Hamilton fears "difficult weekend" amid engine delay

Mercedes decided this week to postpone the introduction of its upgrade across all six cars because reliability had not been proven in dyno testing.

The current engines have only run six races thus far, and with 21 on the schedule, each example has to complete seven weekends.

The plan for the works cars was to switch to the new spec for Canada and then use the original units again for a seventh time in Hungary, the track where ultimate power counts less than elsewhere.

Hamilton says the loss of the upgrade, plus the inevitable drop in performance that comes with high mileage, will make life difficult.

"This is a power circuit, so it was our target, and definitely would have been helpful," said Hamilton.

"The guys worked as hard as they could, and we had to take the sensible decision to not bring it, which is definitely unfortunate. We have to try and make do without.

"But it will mean our performance is not probably the greatest. It's the seventh race on the engine, and the goal is to make the engines stay the same the whole way through, so naturally it's degraded, you lose horsepower over races.

"If we're at 7000kms or whatever it is, it definitely would have lost performance. So at a power circuit it will probably be magnified."

Asked if he expected main rival Ferrari to have an advantage in Canada, Hamilton said: "Yeah, also particularly if they do bring their upgraded engine. So it might be a difficult weekend.

"All I'm hoping for is reliability. If I'm on the seventh race at a difficult circuit on the engine, I want to see it through. That's my only concern.

"Naturally I'm still here to win, but as I said, if they've got upgrades in their engines, which can be from a tenth to two tenths, Ferrari are particularly very strong on the straights.

"It will be interesting to see whether we're able to match that or not. But we're going to give it everything we've got, that's for sure."

Teammate Valtteri Bottas, for his part, played down the impact of the engine upgrade delay, insisting it will only be "a small penalty".

"We were initially expecting to bring the new power unit to this race, which would have been a small gain compared to the old one," said the Finn.

"We found some issues, so just to be safe we still need to make it perfect and hopefully run it in two weeks.

"For sure the new one would have been a little bit better but it is not like our old engine is a bad one. It is a good one and it is still all healthy and it is reliable so there are no concerns on that.

"We also planning to use it again later this year in Budapest, but now instead of that we will use the new one in Budapest.

"I think it is going to be a small penalty. Obviously it would have been nice [to have it] but that is how it is."

And contrary to Hamilton's worries, Ferrari driver Sebastian Vettel was dismissive of the effect mileage has on performance.

"We have done a pretty good job, the mileage effect is not so big," he said. "It’s not like after 2500km you lose a lot of power just because of the mileage. That’s not a big problem for us."

He added that he didn't expect it to be an issue for Mercedes this weekend: "With this family, or generation of engines, I don’t think that’s a big problem."