Last time I did it from Ryerson, it was about 25 miles. Now granted, I ducked in at lot c and took it up to the race course and then down to shepards. Depending on the speed its anywhere from a 2hr 15 min ride to about 2hr 45 min ride.
I usually park at Ryerson School and pedal to Sheppard's Lake and take the trail form there. The whole loop including Sterling ends up to be about 25 miles. Takes about 2 1/2 hours depending on the crew.