One of the fondly repeated digs on suspension forks is that they are lossy.
The mountain bike industry and the internet community have done a ton of work in the last twenty years on the losses incurred by
rear suspension. It all concentrates on isolating and preventing the input to the rear end caused by pedaling, and it's been
really successful. However, I went looking for something about front suspension, and found little about measured
power losses from suspension, either from rear or from forks. Most of the work done on forks is instead about how the longest travel forks feel when they handle the worst obstacles.
Here's a pretty old literature review (2004) on the topic. Most of the studies quoted in it are from the 90's and predate or don't use power meters. However in general all the studies come down in favor. The couple-percent losses seen are worth the benefit.
What I
did turn up was everyone's favorite Jan Heine and his tire tests. While not going into the tire stuff for the sake of this thread, I wanted to note that he also tested:
- a Rockshox Ruby SL fork from the 90's, already old even at the time, that had elastomers (here's an article about it)
- a springy light steel fork (Reynolds 531 SL blades) from his custom Alex Singer
- a heavy duty stiff steel fork (from a "Trek hybrid" most likely a 7 series Multi Track
The Trek fork took by far the most power. It was somewhat improved by excessive padding on the handlebars. The springy forks were way better and nearly equivalent, whether the spring was in a tube or not. The same trends were found both on the rumble strips and the fresh pavement. He shows they saved thirty-ish watts on the level, 203-213 vs. 242. That's about 15%! This is probably fully metabolized by the roadies, they are all riding around on carbon forks well known for having suspension properties. What it really shows is that a
very rigid fork... sucks.
Heine is fond of saying that steel drum tests of his tires don't measure everything. It would not seem impossible to put the fork, and some kind of spring to be the human, into one of those steel drum tests and see what happens.
He wrote,
Interestingly, the RockShox fork was more comfortable, but no more efficient, than the flexible steel fork of my Alex Singer. Some energy gets lost in the RockShox’s elastomer damping, whereas the undamped Singer fork has next to no internal losses.
But in fact the Rockshox actually shows only about half a percent difference at high power on the rough rumble strips and 10W
less power lost on level ground. Gotta wonder what he'd find with a coil or air spring and oil damped fork.
The tests were in BQ in 2009 and reblogged in 2012 and 2018:
https://www.renehersecycles.com/suspension-losses/
https://www.renehersecycles.com/myth...des-dont-flex/ (this one has the power numbers)