Kart racing

Kart racing (as the word is so spelled by enthusiasts) or karting is a variant of open-wheeler motor sport with simple, small four-wheeled vehicles called karts, go-karts, or gearbox/shifter karts depending on the design. By definition a kart must have no suspension, (relying on chassis flex), and no differential, (solid back axle). They are usually raced on scaled-down tracks, but are sometimes driven as entertainment or as a hobby by non-professionals. Karting is commonly percieved as the stepping stone to the higher and more expensive ranks of motorsports.

Components

Chassis

The chassis is an extremely important element of the kart, as it must provide, via flex, the equivalent of suspension to give good grip at the front, and must be stiff enough to enable the inside rear wheel to unload in corners. If this did not happen, the grip of the rear wheels trying to hold the kart in a straight line would overcome the grip of the front wheels trying to turn the kart into a corner. Karts have no suspension, and are usually no bigger than is needed to mount a seat for the driver and a small engine. Chassis construction is normally of a tubular construction, typically steel, with different grades and diameters of tubing as well as their actual configuration offering different amounts of flexibility. Chassis designed for indoor or non-professional racing usually have large bumpers on all four sides, while high speed shifter or direct drive karts have plastic or fiberglass spoilers to improve aerodynamics and crash protection.

Related Topics:
Chassis - Suspension - Steel - Plastic - Fiberglass - Aerodynamics

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Kart chassis are also classified as 'open' or 'caged'. Caged karts have a roll cage surrounding the driver, and open karts have no roll cage. Caged karts are not used in Europe.

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The stiffness of the chassis enables different handling characteristics for different circumstances. Typically, for dry conditions a more flexible chassis is better, while in wet or other poor traction conditions, a stiffer chassis is preferable - for some karts. For other classes / driving styles, there will be stiffening bars on the kart which are done up tightly for dry and loosened to give more flex for wet conditions. Further complications can be added by changing floorpan materials / fastenings to change the effective stiffness of the chassis.

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Professionally raced karts typically weigh 200 to 300 lb (100 to 150 kg). Avanti, Birel and CRG are a few well known examples of the many European manufacturers of race-quality chassis. These usually cost around £1700. American companies in the shifter kart market include Trackmagic and Margay. (List of karting manufacturers)

Related Topics:
Avanti - Birel - CRG - List of karting manufacturers

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Motor and fuel

While hobby go-karts depend on gravity for propulsion (these are called soap-box carts or billy karts), racing karts use a small engine. Several types are available, as well as differing fuel options. Gasoline 2-stroke or 4-stroke engines are the most common type, but other types of propulsion are available:

Related Topics:
Gravity - Soap-box carts - Engine - Gasoline - 2-stroke - 4-stroke

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• Engines running methanol or other alcohol-based fuels)
• Gasoline engines converted to run on propane or methane
• Pressurized gas, using a cylinder carried with the kart
• Electric motors powered by kart-mounted batteries

4-stroke engines are typically standard lawn mower, generator, or even chainsaw engines, sometimes with small modifications, developing from about 5 to 20 hp (4 to 15 kW). Briggs and Stratton and Honda are manufacturers of such engines.

Related Topics:
Lawn mower - Generator - Chainsaw - Briggs and Stratton - Honda

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2-stroke engines were originally taken from motorcycles, but have become a kart-specialized item with dedicated manufacturers, Vortex being one example. These can develop from about 16 hp to 30 hp (12 to 22 kW) for a single-cylinder 100 cc unit to 90 hp (67 kW) for a twin 250 cc. The most popular categories worldwide are those using 100 cc engines and the "Touch-and-Go" 125 cc units. A typical 100 cc or 125 cc TaG engine costs around £1500, and a 125 cc gearbox engine about £2000.

Related Topics:
Motorcycle - Touch-and-Go

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Transmission

Karts do not have a differential. Recreational karts have fixed gearing, which in part determines their top speed. They are usually limited to about 60 mph (100km/h) for sprint karts and about 90 mph (145 km/h) for enduro karts. In the very early days karts were direct drive, but the inconvenience of that setup soon led to the centrifugal clutch for the club level classes. At first the clutches were "dry", but the oil bath or "slipper" clutch became common later. These slipper clutches allow the high rpm kart engines to stay higher on their power curve at low speeds, and produce impressive acceleration as they engage. However, the top international classes still use direct drive engines, the reasoning being that at this level drivers should be good enough to stay on the track during the race and hence not need to restart their karts. Unclutched engines will be used at this level until 2007 when the rules will change.

Related Topics:
Differential - Centrifugal - Clutch

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More serious kart racers in the USA prefer shifter karts, which have a six-speed manual transmission and a clutch to make better use of the more powerful engine. Some of these gearboxes are operated with wheel-mounted paddles. In Europe, competitive kart racers tend to prefer fixed gear 100 cc or 125 cc machines although shifters of 125 cc, 250 cc and occasionally 210 cc are also raced.

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Typical top speeds of racing karts are around 90 mph (145 km/h) for fixed gear and in excess of 160 mph (260 km/h) for the best shifters.

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Tyres

Wheels and tyres are much smaller than those used on a normal car. Similar to other motorsports, kart tyres have different types for use appropriate to track conditions:

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• Slicks for dry weather. In international level racing these are some of the softest and most advanced tyres in motorsport and a development ground for Formula One.
• Rain tyres for wet weather
• Intermediates for damp or low traction conditions. Sometimes worn wet tyres can be used.
• Special, such as spiked tyres for icy conditions

Tyres are sometimes prepared with special solvents to soften them and increase grip, however this is banned by many racing organizations. The tyres can support acceleration round corners at 2 G (20 m/s²), depending on chassis, engine, and motor setup.

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