09 Jan 2019

Rounding spoke lengths

Webmaster

The correct spoke length is one that penetrates the nipple just right — not below the screwdriver flats and not past the top of the nipple. You don’t want to go too short because spoke threads reinforce nipples internally. Nipples, particularly aluminum nipples, have higher failure rates when paired with short spokes. You don’t want to go too long either. I define too long as past the end of the nipple. This is strictly true for some nipples however the nipples sold here can tolerate a couple turns past the end without issue. Turning past this baked-in limit causes nipple threads to grind into the unthreaded spoke shank, which creates a weakness in the spoke and is associated with spoke breakage.

The rounding part

Spoke length calculators output lengths to the tenth of a millimetre, which must be rounded to match available supply. There’s no universal rounding algorithm because it depends on how you calculate spoke lengths in the first place. It depends on ERD measurement technique.

In my process I use measuring tools based on theoretical spoke penetration to the bottom of the nipple screwdriver slot. I don’t want my actual spoke penetration to be short of this mark, so I’m cautious about rounding down. My baseline is rounding to the nearest millimetre. If my target tension for a spoke is high, say 125kgf / 1200N, I’m not bothered rounding down as much as 0.6mm. This is because spokes stretch a fraction under tension and stretch is more pronounced at high tension. I’m not bothered rounding down 0.7mm if the spokes I take to high tension have a skinny diameter (the minor diameter in the case of butted spokes). Thinner spokes are more elastic. The opposite holds as well — a spoke built to 60kgf could be rounded up 0.6mm. As an example when building a rim brake rear wheel, where tension is quite imbalanced between sides, a wheelbuilder might round up on the low tension side and down on the high tension side if both lengths are halfway between sizes.

(Hopefully you can see this rounding logic doesn’t make sense if your theoretical spoke length targets the end of the nipple. In that case you would rarely round up.)

Traditionally spokes are stocked in two millimetre increments, which invites compromises depending on your calculated lengths. You can be forced to reckon with the the risks of going too short or too long. Maybe the uncertainty steers you to brass nipples instead of aluminum. Maybe it causes you to pick up nipple washers as an insurance policy. Bottom line: it’s not doing you any favours and to build the best wheels you ought to shop in one millimetre increments.

About this series

This is a series about spoke length. These aren’t tutorial articles but rather a collection of practical hints. The focus is correct inputs to spoke length calculations — correct input leads to correct output — and how to use outputs. For more general information, see my books list.

18 Dec 2018

Season’s greetings

Webmaster

This is a reminder for those who may have missed the announcement on Twitter: SpokeService will close on December 24 for the remainder of the year. The time is needed for shop updates, tool service, inventory and reams of government paperwork. On a best-effort basis some orders may ship during this period but no guarantees — place orders now to avoid disappointment.

Happy holidays from SpokeService.

17 Dec 2018

Industry Nine fat wheels

Webmaster

Some parts of Canada call for a different approach to winter riding. These wheels are the full fat approach, marrying Industry Nine fat hubs to DT Swiss BR710 rims. The hubs are 142×15 in the front and 177×12 in the rear. These wheels are going to be rippers in the snow.

Spoke length

These rims are a good example of ERD issues discussed in my last blog. The DT Swiss rim decals include technical information stating ERD to be 549mm. I like that but it doesn’t change my process — I measured them anyway getting 547 on the front and 546 on the rear. To add intrigue the DT Swiss spoke length calculator lists 547 for this rim. Going my own way resulted in perfect penetration, a hair below the top of the nipple in each case. With single wall rims you want to be more fussy about spoke length, particularly avoiding penetration past the top of the nipple.

27 Nov 2018

ERD seriously

Webmaster

Because spoke lengths depend on ERD, I always measure my rims. People tell me they’ve ordered spokes for use with XYZ rim and sometimes it leads to conversations like this:

Wheelbuilder: These spokes are for my build with XYZ rim.
SpokeService: Did you measure your XYZ rim?
Wheelbuilder: No I used numbers I found with Google.
SpokeService: Sorry your spoke lengths are wrong — Google is confused.

There are two ways ERD goes wrong.

First there are variances in rim manufacturing. Some manufacturers are better than others and to some extent you get what you pay for. But I always measure and frequently find rims out of spec or find differences between pairs of identical rims. If you know what you’re working with, variances are not a big deal. If you input correct dimensions, you’ll get correct spoke lengths.

The second issue is differing definitions of ERD. Typical definitions include penetration of the spoke into the nipple head, which is important for maximum strength. But how far the spoke extends beyond the nipple seat (into the rim) is unclear. It depends on nipple geometry and encodes some preference for how much penetration is ideal. In other words ERD is relative to an undisclosed nipple and opinions regarding its use.

Typically the magnitude of these errors is pretty small, maybe 0.5mm each. Additional error is introduced when you round spoke lengths to match availability (why buying spokes in 2mm increments is rough). Maybe these errors add up to a problem and maybe they cancel each other out.

This sounds like a pain but it’s not at all. You simply make your own tools and take your own measurements. The parts cost next to nothing, assembly takes 10 minutes and you’re left with tools you can use forever. Maybe it seems like a pain because you want your spokes and rims to arrive at the same time. That’s fair but getting it right the first time is always fastest. SpokeService is here to help with spokes in 1mm increments, shipped daily from Canadian soil for five bucks.

18 Nov 2018

Postal strike and shipping

Webmaster

The rotating postal strike has been negative for small businesses, particularly those that send lightweight packages like spokes and nipples. As a result please be aware of temporary changes to our normal shipping terms. These temporary changes affect sales in the online shop.

Canada Post

Due to delays all shipments must now carry tracking and insurance. This uniquely impacts orders under $60, which will pay an additional $5-10 for upgraded shipping. Orders over $60 see no change as tracking and insurance is subsidized. Orders over $120 still ship for free. No timelines are guaranteed for shipments with Canada Post however tracking will allow us to check progress.

Other shipping carriers

Other means of shipping are being implemented as quickly as possible. UPS and Purolator are now available at an additional cost reflecting their prices for lightweight shipments. Rates go down (i.e. shipping subsidies go up) at order thresholds of $60 and $120.

UPDATE: temporary changes to shipping have ended with the postal strike. In the short term, an extra day or two of transit time is expected as Canada Post recovers.