FLEETS have been warned to avoid selling vehicles during the autumn of 1999. Glass's Guide predicts that the arrival of the twice-yearly registration plate changes in March 1999 will bring new car sales booms in March and September, but the downside will be a fall in residual values - especially in the autumn.

This year's August plate change will be the last under the current system. From March 1999 plates will change every six months, until a new plate format is introduced in September 2001. Adrian Rushmore, editor of AutoProVision - Glass's new computerised system for forecasting future residual values - said fleets which would normally replace vehicles in August 1999 might wait until September. However, they are likely to find prices hit by the winter decline in demand for used cars.

'Traders will be wary of buying stock in September, especially if they predict falling prices,' he said. 'We would therefore anticipate a very nervous market in the autumn of 1999 and, certainly from a fleet perspective, it will be better if disposals can be avoided at this time. Disposing of used cars in the following March presents fewer risks. At this time dealers are buying frantically in anticipation of the normal upturn in seasonal retail demand.'

Rushmore said that while many fleets would wait until September 1999 rather than replacing vehicles in August, fewer fleets would be willing to defer replacement of vehicles by two months from the historic January sales peak.