Earl Grey

I have searched, and can't find an answer on this anywhere - is there a customary standard for trueness (hard to measure accurately, but you can look at 'wobble' on a known flat surface) / roundness of new, unlaced rims?

FBinNY 

There's no real standard, but rims shipped warped earn their makers bad reputations.

Of course the rim's cross section and rigidity plays into this, as does spoke count. With 36h on a light rim, just about any kind of error can be pulled into place with slight changes in spoke tension. However very rigid rims and/or fewer spokes makes the rim's original condition much more important.

It's almost impossible to correct local wobble on a low spoke wheel, and deep rims that are oval take great differences in tension to correct.

I check new rims for wobble by laying them on the floor, and for roundness by rolling them. Sometimes, if I'm worried, I'll check the diameter at a few places with a measuring tape. If a rim isn't spot on or very close, I'll flex it in my hands and make a judgement call about whether to build or not.

BTW, yeas ago, rims were stacked imperfectly making sort of a big spring, which was compressed and wrapped. Obviously warped rims were fairly common. Better rims were stacked in neat cylinders and traveled better, but smart builders always let someone else get the end ones. These days most of the rims for the after market are shipped in boxes of 12 or so, and should arrive OK.

Earl Grey

Thanks FB. Informative as always!

The inevitable followup - what do you consider 'very close' to 'spot on'? Are we talking about similar tolerances in a new unbuilt rim as you might accept after they're built? I see 1mm thrown around as a target in both axes, although others want to get closer laterally (.5mm or less).

At this point I'm just wondering out of curiosity.

I have a set of Velocity A23s on order (32h/28h) for my first ever wheel build, and it occurred to me that I have no clue how to evaluate the rims themselves before investing all the time (especially as a noob) in building them up. They'll have been subjected to the indignities of USPS en route.

450g, 32h and a very shallow V section makes me think, based on your comments above about weight and spoke count, that I probably wouldn't have much to worry about unless there's a gross warp.

1nterceptor

From Peter White's site:

"But sometimes I can't get a wheel to be both round and true, and have perfectly even tension all around. That's because of irregularities in the rim itself. If the rim isn't perfectly round and/or true, the spoke tension cannot be even, and end up with a round and true wheel. In order to have a round and true wheel in that case, the spoke tension must be uneven. In that case, I have a decision to make. If the rim is so out of true that the wheel cannot be built with adequate tension in all of the spokes, I cut out the spokes, get another rim and start over again. But if the rim is just a little bit out, and I can correct it with moderately uneven spoke tension, I'll finish the wheel. As long as I can build it so it stays true, I'll do it. And it may end up with a slight vertical hop or dip, but not enough to notice while riding.This is a compromise. But it is a necessary one, since not everybody can afford the best rims. And not everyone can afford to have a builder spend hours testing each rim from the factory and building and rebuilding the same wheel looking for the perfect inexpensive rim."

Read the full article:
Custom Wheel Building

FBinNY 

My standards are probably too low, since I go back to those baled rims I described.

But the numbers alone don't tell the story. Picture the difference between a rim that's a nice gently formed potato chip, and one with a local bend, Likewise for radial error, is it gently oval, or is there a local more pronounced distortion?

One thing I do is flex the rim in my hands to get a sense of how much resistance it'll put up against spokes pulling it true.

In any case, asking unbuilt rims to be as perfect as built wheels is probably unrealistic. They don't have to be true, just trueable.

Earl Grey

Thanks for the link, 1nterceptor.

FB - point taken, thanks. And I can appreciate that a wobble between two spoke holes is a different story to a deflection of equal magnitude occurring over the whole diameter of the rim.

FBinNY 

BTW- I used the word(?) trueable. That means different things to different people. Some, who are used to it, don't have issues wrestling rims into line, but less experienced people may find it a struggle.

seely

Using a surface plate, our standard is >0.2mm with 3lbs of weight on the rim. If we can fit the 0.2 gauge through the rim with two 3lbs weights on the rim (on opposing sides). A floor or really any surface short of a purpose specific surface plate really isn't flat enough to gauge flatness accurately in my experience. Achieving tension with an out-of-round rim is one of those things that can really vary. As you get closer to tension, sometimes the tension of the other spokes will be enough to "pull" the rim into round with an acceptable, sometimes even more than acceptable, tension variance.

GamblerGORD53

I bought 3 Velocity Dyad rims 2 years ago. They were 100% true.
Stacked together you couldn't put a piece of paper between anywhere.

RandomTroll

A rim may have non-uniformities in strength: it may be flat and round unlaced but not when laced to correct tension; or may be flat and round when laced to correct tension then wobble when ridden.

I don't have a tensiometer - I don't even have truing stand: I build wheels holding them in my lap using only a spoke wrench and home-made dish tool, but I take care to keep the dish correct and tighten the spokes evenly until the threads disappear by inspection, then work slowly, and I have built wheels that were true and round and dished (and reasonably tensioned, as judged by plucking) but wobbled when ridden (with used rims that I must have damaged).

I hope that a new rim has a perfectly-uniform composition but some may not.

FBinNY 

A true wheel wouldn't wobble when ridden, that's what true means. OTOH in the pecking order of what's important in a wheel build, being true trumps having even tension.

The above notwithstanding, it's a question of balance, getting reasonable trueness both radially and axially, while keeping tension reasonably even. Often there's b some sacrifice of ideal of one property to stay within bounds on other. So the rule is to get the best true possible, while keeping tension variation within bounds.

BTW- as for no tools, I'm with you 100%. I built countless wheels without a tension gauge, and continue to use one only to spot check 3 spokes or so to see if the average tension is within my target. This wasn't necessary when wheels were all similar 32h 3x, 14g DB, but these days there are so many variations that I can' be sure that my fingers are calibrated properly.

fietsbob

Manufacturers tolerance criteria may come with Price Point also .. do you cut up a non conforming finished product?

Or ship it on as part of the truckload lot, to the next level of distribution, in the supply food chain? and thus keep costs down.

RandomTroll

Okay, then I mean something different. I can make a wheel that's true when my bicycle is upside down and I have just finished building it but when I ride it isn't true, but when I turn my bicycle upside down to check the true, it's true. Judged by plucking, the spokes are tight enough that the wheel isn't loosely-built. I've taken such a wheel apart and laid the rim on the floor: it's as flat as I can tell, no different from a new, undamaged rim. Is that flex, as opposed to wobble?

The lesson I meant to impart is that materials have variable composition and strength that don't show until stressed.

I have also started building wheels and had them potato-chip only when I got the spokes tight (but still short of tight enough to ride); I could unlace the wheel, set the rim on the floor: flat.

FBinNY 

Something doesn't add up. A normal wheel will deflect slightly under side loads, but slightly under load, is the operative. When leaning the bike to climb, or sprint, the wheel may deflect enough to touch the brake shoe, or about 2-3mm.

However it won't appear to wobble and will still seem true in the deflected position.

If your wheel appears to wobble when when riding -- touches brake shoes on one side than the other -- it's probably too loose. And I don't mean slightly loose, but seriously loose. Could be something else, or a problem with the description in the post, but you might want to have your fingers (or ears) recalibrated.

RandomTroll

The spokes weren't loose, the wheel was true when not-ridden. It was a rim that had long use; it was a cheap single-wall rim. I haven't had the same experience with a new rim. I hypothesize that the rim had suffered damage that didn't show until the stress of riding. Spokes apply tension equally around the wheel; riding applies it at one point.