Rims

I've got the wheel hubs, but have been kind of dawdling about the rims.  There really isn't a lot of info out there.  The big question is "tubeless" or "clincher" - which has a simple answer for me - clincher - since its the easiest to repair when touring. Tubeless rims with self-sealing goop are probably less likely to flat, but seem to be more of a problem if you have to deal with a major breakdown. I'm sure there's someone who would argue the point - but I'm admitting complete ignorance up front, so you can consider that you've already won.

Some manufacturers claim their welded rims are better than pinned rims.  Here I think I'll go with Roger Musson in The Professional Guide to Wheel Building: it makes no difference (you can buy a copy of the book at http://www.wheelpro.co.uk/wheelbuilding/book.php - it's definitely worth the $15 you've got to shell out).  Musson argues that the strength of the wheel comes from the spokes pulling the rim inward, so that the entire rim is in compression and whether welded or pinned it will have the same basic performance.  I would speculate that the failure modes under extreme stress might be slightly different - that is, they might break in a different way or at different points under extreme stress, but what the hell - the rim will be so deformed before breaking that it really shouldn't matter.

You can spend a boatload of cash on carbon rims, but that seems silly for a touring bike.  I'm sticking with aluminum.  At the upper end I was looking at Mavic EN 821 Disc rims, which are 21mm width, 32 hole and weigh in at 460 grams. PricePoint had them on sail for $60 (listing at $105).  A similar price can be had on the Mavic XC 717 and EX 721. At the lower end, the Mavic XM 119 goes for only $25 ($38 MSRP).  The EN 821 uses Mavic's FORE technology that claims stiffer and stronger  http://www.mavic.us/wheel-tyre-system/fore.  Looks like this is more important for tubeless tires.  A big question in the decision is how wide the rim should be.  The EN 821 and XC 721 have 21 mm rim widths and the XC 717 has a 17 mm width - hence the x21 and x17 (hey, the numbers mean something, why isn't this on the web somewhere?)  The 21 mm rim widths are typically good for 35 or 37 mm (1.5 inch) to 69 mm or 76 mm  (2.75 or 3 inch) tires, while the 17 mm rim is good for 25 mm (1 inch) to 52 mm (2 inch) tires.  On the one hand, I doubt I'll be putting any 3" tires on the bike, but I'm also unlikely to go below a 35 mm.  One of the considerations for the rims is that a narrow rim with a wide tire is more susceptible to pinch flats, so the wider rim would be preferable.

Eyelets?  aaarrrghh.  Traditional wheel builders seem to prefer double eyelets (which distribute load), but most rims seem to be single or non-eyelet.  Arguments against non-eyelet wheels is that the spoke is loaded against the rim aluminum directly, which is more likely to result in failure.  It does seem that non-eyelet is being done at the low end of the price spectrum.

Asymmetry? At the upper end, some of the rims have holes drilled to account for asymmetry in the spokes - that is the "dish" that allows the wheel to be centered while having the disc brake (in the front) and gearing (in the rear). This supposedly allows for more even spoke tension.  The Mavic EN821 has this, but none of their lower end products.

After digging down further in the PricePoint web site, the EN 821 is out because they only have the 29er on sale.  I'm thinking of the x19 rims, but I don't like the XM 119 as they're not eyeletted.  Then I was googling around and found that travellingtwo ( http://travellingtwo.com/13732 ) has reported problems with the Mavic XM 719.  So back to the drawing board...

Decided that its probably better to go cheap at this point.  The Alex TD17 can be gotten for $25 each - so I'll start there and see what happens. Damn - tried to pull the trigger and only one left in stock.  So back to the drawing board (again)...

UPDATE:  Found some recommendations for strong (but not too heavy) low end rims - the CR18 from Sun Ringle ( http://cyclescribe.blogspot.com/2011/01/humble-rims-for-your-humble-tires.html ).  I ordered a pair of rims that are black with silver sides, which were cheaper than the straight black anodized or straight silver (why?).  Weird thing about online ordering - I first went through my list of online bike sites, including Niagara Cycle, where I've gotten stuff in the past. Ordering direct from Niagara included a $20 shipping charge ($10 per rim) on top of the $21 per rim.  But going through Amazon I could get the rims for $23 with a $5 shipping charge (combined). OK, not so weird, except that the Amazon order is being fulfilled by Niagara Cycle. Seems like someone needs to rethink their shipping costs.  The rims I ordered are 559 (26") with 17.5 mm inner cross-section and 22.5 outer cross-section widths ( http://sun-ringle.com/wp-content/uploads/2012/09/rim-profiles_rev_.pdf )

Hubs

So the first step to building wheels is figuring out which hubs to use.  This turns out to be a matter of no small consequence for your budget.  After much anguish and poring through incomprehensible part names like M285 Saint,  105 5800, SRAM XO...  I came away with a few insights.

First, more expensive hubs are not necessarily better for a touring bike - often you're paying for lighter weight, which might be better for racing, but less durable for touring.  It seems like the best bet for a touring bike is to stick with mountain bike hubs.

Second, part numbers change on a regular basis and it's actually rather difficult to figure out which of a manufacturer's offerings are the latest, and which are leftover stock from last year.  At least I couldn't find anything to tell me which was which.

Third, not being a mountain bike geek, I wasn't aware that there's a whole new hollow axle - or "through axle" or "thru axle" that's considered the latest and greatest thing.  Fortunately, you've got to decide you want hollow axles when you buy your frame as they don't fit on the standard QR (quick release) mounts that have been around for decades.  Since the Surly frame I've ordered has standard QR mountings, I don't have to even think about the choice.

Four - something fairly obvious, but perhaps worth noting - if you're fitting up a bike with disc brakes, then you've got to have hubs designed to mount the discs.  There is an ISO standard that uses 6 bolts to mount the brake rotor.  Shimano has a proprietary standard they call "Centerlock".  No doubt there are other proprietary systems as well.

It seems like the "go-to" hubs for most touring bikes are Shimano; possibly because they have a wide range of capabilities and prices.  The folks at TravellingTwo have been using Shimano Deore LX which are inexpensive ($15 to $25) and supposedly really sturdy. It's not clear that Shimano is still using the LX designator for these. Although you can still find Deore LX for sale on the web, Shimano doesn't have an LX on any hubs in the mountain bike section of their web site. It looks to me like the have a "Deore" without any fancy letters (model FH-M615), then the SLX and Deore XT as the next two levels up (XTR is apparently the top - but is way out of my budget).

At the end of a lot of reading and research,  I still didn't (and don't) feel like I had a good idea of what hubs would be best.  As I'm building on a Surly Disc Trucker frame, I decided to take a cue from their build with the older Shimano M756.  That hub was superseded by the Shimano M785, and now by the M8000.  Anyway, after much indecision, I found a good deal at PricePoint.com and got the XT M8000 hubs at $50 for the front and $65 for the rear.  The M785 are still available online, and I could have gotten those for about $35/$50 for front/rear, but I decided to splurge and go with the latest.

A possible drawback to the M8000 is that it is only (as of Oct 2015) available in a 32 hole configuration (i.e. for 32 spokes) and most touring bikers seem to prefer 36 hole hubs.  Only time will tell if I've made a mistake.