A Diesel Bike, Would You?
When asking “why so few diesel bikes?” some answers pop up and they might set back almost anyone dreaming of such a contraption. The first reason for having so few diesel-powered motorbikes lies in the very construction of the engine.
Diesel engines are bigger than the petrol ones and, inherently, – heavier; when it comes to motorcycles, bigger and heavier is by no means better. It may come in handy when trying to create a monster-chopper, but with fuel prices rocketing these days it's hard to believe that a manufacturer would overlook the impact of increased weight on a bike project.
With petrol engines being light and small, bikes can also be lighter, making little compromise to power. Retrofitting a diesel engine into an existing frame is not at all easy, and the dimensions are probably one of the lesser worries.
If you've driven both petrol and diesel cars, you've probably noticed that the diesel ones come with way more vibrations than their petrol siblings. The very nature of the engines' construction differs a lot, and this demands a complete re-thinking of a bike's frame if it's going to house a diesel core.
Even more, a diesel engine is a lot noisier than a petrol one. You may have not noticed that when driving a car, and that's because a car's engine compartment has a lot of room for sound insulation, a luxury the bikes simply can't afford. Hence, the need to design a diesel engine with a reduced noise floor, compliant to the automotive industry regulations and standards; even more, riding itself comes with a lot of noise caused by wind – and adding the thunderous breath of a diesel engine may not be to every rider's liking.
Another setback for diesel-powered bikes is the bigger compression of the engine and the need of a bigger flywheel. Due to the nature of the working principle, a diesel engine needs more energy to start than a common petrol one.
Back in the day when bikes used only kickstart levers, starting a diesel engine would have been quite a small adventure. With slightly colder weather and all the things that can go a bit wrong when it comes to the functioning of a motorbike, it would be little wonder that kickstarting a diesel could take quite a long time.
Nowadays, with almost every bike having an electric start, this problem has been solved and provided you've got a big, strong and healthy battery, starting may not be such a big problem, at least not until winter.
During the 1980s, NATO has used the already famous diesel version of the Kawasaki KLR650 but, for some reason, the fad did not spread. Military or not, that diesel bike had a lot of strong points such as multi-fuel capability (plain common diesel, old Kerosene, aviation Kerosene, Bio-Diesel and, of course, NATO-spec diesel).
It had the first bike-purpose diesel engine designed by the Hayes Diversified Technologies research company and delivered 28 BHP, with a flat response between 1500 and 7000 rpm. Not quite the sportsbike some might dream of, but with 110 mpg (roughly 2.1 l/ 100 km) we're talking some serious fuel economy.
All in all, diesel-powered motorcycles are a tad different from the generic idea most people (and even common riders) have about the two-wheeled fun. They're nowhere near as powerful as their petrol counterparts, and neither are they as responsive to the throttle. On the other hand, a diesel engine comes with a lot of usable torque available from the very low rpm zone, and beautifully spread up to the high-rev section.
The fuel consumption of a diesel engine can sometimes be half of that of a petrol one and this is probably an element of crucial importance in today's world. Low sulphur fuel means a cleaner environment, and the bio-diesel (soy and so on) are becoming more popular, adding to the overall pros of choosing such a motorcycle. The higher price tags of a diesel two-wheeler may be a setback, though.
The diesel bike dream has not ended, though; it's absolutely fantastic to see bike manufacturers committing to creating new, better machines powered by diesel engines. Hopefully, these new bikes will attract more followers and will become more popular – the Dutch EVA seem to become successful with their Track T-800CDI (also with a 2-wheel drive option), and Irish mechanics offer Triumph Tigers with diesel engines taken from Smarts, and still there is room for a lot of development.
This list is actually longer than you'd expect and we're glad about that – more bikes equals more options and this means more fun!