Originally Posted by
Andrew R Stewart
Bill K offers real life info.
I almost laughed at the OP's questions about tolerance in wheel building. Real rims are not perfect ones. They have deviations from round and flat right from the factory floor. Often even if the radial/roundness is good about the seam this portion of the rim usually has a different manor in how it responds to the spoke tensions than the rest of the rim does. Then there's the issue of tires having far greater deviation than a nice wheel has...
I long ago accepted the Wheelsmith philosophy that a slightly out of true wheel with more consistent spoke tensions is a better long term part than a wheel that looks dead straight but has spoke tensions all over the place.
How true VS how consistent the spoke tensions are and how high does the tension levels get can be explained with numbers but in my world is not a must be or a given. I let the parts give me feedback and make judgements form that. generally I'll try for around 1ishmm radial and the same for lateral. But there are many wheels I have built that have greater run outs and still are giving miles of pleasure. Andy
+1 For me, the goal is a "happy wheel" that will give me years and thousands of miles of trouble free riding. And the mix of spoke tensions and trueness, both side to side and roundness depend on the rim, spokes and hub I start with. Some of those happy wheels I can set the brake pads to almost touching, others I need to back off a ways. (I don't like instant contact anyway when I squeeze the brake lever, so that's rarely an issue on my bikes.) Some wheels are better rides with slightly larger and softer riding tires because I could not hit "round".
All rims are made by factories of machines and people. Mondays and Fridays the people are often not so sharp. Machines get old, lose their "edge". Dies for the rims get tired and bigger inside so the extrusions get heavier. The seams are a combined challenge of 1) can that extrusion be bent continuously and perfectly to the ending at the seam? and 2) does that mechanical or weld at the joint distort the extrusion? Different rims are made with different techniques. Some are famous for the extrusions going near straight that last inch or two at the seam. Others for angular distortion caused by the plugging method. Or from the weld head and sequence,. If people were involved, Monday, Wednesday or Friday?
Rims then get sent, perhaps across town, perhaps across continents and oceans. Get stored. Lifted in pallets by forklifts. Hung on racks by near kids who simply don't care. ... We then expect to make dead on perfect wheels out of them. Or just settle for "happy" and sleep better. I build wheels with NOS rims. Some of them were made and shipped from the factory 40 years ago. There's room for a lot to happen over that time span!