From there, health issues with rheumatoid arthritis set in, and the dream disappeared into the background.
Ten years later, at her 60th birthday party in 2016, the idea was revisited in a discussion with Chris, a cancer survivor.
"I felt that it was time to tell rheumatoid arthritis who was boss. And Chris needed to tell cancer who was boss," says Karen.
They spent many hours and kilometres together training, riding in all weathers, fitting it into their busy lives and juggling injuries and illnesses.
"It was a massive undertaking. It consumed a big part of our life. You do have to make sacrifices to reach goals," says Karen.
In consideration of their respective health conditions, they minimised their training and changed their entries to the half-lake ride, instead.
Karen however changed her mind and decided to revert to the original 160km plan.
"We always said we would cross the finish line together, so it was a tough decision – and nine hours is a long time to be biking by yourself," says Karen.
"The hardest thing for me was that we weren't together doing it together.
Karen completed the full lake ride on her 61st birthday, in 9 hours, 1 minute and 27 seconds.
"The sense of achievement on the day was awesome. I've done a lot of momentous things in my life, but nothing compared to this achievement," she says.
"We made adjustments along the way. We both had injuries, we had sicknesses, we had health issues that arose.
"We never gave the goal away – we just revisualised it."
The two women believe their experience will be good inspiration for Training for You students and help them understand goals can still be achieved when the goal posts are shifted.