Well, I think Don's point was that the variation in spoke length for sewups is independent of the make or model of rim. In Sutherland's, the variation in number of holes is handled in the first two sections along with the variation in hub diameter and cross pattern, then the final section gives a "Rim Correction Factor" for each model of rim.
Ideeed there is very little variation for "normal' sewup rims, which all have Rim Correction Factors between -6 and -8. One could almost just use -7 for all of them. There are however exceptions for "unusual" sewup rims, like aero section ones, or the Hi-E rims which I worked on to bad results this past weekend. And I'm sure wood rims would be an exception as well.
BTW, I never thought about this before, but I just realized that all the Sutherland's rim correction factors are negative, i.e. one always calculates a spoke length from the hub diameter and cross pattern, then reduces it acoording to the rim model. So what did the uncorrected length represent? The spoke reaching all the way to the tire bead perhaps?
While I'm on the subject of spokes, anyone know a source where one can get boxes of 100 15 gauge butted spokes (15/16, 15/17, 15/whatever) at a significant discount compared to the single spoke price of nearly $1 each? DT and Wheelsmith are still (or maybe again) making 15 ga butted spokes in a variety of lengths and DT at least provide them in boxes of 100, so I'm looking for a source where I can get some reasonable discount by purchasing a full box. Leaving aside pre-built wheels, 14 ga has become prevalent in recent years, but I'm trying to build a couple of Hi-E wheels with the special Hi-E nipples, which seem to be 15 ga. Plus one still runs into old wheels with 15 ga spokes, and it's a real pain to have to use a couple of 14 ga replacement spokes in an otherwise 15 ga wheel. I try to keep a stock of 14 ga spokes in all the commonly used sizes (or at least every 2 mm), and I'd do the same for 15 ga, if I don't have to pay single spoke prices.
Regards,
Jerry Moos
Big Spring, Texas, USA
> From: earle.young tds.net <earle.young@tds.net>
\r?\n> Subject: [CR] Spocalc : Not necessary for Vintage Tubular rims?
\r?\n> To: classicrendezvous@bikelist.org
\r?\n> Date: Monday, November 2, 2009, 6:38 AM
\r?\n> Don Gillies said:
\r?\n>
\r?\n> >So if you take an ERD of 622 mm, and intend to have the
\r?\n> spoke tip seat
\r?\n> >3 mm below the tire bed, then you could use 616mm for
\r?\n> ERD for just
\r?\n> >about all tubular rims in the vintage era, couldn't
\r?\n> you?
\r?\n>
\r?\n> While there is not as much variation in rim depths among
\r?\n> vintage tubular
\r?\n> rims, there is some. It is always best to measure. Also, It
\r?\n> is probably
\r?\n> better to have the spoke tips a little lower than is
\r?\n> suggested here. When I
\r?\n> build wheels, I like the spoke tips to be through the rim,
\r?\n> but not through
\r?\n> the spoke nipple, even though you can get away with that
\r?\n> when you build a
\r?\n> tubular wheel.
\r?\n>
\r?\n> Spoke length also varies by the number of spoke holes.
\r?\n> Thus, the chart of 16
\r?\n> spoke sizes expands tremendously when one considers 28-,
\r?\n> 32-, 36- and
\r?\n> 40-hole rims.
\r?\n>
\r?\n> I have found that to cover the even the range of practical
\r?\n> lacing patterns,
\r?\n> I need spokes of every other length from 288 mm to 304 mm.
\r?\n> And if I wanted
\r?\n> to be dead-on accurate with the spoke length, with the
\r?\n> spoke tip coming to
\r?\n> the bottom of the slot in the spoke nipple, I would need
\r?\n> spokes of every mm
\r?\n> length.
\r?\n>
\r?\n> And this does not even count for slight differences in hub
\r?\n> diameter and
\r?\n> flange spacing.
\r?\n>
\r?\n> So, for best results, avoid over simplification, measure
\r?\n> each rim you use,
\r?\n> and run a spoke calculation based on the hub at hand. Then
\r?\n> order your spokes
\r?\n> to fit correctly.
\r?\n>
\r?\n> Regards,
\r?\n> Earle Young
\r?\n> Madison, Wisc.
\r?\n> Offering expert wheelbuilding services for classic and
\r?\n> modern bikes.