Getting Serious About FTP

[RapDaddyo]

You can use speed as a proxy for power on a trainer. Just be careful of the influence of press-on force, tire pressure and the tire itself. I sometimes run VO2MAX tests for other riders on my CompuTrainer and of course their tires are all different. I have been astonished to find out how much difference there is in press-on force when I calibrate their tires for power. It's really eye-opening.

 

[bgoetz]

Yeah, speed on a trainer never = watts, never. Speed on a given trainer = speed on that trainer and only if tire pressure is the same, clamp on is the same, and warmup is the same. And from using the CP trainer with a actual PM clamp on has to be done with some torque measuring device.

 

[smaryka]

I've found using the speed/power curve for my Kurt Kinetic is pretty bang-on my regular watts (having tested it extensively against a powermeter first). But yes you need a consistent tire, tire pressure and tightness of the clamp.

More importantly, it's only useful for longer steady efforts. Something like Tabatas, sprints, even over-unders will be pretty useless I think to estimate watts from the speed/power curve. It greatly underestimates the watts you need to speed up, and overestimates what you need to keep the wheel moving at that speed.

It's fine for 2x20s and tempo work though, as long as you ride steady.