been curious about this. Tell me if my summarization is wrong…A while back I think Jerry U who is pretty knowledgeable let the “cat out of the bag” on my interpretation:
The cars brake by wire, ABS system is designed to stop the car at a certain distance. Due to the skidding issue for amateurs in a mid engine car- the system has been “dumbed down”. My interpretation is that if you have z51, non z51 or some aftermarket pad the stopping will be about the same. Only tires make a slight difference. To truly modify system you would have to go deep into cars computerized brake system. I am not sure what the word bite means in reference to brakes. Also I am not talking about prolonged high speed braking and track use. Please explain to me if my layman’s interpretation is not correct!
It was actually a Pro with a Pro-Video that found out what I (and others) have wondered before I placed my order for a C8. Why The Porsche Cayman GT4 had much bigger brakes that the C8 Z51! In fact, now that data is out the C8 Z51 stops take longer that the C7 Z51 and significantly longer than The Porsche that has smaller width tires! Both take longer to stop than my C7 Grand Sport. AND it's NOT all tires.
Listen carefully and you'll see Jason Fenske interviewed the GM Brake engineers who picked "smaller than they could have brakes" for the C8 Z51. It includes some words about the ABS algorithm BUT mainly they had to meet the criteria Tadge Juechter insisted on with the C8 design, quoting: He was Paranode and deathly afraid (his words) of trailing throttle oversteer like his Dad's Porsche! I was racing a 60% rear engine car probably from the same era an it was more than trailing throttle oversteer. If you were forced to take other than your preferred line thru a turn by another driver and were going too fast, you could countersteer a fraction of a second prior to turning and "might" avoid having the rear end slide off the road! Tagde has also said it took Porsche several generations to fix the 911 types and they had to get it right the 1st time. They did as he said setting everything to have the car handle benignly! https://www.youtube.com/watch?time_c...ature=emb_logo
Pic I posted before I place my early C8 Z51 order as was concerned what to me looked like anemic brakes. Jason quotes the GM engineers as saying there is nothing about an ME that makes it brake slower than the C7 and larger brakes could make it stop faster. They said with aggressive braking there is a better balance in brake loads front and rear over a FE car. But could make it a bit tail happy (oversteer) in aggressive stops and some drivers could get in trouble.
Brake size has to do with capacity and marketing not stopping distance. Stopping distance is mostly determined by the tires, weight transfer and bias. GM purposely reduced the rear brakes contribution to prevent brake induced oversteer.
Brake size has to do with capacity and marketing not stopping distance. Stopping distance is determined by the tires, weight transfer and bias. GM purposely reduced the rear brakes contribution to prevent brake induced oversteer.
I said this before BUT will one more time. I use this approach to test physics and engineering principles. Take what you said to the extreme. If GM engineers made the brakes 1 inch smaller it would till stop. ABS would still activate but over would take longer. If you don't agree, try 2 inches smaller. The GM engineers said they could have made it stop shorter with bigger brakes. Listen to the video. But to keep the C8 handling beinley they used smaller brakes than they could!
Brake size has to do with capacity and marketing not stopping distance. Stopping distance is mostly determined by the tires, weight transfer and bias. GM purposely reduced the rear brakes contribution to prevent brake induced oversteer.
Correct. Jerry is probably thinking of brake BIAS which is front to rear. You can adjust this for enhanced stability. You can also use different pad compounds front to rear to alter bias.
If the tires can already be easily broken loose with our brake size it's not as though our "small brakes" are there to... purposefully not work well so we don't skid out of control.
Without ABS and ESC they absolutely will. Add a race pad up front and a street pad on back and take it to the track and you'll be spinning in no time
I said this before BUT will one more time. I use this approach to test physics and engineering principles. Take what you said to the extreme. If GM engineers made the brakes 1 inch smaller it would till stop. ABS would still activate but over would take longer. If you don't agree, try 2 inches smaller. The GM engineers said they could have made it stop shorter with bigger brakes. Listen to the video. But to keep the C8 handling beinley they used smaller brakes than they could!
You should watch the video again and listen to what he said.
He said they limited the bias to the rear brakes for stability. That's not surprising to anyone as that's what you would do.
trying to extrapolate that to purposefully using smaller brakes is...odd. larger brakes are there for repeatability....track work. Not stopping distances.
The z06 has 15.7" discs up front and 15.4" at the rear.... for repeatability. It stops on 95 feet...a whopping 2 feet better than the z51 while on grippier tires
Correct. Jerry is probably thinking of brake BIAS which is front to rear. You can adjust this for enhanced stability. You can also use different pad compounds front to rear to alter bias.
If the tires can already be easily broken loose with our brake size it's not as though our "small brakes" are there to... purposefully not work well so we don't skid out of control.
Without ABS and ESC they absolutely will. Add a race pad up front and a street pad on back and take it to the track and you'll be spinning in no time
It's funny I ask folks to listen to the video of Jason Fenske (a pro) on what he found talking with the GM Engineers. They clearly said they could have used bigger brakes and it would have stopped faster!
I have been at this with only a few others since 2007. I said then what I will now. Not worth my effort to argue or others to have listen.
This is not correct. At some point capacity would be a factor, but for 60-0 it would have to be much smaller.
Originally Posted by JerryU
I said this before BUT will one more time. I use this approach to test physics and engineering principles. Take what you said to the extreme. If GM engineers made the brakes 1 inch smaller it would till stop. ABS would still activate but over would take longer. If you don't agree, try 2 inches smaller.
He made a mistake, or this was taken out of context or incorrectly quoted.
Originally Posted by JerryU
The GM engineers said they could have made it stop shorter with bigger brakes. Listen to the video. But to keep the C8 handling beinley they used smaller brakes than they could!
It's funny I ask folks to listen to the video of Jason Fenske (a pro) on what he found talking with the GM Engineers. They clearly said they could have used bigger brakes and it would have stopped faster!
I have been at this with only a few others since 2007. I said then what I will now. Not worth my effort to argue or others to have listen.
He said they reduced rear bias...the devil's in the details Jerry.
This is not correct. At some point capacity would be a factor, but for 60-0 it would have to be much smaller.
He made a mistake, or this was taken out of context or incorrectly quoted.
Glad you considered that approach as it's very helpful when taken to extremes and makes the issue clear.
So if you think making the rotors 1 inch smaller will not increase 60 to zero times when activating ABS(I do) then take it to 2 inches smaller. ABS will still activate and stop the tire BUT it will take longer! Each fraction of a second takes more feet to stop! The GM engineers said they could have used larger brakes and it would stop faster. I would have preferred that as I can deal with an oversteering car!
Glad you considered that approach as it's very helpful when taken to extremes and makes the issue clear.
So if you think making the rotors 1 inch smaller will not increase 60 to zero times when activating ABS(I do) then take it to 2 inches smaller. ABS will still activate and stop the tire BUT it will take longer! Each fraction of a second takes more feet to stop! The GM engineers said they could have used larger brakes and it would stop faster. I would have preferred that as I can deal with an oversteering car!
The GM engineers HAVE used MUCH larger brakes on our car. 15.7 front and 15.4 rear and it did nothing to stopping distance if you take tires out of the equation.
He made a mistake, or this was taken out of context or incorrectly quoted.
To answer your question of the GM engineers being misquoted. This is what another good automotive writer states:
Brian Gillogy wrote about the2020 Stingray and 2014 Corvette taking an additional 7 feet to stop: 97 feet compared to 90. The C8’s mid-engine configuration is biased heavier in the rear then switches to more weight on the front tires as the brakes are aggressively applied. As the rear tires get closer and closer to the limit, any steering input makes the car twitchy. The engineers decided that predictable handling at the braking limit was a priority over stopping distance. When pushed to its limits C8 Stingray will tend to Understeer and helps keep novice drivers from swapping ends and winding up in a ditch!
Now aggressive braking in an ME car is complex. That transient weight transfer to the front from the static 40/60 to probably ~60/40 is dependent on a number of factors including spring stiffness, shocks etc. Just to show it’s more than tires: A Ferrari 488 that even looks from a side view like a C8 with the same size tires and 15.6” front brakes and 14.1” rears versus the C8 Z51 13.8” front and 13” rear stopped from 70 mph in 124 feet and the C8 took 149 feet!
Understand you can't compare different cars directly BUT as I showed in pic Post #63, the ME Porsche Cayman GT4 with 15" rotors front and rear stops faster with somewhat smaller tires (same Michelin PS 4S: 235/295 versus C8 245/305.)
BTW one reason I am interested in Brakes is a 2017 Grand Sport stopped from 70 in 136 feet with Cup tires and with Cup 2 and Carbon Ceramic Brakes in 129 feet. With standard ZPs mine stopped from 60 faster than the C8 Z51. As I said aggressive braking is very complex. Yep the GM engineers have to deal with the ABS algorithm issues that use sensors on each wheel, accelerators, consider road conditions etc, etc. BUT that is what the GM engineers said they did used smaller brakes than they could to maintain benign handling to cover all driver skills.
You said brakes would have to be much smaller to affect 60 to 0. As I showed in post #27 with simple math, if the ABS takes just 0.1 seconds longer that is ~10 feet!
To answer your question of the GM engineers being misquoted. This is what another good automotive writer states:
Brian Gillogy wrote about the2020 Stingray and 2014 Corvette taking an additional 7 feet to stop: 97 feet compared to 90. The C8’s mid-engine configuration is biased heavier in the rear then switches to more weight on the front tires as the brakes are aggressively applied. As the rear tires get closer and closer to the limit, any steering input makes the car twitchy. The engineers decided that predictable handling at the braking limit was a priority over stopping distance. When pushed to its limits C8 Stingray will tend to Understeer and helps keep novice drivers from swapping ends and winding up in a ditch!
Now aggressive braking in an ME car is complex. That transient weight transfer to the front from the static 40/60 to probably ~60/40 is dependent on a number of factors including spring stiffness, shocks etc. Just to show it’s more than tires: A Ferrari 488 that even looks from a side view like a C8 with the same size tires and 15.6” front brakes and 14.1” rears versus the C8 Z51 13.8” front and 13” rear stopped from 70 mph in 124 feet and the C8 took 149 feet!
Understand you can't compare different cars directly BUT as I showed in pic Post #63, the ME Porsche Cayman GT4 with 15" rotors front and rear stops faster with somewhat smaller tires (same Michelin PS 4S: 235/295 versus C8 245/305.)
BTW one reason I am interested in Brakes is a 2017 Grand Sport stopped from 70 in 136 feet with Cup tires and with Cup 2 and Carbon Ceramic Brakes in 129 feet. With standard ZPs mine stopped from 60 faster than the C8 Z51. As I said aggressive braking is very complex. Yep the GM engineers have to deal with the ABS algorithm issues that use sensors on each wheel, accelerators, consider road conditions etc, etc. BUT that is what the GM engineers said they did used smaller brakes than they could to maintain benign handling to cover all driver skills.
You said brakes would have to be much smaller to affect 60 to 0. As I showed in post #27 with simple math, if the ABS takes just 0.1 seconds longer that is 10 feet!
You sure do ignore that the c8 had 15.7" and 15.4" brakes on the z06. It stops in the same distance.
It's brake BIAS which was stated in the video you linked to...
This is not correct. At some point capacity would be a factor, but for 60-0 it would have to be much smaller.
He made a mistake, or this was taken out of context or incorrectly quoted.
Originally Posted by JerryU
Glad you considered that approach as it's very helpful when taken to extremes and makes the issue clear.
So if you think making the rotors 1 inch smaller will not increase 60 to zero times when activating ABS(I do) then take it to 2 inches smaller. ABS will still activate and stop the tire BUT it will take longer! Each fraction of a second takes more feet to stop! The GM engineers said they could have used larger brakes and it would stop faster. I would have preferred that as I can deal with an oversteering car!
I just saw this thread and would like to provide some more conceptual information.
@Drew888 is correct here. The way to prove him correct is simple. Deactivate ABS and stomp on the brakes. The brakes on C8 (Z51 or standard) are more than powerful enough to lock up right away. Assuming the brake calipers, rotors, and pads are powerful enough to lock the wheels, going with larger diameter rotors and larger calipers will not affect the stopping distance for the first stop or first few stops. What the larger rotors, calipers, pads buy you is a bigger heat sink which allows the brakes to function effectively and predictably under continued heavy use. We see this all the time in racing. We are always trying to save weight. Especially rotating weight and unsprung weight. So we don't want brake setups to be larger than they need to be. But, we have to be careful not to go too small. Typically we go a little bit bigger than we need to just to have a fudge factor.
Bigger is not always better and certainly does not guarantee shorter stopping distances. ABS does not magically work better with larger rotors.
This doesn't even take into account tuning brake bias front to rear....
^^^^
Yep bigger brake are not the whole answer, just an indicator. Braking distance activating ABS is NOT the end-all it's also an indicator. All my comments relate to passing up a turn I make with room temp brake pads. When I leave my home merge into a 4 lane divided highway with often heavy traffic going ~70 mph to Myrtle Beach. I turn soon after onto another narrow rural highway with no shoulder to slow. I brake aggressively so the pack of cars (with trucks RV's etc) don't have to slow significantly for me. If I slowed normally making that turn, due to reaction time to brake as folks in a pack a vehicles do progressively, someone would be rear ended! NOT me, folks 4 or 5 back in the pack!
When driving aggressively, tracking or racing you don't activate ABS, as I said it’s an indicator. But brake pad friction at different temps and modulation, brake feel are key.
Funny a "poster" recently expressed concerned on an E-Ray Thread about the CCB brakes that come standard (I'm at 3000 for an E-Ray, sold my 2020 Z51.) As he noted the C8 Z06 with CCB brakes is not a "stopping numbers top performer." He related that to the Jason Fenske findings after talking with the GM brake engineers! He wondered if GM has done the same as Jason said, limited max braking ability quoting, "So folks who didn't know what they are doing behind the wheel don't get in trouble.” Or quoting Tadge about his biggest concern when designing the C8, “He was paranoid n deathly afraid it would have the handling issues of hos Dad's early Porsche!" I raced a 60% rear weight rear engine car about the era of his Dad’s Porsche so clearly understood his concern!
I had similar concerns re CCB brakes that are not know for good stopping with room temp pads. BUT I have done enough research and the quality of brake modulation braking control appears to be good. Will have to see just how they perform on my often needed quality room temp pad stops. Here is braking data and all can make their own decisions. Jason asked the question of the GM brake engineers because the C7 Z51 stops faster that a C8 Z51. They provided the answer and said in fact an ME can stop faster then a similar FE car. They could have made the C8 stop faster but that could cause the rear end to "step out" in aggressive braking. Tadge had said they did everything possible to make the C8 handle benignly. They followed his dictate.
Brake pads for tracking can handle the higher temps that produces. But at room temps the pad friction is lower. There is no free lunch. Street only pads have high friction from room to temps encountered in street driving 800 to 900 F BUT can't handle Tracking temps.
There is a lot more to braking. Confidence and quality/linearity of modulation is what I require in my stopping aggressively with room temp pads as I turn into a narrow rural road to go into town. If a car is waiting to merge don't have much room when slowing from ~70 mph to turn.
I'm not sure why ABS activation is considered in a brake test, for street or for racing. If the argument is "I can activate the ABS no matter what pads I install", to me it is equivalent to the argument of "I can activate the airbags no matter what species of tree I run into". It's a safety feature, not a prime standard for braking capabilites in any situation.
I have done extensive brake modifications on dual purpose performance cars ranging from calipers, rotor size, rotor material, rotor design (slotted/drilled), pad type, fluid type, and brake lines. I have activated my ABS before on the various setups (usually out of morbid curiosity). But to say I was able to activate the ABS and call each setup the same because I could activate it... Yeah I'm going to say that is a false positive. There is no mistaking that certain setups are vastly superior than others just by their driving characteristics when ABS isn't activated. And I'm not referring to turning the ABS functionality off, I mean by stopping in a manner that doesn't set off ABS. Cold/hot, street/track, dry/wet... You can have different setups with different results and never activate ABS. Again, ABS is a safety feature, not a prime standard for braking capabilities.
The reason that the C8 does not stop as well as the C7, as hinted by the GM engineers, is the brake bias is more to the front than is otherwise ideal for braking. In other words, the rear braking performance is not what it could be so the car does not slow down as fast as it could. They compromise the braking to make the car safer for the average Joe....too bad.
By the way, with the modern ABS racing systems, such as the Bosch Motorsport ABS 5, racers certainly do activate ABS. Like all the time.
I race an air-cooled 911 (rear engine) with a weight distribution of about 35%F/65%R. I run a lot more bias toward the rear than the typical street 911. But I run a lot of rear wing and 14" wide slicks....
I'm not sure why ABS activation is considered in a brake test, for street or for racing. If the argument is "I can activate the ABS no matter what pads I install", to me it is equivalent to the argument of "I can activate the airbags no matter what species of tree I run into". It's a safety feature, not a prime standard for braking capabilites in any situation.
I have done extensive brake modifications on dual purpose performance cars ranging from calipers, rotor size, rotor material, rotor design (slotted/drilled), pad type, fluid type, and brake lines. I have activated my ABS before on the various setups (usually out of morbid curiosity). But to say I was able to activate the ABS and call each setup the same because I could activate it... Yeah I'm going to say that is a false positive. There is no mistaking that certain setups are vastly superior than others just by their driving characteristics when ABS isn't activated. And I'm not referring to turning the ABS functionality off, I mean by stopping in a manner that doesn't set off ABS. Cold/hot, street/track, dry/wet... You can have different setups with different results and never activate ABS. Again, ABS is a safety feature, not a prime standard for braking capabilities.
Agree! Yep stopping with ABS means nothing when Tracking, racing or driving aggressively. That is not controlled braking! In fact my issue was not stopping but slowing rapidly with confidence so I can turn into a narrow rural road from ~70 mph especially when there is a car stopped waiting to merge!
The reason that the C8 does not stop as well as the C7, as hinted by the GM engineers, is the brake bias is more to the front than is otherwise ideal for braking. In other words, the rear braking performance is not what it could be so the car does not slow down as fast as it could. They compromise the braking to make the car safer for the average Joe....too bad.
By the way, with the modern ABS racing systems, such as the Bosch Motorsport ABS 5, racers certainly do activate ABS. Like all the time.
I race an air-cooled 911 (rear engine) with a weight distribution of about 35%F/65%R. I run a lot more bias toward the rear than the typical street 911. But I run a lot of rear wing and 14" wide slicks....
Yep give Porsche engineering a lot of credit for making a 60+% rear weight car become excellent handling. Tadge said it took Porsche several generations to solve the oversteer issues of his Dad's early Porsche and they (GM) had to get it right the first time- and did.
Yep, my 60% rear weight rear engine car even with parallelogram rear suspension would snap out if going too fast for a turn. Usually happened when another car caused you to take other than your planned line thru a turn! We and those early Porsches had fun dealing with the issue but had to drive like Tony Stewart in his dirt car. If planned would counter steer as you initiated the turn!
Frankly I was surprised when I made my often 1 "g" turn that there was no indication of the rear trying to "hand out" out when I made (in case below) a tighter turn than usual. Car was very neutral. Saw on the PDR after I still kept some throttle from my old experiences. I'm anxious to see just what torque vectoring can achieve in my favorite high "g" turn in my E-Ray (@ 3000.) Don't Track (and racing days long over) but this is an area with no homes, farm fields on both sides and often no traffic.
06-29-2023, 03:32 PM
