Lateral wheel flex
 

Watching the Olympic track racers in slow motion, I could see the front wheel nearly hitting the forks during sprints. I was looking at the rim to brake shoe clearance on Mavic Open Pro wheels on Campy Daytona hubs and pushed on the side of the rim and was surprised at how easily it deflected. I wondered how much deflection occurs when serious forces are put on the rim as in a hard turn. Or are the forces on the wheel during turns mostly not lateral due to leaning?


Is lateral wheel flex anything to even think about and what makes one wheel stiffer in this regard than others?

Correct. If cornering caused significant lateral force on the tire, you'd fall over.


I suspect the lateral flex you are seeing in the sprinters tires is as a result of them rocking the bike.

The wheel does not flex into the brakes. The wheel shifts at the top precisely because it is not flexing. When you ride, you apply force through the axle down to the contact patch; if there was flex, it would happen betwee those two force vectors, i.e. the bottom half of the wheel. The wheel would run straight acorss the top half.

Instead, what is happening is a small amount of flex at the axle, in the fork legs axle, and dropout, is allowing top of the fork or the brakes to deflect into the wheel.

This is why fork through axles are lauded, because they are oversized and stiffer.

I have been riding without lateral wheels since age five ... since then my bikes have just had the two main longitudinal wheels.

While sitting neatly in the saddle and JRA, there's very little lateral force on bicycle wheels.
Various dynamic events, skids, falls etc can cause dramatic loads. Riding out of saddle, forcefully tilting the bike, or hanging off the side of the bike can cause some forces.

Things that make wheels stiffer are thicker/more/shorter spokes, wider hubs , and stiffer rims.