Although it is more common for racers to be concerned with the weight of their bikes, it will pay in performance – both in top speed and mpg – to keep the weight as low as possible on any machine, and classics are no exception. However, at this point, it is worth mentioning that making modifications to a motorcycle raises all sorts of safety issues and any changes to the original manufacturer's specification must be done by professional mechanics ideally with the guidance of a qualified engineer.
Many of the components supplied by aftermarket companies are considerably lighter than the OEM part. The following lists some of the components that can be considered with a view to reducing the overall weight of a motorcycle:
The majority of people modifying a motorcycle will change the style of handlebars. However, if weight is a major consideration, replacing a stock set of touring bars with a set of clip ons, for example, may add weight to the bike as the clipons must be bolted to the fork legs with additional brackets and bolts. In many instances, a set of low rise or even straight bars will suffice and save weight at the same time—over both the stock bars and clip ons.
Replacing steel levers with lightweight aluminum items is a good way to save weight and in many instances improves the looks of the bike, too.
A typical front fender on a classic bike from the 60s will be manufactured from steel (pressed and/or rolled at the factory). Replacing these steel fenders with an aluminum equivalent will again save weight. Alternatively, the rear fender can be removed altogether and replaced with a seat that has a built-in mini fender. Needless to say, a carbon fiber fender will often be the lightest choice but fitting one of these may devalue the bike (this material was not used on motorcycles for the most part until the 80s).
If the original fuel tank was made of steel, a useful amount of weight can be saved by fitting a good quality aluminum replacement. The original café racers all used aluminum fuel tanks manufactured by craftsmen, for instance.
Note: Fuel tanks made from either fiberglass or carbon fiber should be avoided due to the potential for leaks. They are not legal in some countries.
Small board track racer style seats on bobbers or single seats made from fiberglass for café racers will both save a considerable amount of weight over any street bike and gain the looks an owner may be looking for.
By removing a stock airbox and all the associated bracketry, and replacing them with free-flowing filters - such as a Uni filter or a K & N - will save a lot of weight and often have the added bonus of improving the air flow and therefore the performance of a bike.
For serious builders, the frame and/or swing-arm can be replaced on many bikes. This approach was very popular during the café racer boom in the UK and later when a number of aftermarket companies (Dresda, Harris, Rickman or Seeley) began producing frames for Japanese superbikes. Replacing the swing-arm only on some of the early Japanese superbikes was good for weight reduction and also for improvements in handling as the originals were often flimsy and would bend in use!