0 to 100 is a very poor measure of performance

[merlin]

I was talking to a mechanical engineer yesterday and we were discussing cars he was saying how 0-100 times mean jack all. It got me thinking to a thread I read a long time ago on another forum which I was luckily able to find and cut and paste for you guys to read below.

I think the basic premise is that aceleration is never a constant so how can a time based measure be accurate? Anyway here the original post in italics:

Hey all,

There seems to be a lot of people who seem to be using the 0-100km/h time as a bench mark for vehicle performance. However, in my experience the 0-100km/h time is not a great reflection. Why is that? Many of the real world traffic light grand prix events are from rest (0km/h) to the speed limit, or just over it (so about 100km/h), so surely this would be the definitive measure of a cars on street performance? Not really, no. I will use an example to illustrate my point.

Three cars line up at the traffic lights. All three cars have an identical 0-100km/h time. For simplicity, let's make it 10 seconds. The speed limit of this road is 100km/h, so it will be a race to the limit. Nothing illegal here

Car number one is a concept vehicle (why it's at the lights I don't know...). An electric vehicle. It doesn't make much power (in fact the top speed is only 100km/h), but it is ultra light, and has 4 in-wheel electric motors giving full torque from 0 rpm, meaning it can charge of the line hard. Car number two is a regular family car. The long geared automatic with big six cylinder power means that acceleration is fairly constant throughout the rev range. The final car has a big turbo, front wheel drive, and manual gearbox. This makes it tricky to get off the line, but once it's hooked up and the turbo spooled, the acceleration is very good.

The image below shows a representation of these three cars' acceleration curves. As you can see, all three will hit 100km/h at the exact same moment.


(for those who care, the electric car's speed was modelled by a quadratic equation speed=-(time-10)^2+100, the family car by a linear equation speed=10xtime, and the turbo by another quadratic equation speed=time^2)

So it's a race to 100km/h, and all three cars have an identical 0-100km/h time, so it should be a pretty close race, right?

WRONG!

The hard launching electric car gets the jump from the start, and wins by a full 45m over the family car, and a whopping 90m over the turbo car - that's about 18 car lengths!!!!

(For those who care, distances were obtained by integrating the speed equations stated earlier. If I made any errors then they were deliberate and hence I don't care - don't bother pointing them out, the electric car would still win.

This is obviously an extreme case, but I think it illustrates my point nicely. 0-100km/h times are stupid.

chose those formulas with the 0-100km/h sprint in mind, and to extend them outside that will make them less representitive of a real world situation - they are simply too primitive to be extrapolated and still reflect real world situations. Particularly the turbo car, which by the formula will keep on accelerating faster and faster at a rediculous pace, but for the fun of it I will do it anyways

Due to the electric car reaching max speed at 100km/h, the after 10 seconds the family car will start closing the gap. Similarly, after 10 seconds, the faster acceleration of the turbo car at high speed means it will start running down both the family car and the electric car.

At the 15.0 second mark, the turbo car will catch the family car.

At the 15.4 second mark, the turbo car will catch the electric car.

At the 15.8 second mark, the family car will catch the electric car.

The turbo car runs a 16.3 at 265.69km/h (see what I mean about unreallistic

The family car runs a 17.0 at 170km/h

The electric car runs a 17.7 at 100km/h



Whilst the 0-100km/h was a reallistic enough to show what could happen in the real world, this quarter mile situation is unlikely.

Think of it like this. Both cars accelerate for 10 seconds. Car one accelerates very quickly to almost 100km/h in the first one second, then slowly accelerates to 100km/h over the next 9 seconds. It spends most of its 10 seconds at high speed. Car two accelerates very slowly for the first nine seconds, the quickly accelerates to 100km/h at the end. So it spends most of its 10 seconds at low speeds.

Both cars will reach 100km/h at the 10 second mark, but car one will have travelled more distance because it has spent more time at higher speeds than car two, so the AVERAGE speed over 10 seconds was higher.

This is an extreme example, but it applies to real world situations - a more reallistic example might be a stock GTR (all wheel drive) and modified GTST (rear wheel drive). These might have the same 0-100km/h time of 5 seconds, but the GTR will launch harder, and will hence get ahead quickly and cover more distance before the 100km/h speed is reached.

If that makes any sense to anyone...



Example 2

I’ve always been really good at grasping this sort of thing (it’s the engineer in me), but terrible at explaining it! If I break it down into sections, including time, speed, acceleration and distance all together, maybe people will understand better.

Taking the V8 vs turbo route:

0-1 second

The V8 accelerates harder than the turbo over this increment because of its strong torque. The V8 gains 20km/h compared to the turbo’s 10km/h. The V8 is accelerating harder than the turbo (speed rising at 20km/h per second vs 10km/h per second). The speed of the V8 at this point is now 20km/h, the speed of the turbo at this point is 10km/h, so the V8 is pulling away from the turbo.

At 20km/h for one second, the V8 will travel 5.5 meters. At 10km/h for one second, the turbo will travel 2.8 meters. So the V8 will be 2.7 meters ahead of the skyline after 1 second.

1-2 seconds

The V8 keeps accelerating as before, gaining another 20km/h over this second. The laggy turbo starts seeing positive boost pressure and accelerates 15km/h over this second.

The total speed of the V8 is therefore 40km/h (20km/h + 20km/h), and the total speed of the turbo is now 25km/h (10km/h + 15km/h). The V8 has a higher speed than the turbo, and is therefore pulling away from the turbo, increasing its lead.

At 40km/h for one second, the V8 will travel 11.1 meters. At 25km/h for one second, the turbo will travel 6.9 meters. The total distance travelled by the V8 will be 16.6 meters (5.5 + 11.1). The total distance travelled by the turbo will be 9.7 meters (2.8m + 6.9m). So the V8 is ahead by 6.9 meters after 2 seconds.

2-3 seconds

The turbo continues to spool up and acceleration improves again, gaining 20km/h this second. The V8 also gains 20km/h. At this point the ACCELERATION of both vehicles is the same – both are gaining speed at the same rate (20km/h gain per second).

But the SPEED of the V8 is higher at 60km/h (20km/h + 20km/h + 20km/h) vs 45km/h for the turbo (10km/h + 15km/h +20km/h). So even though the acceleration is identical, the higher speed of the V8 means that it continues to extend its lead over the turbo (it should be obvious that the car travelling faster will be pulling away, ya?).

At 60km/h for 1 second, the V8 will travel 16.6 meters. The total distance travelled by the V8 is now 33.3 meters (16.6m + 16.6m). At 45km/h for 1 second, the turbo will travel 12.5 meters. The total distance travelled by the turbo is now 22.2 meters (12.5m + 9.7m). So the V8 is now ahead by 11.1 meters.

3-4 seconds

The turbo is really starting to cook now, accelerating 25km/h this increment, vs the V8s 20km/h. So at this point, the ACCELERATION of the turbo is better than the V8. It is gaining speed more quickly than the turbo (25km/h per second vs. 20km/h per second).

The total SPEED of the V8 is now 80km/h (20km/h + 20km/h + 20km/h + 20km/h) and the turbo is now doing 70 km/h (10km/h + 15km/h + 20km/h + 25km/h). The V8 has a higher speed than the turbo, so it continues to extend its lead over the turbo.

EVEN THOUGH THE TURBO IS ACCELERATING HARDER (25km/h/sec vs 20km/h/sec), THE SPEED OF THE V8 IS HIGHER (80km/h vs 70km/h) AND THEREFORE THE V8 IS STILL EXTENDING ITS LEAD!!!

At 80km/h for one second, the V8 will gain 22.2 meters. The total distance travelled by the V8 is now 55.5 meters (22.2m + 33.3m). At 70km/h, the turbo will travel 20m in one second. The total distance travelled by the turbo is now 42.2 meters (20m + 22.2m). So the V8 is now ahead by 13.3 meters.

4-5 seconds

The turbo is now on full boost, gaining a full 30km/h over this second, vs the V8s 20km/h. The ACCELERATION of the turbo is now significantly greater than that of the V8.

The total SPEED of the V8 is now 100km/h (20km/h + 20km/h + 20km/h + 20km/h + 20km/h), and the total speed of the skyline is now also 100km/h (10km/h + 15km/h + 20km/h + 25km/h + 30km/h). The speed is identical, so no car is gaining or losing ground against the other.

Both cars will cover 27.7 meters in one second at 100km/h. So the total distance travelled by the V8 is 83.2 meters. The total distance travelled by the turbo is 69.9 meters. The V8 is ahead by 13.3 meters.

There we go! Two cars with an identical 0-100km/h time, but in a race to 100km/h, the V8 wins by nearly 3 car lengths!


Example 3

Heres something I knocked up which may simplify it...?
(btw, it is not mathmatically accurate, and is just to highlight the issue)

CAR A: Fast starting car with tapering off top end

0-10kmh = 1 second = 2 metres
10-20 kmh =1 second = 4 metres
30-40kmh =1 second = 8 metres
50-60kmh = 1 second= 12 metres
70-80kmh =2 seconds= 40 metres
90-100kmh = 4 seconds= 160 metres

Total 0-100 time is 10 seconds and covers 226metres

CAR B: Slow starting car with strong finish

0-10kmh = 3 seconds = 6 metres
10-20 kmh = 2 seconds = 8 metres
30-40kmh = 2 seconds = 16 metres
50-60kmh = 1 seconds = 12 metres
70-80kmh = 1 seconds = 20 metres
90-100kmh = 1 seconds = 40 metres

Total 0-100kmh time is 10 seconds and covers 102metres


Well I found it interesting anyway!

[james22]

shlt, that was a post and a half... interesting to see though.

[Lukeyson]

nice work there chap

[Wally]

Would have been simpler to say that speed is the integral of acceleration.

[henry_ford]

yeah well umm. i knew that.

[MITCHAY]

I somewhat already knew that.

Besides that 0-100 is all I care about. I don't go to the track so 1/4 mile means dick all to me. Acceleration, braking and handling is what I wanted and it's what I got.

Getting to the speed limit as fast as possible because I'm not exactly going to run the speeds you do on the quarter on a street am I now?

[Xitdxr]

No times matter because it comes down to reaction time and the driver on the street. The car only comes into it after about 120km/h.

[XRchic]

Ive never had much interest in 0-100kmh times anyway, pretty much for that reason. And the fact that there are so many other factors to consider in "performance' anyway, like handling, max power at what revs, gear changes, launching, grip, weight etc, etc... Only really interested in time v distance at the end of the day.

[Powdered Toast Man]

And thats why I drive a V8! Its the drivability through the range that makes it good. (Im not picking on turbos, I could probably word that sentence better)

Good logical examples there Merlin, it was a good read.

[Xitdxr]

Originally Posted by V8GLI

And thats why I drive a V8! Its the drivability through the range that makes it good. (Im not picking on turbos, I could probably word that sentence better)

Good logical examples there Merlin, it was a good read.

I use to own an EF XR8 manual, i thought it was very good, power delivery was sufficient, handled well because of the suspension upgrade, it was a top car. I now own a VW polo GTI, It is turbo and has all of 110kw and 220nm of torque, but it out paces the xr in a straight line, especially once u get into 3rd gear.
Not all turbo's have lag, especially in 1st taking off, most will launch fine and sprint for the horizen. The only time mine has lag is when im in second and going around a corner under 20km/h.

[XR8-260]

How much would those Vbox devices used by motor magazine cost? I don't really trust the g-tech to give accurate measurements.

[S3SR]

who cares i own the falcon so im already the winner!

[Cooper69S]

good points and an interesting read, but I'd disagree with the bit that says "0-100 is a very poor measure of performance"...
i think that post is not so much proving that 0-100 is meaningless, but that there are exceptions to the rule. A 0-100 figure on its own is obviously not going to give conclusive proof of who'll win a drag, esp if the figures are close. your examples demonstrate that and comparing terminal speeds on cars at the drags would demonstrate it too, but i think that for the majority of cars that don't have huge turbo's with massive lag, or electric motors with monster torque at 0rpm, 0-100 times are a pretty good indication of how the car will perform in normal city driving...

[merlin]

Originally Posted by Cooper69S

good points and an interesting read, but I'd disagree with the bit that says "0-100 is a very poor measure of performance"...
i think that post is not so much proving that 0-100 is meaningless, but that there are exceptions to the rule. A 0-100 figure on its own is obviously not going to give conclusive proof of who'll win a drag, esp if the figures are close. your examples demonstrate that and comparing terminal speeds on cars at the drags would demonstrate it too, but i think that for the majority of cars that don't have huge turbo's with massive lag, or electric motors with monster torque at 0rpm, 0-100 times are a pretty good indication of how the car will perform in normal city driving...

I agree completely, wrong thread title, cant edit it now.

In regards to the example, they are just made up hypothetical examples to get a concept across to people not an attempt to start some V8 vs turbo war.

[Grasshoppr]

There is no actual facts listed in this long post...

We can all make guesstamates on everything but all the other factors that make data real have not been included. How about weight of the 2 cars, driver reaction (given there are 2 different drivers), power and tourque outputs etc etc.

In theory it provides a great explaination of why and how data can be used to prove any view point.

My 2c

[[Tonko]]

Very interesting....
But i always knew V8's walk all over the hairdryers...

[freaky]

Originally Posted by TonkoXR8

Very interesting....
But i always knew V8's walk all over the hairdryers...

lol.. yes.. the same way a GT walks over the F6..

[Ford_Boy]

Originally Posted by freaky

lol.. yes.. the same way a GT walks over the F6..

it does lol

[Skooter]

Isn't the 0-100km/h just an alround way to compare all different types of cars in the same way, sure turbo powered cars have to wait for the turbo to spool up and some v8 just have power on tap at all revs, I thought is was a way of making the field even and a good comparison between cars in a real world situation because in city driving when are you going to go over 100km/h?

[XR8-260]

I don't really care much about 0-100. I reckon the 1/4 mile is a better test of performance.

[05MkIIFutura]

Originally Posted by 30487256

I don't really care much about 0-100. I reckon the 1/4 mile is a better test of performance.

Nup, best test of performance is laps on a track. Measures, power, brakes and handeling - the complete package

[[Tonko]]

Originally Posted by freaky

lol.. yes.. the same way a GT walks over the F6..

Touche :

[SXCXR6]

I like this post means that i dont have to drag turbos no more i can just tell them i already win haha

[Ford_Boy]

0-100 would be better if they timed it better. they measure it with by the speedo in the car. they should measure it by seeing how far it gets from 0-100 eg. it takes 6 seconds to get to 100kmp/h but it travels 250metres

[sfr rob]

Very interesting, and have always though the same, but i am not good with maths so i didnt bother proving it to my self :P
I for one, dont really give a toss about how fast a car can cross the 1/4 mile, its more about how the car moves when you put your foot down while your moving!

[XRchic]

I think all of the above measure performance - circuit and drag racing, driving on a nice windy road, overtaking power - the whole lot. I certainly dont have any intrest in the 0-100kmh thing, and my personal interest lies in drag racing, but I think there are many ways that a car can be considered to "perform well".

[ThoR_]

Originally Posted by merlin

Three cars line up at the traffic lights. All three cars have an identical 0-100km/h time. For simplicity, let's make it 10 seconds. The speed limit of this road is 100km/h, so it will be a race to the limit. Nothing illegal here

Well actually it is illegal. Accelerating to fast to the speed limit is actually illegal. Most people dont think so because there not even at the speed limit yet. As a matter of fact i have not met one person that thinks its illegal and are suprised when i tell them. I know alot of people that have been done for it. Plus my Dad just retired as a cop.

Just thought i would let you know

[brendo83]

Originally Posted by ThoR_

Well actually it is illegal. Accelerating to fast to the speed limit is actually illegal. Most people dont think so because there not even at the speed limit yet. As a matter of fact i have not met one person that thinks its illegal and are suprised when i tell them. I know alot of people that have been done for it. Plus my Dad just retired as a cop.

Just thought i would let you know

Yep, cops have a lot of discretionary power, there are several laws you can break, But does anyone really think that street drags are legal so long as you're under the speed limit? Anyone who does will get a rude shock when the cops confiscate their car.

Oh and I know the figures are only illustrative, but a turbo taking 5 seconds to hit full boost??, a turbo of similar power to an 8, should only be a fraction of a second behind in making that power, and if you flat shift, or its an auto, the turbo will stay on boost, so its only a small lag on initial takeoff.
Its a bit contradictary to use theoretical, exagerated figures to argue 0-100 times dont mean anything in practice. 0-100 time is a pretty good performance indicator, and thats exactly what it is, an indicator, not an absolute, but that certainly does not make it mean jack all.

[weenie]

that was a very interesting post there. maybe 0-100 plus distance covered would show up some interesting differences. it might explain the pursuit ute i saw oneday get punished by one of those avalanche things twice off the lights. similar 0-100 times but distance was a different story.

[merlin]

Originally Posted by brendo83

Oh and I know the figures are only illustrative, but a turbo taking 5 seconds to hit full boost??, a turbo of similar power to an 8, should only be a fraction of a second behind in making that power, and if you flat shift, or its an auto, the turbo will stay on boost, so its only a small lag on initial takeoff.
.

Of course in the real world the difference would be FAR smaller I believe the author exagerrated the figures to demonstrate the concept only.