Originally Posted by
69chevy
Fluid trainers have a known resistance at a given speed.
In theory, a fluid trainer should provide you with a more accurate and consistent power reading than any meter measuring strain/acceleration.
In theory, but the reality is the viscosity of the resistance fluid changes with temperature. This generally is a problem when the trainer is cold up until the fluid warms and then can be a problem again after a certain duration and speed. Many of the mainstream fluid manufacturers attempt to compensate for this with various different design and cooling mechanisms, but I'd take a strain gauge any day over a prescribed resistance curve.