Bithell acted as the crew to skipper Luke Patience in the 470 at the London 2012 Olympics last summer, winning silver behind Australian duo Mathew Belcher and Malcolm Page.
However it was with a heavy heart that they decided to part company at the end of last year, unlike Weymouth, adamant their combined weight would be too great for the light winds expected in Brazil.
And, while Patience is yet to announce his new 470 crew, Bithell has revealed he is to become skipper of a different boat altogether, the high performance 49er skiff with Grube.
Bithell and Patience beat the partnership of Grube and double Olympic silver medallist Nick Rogers to sail the sole British boat at London 2012 after finishing second at the World Championships late in 2011.
And Bithell, who has actually been training with Grube in the 49er since October, fully believes they will be able to challenge for gold at the Rio Olympics in less than four years time.
"It's a very exciting new challenge for us both," said Bithell. "Chris is a great crew and I know that he fully shares my dreams of gold in Rio so we'll both be putting in the hard yards to try and make that happen.
"For me it's a change of boat and a change of position on the boat from crew to helm, so there's a lot to learn but we've been having a great time so far and I think we have so much potential as a team."
Grube actually acted as Patience's crew in the 470 up until 2009 before Bithell came along and, despite missing out on London 2012, he is adamant he will have plenty to offer the partnership.
"The opportunity to sail with Stuart, and in such an exciting class, was one I jumped at," said Grube. "We've got a lot of work to do, but we're both really excited about the challenge.
"We've had some great training over the past few months, both in the UK and in Murcia, and with a lot of British talent in the 49er we know we're going to be pushed hard, which is great motivation.
"I've had the opportunity to sail with three silver medallists now, Luke, Nick and now Stuart, so I have a lot of experience of my own of Olympic campaigning which will hopefully complement Stuart's skills and make us a dream team for Rio."
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- Recreational Watercraft