Have you ever heard of SWEDAC? What about the PML within NIST? Maybe you’ve heard of NMRO, then? OK, you probably haven’t, but those offices in Sweden, the USA and the UK do something that’s quite important: they regulate instruments that are used to weigh and measure things.
They are there to ensure that the fuel pump actually gives you the litre or gallon of petrol that you’re paying for, that the kilo of steak you pick up from the supermarket actually weighs a kilo. They don’t actually measure individual items. They set the standards that measurement machines are built to. The theory is that if the standard is correct, machines built according to that standard can be trusted to accurately measure the things that we use and buy. This ensures that there’s consistency and integrity in the market.
You probably don’t think about it that much, but weights and measures are very important. So important, in fact, that governments around the world have agencies like those mentioned above keeping an eye on things to protect consumers.
Pivot to cars…….
In simple terms, dry weight is the weight of the vehicle on its own with no fluids. Curb weight is the weight of the vehicle “ready to drive” – with all oils, coolants, fuel and other liquids. If you want to dig deeper, there are weights that we, as manufacturers, are legally obliged to declare as part of the Type approval process. For the EU, we use ‘Mass In Running Order’, which is curb weight plus 68kg for the driver. In the US, we have to declare the ‘Gross’ weight, which is curb weight plus 300lbs.
Some manufacturers don’t calculate curb weight with a full tank of fuel, but with a “nominal” fuel level (e.g. 50%). Various requirements define different amounts of fuel to be included.
As you can see, it can be difficult to compare apples to apples.
It’s not unheard of to see ‘dry’ weight being used by manufacturers in their sales literature. It’s great for marketing but it’s not really any good for customers for one very important reason – you can’t drive a car at its dry weight. The lack of fuel won’t allow it to start and even if it did, the lack of lubricants and coolants would seize everything up in a matter of seconds. If, by some miracle, you managed to actually move the car, you wouldn’t have any brake fluid to stop it.
At Koenigsegg, it’s our policy to put the curb weight in our press and publicity materials. There are occasional variations within that definition, but we specify any variations so that you’ll know exactly what we’re talking about.
For example, when we did the One:1 program, we initially thought it would be very difficult to reach the One:1 power-to-weight ratio if the car was weighed with a full tank of fuel. So, in order to make sure we hit the One:1 ratio with our factory development car, we used a nominal fuel load of 50%. Using a nominal fuel load is a common way to measure curb weight and the nominal level can be anywhere from 50% to 75%. With the One:1, our fears were unfounded in the end, as we managed to get our customer vehicles under 1360 kg with a full tank of fuel. Our press material still talks about the 50% fuel load because that’s the way it was done at the time, but One:1 owners know they have a car that is well and truly 1:1 in terms of power-to-weight.
And as an aside, if one of our production One:1’s is driven with very little fuel and with a light driver, it can still have a One:1 ratio even with the driver included! But we digress…..
In the Agera’s case, the curb weight of the car is around 90kg more than the dry weight. The difference is about 120kg for the Regera. That’s a significant difference in the hypercar/megacar sector where weight is such a crucial figure. You can see why some might be tempted to quote the dry weight. Ask any hypercar company if they’d like to save 120kg or more with the stroke of a pen and they’d give you a resounding ‘yes’.
So as you delve into all the information that comes your way, take a look at the weight measurements that manufacturers use. Do they use curb weight, dry weight, or do they muddy the waters and just use ‘weight’ without specifying which?
There’s something else we’d encourage you to check out, too – power ratios.
The most obvious one is the power-to-weight ratio, which tells you how many horsepower per kilogram. This is the ratio that the One:1 was named for as it has 1 horsepower for every kilogram of mass (measured as curb weight, with all fluids). The Agera RS has a power-to-weight ratio of 0.84:1. Do the sums on our competitors and we think you’ll find those numbers quite compelling.
There’s another ratio we like to use when comparing our cars – power-to-weight-to-weight (PWW).
Weight and power are interesting measurements on their own but measuring their combined value against the weight of the car is a great way to understand a sports car’s propensity to perform well around a race track.
For example: A sports car with 3000kg curb weight and 3000hp will have a power-to-weight ratio of 1:1. A car with 500kg curb weight and 500hp will also have a power-to-weight ratio of 1:1. Which one is likely to be faster?
Given an endless straight, the 3000kg car would be faster, as long as the aerodynamics are similar to the 500kg car. The 3000kg car has more power and its weight is not such a huge penalty for top speed (as long as the tires can take it). This means little around a race track, however, as straights are always limited in length. If fact, the 3000kg car will be almost undriveable around a track. It’ll have terrible brakes because there’s so much mass to stop, it will pull minimal G´s in the corners and acceleration in a straight line will be impacted by the shorter straights.
In contrast, the 500kg car will have blistering corner performance, great acceleration and incredibly short braking distances.
How do you calculate a simple PWW?
Find out the power figure and the true curb weight of the car in kg. Then take the weight and divide it into the car’s horsepower figure (P/W). Then divide the result again with the curb weight of the car. In order for the number to be easily readable, multiply the result by 10,000.
The higher the number, the better the result. Here are a few examples:
Formula – (P/W)/W*10000
Koenigsegg One:1 – (1360/1360)/1360*10000 = 7.353
Koenigsegg Agera RS (MY15 EU spec) – (1160/1382)/1382*10000 = 6.074
Again, if you do your own sums using competitor vehicles, you’ll find that our numbers are quite favorable.
Of course, there’s more to how a vehicle performs than this simple calculation. Chassis setup, suspension, steering, brakes – all of these play an important part in a car’s performance. But it’s good for providing a thumbnail view to compare from car to car.
Our advice – weigh the hype. Assess whether you’re getting all the information you need and make an informed judgement about what you’re reading.