Sergio Perez admits Force India's performance in the second half of the 2015 F1 season well exceeded the Mexican's expectations.
The team was forced to delay the introduction of its B-spec car and so started the year with a slightly updated version of last year's single-seater.
But after the upgraded car was introduced, Force India finished in the points in all but one of the final 10 races of the season.
The Silverstone-based team went on to secure fifth place in the standings, its best ever result in F1.
"It really surprised me massively," said Perez. "It's been a very strong second half of the year. We had great results, great races, some back luck here and there, but that's quite normal. But it really surprised me.
"The part that surprised me the most was how we managed to get the maximum out of the car before the upgrade came.
"Before Silverstone we were fifth in the constructors' championship and we were always a good three, four tenths away from Lotus.
"And that's a big number. Every simulation said we were going to finish behind them and we managed to beat them race by race and once the upgrade came it turned around the season, but before that - that's the best part of the year for me."
Best season yet
Perez, who managed Force India's only podium of the season at the Russian Grand Prix, finished the year in ninth place and ahead of teammate Nico Hulkenberg.
Although he scored three podium finishes in 2012, the Mexican believes 2015 has been his strongest season so far.
"I think it's been a pretty good year," he said.
"I think my Sauber in 2012, obviously with three podiums, is a lot more points, but I think the consistency that I've shown this year, the way that I drove throughout the year is more important than the result or scoring more points than ever in a Formula 1 season.
"For me it's important that level that I managed to achieve in terms of driving and confidence, experience. I think definitely I've had my best season so far."