It began in 1892 with an eccentric idea of Rudolf Diesel, a French refrigeration engineer. He wanted an engine that would run on cheap fuel that didn’t evaporate or explode — so he made one.
Although well suited to industrial and commercial vehicle applications the weight and lack of refinement of diesel engines held back their widespread use in cars. Not any more. Now vastly smoother, quieter and even more economical, they are challenging the dominance of petrol power. And the first purpose-built diesel motorbikes are about to come off the production line.
You won’t be able to buy one in a dealership. They are being built in America for the US Marine Corps, and, if the Ministry of Defence approves, for the British Army. If there is conflict in Iraq the first troops over the sand dunes could be riding diesel bikes.
A diesel engine in a motorbike? Surely, it will never work, and even if it did it would never catch on as a road bike. In fact, BMW’s engineers are already running their slide rules over the project. The military want them because they are rugged, go-anywhere machines that run on the same fuel as their tanks and aircraft, simplifying supplies and reducing costs. They also give twice as many miles to the gallon. Now manufacturers predict that just as US army Humvees — military 4x4s — were “civilianised” after the 1991 Gulf war (page 16), the first diesel road bikes will be not far behind. And believe it or not, they were invented near Swindon, at the Royal Military College of Science. Whitehall agreed to give me access and there, surrounded by stripped-down tanks, were two M1030 M1s, the American military codename for the prototype diesel-powered motorcycles.
“The US army approached us and said, ‘Can you build a bike that runs on both diesel and JP8 aviation kerosene?’” says Stuart McGuigan, who heads the design team. “Petrol is dangerous stuff to carry around a war zone, and worse in hot climates.”
The first M1030 M1 was built from cannibalised engines and bits machined on lathes in the military labs. Once the design was right, army technicians drew up blueprints and ordered specially made components. McGuigan went to America to get them mass produced and his team is now working with Hayes Diversified Technologies of California.
The bikes look little different from the petrol Kawasaki KLR650 trail bike from which they are derived and the kind already used by the US Marines. But you can tell when you start them there is something special under the camouflage paint. The four-stroke, liquid-cooled engine kicks into life like a Harley-Davidson Fatboy. With the throttle open the exhaust note sounds like a flatulent rhino — presumably a drawback if you are hoping to creep up on the enemy.
Inside the cylinder head there’s a Formula One-type design with four valves to give the biggest possible bang. All that explosive energy is nicely harnessed. Maximum torque is produced at low revs so you almost never have to change down — what other bike would pull away in third gear? The machine is heavier than its petrol counterpart but the 600cc power plant’s solid, bottom-end tug copes easily with the extra weight. Flat out, it reaches 85mph, but it really comes into its own off road where grassy banks, rutted earth, even ditches are no obstacle.
Now before I sound too enthusiastic, it is not fantastic. The low-revving engine is less responsive than a four-stroke and downright sluggish compared with a two-stroke. And, yes, there is an occasional whiff of diesel fuel. But for the army it is perfect, especially chugging about in battlefield mud loaded down with kit.
But what about low-testosterone riders who want to ride on tarmac? Driving persuaded the army to lend its prototype diesels to two female testers. Wendy Swales and Harriet Ridley normally ride Yamaha YZF-R6 compact sports bikes, so they would be the least likely fans of a heavyweight off-roader.
After half a day’s riding the verdict was a qualified thumbs-up. Swales, 26, a personal assistant from Isleworth, was impressed enough to want to take it home. “I am normally a pink and fluffy person but it is less cumbersome than I thought it was going to be,” she says. “Even for a lady rider it was quite manageable.”
Ridley, 31, who works for a publisher in Peterborough, is more circumspect. “I wouldn’t buy one for road use, but for off road it is excellent and it could be very useful in traffic when you are crawling along.”
So, has Rudolf Diesel’s invention scored another victory in its relentless march towards world domination? Jeremy Clarkson would be horrified. Diesel is, after all, the fuel of plodding tractors and combine harvesters. Bikes are traditionally high-revving, high-octane petrol machines designed on lean-and-mean principles.
But diesels are rapidly getting more compact and, therefore, better suited to bikes. Designers hope in the near future to have a turbocharged bike engine with a power-to-weight ratio comparable with a petrol engine’s.
Which still leaves the diesel’s trump card — fuel efficiency. The army’s bike can run 400 miles on one tank. Manufacturers predict diesel bikes will do 140mpg once the technology is refined. That is because a litre of diesel contains more energy than a litre of petrol and because diesel engines convert chemical energy in fuel into mechanical energy more efficiently.
New EU regulations will also soon demand lower emissions and better fuel efficiency from all vehicles, including bikes. That means, environmentalists argue, the days of the race-tuned Honda Fireblades and Yamaha R1s are numbered. Could their replacements be descendants of the M1030 M1? In this brave new authoritarian world, diesel increasingly seems to have the edge.
