Haas F1 boss Guenther Steiner admits the rule changes for 2019 are worrying him when considering the competitiveness of the team this year.

The American outfit enjoys their best ever season last year finishing fifth and had a car capable of fighting at the front of the midfield pretty much throughout.

A series of aerodynamic tweaks to the front and rear wings among other alterations could lead to a shake-up in the order, however, as has been the case in previous years.

"Everything is on schedule as it should be," Steiner said. "It is like every year, you have some stuff which is a little bit behind but it's nothing abnormal. I'm confident we'll have a good car but I don't know how good the other ones are.

"We are happy with our numbers and what we do but with the new regulations, if somebody found something we are not aware of, how can I know that? But I'm pretty confident that we are doing a good job."

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Williams technical chief Paddy Lowe doesn't think the changes designed to promote closer racing will provide too many shocks though, due to how they have been implemented.

"The teams have been quite ready and open, at least some of them, to put stuff on the table that's then been heavily constrained," he told Autosport. 

"The regulations are very restrictive. I hope it's the case for everybody else, but we're struggling to find a lot of performance out of these front wings.

"I think generally the teams are of a mindset that they want clarity, and not to have a lot of arguments when we turn up in Australia over poorly defined aspects of the regs.

"With that spirit, everybody has been quite enthusiastic to define things in more and more specific details so everybody knows what they're working with."