Those numbers check out. But consider this: for a 150 lb - 250 lb bike/rider system, 3.2 lbs is 2.1% to 1.3% of the system weight--that's not much, relatively speaking. This is why the vibration that's so obvious on the workstand is almost always imperceptible on the road. In contrast, sprinting at 35 mph means you're generating 5-6 lbs of thrust at the rear tire contact patch on average. But the actual thrust varies (roughly) sinusoidally between 0 and maybe 10 lbs of thrust depending on where you are in the pedal stroke. A 3-lb oscillation doesn't mean much when projected onto a 10-lb oscillation. I mean, it's not nothing, but we don't see Cavendish's rear wheel (or the rear wheel of other pro sprinters) skipping around because it hasn't been properly balanced.
Butcher wrote: ↑
Mon Mar 18, 2019 3:56 pm
When you have nothing else to do and have the best components, why not spend a bit of time to have them work in harmony.
Why not? Because your wheels are already working in harmony--they're both round. Plus, adding weight is counter to the ethos of Weight Weenies.
More seriously, "working in harmony" sounds like a really desirable thing, but the phrase doesn't have much meaning in this context. I'm not criticizing you, Butcher, but rather the sloppy thinking that often surrounds this issue. One often hears this language as part of an appeal to intuition and "rightness" rather than science. I suspect many people have experienced an out-of-balance front wheel on their car and felt the resulting steering wheel vibration. When the out-of-balance wheel is balanced, the vibration goes away, which feels much better. The thing is, a car wheel is a lot like a bike in a workstand because it's attached to the car with a soft spring. (The workstand's soft spring is the main vertical shaft).
Josh Poertner at Silca is definitely a smart guy and I respect his work. But he calls the spike in rolling resistance on rough surfaces at high pressure "impedance losses." IMHO, this is an understandable-but-suboptimal metaphor for what's going on, but I also sense some cognitive dissonance here. Silca sells wheel-balancing weights, but in nearly every real-world case, unbalanced wheels are imperceptible by the rider. This is a high-impedance system because the forcing frequency results in almost no relative motion. In other words, the impedance is high but the losses are negligible. I respectfully disagree with the term "impedance losses" for rolling resistance, but if Poertner likes that term, he should refrain from making his claim of "improved handling" due to wheel weights, because the mechanical impedance between the bike/rider system and the unbalanced wheel is so high that a balanced wheel isn't perceptibly different.
The paragraph above isn't there to call out Poertner or his collaborator Tom Anhalt; IMHO they both do solid work, Anhalt especially. This is just (IMHO) an easily-overlooked point of cognitive dissonance. Plus, wheel weights have a whiff of snake oil about them. On the other hand, people eagerly buy these things and Poertner has to keep the lights on* at Silca, so I'm not unsympathetic.
I agree that balancing wheels gratifies some people immensely and does no harm, so IMHO your advice is totally sound. One interesting experiment would be to attach a weight near the valve stem to exaggerate the imbalance and see if you can tell the difference. Ideally, you'd have a friend attach the weight to either eliminate the imbalance or accentuate it; if the rider can reliably call the wheels balanced or unbalanced, then it's likely their perceptions are worth something. If you do 10 runs and the rider correctly calls the weight position 6 times out of ten, you need to do more runs. If you did 100 runs and the rider deduced the weight position correctly 67-90% of the time (roughly speaking) then the perception is likely real.
Another thing: lots of valve stems on high-end tubes are made of brass. Silca's Vittoria-sourced latex tubes use aluminum valve stems, as may some other brands. If your wheel is heavy at the valve, doesn't it make more sense to use a lighter valve than to add weight opposite the valve? And if you're going to add weight to the valve, why not get a more robust brass stem to start with rather than adding weight next to an aluminum valve?
The upshot is that it's fine to balance your wheels if that makes you happy. It just won't make you any faster or make your bike handle any better.
* Margins in the bike industry suck, possibly even for $36 wheel weights. Virtually no one gets rich from bikes, and those that do get rich very slowly (e.g., Mike Sinyard and the Burke family, which owns Trek). The idea that bike-industry titans are manipulating the bike market so they can swim in vaults full of gold coins like Scrooge McDuck is laughable to anyone who has spent substantial time in the industry.