Samuel D wrote:I’d be interested to see the worked out example, because it all depends on the relative magnitude of source (2). My gut instinct – often wrong! – says it must be tiny over the necessarily small deflections that may be permitted when using rim brakes, and that even if it isn’t, there’s not much wheel-to-wheel variability within the range of preloads available to us in functional wheels.
Here’s a thought arising from the small deflection that I observe with my XR2 rims, even with a 32-spoke SONdelux wheel (though it must be said that I’m barely 65 kg). The lateral force on the wheel occurs at the contact patch. For that to displace the rim in the other direction at the brakes implies the rim is transmitting this force. So paradoxically, stiffer rims may show more deflection at the brake, given a few givens (as Brucey likes to say). They may do this even as they deflect less at the contact patch (not that you’ll notice that).
Perhaps I’ve overlooked something obvious.
The rim is a continuous arch, kept in compression at all times by the spokes.
It rotates around the axle in all three axes - but the rim isn't going to deform sideways significantly unless it is pushed from top and bottom in the same direction.
Well....maybe if we consider that this rim deflection is not wholly to the rim and its component parts fixing to the hub.
That leaves the bearing, they are not that truly rigid like motorised vehicles, and their design (excluding cartridge) allows to displace the balls (riding up) on the cone and cup.
If we consider the force at bearing which is many times that of the lateral force at rim. (vector / moments etc)
As the rider pushes on pedal and turns the steering which is a reaction to the body sway, the rim deflects and unloads the downward weight of rider and bike (later is smaller) on the bearing, pedal side of bike.
Similarly the opposite side (bike) bearing is seeing / sharing the unloading force of pedal side.
This could easily be mimicking rim and spoke deflection.
Though I discounted the forks they might be adding some percentage however slight.
At a point in increased tension (to practicable gain) in spoke when building, it might not add any discernable rigidity, masking the deflection at bearings.
I don't have the tools you would need to show this, a simple dial test indicator clamped to fork will show bearing deflection.
Simple thumb pressure deflects the rim at brake easily.
The force at road end on rim will be considerably more? But whether this force is transferred equally or not to the brake side is questionable as said further up posts.
My gut says it is not wholly transferred but I cant say what percentage.
Of course I think we agree? That 5 mm is still excessive, this might be largely due to the taboo wheel build component's as said up posts, for me 1.5 mm is best I can get approaching pretzel on a standard touring front wheel.