Vettel believes that his team have had the car to challenge at Suzuka in previous years, but accepts that the fast corners could prove their undoing.
"It's difficult to know and difficult to predict at this stage - we have to get out tomorrow," said Vettel. "The weather should be quite consistent, in that case tomorrow could be quite important already and good to find out where you are.
"Historically, this is a circuit that we used to like and we always have been very competitive around here. So I think we should have a good weekend, but this year as well in fast corners we are struggling a little bit more than in the past.
"Obviously there's a lot of fast and medium speed corners around this track, so we'll see."
Vettel is the reigning F1 world champion.