Cars are becoming less reliable, according to a big study done by the German motoring club, the ADAC. And at least one expert blames car-makers' obsession with speed.

Not 0-60 acceleration, or top speed - though no doubt repeated stints of hard driving will hurt the trustworthiness of your motorised steed. Rather, it is an obsession with developing cars in the shortest possible time that is hurting reliability. Says Dr Ernst Fiala, former head of product development for Volkswagen, "only a fool thinks he can design a completely new model from inception to production in three years". Which, incidentally, is the time frame most European manufacturers now work to - including Fiala's ex-employer.

Volkswagen, and Mercedes-Benz, hitherto regarded as the most boringly thorough of all car companies at getting every last detail right, have special reason to heed Dr Fiala's words. Both have suffered acute embarrassment in the past year, when apparently insufficient development time has caused them to botch up crucial new cars.

Mercedes' cock-up is well-documented. It boasted at the unveiling of the new A-class baby car, at the Geneva Show last March, that the newcomer had been developed in record time. Its policy of triple-checking every last grommet had finally been fast-tracked. Unfortunately, it also resulted in a major testing oversight. In a severe slalom test, the A-class - promoted as "the biggest single motoring revolution of 1997" - lived up to its billing all too literally. It tipped over. A hugely costly and embarrassing halt to production, and the recall of all models sold, will teach Mercedes to be a bit more careful next time.

Volkswagen managed to escape from its embarrassment rather more discreetly. After production started, VW decided to strengthen the B-pillar (the side post that runs between the front and rear doors up to the roof) to improve side-impact protection. Many early cars were scrapped; others had expensive retro-fit modifications.

VW now "proudly" boasts about being able to develop new cars in three years. A few years ago it was six years. It is still committed to three- year development programmes (that's how long the New Beetle took).

Nonetheless, methinks Dr Fiala's warning may ring a few alarm bells in his old office.

That other great German icon, BMW, is also not immune to sloppy development. Anyone unfortunate enough to buy an early example of the current BMW 3- series - a marvellous car, once it was debugged - will remember the cheap door trim falling off in their hands, and the insubstantial feel of the car. That was also a "fast-tracked" development programme. A new 3-series is launched next month. BMW has quietly promised that it won't be making the same mistakes again.

Europe's car makers are increasingly speed-obsessed, because they have to compete with the Japanese. And the Japanese, who tend to be better organised and more efficient than Europe's makers, have long been used to three- or four-year development times. And they rarely (in fact, never) launch inadequately engineered cars. They may not be as finely honed or as lovingly crafted overall as the very best European cars. But nor do they contain embarrassing oversights.

The Japanese are far more task-driven. Thoroughness, rather than inspiration, is their hallmark. That's why, despite short development times, their cars are usually more reliable than European cars (as the ADAC study again revealed). Another reason is that "new" Japanese cars tend to have far more carry-over (and therefore proven) components than "new" European cars. Often their "new" cars are merely last year's mechanicals repackaged in a new body. But at least they don't break down, trip over, or use bits that fall off in your hand.