Valtteri Bottas accepts that some teams made "bigger jumps" than Williams over the winter but believes the Grove team can catch up.
With Mercedes and Ferrari are expected to lead the charge this season, the midfield promises to be closely contested.
Williams are up against Red Bull, Force India and Toro Rosso for the 'best of the rest' title.
And although Bottas and his team-mate Felipe Massa both lost out to Red Bull Racing last time out in Australia, the Finn says Bahrain will give a better indication of the true pecking order.
“The track here in Bahrain is rather a normal track, and for us it will be very interesting to see where we really stand,” he told the official F1 website.
“For us primarily we have to focus on further developing the car if we want to fight for podiums.
“I still see some weaknesses of our car in the slow-speed corners, although it is a bit better than it was last year.
“Fact is that everyone is improving and everyone is going forward and there are some teams that have made bigger jumps than we did.”
Williams arrived at the Sakhir circuit with updates for the FW38 with Bottas revealing that they have yet to decide whether they will race the new nose design.
“We are bringing a new floor and some other minor improvements, but we will most likely not bring any major step forward to this race here. We are working on a new nose, and I am not sure if we will make it for this race," he explained.
“If so, if we will get both cars updated. But since Felipe is ahead with the points, it might be that he will get any of the updates that are only available for one of the cars.”