I’ve seen posts complaining about wheels rubbing on brake pads when sprinting out of the saddle and blaming it on flexy wheels and it got me wondering (and mind you I’m not an engineer), wouldn’t wheel flex occur between the ground and the axle, and if wheels rubbed on brake pads wouldn’t that be from frame flex?
Looking at it another way… if you could fix the frame in a frame stand (theoretically, not actually) and then try to deflect the wheel at the point where it would contact the ground, would you have a resulting flex at the opposite end of the wheel, i.e. the brake pads?
There was a good article about wheel flex in the latest Velonews, by one of the Mavic engineers. Some of what he said is counterintuitive, but it does make sense.
IIRC, a very laterally stiff wheel can be more likely to have brake rub than a laterally flexible wheel (I think this is more around rim stiffness than spoking stiffness), since the forces transfer up the entire wheel system.
It could also be a wheel that is not laterally stiff due to the spoking arrangement, but has a stiff rim. There are a number of factors that work in combination.
I don’t think that frame flex has much to do with wheel stiffness, but frame flex may be more noticeable with a stiffer wheel as the top of the wheel would deflect in the opposite direction.