Dragy

[shellderp]

Here’s the quote from Tesla’s site:
“Performance
Performance acceleration ratings are based on maximum battery power mode and follow Motor Trend's test procedure of subtracting the first foot rollout time to represent drag strip performance.”

It’s my understanding that all claimed acceleration numbers for all Tesla’s cars include the 1 foot rollout error. I believe the error is about half a second in the Performance S. I could be off a bit. Who knows? The only thing we do know is that Tesla’s numbers are wrong.

but motor trend claimed 2.28 with rollout, and tesla claims 2.4. Actual dragy times are like 2.5 without rollout

 

[D.E.]

[

but motor trend claimed 2.28 with rollout, and tesla claims 2.4. Actual dragy times are like 2.5 without rollout

Those are pretty awesome times in any case. I downloaded dragy’s app. Most of the P100DL are in the 2.8 range. There are some 2.7s and one 2.62. I didn’t see any in the 2.4 or 2.5 range.

It’s still a very quick car.

 

[TIppy]

It's GPS based so there's inherent flaws to timing something that does 0-60 or 0-whatever.

It's relatively accurate but there's also a margin of error that's probably around 10-15% possibly even more. I didn't read the documentation or reviews but I've used these GPS based devices in the past and they're not super accurate. It's best for comparing before/after mods since whatever error exists is more likely to exist across runs.

In other words, the difference between two different measurements will be more accurate/useful than just an individual measurement. This is where these devices shine is you do some baseline measurements and then perform whatever mod you have planned and then take some more measurements to get an idea (read: estimate) of how much power you gained via that mod.

If you plan to measure your car with a $150 consumer grade GPS device and then sue Tesla over the 0.01 difference in your 0-60 I think you're in for a rude awakening.

Bottom line: It's a toy. If you bought a six figure car you can likely afford something that's $150 for pure entertainment value. If you're trying to "time share" the $150 then you don't seem to fit this category so I would say it's not going to be worth your investment on something like a Tesla. If you want an idea of what the performance #'s are just Google it and you'll get more accurate #'s than what that device will get you after you spend your hard-earned duckets.

The results of the dragy vs timeslip look pretty good at this link.

Track vs vbox vs Dragy results

The 60' is off a little, but this could just be depth of staging.

 

[bhzmark]

It's GPS based so there's inherent flaws to timing something that does 0-60 or 0-whatever.

It's relatively accurate but there's also a margin of error that's probably around 10-15% possibly even more. I didn't read the documentation or reviews but I've used these GPS based devices in the past and they're not super accurate. It's best for comparing before/after mods since whatever error exists is more likely to exist across runs.

In other words, the difference between two different measurements will be more accurate/useful than just an individual measurement. This is where these devices shine is you do some baseline measurements and then perform whatever mod you have planned and then take some more measurements to get an idea (read: estimate) of how much power you gained via that mod.

If you plan to measure your car with a $150 consumer grade GPS device and then sue Tesla over the 0.01 difference in your 0-60 I think you're in for a rude awakening.

Bottom line: It's a toy. If you bought a six figure car you can likely afford something that's $150 for pure entertainment value. If you're trying to "time share" the $150 then you don't seem to fit this category so I would say it's not going to be worth your investment on something like a Tesla. If you want an idea of what the performance #'s are just Google it and you'll get more accurate #'s than what that device will get you after you spend your hard-earned duckets.

All the information above about Dragy is totally wrong. As I said, ignore people who don’t own Dragy. Just get it.

 

[bhzmark]

The 60' is off a little, but this could just be depth of staging.

Exactly. Dragy is more accurate than even timeslips because of the variability of staging. Dragy is simply the most accurate and comparable metric to use for your own car to measure how you might modify it and try new tires etc, and in comparison to others.

There are a bunch of YouTube videos and forum posts all over comparing Dragy to drag strips and Vbox and it is rock solid accurate and more user friendly than anything else. And the leaderboard and social aspect of it makes it additionally useful.

Trust me, ignore people who don’t own Dragy and don’t know what they are talking about.

 

[Ostrichsak]

All the information above about Dragy is totally wrong. As I said, ignore people who don’t own Dragy. Just get it.

Oh, so it doesn't use GPS.

 

[bhzmark]

Oh, so it doesn't use GPS.

More specifically, GPS using a sampling rate of 10hz.

As a public service for doubters:

Quick Tech: Dragy GPS-Based Performance Meter - DSPORT Magazine

Dragy GPS Performance Meter Review and Racelogic VBOX Comparison

Track vs vbox vs Dragy results

Track vs vbox vs Dragy results - Page 2

 

[shellderp]

[


Those are pretty awesome times in any case. I downloaded dragy’s app. Most of the P100DL are in the 2.8 range. There are some 2.7s and one 2.62. I didn’t see any in the 2.4 or 2.5 range.

It’s still a very quick car.

yeah I was wrong, it is around 2.7 without rollout. I was looking at vbox numbers which include rollout

 

[bhzmark]

[


Those are pretty awesome times in any case. I downloaded dragy’s app. Most of the P100DL are in the 2.8 range. There are some 2.7s and one 2.62. I didn’t see any in the 2.4 or 2.5 range.

It’s still a very quick car.

with the rollout there are one 2.4 and a handful of 2.5s on Dragy.

 

[Simon21]

All the information above about Dragy is totally wrong. As I said, ignore people who don’t own Dragy. Just get it.

I took your advice and got one. I'm a little disappointed. The app sucks. But what really disappoints me is that this car is not even breaking under 3 seconds 0-60. I feel ripped off

 

[UkrHog]

I took your advice and got one. I'm a little disappointed. The app sucks. But what really disappoints me is that this car is not even breaking under 3 seconds 0-60. I feel ripped off

Which car is not breaking 3 seconds?

 

[UkrHog]

Some runs from today. Dragy times are with out a 1ft roll out.

 

[Dithermaster]

I took your advice and got one. I'm a little disappointed. The app sucks. But what really disappoints me is that this car is not even breaking under 3 seconds 0-60. I feel ripped off

I'd been interested in getting one, and this thread convinced me to do it. I don't mind the app but it takes some getting used to. I wish there was a web interface to review results on my laptop instead of my phone.

My very first Dragy 0-60 run, at 70℉, with launch mode but no significant battery pre-heat, was 2.92 seconds. This is a 2019 Raven Model S Performance Ludicrous Mode with 19" wheels and Michelin Pilot Sport 4 tires. With a warm battery and cleaner pavement I'm sure it would be lower. Good luck with your car!

 

[Dangerous Fish]

Performance boxes and data loggers use more than just raw GPS data to measure acceleration.
I haven't used the Dragy myself but I suspect it's like some others and perhaps uses accelerometers in conjunction with GPS to get more accurate results than just GPS data alone. How accurate any of these low cost devices is will be down to the spec. of the components used inside and how good the software is.

Like any instrument used to measure stuff, unless they are properly calibrated you can't really expect them to correspond exactly with data from another device, even from the same manufacturer.

They are all probably accurate to within a couple of tenths for 0-60 measurements. If you want more accuracy you need to spend a lot more money.

 

[TIppy]

Performance boxes and data loggers use more than just raw GPS data to measure acceleration.
I haven't used the Dragy myself but I suspect it's like some others and perhaps uses accelerometers in conjunction with GPS to get more accurate results than just GPS data alone. How accurate any of these low cost devices is will be down to the spec. of the components used inside and how good the software is.

Like any instrument used to measure stuff, unless they are properly calibrated you can't really expect them to correspond exactly with data from another device, even from the same manufacturer.

They are all probably accurate to within a couple of tenths for 0-60 measurements. If you want more accuracy you need to spend a lot more money.

They don't use acclerometers. They use integrated doppler, i.e., phase of the gps carrier frequency. They keep track of the change in the number of carrier cycles from the starting position to a fraction of a wavelength. This can give them a delta position accuracy of a few millimeters. Together with the short term stability of the onboard crystal clocks, this provides very accurate measurements

 

[Dangerous Fish]

They don't use acclerometers. They use integrated doppler, i.e., phase of the gps carrier frequency. They keep track of the change in the number of carrier cycles from the starting position to a fraction of a wavelength. This can give them a delta position accuracy of a few millimeters. Together with the short term stability of the onboard crystal clocks, this provides very accurate measurements

"a few millimetres" - over what distance?
Sorry, but that's very unlikely whatever they might have told you.

 

[TIppy]

"a few millimetres" - over what distance?
Sorry, but that's very unlikely whatever they might have told you.

The phase of the the carrier can be tracked to about 1 or 2 percent. The wavelength is 19 cm, so 1 percent would be 1.9 mm.

The ultimate accuracy of the measurements depends on how carefully they process this data. But this is from vbox's website.

How is distance measured so accurately given GPS is only accurate to a few m?

GPS position has limitations in accuracy. If we were to use GPS position to measure distance, then we could only achieve distance accuracies of a few metres rather than centimetres. For this reason we use the velocity (derived from Doppler measurements) to measure distance instead. This eliminates the majority of the normal errors associated with GPS accuracy, and allows us to measure distance to within a few centimetres during a brake stop.

Product Velocity Distance Absolute Positioning* Height* Heading Acceleration
VBOX Video HD2 10 Hz 0.1 km/h 0.05 % ±3 m ±10 m 0.3° 1 %
Video VBOX Pro 10 Hz 0.1 km/h 0.05 % ±3 m ±10 m 0.1° 1 %
Video VBOX Pro 20 Hz 0.1 km/h 0.05 % ±2.5 m ±6 m 0.1° 0.5 %
VBOX Micro 10 Hz 0.1 km/h 0.05 % ±3 m ±10 m 0.1° 1 %

Notice that distance is given as 0.05% accuracy. The 0 to 60 distance for a ludicrous model s is about 130 ft or 39624 mm . 0.05% of that is about 20 mm.

Also, the dragy seems to be more accurate than vbox when compared to timeslips.

 

[Simon21]

Not sure why but the mph displayed in my cars aren't the same as displayed on the Dragy app

 

[TIppy]

Not sure why but the mph displayed in my cars aren't the same as displayed on the Dragy app

The car mph is derived from wheel rotations. It can be affected by changes in tire diameter caused by wear and inflation pressure. Plus, it always seems to be a little high so that you won't be going faster than the posted limit. The gps speed is usually accurate to about 0.1 to 0.2 km/h.

 

[Bill Price]

Here's an idea...........talk your buddy into buying a dragy and then just borrow it for a day? Failing that, why not just go to the local dragstrip and run your car? The local dragstrip here has one day a week when you can run your own car down the dragsrip as many times as you like for an entrance fee of $25. Not as cheap as borrowing from your buddy for a day, but far cheaper than buying a dragy that you will use one or two times?