I've got a disc-braked CX bike and I've always been slightly concerned about how flexible the front fork feels fore-aft compared to my rim-braked road bike. My perception of flex was based on the standard "hold the front brake and rock the bike forward and back" which feels dramatically less-rigid on the CX bike. I had attributed this behavior to having a more flexible fork on the CX bike.

But as I thought about this more, I realized that perhaps my rigidity test is really more related to the type of brakes on the bike. When you hold the front brake of a disc-braked bike and push/pull the bike fore/aft, the braking force has to be transferred from the hub to the tire contact patch through the spokes whereas on a rim-braked bike, the braking force is transferred through the rim. With rim brakes spoke deflection is still involved since you're pushing on the bike fore-aft at the hub, but this fore-aft motion is working on the spokes in pure tension rather than winding up the spokes torsionally.

Anybody else notice what I'm talking about? Does it make sense?

If so, then it would seem that disc brakes are subject to some "windup" forces when in use that aren't there in rim brakes. And while I really like the feel of disc brakes in terms of stopping power, reliability, performance in the wet, etc. they don't feel as direct and rigid as caliper brakes to me.

- Mark