The 2.25 drums have approximately 90% more resistance compared to the 4.5 drums. Only the strongest of riders are able to ride the 2.25 drums. The 2.25 rollers were originally designed for the USA Cycling Team when they were looking for smaller rollers for travel that also provided enough resistance for interval workouts or sprint warm-ups. If you do not routinely average over 20-25mph on your solo road rides, look to the 3.0’s or 4.5’s.