There’s a saying “light is right.” Instead, we are always too engrossed with horsepower.
Let’s compare in this article.
We’re all so caught up by horsepower figures that we usually overlook many other areas of performance. One very important principle regards weight, or the lack of it, to be more specific which leads to the saying, “light is right.”
That’s what all the brow-ha-ha over the Ducati Superleggera V4. Its engine hits 234 hp and the bike weighs only 152 kg in race guise, giving us a whopping 1.5 hp/kg power/weight ratio!
What does lightness bring
In Newton’s Law of Motion, the lighter an object, the less force is required to make it change direction of motion. It’s all in the equation: F = ma where F is force, m is mass and a is acceleration. As such, force has a larger figure when mass is higher, acceleration being equal.
For the rider in you and I, it means that it’s easier to make a bike change directions, accelerate and decelerate.
But an even easier term to understand is “power-to-weight” ratio. It’s a simple math by dividing the engine’s horsepower to the bike’s weight. Let’s show you a few calculations so you can see for yourself.
How to do it?
Let’s take a generic 1000cc sportbike, as an example, and compare the two different routes. Let’s say that the engine produces 200 hp and the bike weighs 180 kg.
So, 200 hp/ 180 kg = 1.11 hp/kg
The Weight Loss Route
Now, say you managed to drop some weight by swapping out the stock exhaust system with a lighter aftermarket item, shaving 15 kg in the process.
200 hp / 165 kg = 1.21 hp/kg
Now, let's drop even more weight after dumping the rear passenger’s seat and the footpegs. Besides those, we remove the entire tailsection and install a tail-tidy. Additionally, we replace some body parts to carbon fibre. We shaved another 8 kg in the process.
The power-to-weight ratio now is:
200 hp / 157 kg = 1.28 hp/kg
That's a 0.17 hp/kg increase already.
The Brute Force Route
For comparison’s sake, let’s assume that you don’t want to swap anything out, thereby maintaining the bike’s stock weight of 180 kg. Instead, you look to push power higher by performing modifications to the ECU, injectors, etc., which nets you an extra 10 hp.
210 hp / 180 kg = 1.16 hp/kg
That’s just small 0.5 hp/kg gain.
Let’s try to equal 1.28 hp/kg. To reach that ratio, we would’ve to modify the engine to produce:
1.28 hp/kg X 180 kg = 230 hp
Yup, our engine needs to produce a WSBK-level 230 hp.
As you can see above, the easiest route to making you bike go faster is by lightening it. It’s also much cheaper because you can remove superfluous parts on your bike, compared to installing go-fast stuff such as ECU, exhaust system, injectors, valves, pistons, conrods besides engine work such as porting and flow. You might as well just buy a homologation special superbike!
Additionally, and perhaps more importantly, your bike will be much easier to ride with lower weight. It’ll accelerate quicker, stop quicker, and turn quicker, while saving much more engine power and fuel in the process. We will also retain the engine's characteristics, plus the engine will last a lot longer.
To wrap up, there’s another saying: “Losing weight is free horsepower.”