Fizik Spine Concept

The science behind Fizik Spine Concept

The ever popular Antares also looks very different when you add the extra width
The ever popular Antares also looks very different when you add the extra width


Professor Roger Kram sought to build a system and tools to discover the numbers needed to support rider comfort. Fizik’s Luca Viano explains: “We wanted to find out what most of us [riders] have taken for granted, feeling comfortable on the bike has always been only on feel, we want to quantify that.”

The experiments consisted of a study on power and how forces on the stem, bottom bracket and saddle are affected by power. They found that an increase of 1w per kg (between 1 and 4) lead to a decrease in saddle forces as power increased — and surprisingly the same happens on the stem forces, with only the forces on the BB increasing. When cadence increases from 60rpm to 110rpm you see an increase in saddle forces and stem forces with the BB forces reducing.

From this starting point they then went on to study hand positions, rider position and perform a saddle study (where riders actually sit on the saddle). This found that even when moving the saddle for and aft by 3cm, the centre of pressure stays in exactly the same place. Luca explains that we automatically sit in the same place and “that means that riders can compromise their geometry and position to sit in the same place on the saddle.”

So are individuals able to discern differences between saddles during bicycle riding? And are there individual anatomical measures that can predict saddle comfort? This is the question Fizik put to Professor Kram and his team, and this lead to a further slew of studies.


Side by side, the Aliante regular and large certainly look plenty different
Side by side, the Aliante regular and large certainly look plenty different

They  found that some with narrow sit bones chose the wider saddle, and some with larger sit bone widths the narrower, which is counter to popular saddle choice systems from rival brands. Luca is quick to add though, “Sit bone width is important, especially when you’re looking at saddles for more upright urban bikes. We aren’t dismissing anyone else’s fitting systems, it’s just our research showed that pressure [weight] distribution is in our findings more important. Especially as the sit bone pressure point can change depending on your position and your hip’s rotation.”

So this is where Fizik has chosen to take its saddle design, they believe pressure or weight on the saddle is the defining factor and not sit bone width. This is a bold statement when you compare it to sizing systems other stablemates

Luca rounds up: “From this study it has meant we have been able to build a power matrix, with two equations to work from the numbers we now have give us a huge reference that makes it easier to find the correct saddle. For the maths geeks amongst you here’s those equations that provide the data for the matrix in full…

  • % Body weight on saddle = -0.0324X + 0.4555 Where X = Power in W/KG


  • pW = [[P x(p/100 + a) + (KS x V92 )] x v] x g


  • P = riders weight + bike weight
  • p = Climbing grade (fixed to 0)
  • a = Coefficient of friction (fixed to 0,01)
  • KS = Drag coefficient (fixed to 0.021)
  • v = Speed in m/s
  • g = gravitational acceleration

We are certainly glad that Fizik and the team at the University of Boulder have done all the hard work for us. You can try the Spine Concept selector tools out at


Article from Bike Radar