England at Twickenham poses a bigger challenge than France in Paris, according to Ireland boss Joe Schmidt.
Ireland will fight for their first Triple Crown since their 2009 Grand Slam on Saturday, February 22.
Victory over Stuart Lancaster's men would set up a potential Grand Slam decider against France in Paris on March 15.
Regardless of that scenario though, former Leinster coach Schmidt believes England offer the tournament's greatest threat.
After victories over Scotland and Wales, Schmidt is steeling his squad for more hard grind yet.
"So far we've learned that it's always going to be tough, and we've had a little bit of luck go our way too," said Schmidt.
"There are tougher games coming and probably the toughest of all coming next, at Twickenham against England."
Ireland have spent their fallow week at a training camp in Clonmel, where tactician Schmidt has no doubt got to work in earnest on the England masterplan.
Ireland dismantled Wales' tactical approach in their comprehensive 26-3 victory in Dublin in round two of the tournament.
Schmidt is happy to adapt his approach to fit each individual challenge and has made no secret of the fact he will do so again if required at Twickenham.
After battling on through gale-force winds and nasty weather in Clonmel, a host of Ireland's squad will be made available for club action this weekend.
Jack McGrath, Sean Cronin and Martin Moore are now established as Ireland's understudy front-row, but that trio will be back in Leinster action against the Dragons on Friday night.
Eoin Reddan returns for Leinster after injury, boosting Ireland's scrum-half options for the England clash, with wing Luke Fitzgerald also fit to start.
Schmidt remains hopeful Munster's Donnacha Ryan can boost his second row resources after Dan Tuohy broke his arm against Wales.
"I think those guys should be available post-injury, and we're very interested in seeing how those sorts of guys come along," he added.
"We'd be interested to see how Tommy O'Donnell goes for Munster as well.
"You've got to balance selection on form mostly. One of the difficult things of trying to grow the squad, if they are on great form, it's hard to leave them out of the side.
"So that's their challenge, to keep performing and delivering, and it's a challenge for the other guys to put in the best performances they can as well."