The crash occurred on the A-30 near Newquay, about 50 miles from Land's End, at 8:30 a.m., The Scotsman reported. Police inferred from the gear and supplies the two men had with them they were planning the more than 800-mile ride to John O'Groats in Scotland.
The trip from the southwest tip of Britain to the northernmost point on the mainland is a popular one with cyclists, especially those riding to raise money for charity, The Scottish Sun said.
The identities of the men were not released pending notification of next of kin. Police said one, in his 40s, was an Edinburgh resident, while the other was in his 30s, The Scotsman reported.
The truck driver was arrested on suspicion of dangerous driving resulting in death and released on bail.
Witnesses said one cyclist was thrown into a ditch by the impact, while the other was dragged for about 100 yards down the highway. The wreckage of their bicycles remained on the scene for hours.