The onset of summer sees a rise in the value of convertibles.

Traditionally, wholesale values start to increase in the spring, while a good early autumn can extend the ‘season’. Activity slows considerably in the winter.

That said, there is always interest for the Audi, BMW and Mercedes-Benz models, while values for Mini convertibles seem weatherproof.

According to BCA’s consolidated data, this year has seen an erratic pattern to the values of convertibles, particularly when compared to the gradual price decline for all stock.

Convertible value peaks occurred in February, May and June, while January, March and April values trail by around £1,000.

In comparison, average values across all stock at BCA peaked in January and have been in gradual decline ever since.

Comparative CAP performance suggests the seasonality factor remains in full swing, with a slow start in January, then rising in spring.

However, by June, CAP performance is on the wane as values go from nearly 100% in May to under 98% the following month.

Price is the defining factor for the used buyer with running costs being taken into the equation.

For any top end convertible, a great specification is taken as a given, so mileage and condition come into play.

This makes the service history a vital part of the package.

A major service being due very soon can be a real turn-off.

For the seller, it could be worth getting the work done in advance and declaring this when the car is sold.

The nearly-new convertible – mainly, but not exclusively direct from manufacturer sources – is sold on average at eight months and has covered a little over 5,000 miles.

The average value in June was a substantial £24,668 and was ahead of CAP Clean by nearly two points.

Values peaked in May at £26,500 and February at £25,500.

The lowest average value recorded by BCA this year for nearly-new convertibles was in April at £20,500.

Obviously volumes are fairly low from these sources and model-mix at BCA will affect values.

Cars of this value are generally not snap-purchases. Many are brought to order.

Convertibles from fleet and lease companies are available in greater numbers than ever before, but demand still remains high.

At an average of three years and around 35,000, miles these convertibles are much more affordable for the average motorist, with values of around £11,600 recorded in June – the top figure for the sector this year.

The typical part-exchange convertible sold at BCA is nearly seven years old with a below average 60,000-66,000 miles.

An average value of £5,500 was recorded in June, the lowest this year.

More typically, values have been around £6,000 or more during 2008.

CAP values range from 89% – to 93% of CAP Clean.