LAMBRETTA PERFORMANCE ANALYSIS SERIES THE POWER TO WEIGHT RATIO
The power to weight ratio is one of the many important factors in gaining the full potential of the performance from your Lambretta. Stu Owen explains why…
Mathematics
Aerodynamics play an important role in the overall equation, the power to weight ratio is another important factor in determining these figures. There are two ways used to calculate the power to weight ratio (PWR) when referring to a vehicle, either by bhp per tonne, or per lb. We will use the lb formula, and the higher the figure the better the ratio, thus the faster you will accelerate. The formula is simple enough: the power of the engine divided by the mass of the whole vehicle. So if you take the GP200 as an example its power is 11.7hp (factory figure at the crank) and it weighs approximately 270lb. If you divide the first by the latter you get a figure of 0.043hp per lb. If you compare that to a Yamaha R1 (2015 model), its PWR is around 0.45hp/lb. As you can see, there is a massive difference in the figures with the Yamaha’s being 10 times that of the Lambretta. This is clearly highlighted in the performance differential between the two.
Now imagine you still have the same GP200 but put a tuned engine in it with 25bhp. The figure is now improved to 0.092hp/lb. Next, suppose you decide to remove some excess weight from the machine, say a total of 40lb, so it now weighs 230lb. The figure is now improved to 0.108hp/lb – more than doubling the PWR you started off with. All the time the figure is improving, so too is the performance of your Lambretta.
Things to consider
This all starts to sound very impressive but before you go off and buy the most powerful engine possible and then hacksaw everything off the frame, there are a few other things that need to be considered. Firstly the engine and what
Top: A stripped back Group 4 Lambretta used on the road but only carrying what is essential.
Above: Chrome looks good on a Lambretta but is far heavier than you think. Right: A spare wheel and its carrier can be of use but add a significant amount of weight to the overall mass of the machine.