The 2010 world champion from Wrexham, 32, was part of the lightweight men's four that missed out on gold by less than a second four years ago.
Bartley is part of the Team GB quad that competes in the men's lightweight four heats on Saturday.
"To get on the podium in our event at the moment is very tough," he said.
"There's very, very strong crews out there... There's more depth over this four years.
"There is one or two stand-out crews each year, but the field behind that is so tightly packed and making the final from the top three in the semi-final just gets harder and harder every year and that semi-final has turned into a final in itself.
"If you don't get the pressure on yourself right in that position you're not going to make it.
"We've got to row two gold-standard A finals just to get there."
Bartley has been an ever-present in the four since 2009 and is one of Team GB's most experienced rowers.
He says the disappointment of missing out on gold in London motivated him to continue to Rio.
"I never intended to carry on after London. The plan was for that to be the end for me," he said.
"We just missed out by a tiny margin in the final, which I think in front of the home crowd is pretty painful.
"I think we all thought we were good enough to win, but things just didn't quite go our way.
"I think had they gone our way I might not be here now."
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Bartley's journey to Rio leads him to be philosophical about Team GB's chances of going one better than 2012.
"Winning a gold in Rio is not the be all and end all," he said, adding: "I've had a great time along the way... I've really enjoyed my four years.
"[I have] the hope that we'll stand on the top step definitely, but I think it's not going to be the end of the world if we don't, [but] obviously we'll be aiming up there."
Olympic silver medallist Chris Bartley says it will be harder to get on the podium at Rio 2016 than it was at London 2012.