One of the things we're constantly harping about is how our wheels are build 100% by hand, but one of the primary rules of selling is that you talk about benefits, not features. We've done a much better job of talking about the feature than the benefit, so what are the benefits? I'll approach this topic in a slightly unusual way. I'll also add the disclaimer that we're not perfect and we know it. Less than 100% of the wheels we've shipped have been perfect.
The goal of a wheel build is to have the wheel turn out and stay round and straight, otherwise known as "true" in both the radial (round) and lateral (what most people call true) dimensions. Okay, so what qualifies as true, then? Great question, and one without one clear answer. For wheels we ship, we aim to have within .25mm of radial true, and .125mm of lateral true. I've heard a lot of wheel companies spec a tolerance of .7mm for round and .3mm for lateral true. This "Ask A Mechanic" video says that lateral true is "within about 1mm." This is really a case of "more true is better," so we keep working until we think we're at the limit of what that rim can do. Sometimes that's no discernable error in round or straight, most often it's right about to the target I led with, and sometimes it's a bit outside of that but still better than necessary.
Some aluminum rims will have a bit of a jump at the joint, and the simple fact is that leaving a .25mm hop there is better for the wheel than doing a bunch of handstands to try and iron it out, as the ride would never ever notice that hop, and you'd just cause other problems if you tried to iron it out too much. The rim's quality will dictate the tolerances to which a wheel can be build round and straight. There have been rims we worked with where the limit of what the rim can do is often not good enough for us, and we no longer work with those rims. Disc rims also deserve special mention here. The sidewalls on a disc-specific alloy rim are not machined, and thus they are often-to-usually not capable of being built to that .125mm straight goal, and since you aren't using the rim's sidewall for a braking surface, it's way less critical.
Dish often gets lost in the bargain. Ideally, the rim is precisely centered between the hub ends, and that's certainly what we aim for with fronts. I remember Lennard Zinn talking about his tolerance being .3mm for dish, as that's what he needed to up his cross bike's cantilever brakes with the precision he was after. A tricky one is that we do initial rear builds with the dish ever so slightly favoring the non-drive side. This is because when you inflate a clincher tire, the tire exerts inward pressure, and the rim will actually creep ever so slightly toward the higher-tensioned drive side spokes. Some rims (ones with off center spoke holes, for example) exhibit this behavior a little less than others, and of course now front disc wheels act more like rear rim brake wheels than they act like front rim brake wheels, so there's that.
I don't know how to artfully integrate this point so I will do it awkwardly, thus: your tires observe NOWHERE NEAR the build tolerances that well built wheels do, in any dimension. Don't make the mistake of watching your tire spin to evaluate wheel straightness, as you're just looking at tire straightness, and that tire is probably only slightly more straight than the Halloween parade in the West Village (which every person should encounter - it's totally worth seeing).
Since I'm about to get the hook for running long, I'll leave it to the next part to talk about the benefits of the process of hand building wheels, and also to discuss how you can evaluate how well built your new wheels are when you get them.