Bridgestone takes tyre precaution

The definitive cause of the tyre blow out when the world champion was chasing the two Ferrari cars for the lead at Hockenheim remains a mystery.

Yoshihiko Ichikawa, the Japanese tyre manufacturer's technical manager, said blistering below the surface may have contributed to the blow out but choosing a harder compound was merely a 'precautionery measure'.

It has added to Bridgestone's concerns that a number of teams suffered from blistering at the recent test at Monza - a circuit similar to Hockenheim.

But the blistering below the surface on the McLarens in Germany may have been the result of the way the tyre was being used on the ultra-high speed circuit rather than any inherent weakness in the construction.

Bridgestone engineers believe another factor, such as debris on the track, ultimately triggered the failure.

Both team and tyre manufacturer has completely ruled out the possibility that a sharp edge of the wing or suspension leaned far enough to slice the rubber.

That was the early line of investigation in the hours just after the accident because of the massive odds against both cars running over sharp debris on successive days - and no other team having the problem.

The day before David Coulthard had a seventh-gear blow out - escaping unscathed - and the cause of that blow out remains a mystery too.

Bridgestone has said the inquiry is not yet over.

So far inquiries have shown that Hakkinen's accident is not due to a car failure or tyre composition failure but could be down to tyre pressures or temperatures.

McLaren boss Ron Dennis has denied running the tyres at too low pressures could be at the heart of the failure.