That Motor Trend 1 foot rollout

[D.E.]

Does anyone understand the logic behind that Motor Trend 1 foot rollout? Their claim:

We subtract a one-foot rollout from the launch to simulate dragstrip performance (dragstrip runs started the whole quarter-mile acceleration craze and remain the only practical way for most owners to test their own cars, so we want our numbers to match those acquired in this way)​

So as I understand it, Motor trend doesn't count the first foot of travel. According to Motor Trend regarding the SP100D:

The car crosses 1-foot mark and official timing starts. The car is traveling at 5.9 mph, averaging 1.30 g of longitudinal acceleration.​

So with the SP100D, the car isn't at zero MPH when the timing starts, it is traveling at 5.9 MPH. So isn't that 2.28 seconds a 5.9-60 time? That near 6 mph that isn't really included is nearly 10% of the final 60 MPH speed. At an acceleration of 1G, that first foot takes 1/4 second. Motor Trend says the Tesla is accelerating at 1.3Gs at that point so the elapsed 1 foot time should be less.

Don't get me wrong, accelerating to 60 MPH in 7.4 car lengths is amazing, going from "6-60" or even a fudged 0-60 in 2.28 seconds is just as amazing. Still, it just doesn't seem all that accurate.

 

[sorka]

Does anyone understand the logic behind that Motor Trend 1 foot rollout? Their claim:

We subtract a one-foot rollout from the launch to simulate dragstrip performance (dragstrip runs started the whole quarter-mile acceleration craze and remain the only practical way for most owners to test their own cars, so we want our numbers to match those acquired in this way)​

So as I understand it, Motor trend doesn't count the first foot of travel. According to Motor Trend regarding the SP100D:

The car crosses 1-foot mark and official timing starts. The car is traveling at 5.9 mph, averaging 1.30 g of longitudinal acceleration.​

So with the SP100D, the car isn't at zero MPH when the timing starts, it is traveling at 5.9 MPH. So isn't that 2.28 seconds a 5.9-60 time? That near 6 mph that isn't really included is nearly 10% of the final 60 MPH speed. At an acceleration of 1G, that first foot takes 1/4 second. Motor Trend says the Tesla is accelerating at 1.3Gs at that point so the elapsed 1 foot time should be less.

Don't get me wrong, accelerating to 60 MPH in 7.4 car lengths is amazing, going from "6-60" or even a fudged 0-60 in 2.28 seconds is just as amazing. Still, it just doesn't seem all that accurate.

It's not just MT. The 1 ft rollout is the standard in the US for declaring 0-60 performance specs so all pubs use this in the US unless they specify otherwise.

 

[whitex]

It's not just MT. The 1 ft rollout is the standard in the US for declaring 0-60 performance specs so all pubs use this in the US unless they specify otherwise.

Tesla used to mix the specs without specifying at all (P's used the roll-out, non-P's used no rollout - presumably to make the P's look faster justifying the price premium). Then they added a footnote about P's using roll-out, but continued to mix them. Most recent I think they switched to all numbers using rollout (makes the new 75 seem even faster).

 

[sorka]

Tesla used to mix the specs without specifying at all (P's used the roll-out, non-P's used no rollout - presumably to make the P's look faster justifying the price premium). Then they added a footnote about P's using roll-out, but continued to mix them. Most recent I think they switched to all numbers using rollout (makes the new 75 seem even faster).

This is all true. Not only that, they didn't add the footnote until after the outrage started in Norway and Denmark. Without the disclosure, they appeared to be comparing apples to apples when in fact it was apples and oranges. I've pointed this out myself at least a half dozen times.

 

[P100DHG.]

Here is your answer

The Importance of 'Rollout' - Feature

Makes sense to me, evens things out.

Where is the edvidence that Tesla wasn't using 1 foot roll outs previously on their non P cars and now is?

 

[snd92]

1 foot roll outs is total BS. You're actually not measureing 0-60 mph or 0-100 km/h, more like 5-60 or 8-100.

Buy a 250 gram burger with subtraction of 25 grams. Yeah, that seems right

 

[tonglaji]

1 foot roll outs is total BS. You're actually not measureing 0-60 mph or 0-100 km/h, more like 5-60 or 8-100.

Buy a 250 gram burger with subtraction of 25 grams. Yeah, that seems right

Exactly what the lumber business is doing. You buy a 2x4, it's actually 1.5x3.5, buy 2x8, you get 1.5x7.25.

 

[D.E.]

OK, I'm old. I know that makes me opinionated. I never knew why old people were so opinionated. Now that I'm old, I know. It's all that experience, it gives one a better "that's crap" filter. So in my mind I'm sharing wisdom. Young people will see me as a narrow minded curmudgeon. They're just inexperienced. They have my sympathy.

In the lumber business, the 2X4 is the rough size, then they are nice enough to plane the wood so it is smooth. They throw away the chips then we get the smaller but smoother piece of wood. That is my pollyanna take on it. I made it up. It makes me happy.

Burgers... they cook it for me and toss out the grody stuff that cooks out of it. I'm happy about that too.

Chickens and turkeys, they add water then they weigh it. That I can't really justify. Worse, that extra water weeps out and makes nasty runny salmonella puddles all over the counters as it is prepared. It's foul. Everyone does it but that doesn't make it right. I wish they'd just charge me more and keep their water.

I think I agree with Edmunds on the rollout issue.. Here is their take on it:

The term "rollout" might not be familiar, but it comes from the drag strip. The arrangement of the timing beams for drag racing can be confusing, primarily because the 7-inch separation between the "pre-stage" and "stage" beams is not the source of rollout. The pre-stage beam, which has no effect on timing, is only there to help drivers creep up to the starting position. Rollout comes from the 1-foot separation (11.5 inches, actually) between the point where the leading edge of a front tire "rolls in" to the final staging beam — triggering the countdown to the green light that starts the race — and the point where the trailing edge of that tire "rolls out" of that same beam, the triggering event that starts the clock. A driver skilled at "shallow staging" can therefore get almost a free foot of untimed acceleration before the clock officially starts, effectively achieving a rolling-start velocity of 3-5 mph and shaving the 0.3 second it typically takes to cover that distance off his elapsed time (ET) in the process.​

We believe the use of rollout for quarter-mile timed runs is appropriate, as this test is designed to represent an optimum drag strip run that a car owner can replicate at a drag strip. In the spirit of consistency, we also follow NHRA practice when calculating quarter-mile trap speed at the end of the run. So we publish the average speed over the final 66 feet of the quarter-mile run, even though our VBOX can tell us the instantaneous speed at the end of the 1,320-foot course, which is usually faster.​

On the other hand, the use of rollout with 0-60 times is inappropriate in our view. For one, 0-60-mph acceleration is not a drag-racing convention. More important, it's called ZERO to 60 mph, not 3 or 4 mph to 60 mph, which is what you get when you apply rollout. While it is tempting to use rollout in order to make 0-60 acceleration look more impressive by 0.3 second, thereby hyping both the car's performance and the apparent skill of the test driver, we think it's cheating.​

So Edmunds knows crap. I like them.

 

[zer0cool]

Just add 0.2-0.3 secs to any US 0-60 time, then you get the actual launch number. 5-60 is generally significantly slower due to not using launching mechanism. Then for 0-100km, generally add another 0.2 secs on top of 0-60 since there's an additional 4km/hr.

 

[Burnt Toast]

Motor Trend also reduces the time they actually get to compensate for temperature/barometric pressure. Basically, their numbers are complete bullshit to sell magazines.

 

[Electroman]

or a flash drive or a smart card, or a USB drive or any disk. You buy 1 TB, but the actual usable space is only 950MB.

or an 85kwH Tesla that gives you less than 80KwH energy for propulsion.

 

[llavalle]

or a flash drive or a smart card, or a USB drive or any disk. You buy 1 TB, but the actual usable space is only 950MB.

That's actually a unit difference. Most hard drive manufacturers count 1 kilobyte as 1000 bytes. Most operating systems count 1 kilobyte as 1024 bytes. The actual name of 1024byte is "1 kebibyte" but almost everyone uses the name "kb" or "kilobyte".

 

[Electroman]

That's actually a unit difference. Most hard drive manufacturers count 1 kilobyte as 1000 bytes. Most operating systems count 1 kilobyte as 1024 bytes. The actual name of 1024byte is "1 kebibyte" but almost everyone uses the name "kb" or "kilobyte".

Nope thats not it, or thats not the full story. There is space that is reserved to maintain folder structures and such, which is fine, but the way you should address that issue, is to have that as an additional capacity and provide 1TB of usable space to the end users.

Similarly except Kia Soul EV everyone lies about kWh. I don't friggin care if your battery is 300 kWh if I can only use 10 kWh out of that.

 

[snd92]

OK, I'm old.

I'm 25 year old. I do belive it is wrong to use roll outs when both Edmunds and Motor Trend use equipments that are able to measure exact 0-60/0-100...

 

[sorka]

1 foot roll outs is total BS. You're actually not measureing 0-60 mph or 0-100 km/h, more like 5-60 or 8-100.

Buy a 250 gram burger with subtraction of 25 grams. Yeah, that seems right

Yes, but since it's the standard, you have to compare BS to BS rather than BS to truth. Unfortunately in the east part of the country BS seems to be winning out of truth now on a daily basis with Twitter followers having a front row seet

The sad thing is that if the industry standard was not to us use the 1ft roll out (i.e. oranges with oranges rather than apples with apples), the PD cars would have a larger lead in 0-60 performance over their ICE counterparts given that the PD cars kill the 1 ft rollout in far less time than ICE cars given the instance off the line torque.

 

[Uncle Paul]

Traditionally, acceleration data was only available from local drag strips. They were never perfect, as a competitor could choose to early stage or late stage to give them a slight advantage over the competition in the next lane. One could be faster, or quicker than the other guy, but still loose the race to the finish line. Getting to the finish line first determined the winner, not the car with the best acceleration.

To make it even more challenging, some tracks would spray a stickey (VHT) substance on the track to make the cars get off the line faster. On professional races they might even spray the entire track, as dragsters might still be spinning their tires when crossing the finish line.

In addition, one lane was often faster than the other, so that adds additional complication.

Most tracks also use an adjustment factor to try to reduce the effects of air density, temperature and humidity. This will give two sets of numbers, the actual number and the corrected number.

Personal and auto magazine current timiing method is often calculated with a g meter inside the car. This has it's own variables, as two different model meters might still give different measurements.

Until someone comes up with a standard acceptable to all competitors, there will always be some variables to contend with.

Hence, discussions like this often end up going nowhere.

 

[D.E.]

Just add 0.2-0.3 secs to any US 0-60 time, then you get the actual launch number. 5-60 is generally significantly slower due to not using launching mechanism. Then for 0-100km, generally add another 0.2 secs on top of 0-60 since there's an additional 4km/hr.

It isn't that simple. The speed at the end of that first foot will vary depending on the acceleration. So a rapidly accelerating car will be going faster at the end of the first foot so will have more of a head start. The car traveling at 2 MPH at the end of the first foot has another 58 MPH to 60. The car that is traveling at 6 MPH at the end of the first foot only has another 54MPh to make it to 60. The more acceleration a vehicle has, the more inaccurate the Motor Trend results.

The flaw in the magazine's employees thinking is applying a fixed distance solution to a variable distance problem. In the fixed distance 1/4 mile, the subtaction of the first foot makes very little difference, essentially 1 foot in a quarter mile, or 1/1320, an error of 0.075%. But 0-60 measurement doesn't happen over a fixed distance. With the 0-60 test, if you omit measurement the first foot of travel of a car that is going 6 MPH at the end of the foot, you have introduced an error of 6/54 roughly 11%. (This assumes a constant acceleration which really shouldn't be assumed.)

Suppose these magazine employees decide to apply the same logic to get the "0-60" time for a carrier based Navy jet during a catapault launch. That jet undergoes about 4 G (steam catapault). That jet will be moving about 23 MPH after 1 foot. Now the 0-60 error with a 1 foot rollout is 23/37 or well over 60%. The 1/4 mile elapsed time is still accurate to 0.075% with the rollout. This is an extreme example but it does illustrate the fundamental flaw in the reasoning.

Going a step further, it is possible, even trivial to calculate a 0-60 MPH time for a bullet. But you damn sure can't do it if you include a 1 foot rollout.

It's absurd that an outfit that prides itself on their $30,000 speed measuring equipment invalidates the data they collect because they don't quite understand the logic behind what they are doing. No one is going to be able to take a current standard SP100D and go 0 to 60 in 2.28 seconds on a flat dry road with standard tires at sea level. The value is derived from flawed methods.

Tesla quotes this number knowing full well the underlying methods are invalid and the car is not capable of matching it. The disclaimer "that's what Motor Trend measured" is no excuse.

Tesla, you guys are better than that. The car is amazing. It deserves better.

 

[P100DHG.]

The Problem:
Motor Trend says 2.28 0-60 (clearly deceptive at this point) with a 1 foot roll out and arachnids.

The Preface:
Tesla 2.35 0-60 with ludicrous plus (doesn't specify a roll out or not, that I can find)
Tesla 2.5 with ludicrous mode (doesn't specify that I can find)

The Questions:
1. Does Tesla's stats include roll outs for their P cars? Please cite your source.
2. I have been reading on this forum that the 75D increase in 0-60 includes a roll out but those claims haven't been cited anywhere. Can someone cite this or debunk it?

 

[mike-415]

Roll-out dates from a time before GPS timing equipment when a wheel-based timer was used and it couldn't measure accurately without roll-out. We (people who test cars professionally, which I did for over a decade) still use roll-out for continuity. And yes, it's around .2 to .3 seconds for the first foot for most quick cars. When I used a VBox to time our P85DL, 0-60 was 2.9 seconds with roll-out, 3.1 without. I suspect Tesla, like GM, uses roll-out for all stated times.

 

[whitex]

Here is your answer

The Importance of 'Rollout' - Feature

Makes sense to me, evens things out.

Where is the edvidence that Tesla wasn't using 1 foot roll outs previously on their non P cars and now is?

Since you asked, here is what Tesla had on their website AFTER they added the footnote because nobody could actually reproduce 0-60 and after there finally came clean on hp, because again, nobody could get anywhere near the advertised 691hp. Prior to this, the very same page said 691hp for P85D and the 0-60 numbers were identical, just no footnote on the MT test procedure.

Internet has an elephant's memory