In my heart, it's surfing.

Based on time, it's walking/hiking.

Do great athletes even have a runner up sport? 

I'm not sure, but I bet if they do it supports number one.

How does surfing help my bike riding? 

I think it's really helpful for sprinting.  During the sprint, you have to notice what's going on in the pack... where is the energy? who is going to make move that matters?  When surfing, you focus if a set of waves is coming and where will they break.  When the set does start to take shape you cannot let on what your plan is to get that wave or you will be out maneuvered very quickly.  Same with a sprint, it's all about patience... letting the waves come to you and letting the sprint unfold before you.  Surfing also helps with mountain biking:  the balance, the flow and getting comfortable with weightlessness.

My other runner up, walking, is also supportive of my riding.

One, it's good to walk.  But, what I find to be tremendously enjoyable is to walk for an hour on the sand.  This is a great way to massage my feet and work those lower leg muscles and tendons.  Plus, apparently being grounded is a real thing... it actually is important that we get our feeties dirty.

My focus is still singular, and in multi-colored way.

How 'bout you?

What's your runner up?

Why?