Streamliners are among the fastest terrestrial machines on earth, encapsulating the rider, engine and running gear into a highly aerodynamic body.
The front cylinders are wide apart, with the rear pair nestled between, narrowing the aft end of the engine and giving the rider a more comfortable perch and shorter reach to the ground when stopped.
One wild version, with a 502-cubic-inch V-8 engine slung under the rider's legs and a high-finned, pinstriped rearend that resembles a 50's Chevrolet, is $45,000.
Alex Dowsett – who beat everyone on stage 8 – has struggled in the mountains and may do so here too, but bet365's 400-1 looks incredibly generous, giving punters the chance of an interesting experiment in the value of a rider's engine and pace judgment versus sheer climbing ability.
Its ample floorboard, low-riding seat and enclosed engine (which protected the rider from exposure to grease and dirt) made it particularly suitable for women, who could ride in skirts without compromising modesty.
One was that engine heat gushed over a rider's legs.
In preparing the Castrol Rocket, he detuned the linked engines powering the streamliner to give the rider a more controllable power curve and increase engine life across the five-mile speed trials course.
Scooters have a flat floor and an upright riding position; motorcycles force riders to straddle the engine.
Its naturally aspirated 998cc in-line four-cylinder engine is rated at 200hp, and riders benefit from the assistance of MotoGP-calibre electronics to harness those horses.
The best change in recent years has been a switch to rubber engine mounts, which help to isolate the rider from the 883 cc V-twin's vibrations.
This allows the rider to control when the engine will power the scooter.
