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So I say you appear distressed by facts and data and your intelligent response is simply copying me? Good job gramps. Again, why would you get so upset with facts and data? That is the only weird behavior around here. It would seem to me, you would want to know what is accurate and what is not. This type of information improves the knowledge of the community so we know what to trust and what is fairy dust.
You can't stop yourself, not sure why you have me living in your head but you obviously do. Hilarious indeed, why don't you ice up a bucket of beers, might help with your issues.
You can't stop yourself, not sure why you have me living in your head but you obviously do. Hilarious indeed, why don't you ice up a bucket of beers, might help with your issues.
I was just hoping for a rational response to your negative reaction to facts and data (you see a lot of this in society these days). Anytime I see someone post something so off-base I try to understand why. I guess asking for a halfway intelligent response from you was too much. I will have to lower my expectations in the future.
I was just hoping for a rational response to your negative reaction to facts and data (you see a lot of this in society these days). Anytime I see someone post something so off-base I try to understand why. I guess asking for a halfway intelligent response from you was too much. I will have to lower my expectations in the future.
Thank You and you can have the last word, maybe that will help.
The dragy is as accurate as the gold standard vbox which is used by every magazine publication im aware of. Compared against nhra track timing equipment on hundreds of runs in a dozen or so different cars from awd audis to rwd camaros, to fwd civics ive found it to be accurate myself to .05 in et and .5mph in trap.
The numbers you see in the dragy video overlay are without rollout. Dragy also gives 1 ft rollout. The runs with rollout are...
Supposedly the pdr is not giving rollout numbers. Either way its off and not off by the same amount each run either making it both inaccurate and with poor reliability (statstical repeatability)
so you’re saying that Dragy is dead accurate and the true 0-60 time is ~ 3.8 secs for the C8?
so you’re saying that Dragy is dead accurate and the true 0-60 time is ~ 3.8 secs for the C8?
For the c8? You mean like the entire platform? Lol, no, but yes the dragy is proven accurate and the pdr has been oroven inaccurate multiple times by multiple people for multiple years.
But yes those are the accurate numbers for my car on that surface in that weather at that weight with those miles on the engine. The pdr numbers certainly were not.
That said im not surprised or disappointed by those numbers. This was a very very early first set of baseline data to compare later when the engine is fully worn in. Its also terrible weather conditions so no displeasure on my side
Thats an odd response. when i researched more the pdr has been shown to be inaccurate for years. There was even a petition started on it to get gm to adddress it. Plus its obvious once you find out they use a 5ghz setup.
Thanks for posting your data.
Wouldn't the PDR system use wheel speed data instead of GPS for speed/timing?
Wouldn't the PDR system use wheel speed data instead of GPS for speed/timing?
Thanks for the reply. I initially thought that as some other oem loggers ive messed wth use ecu data such as engine speed, speedometer, wheel speed vs timestamp. After doing some research it looks like at least on the c7 it is reported by GM that they use a 5hz gps module in their pdr. These just arent accurate enough to be used for real comparison data. The minimum for decades has been 10hz loggers.
Does the non PDR cars also use GPS or an accelerometer to show the 0-60. They also show G loads in all directions and so I don't know if they use the G loads to calculate it or GPS.
Not surprising GM would use the 5hz loggers if it benefits displaying quicker times. Interestingly not once has the pdr shown a slower time than other devices.
Looks like GM only put a 5hz GPS in the unit. No wonder its off.
Looks like c7 track guys even had a petition setup for gm to fix it as lap times are off upwards of 2 seconds at times. I wasnt aware.
Still plenty happy with the car of course and the performance is great. Still beats my 650hp tvs1900 supercharged camaro ss to 60 mph with ease.
As i said i just like to measure performance on cars and on modifications so i always make sure im doing it accurately.
Originally Posted by Gotcha
Thanks for posting your data.
Wouldn't the PDR system use wheel speed data instead of GPS for speed/timing?
Originally Posted by bhvrdr
Thanks for the reply. I initially thought that as some other oem loggers ive messed wth use ecu data such as engine speed, speedometer, wheel speed vs timestamp. After doing some research it looks like at least on the c7 it is reported by GM that they use a 5hz gps module in their pdr. These just arent accurate enough to be used for real comparison data. The minimum for decades has been 10hz loggers.
Bear with me as I'm not a 0-60 or drag race guy but I do have a lot of experience with the PDR and road course work. The PDR does use a 5 Hz GPS and frankly it has been plenty accurate for finding the lap start/finish and I created a math channel to calculate speed form GPS data to compare to the actual speed sensor in the car and determine any skew due to tires. The GPS works well for this too.
At least on the C7, the PDR uses the speedometer data to display speed which comes from a sensor in the transmission (and another in the diff I think). It does not use the GPS to display speed in the video or in the data (at least without you creating a math channel in Pi Toolbox).
Also, the data overlay on the video does lag the video, so for example if you hop off the gas it will show up in the overlay ~2-3 tenths later than where it actually happened in the video. This is a result of processing time since it is written out as the video is recorded as well as the fact that there is some smoothing of the native logging rate to the frames that are overlaid on the video. I confirmed this with Cosworth engineering last Summer. However, if you open up the MP4 in Pi toolbox and look at a time/distance chart next to a video display in the tool they will be correctly synced up.
Finally, the issue with the PDR lap times being ~1.8s off was something I found and reported to GM and which they later offered a TSB to address. There is an Ask Tadge reply on this but it was a result of some changes made to the GPS satellites to use leap seconds to adjust. It didn't happen all the time and when it did it was very noticeable as the lap time would back up 1.8s during the lap in the video.
I don't know if this helps explain your concern but I wanted to at least provide the additional info.
Interesting data, thanks for posting. I guess its somewhat moot where im concerned but it would be fun to learn more about the pdr snd how it captures acceleration data.
It sounds like it may or may not be different from how it captures lap times. So for laptimes it uses 5hz GPS for the actal lap timing and then uses sensor data for speed overlay which seems to make sense.
Now for 0-60, 1/4 mile time and trap i wonder if they use the GPS or sensor data or a combination. They could use sensor data for 0-60, 60-130, 0-100, 100-0 etc but for 1/4 mile and 1/8 mile they'd have to use GPS which it would make sense to use for all the acceleration timers. I dont know enough about it though to know.
Interesting data, thanks for posting. I guess its somewhat moot where im concerned but it would be fun to learn more about the pdr snd how it captures acceleration data.
It sounds like it may or may not be different from how it captures lap times. So for laptimes it uses 5hz GPS for the actal lap timing and then uses sensor data for speed overlay which seems to make sense.
Now for 0-60, 1/4 mile time and trap i wonder if they use the GPS or sensor data or a combination. They could use sensor data for 0-60, 60-130, 0-100, 100-0 etc but for 1/4 mile and 1/8 mile they'd have to use GPS which it would make sense to use for all the acceleration timers. I dont know enough about it though to know.
Hate to disappoint but the pdr and in dash timers are based off of a wheel speed sensor for timing acceleration. That came right from one of the corvette team members themselves.
Anyone wishing to dispute that fact should create an "ask tadge" question and pester that member who controls those questions that are posed to tadge. Good luck getting that past the gatekeeper... getting that one to be answered brings plenty of controversy in this world as shown by the hurt feelings the OP laid on people here to dispel these ridiculous mid 2 second 0 to 60 times NOT THAT THE CAR CANT DO 2.9 WITH A 1FT ROLLOUT. Regardless of how quick or not the C8 is from 0 to whatever, the pdr and dash timer is horrifically inconsistent.
No one is saying the car isn't fast, its the people that actually hang their hat on the accuracy of these lousy in car timers when we have drag slips, vbox, or dragy times that are much more precise.
Exactly.
I think as more owners get their cars and start testing, we'll see legit sub 3 second runs.
The car can do it, just how far below is the question.
I'm really looking forward to what the Z06 brings to the table.
08-01-2020, 01:42 PM
