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Applied mechanics |Прикладная механика

Lesson 9

 Read the text: Pedal tricycles

These may be upright or (increasingly) recumbent. Upright tricycles are often favoured by those with mobility problems. Recumbent tricycles are particularly suitable for long-distance use, including cycle touring and Audax riding. Upright trikes are usually deltas, although the Newton tadpole upright conversion is well regarded. Either type can be made low and large enough to be difficult to overturn on dry pavement, but usually the centre of gravity is high enough that tipping is possible, especially if the rider does not lean into the corners.

Adults may find upright tricycles difficult to ride due to familiarity with the counter-steering required to balance a bicycle. The variation in the camber of the road is the principal difficulty to be overcome once basic tricycle handling is mastered. Recumbent trikes are less affected by camber and, depending on track width and riding position, capable of very fast cornering. A few trikes are designed to tilt into the corners much as a bicycle does, and this also renders them more comfortable on cambered roads. They are discussed as tilting three wheelers (TTW's).

In the case of delta tricycles, the drive is often to just one of the rear wheels, though in some cases both wheels are driven through a differential. A double freewheel, preferably using no-backlash roller clutches, is considered superior. A jackshaft drive permits either single or two-wheel drive. Tadpoles are generally rear wheel drive.

Recumbent tadpole trikes often brake one wheel with each hand, allowing the rider to brake one side. This has led to a geometry (misnamed centre point steering) with a kingpin axis intersecting the ground directly ahead of the tyre contact point, producing a normal amount of trail. This arrangement, elsewhere called "zero scrub radius" is used to mitigate the effects of one-sided braking on steering. It is said to allow the rider to steer by braking. Zero scrub is generally avoided on the grounds that it reduces steering feel and increases wandering. The alternative is to use standard Ackermann steering geometry, perhaps with both front brakes operated by the stronger hand. The KMX Kart stunt trike makes a feature of allowing the rear brake to be operated separately, allowing "handbrake turns".

In the UK, upright tricycles are sometimes referred to as "barrows". Many trike enthusiasts ("trikies") in the UK belong to the Tricycle Association, formed in 1929. They engage in its day rides, tours and time trials. Massed start racing of upright tricycles is limited to one or two criteria such as in Bungay, Suffolk each year.

Makers of upright trikes include George Longstaff, Higgins, and Pashley Cycles in the UK. Italian company Di Blasi make a folding upright trike, which quickly folds to a compact 68 x 28 x 62.5 cm size, and which is available internationally via a network of dealers. Makers of recumbent trikes include Hase (who make the largest-selling delta, the Kettwiesel, improbably named after the British children's programme Catweazle); Inspired Cycle Engineering, who make the Trice range of tadpole trikes; AVD, who build the Burrows Windcheetah or Speedy; Australia's Greenspeed; Big Cat HPV which builds the 6 Catrike models in Florida, and Stein, a recent entrant from North Serbian province of Vojvodina in South-Eastern Europe.

The tadpole trike, while gaining popularity, is still mainly used by middle-aged former bicyclists who are tired of developing back pains and associated pains from normal upright bikes ("wedgies", as they are called in many recumbent forums). Many trikes are homebuilt as trikes are still fairly expensive, due to the use of high quality components (for reasons including the fact that a trike becomes perceptibly heavier than a two-wheeler anyway) and small order numbers. Most good adult trikes cost at least $US2000 - so homebuilders can manufacture their own frames and buy or use cheap 26" wheels instead of the expensive 20" wheels on most commercial trikes.

 1. Match the left part with the right:

2. Complete the sentences with the suggested words: double, rear, clutches, driven

In the case of delta tricycles, the drive is often to just one of the _______ wheels, though in some cases both wheels are _______ through a differential. A _______ freewheel, preferably using no-backlash roller _______, is considered superior.