Originally Posted by
sbs z31
For whatever reason I feel that the 3" rollers comes very close to the same resistance as the road. Now that I have a Garmin 510 I can start doing more structured intervals targeting my cadence goal.
For a sense of the load from road, rollers and trainer look at the Kurt Kinetic site which compares its trainer to road watts where you get a nice exponential graph (note they assume 1% grade so not flat). Then on the Krietler site there is the resistance for rollers which is pretty much a straight line (w * speed).
With 3" rollers all 3 lines meet somewhere around 18-20mph. Double the speed on rollers the wattage doubles. Double the speed on the road at it is more like 8 times more with air resistance (speed ^ 3).
With rollers the resistance depends on the tires, inner tubes, pressure and your weight in addition to roller size. Riding a mtn bike or CX bike with knobbies and low pressure is a work out even on 4.5" rollers, where track tires at 180psi barely get any resistance.