Modifications
Many cutdowns have unneeded parts removed to improve power-to-weight ratio. Typically, the fenders, leg shields, floors, tail section and cowls are removed. Cutting away body parts is the easiest with Lambretta scooters, because they are built on a tubular frame, which means that the body parts do not have a structural role. Vespa scooters, on the other hand, are usually built with a unibody design, so the body panels give the bike its structure. This means that when Vespas are cut down, they cannot be made as bare-bones as a Lambretta. The body panels of a Vespa are modified by slimming them down or giving them a different shape, in such a way that the structural soundness of the bike is not compromised.
Cutdowns are often tuned – much like a four-wheeled hot rod – by overboring the cylinders to increase engine power or adding performance exhausts, modified carburettors, or aftermarket shock absorbers. Some enthusiasts replace the standard drum front brakes with hydraulic disc brakes or add water-cooled radiators. Lambretta owners may replace existing parts with a Nikasil plated aluminium barrel with radical porting, large Dell'Orto or Mikuni carburettors and bespoke (custom-made) expansion chambers, hydraulic clutches, and modern low-profile tyres. Some scooterists use aluminum Fabrizi racing barrels, because they use a rotary induction mechanism. Stock gas tanks may be replaced with YSR tanks, which put the weight of the fuel further forward. Some riders install a windshield to reduce wind resistance and enable higher speeds. To reduce weight, some scooterists use lighter-weight aftermarket parts, such as SIP carbon sports seats and other parts made from carbon fibre, carbon kevlar and fibreglass.
Some cutdowns have been used for drag racing. At scooter races, cutdowns often race in a separate category called the "specials", which is for cutdown and heavily modified racing scooters. The other scooter race categories include stock races with relatively unmodified larger scooters (152 to 250 cc) and "small frame" races for scooters with 136 cc or smaller engines. For races, scooters usually have to have accessories removed, such as center and side stands, mirrors, turn signals that stick out, and luggage racks. Scooter races often disallow performance-enhancing fuel additives such as octane booster.
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