BTW - maybe, that's MAYBE, part of the reason that balancing may now be trendy traces back to history.
BITD - high end double wall rims were joined with an internal sleeve. This sleeve was ALWAYS opposite the valve, so apparently some thought was given to balance. The end result was that whatever imbalance remained was limited to the weight difference between the valve and sleeve, and in any case much less than the weight of the valve, so things were pretty OK, and there wasn't a reason to make them better.
Nowadays, rims are either welded, or built of sheet CF, so all things being pretty equal, we now have imbalance by virtue of the valve, and the amount is greater than before. Whether it's significant or not is something folks will debate, but we do have to accept that things are different now vs. the past.
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