Andrew McMenigall and Toby Wallace were killed shortly after starting a charity ride from Land's End to John O'Groats last July 2.
The married fathers were in the nearside lane on the A30 at Newquay, Cornwall, when they were struck.
The two men had hoped to raise £10,000 for their charities but soon after the tragedy, the total rose to £50,000 with more money pledged.
Mr Wallace, 36, went to Cambridge University and was part of two winning teams in the Boat Race and worked in London, Sydney and Philadelphia.
At Truro Crown Court, Cornwall, Robert Palmer, 32, pleaded guilty to causing the deaths of Mr Wallace and Mr McMenigall by dangerous driving.
He also admitted a charge of dangerous driving on the same road near Okehampton, Devon, 11 weeks later in another lorry.
Palmer, from Bude, Cornwall, was bailed and will be sentenced at a later date.
The two victims had taken on the bike ride to raise money for the Kirsten Scott Memorial Trust, which provides opportunities for young people. Kirsten was a 25-year-old colleague at Aberdeen Asset Management who had died from cancer just five weeks after she was diagnosed.
Mr McMenigall was also raising money for It's Good 2 Give, an Edinburgh-based charity that offers support to young people with cancer and their families. One of his daughters had been diagnosed with a brain tumour, from which she recovered.
Mr Wallace's family said: " He had a remarkable zest for life. He was in peak condition both mentally and physically and was constantly pursuing new challenges, from rowing 3000 miles across the Atlantic and competing in events such as the World and National Rowing Championships, to riding for 24 hours straight in the World Mountain Bike championships."
The family of Mr McMenigall said: "He excelled in all areas of his life, at Aberdeen Asset Management , earlier as an officer in the Army, rugby player and referee; most recently as a triathlete and coach at Edinburgh triathletes, and most importantly as a devoted husband, father, son and brother."