Russell had a full day in the car in Bahrain on Wednesday, before Hamilton took over on Thursday.
While the team's programme meant that Russell's headline times were modest relative to those of rivals, he says that it was already clear that the car is an improvement.
Russell and Hamilton both lacked confidence in the rear end of last year's W14, and crucially that trait appears to have been addressed.
"The car last year was really challenging to drive," said Russell.
"Lewis and I had no confidence in it, it felt like it was going to bite us every single corner.
"We can attack the medium and high-speed corners without the rear end snapping out. And we feel like we've made a really good step in terms of the consistency of the car.
"We can really lean on it better than we've been able to in the past. And this was a huge focus throughout last year.
"We saw many flaws with the W14, which the team have done a really great job to rectify.
Source: Autosport