A competitive rider in a 12-hour time trial can cover 220 with ease and up to 280 with miles with a bit more effort. Some riders have been known to cover as much as 300 miles and more, with top men sometimes reaching over 320 miles. Time trials of 25 miles often produced under the hour results way back in my time and with similar speeds, managed under 2 hours for a 50 mile time trial. It was common to produce speeds of 50 miles per hour in sprints. Prolonged speeds in excess of 20 MPH was and still is normal for the experienced cyclist. My personal best in a 25 mile TT was mediocre at 1 hour 6 minutes 48 seconds which was just over 22 miles per hour back in 1954. Don Taggard of Hebburn Vics.CC frequently broke the hour in 25 mile time trials - AND HE RODE WITH A FIXED WHEEL GEAR. I think his chosen gear ratio was a grinding 72.