Lewis Hamilton is wary of how close Red Bull might be to Mercedes at this weekend's Spanish Grand Prix.

Sebastian Vettel was a close challenger to Nico Rosberg for second place in Malaysia, but since then Mercedes has been comfortably clear of every other car in the field. However, Hamilton believes it is only the power unit that gives Mercedes an advantage and says the characteristics of the Circuit de Catalunya should highlight just how strong the RB10 is.

"The Red Bulls are in the back of my mind thinking that they have a car that has a little bit more downforce than us, they just don't have as much power as us maybe," Hamilton said. "Here is a circuit where it is very much a downforce dependant circuit, so I think this weekend will be a real good indication of how good their car is. Definitely Fernando [Alonso] picked up a lot of pace at the last race, so it's the Red Bulls and Ferraris that we're going to keep an eye out for."

Expanding on why he feels the gap will be smaller in Spain, Hamilton said longer straights give Mercedes the biggest gain.

"We have less straights here and shorter straights as well. When you look at data or you look at GPS followings of other teams their loss is in the latter parts of the straights so you've reduced that significantly here.

"So, naturally already before everyone has put the upgrades on this weekend the gap would be closer I think. Everyone is going to be bringing upgrades this weekend - some more than others - so it will be interesting to see if that gap is still there or not."

While admitting the title fight has made the season "much more intense", Hamilton says he is relishing being part of it.

"Generally I'm able to [switch off]. That's just what I do. You arrive, you switch on and then when you're able to leave you just switch off in to another zone. But this is a much more intense season so far and perfection is required every weekend to get that result, especially when you have a good team-mate who is also doing an exceptional job.

"To come to a race weekend and know that we have a car that we can compete with - we had that last year but even more so this year - is just a feeling that I don't remember having for a long, long time. So I'm just enjoying every moment because you don't know when it comes or goes again."