Wheel Builder: Subjective Rim Quantification
 

So I've been building wheel for over 15 years, every since I started racing in my late teens when I didn't have the money to pay someone. I've built for other racers and friends so I have experience with a varieties of rim. I'm not a pro builder, I've built around 50 or so wheels. So recently I picked up a pair of Alex R390 for my son's bmx race bike. Just out of curiosity I google'ed for "Alex rim review". I found the typical Mavic is good and a mix of responses for Alex rims. What I don't find is real quantified qualities that make a rim good or bad. Most responses where related to the wheel as a complete unit. The wheel went out of true, won't stay true, etc.

So giving similar rim, for example a 32h with similar box, double eyelet, welded, machined brake surface how can you quantify rim quality. Over the years I've build numerous wheel sets with a variety of different rims but all of similar make up: 32 hole, typical box section, eyelets, both pinned and welded. Can't say I've really noticed a difference.

Comparing two rims with similar features the only thing I can think of is the aluminum quality and maybe the box structure. But then my experience seems to show most "quality" rim are more then good enough to survive a season of racing. I've had to replace rims mid season due to problems but those problems have mostly been with a quality "french" company.

So all you experience wheel builder what metrics do you use to justify one rim over the next. Have you notice significant difference in the quality of a build between two rim. I'm not looking for Mavic versus Velocity, versus Brand X but what about a rim have you noticed that makes it a better rim.

one quality of a rim that can be quantified is roundness. if a manufacturer can be deemed to manufacture a more consistently round rim, i'm all for it. anything less round will compromise uniformity of spoke tension that i value in a long-lived and problem free wheel.

If a rim is more true out of the box, is that what makes it possible to get uniform spoke tension, or does it just make it easier to get uniform spoke tension? It was my understanding that it is the latter. I have two pairs of wheels with Alex rims (which came OEM on bikes) that I completely detensioned and retensioned to try to make the wheels have correct and uniform spoke tension. All four wheels went way out of true when they were detensioned, but after a lot of fiddling I got them back to true with the right degree of fairly uniform tension (within +/- one unit on the Park gauge). I'm not saying I'm good at this, as it basically took forever and I was fairly frustrated. However, this experience leads me to believe that someone who knows what they're doing could build a pretty good wheel with an Alex rim.

Heuyhoolihan:

Interesting take on the rim. I didn't think to consider factory roundness as a measure, but I guess you're right. I've been working with rims over quite a few the years, and 20+ years ago, it didn't matter who made the rims, the processes were never perfect, and the wheel builder had to work the rim and there was some art in getting a rim round and true. But, yeah, I have noticed that it's less effort these days with some rims that simply lace up and bang, tension up near perfect and are absolutely round. I guess manufacturing has improved over the years.

Well I was going to say that my two measures of rim quality were:

1. Price-Performance

2. Warranty Claims.

And I'm still a cheap skate when it comes to wheels for the masses. But I field far too few warranty claims on any rim, old or new, to have much data. Either my wheels are good wheels and the manufacturer doesn't matter, or that makers all produce a rim which exceed all but the most intense riders and therefore are fairly equal as far as most consumers go.

Roundness doesn't really quantify the quality of a rim - consistent rim extrusion does.

You can have a perfectly round rim on the outer circumference - but have very uneven tension between spokes because poor extrusion quality results in poor inner circumference consistency.

Very common with cheap or basic and replacement rims.

=8-)

I don't think anybody discussed how to measure roundness. My measure would be a consistent ERD all the way around (within a mm). I think that would include your criterion of consistent rim extrusion.

Similarly, I also check a rim for wobble by placing against a plate glass window.

Not quite, because that can hide the poor extrusion to the outside circumference....checking ERD all around is important for ERD...but not reliable for judging whether a rim is a good candidate where even relative tension is a high priority - as is the case with multi-speed asymmetrical rear wheels.

Way to home test roundness AND extrusion quality concurrently - which is necessary - is to:

1. Use plastic calipers or metal calipers with jaws taped.
2. Adjust to 1mm more than depth of the rim - assuming no eyelets.
3. Place outer jaw flat against outer circumference of the rim.
4. Brace for side to side motion with caliper arm perpendicular to cross section of rim.
5. Rotate rim through calipers with decent backlight.

If the inner wall varies more than a 1/2 millimeter + or - OR more than 1mm total while rotating rim through - that rim will be a poor candidate for a wheel where even relative tension is an absolute must - typically multi-speed asymmetrical rears or disc fronts.

This is how I separate KinLin MX2Ws and MX2Gs and MX3Ts into one pile intended for single speed or symmetrical wheels and one pile intended for asymmetrical multi-speed rear wheels.

=8-)

I knew that if I stuck with you I'd eventually pick up something good...:thumb:

But I'm too stupid to see how this is a test for roundness ?:o
What am I missing ?? is the rim fixed against some reference point as you rotate it ?

I build with a large variety of rims, focusing on relatively light tubular rims.

Overall the first thing I consider is the quality of the extrusion, consistency of curvature, and accuracy of the joint. Quality issues that you won't usually see on heavier machined side rims, but may on light rims are twist, which results in a built wheel where one side or the other will rise or fall while the overall rim is true. This cannot be corrected except by extreme methods, and so can have me avoiding certain brands altogether.

Overall roundness or flatness are less important as they can easily be trued out and corrected within the tension tolerance, but this varies with the rigidity of the rim. It's easy to correct on a 310 gram tubular built 32h, but much harder with a heavy wired-on rim, especially if built with low spoke count. These must be close to round before building.

While overall roundness isn't critical local distortion, usually at the joint is. Often non-welded rims will have joint issues, and like twist, these cannot be 100% resolved by the builder. Years ago, when most rims were not welded, the general attitude among builders was that that the alignment was as good as possible when the joint was the worst area.

Unfortunately, IME it's difficult, if not impossible to really know rim quality until you build. Even with brands having good reputations, you can still find a problem rim, but if problems are more than isolated experiences, I'll abandon the brand, or at least he model.

Glad you brought up the joint - because that is my number one beef when evaluating rims. I absolutely cannot stand it when I have to deal with a rim that does not have a straight joint. Think about it - they go through all the trouble to create a nice extrusion - and throw it away because they couldn't be bothered to set the ends long enough to ensure a perfect 90 degree cut - or matched cut.

Pisses me off...

When importing, I could go with Weinmann which is a buck cheaper on average....I could go with Sheang Lih which is a buck cheaper on average...I could go with some of Alex Rim stuff which costs about the same - but I stick with KinLin for one reason above all - 99% of the time - their joints will be straight - even with their basic rim catalog. I can live with the extrusion defect rate that comes with basic rims - most will still be fine for fronts and rear single speed wheels.

Nor have I run into an attempt by KinLin as of yet to use CNC machining to hide a non-straight joint...a gimmick that a lot of other manufacturers try to get away with.

=8-)

Draw two perfectly parallel lines straight across a paper.
Draw the same two perfectly parallel lines across a paper as a curve as well.

Let one line be the outer rim edge - let the other line be the inner wall edge.

Those lines represent a perfect extrusion before rolling and after rolling. When rolled into a perfect circle, substantively you have a perfectly round rim. Symptomatically, you also have an ERD that will be the same all the way around. Consistent ERD at multiple locations is not a meausure of a round rim, it is simply an ERD.

Now pick one line in each pair - and make it wiggly. Doesn't matter which one...you pick.

Now you have an extrusion with defects.

Let's say you chose the outer edge - try to true that out - all you do is transfer it to the inner wall edge - and voila! - you have uneven spoke tensions...

Let's say you already chose the inner wall edge - then it is automatically a true wheel with uneven spoke tensions...

But it get's worse....imagine it's 43mm deep in profile and triple wall just like a....

...wait for it....

...

...

...a Velocity B43. That is one incredibly stiff rim that requires an incredible amount of force to roll - making the need for a consistent extrusion even more important to begin with to ensure a quality rim.

You can true out a little extrusion error and lack of roundness from a classic double wall 16mm deep rim as FBinNY stated, but you can't do that with a Velocity B43.

Velocity put a lot of money into that line, they're a pain to produce right, and hence why they cost so much.

If you pay attention at all, I'm sure you've noticed that Weinmann Trak Attacks, and other B43 copies such as H+Son's can be all over the map tension-wise...now you know the reason without me saying it outright.

Note that H+Son's best rim extrusion and roundness wise is...their classic style TB14...their only rim I like.

=8-)

There are some really good posts in this thread. I never considered the quality of extrusion to be what makes one rim "feel" easier than another to build up with consistent tension, but this makes a lot of sense. What I have noticed, as has been mentioned, is that between different rim manufacturers, certain rims build "easier" than others. Of the wheels I build, Mavics are easiest to build into consistently tensioned, true wheels. Alex and Weimmann are more and more "difficult" respectively, requiring more time to achieve an overall lower quality wheel. This isn't an endorsement of Mavic necessarily, just my experience churning out about wheelset a week for single speed (internally geared) commuter bikes.