RIght, it's been a long day but an informative one.
Mercedes look to have lost none of their edge despite the wholesale rule changes, while Ferrari and Williams also look very strong.
McLaren and Red Bull had trying days but in both cases they were able to rack up some impressive mileage - and fairly encouraging times - later on in the day.
Andrew Benson's report will be live shortly.
Thanks for your company - we'll be back with day two tomorrow.