Wheel building - finding spoke lengths? Calculators?
 

All,

I am working on a wheel build for my trailer. I am trying to find the spoke lengths. Several years ago I got parts from Ben's Cycle. I don't recall that being that difficult of a process - I got rims and spokes from them and was able to come up with the spoke dimensions pretty easy. This time around I am not finding a method of finding the spoke lengths. Their online "wheel builder" doesn't calculate anything, it just pairs parts together to purchase then they build with the parts you select. I just want to calculate the spoke length then buy the parts from the dimensions.

Are there other wheel builder calculators/resources out there you would recommend that will give me the info I need?

To throw a curve ball in it is I have offset hubs (disk brake hubs - the brake side flange is closer to the center than the opposite of the brake flange) and I want to be able to offset the rim from the centerline. So there are 2 "offsets" I need to compensate for in calculating spokes. The rims aren't going to be centered on the axles as they would in a bike between the drop outs.

There are lots. Bet you can hit a half dozen first page with a search of "spoke calculator". DT's is good All set up for their stuff but you can enter the measured numbers from anything. Offset rims and hubs won't be an issue. There are enough good calculators out there that you can choose the one you like working with.

I use the DT Swiss calculator. Mostly because that's what I got use to after having used the Sutherlands Manual then the BPP/DT wall chart for decades. I suggest you do your own measurements for ERD as published dimensions have been known to be off by a bit sometimes.

As to off set rims and off center wheels just use the flange to center to "adjust" the center to that of the rim holes, not the axle. Andy

Thanks for the suggestion on the DT calc.

I found this one also:
https://leonard.io/edd/

Looking at the numbers both calculators appear to agree with the standard "rim centered on the axle" calculations.

Looking at the availability of spokes I am thinking of trying to balance the dishing so as to allow the same length spoke all the way around. That would allow me to make better use of a box of 100 spokes. It looks like that is an easier way to get spokes. The length I think I am going to go with is 182mm. Oddysey has a 40 qty tube and DT has a 100 qty box that I have found in that size. I will keep looking and see what other options I can find before I order everything.

One thing to note is the QBP calculator does not take hub spoke hole widths into account, so your calculations can be off a bit. I had this happen when building up a set of wheels with Sturmey drum brake hubs. Those hubs have spoke holes in the flanges able to accommodate up to 11ga spokes. The calculator must use an arbitrary hole gauge standard, or possibly just to the optimum circle center point of the spoke holes, which yields a spoke too long for the build. A friend who is a shop supervisor has noticed that the QBP calculator consistently gives long spoke calculations due to the spoke hole gauge. It's an easy calculator to use because it has a lot of hubs and rims in the database, and requires no measurements on the part of the builder, but measure anyways just as an idiot check. I like the Damon Rinard calculator on Sheldon Brown's site, but it requires a bit of measurement to use; the database there is extensive but should be taken with a grain of salt and again, actual measurements should be made just to make sure before ordering spokes.

Spocalc has a cell for offsets-
(edit as to has)
https://www.sheldonbrown.com/rinard/spocalc.htm

As mentioned, there are plenty of free calculators, which are all fine. I've used Spokecalc and found it consistent.

The only advice I can offer is to pick one and stay with it. There are a number of variables which can change the result.

The biggest are the definition of ERD and what calculator considers perfect spoke length. A calculator may want input of the actual rim diameter and factor 3mm or so for the nipple's head. Or it may want the ERD measured to the tops of the nipples and calculate a length that ends there. Or subtract 1mm so the spokes end shy of the tops.

Other variables include 1mm for the difference between the center of the spoke hole and its edge, adding 1mm for the interlace, or a small allowance for elongation of thin spokes, or an adjustment to bias the tolerance high or low.

My point is that if you use multiple calculators you'll get similar, but different results. So pick one, measure carefully buy spokes accordingly. Build the wheel and note the difference between the results and what you prefer. Thereafter you can factor that and get the exact results every time.

I have used Spocalc for decades and it’s never done me wrong. My builds aren’t too weird, though.

Thanks for the detail. Good food for thought.

Though, I don't build enough wheels to get a feel of the detail you mention. That is in a large part why I posted the question here.

The last wheel I built was in 2016.

Until I get another frameset to build up (I have had plans for doing so since about that same timeframe - who knows when I'll get to it) I can't see any need to build another wheel for something unless something breaks.

another suggestion is to keep notes of what the calculator recommended, what you bought, and how the build turned out in terms of spoke length.

and don't absolutely trust the published measurements in the spoke calculators - especially on rim ERD

trailer wheels are kind of a special case requiring you to do all the measurements.

/markp

That's my go-to.

That's why I like Spocalc.
Since it's a spreadsheet, you can save your "recipes". w/ notes. I'll add the spoke length I "should" have used in case my rounding error was off.
It also has a spoke hole diameter cell for the hub.

Absolutely ! ! Has never let me down.