Bicycle Mechanics - Spoke Length Calculation

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View Full Version : Spoke Length Calculation

timin8r
01-03-08, 06:17 PM
So OK here’s my first ever post….

I’m getting into wheelbuilding, slowly but surely. Have built several wheels already, doing well I think.

What I need now is a good reliable easy–to-use web site for spoke length calculation. Not wanting to specify rim/hub models, but instead their measurements. I have the calipers / rimrods / etc. needed for that. Not wanting to rely on my LBS for this info.

When I google “spoke length calculator” I get dozens of results. Some have pix of how to measure, some do not. Sheldonbrown points to several of the sites, not suggesting which might be most useful. Let me know what online spoke length calculator you use. It must have not only the calculator but also diagrams of the measurements needed.

Understand? Just wanting to cut thru the clutter and get to one no-brainer site so I can get on with it....

Thanks
timin8r

HillRider
01-03-08, 06:25 PM
Sheldon Brown hosts Damon Rinard's Spokecalc Excel spreadsheet that is an excellent resource. It has a big data base of hubs and rims but you can ignore the data and plug in your own values for what ever you have or can think of. It will even let you calculate for fractional cross numbers like 2.5x and explains why that might be useful.

DT's web site also has a pretty good spoke calculator but, I believe, only calculates for hubs and rims in it's data base.

Another good source is Jobst Brandt's "The Bicycle Wheel" which has a complete, if rather involved, formula for calculating spoke length based on a number of hub and rim measurements and shows you how to take them.

BTW, there is no no-brainer way to do this. that's why there are so many large data bases and involved spread sheets out there.

waterrockets
01-03-08, 06:25 PM
The calculator at http://www.dtswiss.com/ is very easy to use with measurements. I also use spocalc.xls to cross-check since I'll have all the measurements assembled anyway. You can just type values into spocalc with no problems if the hub and rim aren't listed.

timin8r
01-04-08, 07:29 AM
OK thanks. I tried both DT and spocalc.xls and got the same answers. The wheelpro site was different by a tenth of a mm. So I feel comfortable with the calculations.

I've built a couple wheelsets but have always gone to the LBS to get spoke lengths. They seem to have very complete hub/rim databases, even with some of the very old hubs/rims I have used. Which leads me to another question. Is there a good database of hub/rim measurements online somewhere that everyday types like me can access?

The rims I am using are 1970's Rigida AL1320 27” (double-wall). The hubs are old Suzue high flange. The couple of hub/rim databases I found did not have either one. Of course my calculations are only as good as my measurements and these 53-year-old eyes can be a challenge sometimes. So "real" measurements would be helpful.

Since I'll be heading to the LBS for the spokes I'll let them triple check for me. But home access to a good database would be nice....

waterrockets
01-04-08, 07:45 AM
spocalc is the closest to a public hub database that I know of, and it's really out of date for current models. Measuring should be reliable.

If you're wrong, and buying from the LBS, you should be able to exchange them.

timin8r
01-04-08, 08:24 AM
I downloaded full spocalc, and their ERD measurement for the 1320 rim (27" ISO 630) says 617. My rim rods and ruler say 620. That's pretty significant. I'll definitely let the LBS weigh in....

HillRider
01-04-08, 09:15 AM
I downloaded full spocalc, and their ERD measurement for the 1320 rim (27" ISO 630) says 617. My rim rods and ruler say 620. That's pretty significant. I'll definitely let the LBS weigh in....
The published ERD's for a lot of rims of the same models vary quite widely. I don't know if the manufacturing process varied over time even if the rim name remained the same or if there is a fair bit of variability from rim to rim in the same production run.

If you do your measurements carefully and take the ERD at several points on the rim's circumference I'd trust those values before the published numbers.

smurf hunter
01-04-08, 09:39 AM
I've used a handful of these (only laced 4 wheels). I've got results that in practice were 1-2mm off. If I'm lacing to a deep V style rim, I'll round up at least 1-2mm to get to a standard length. The spokes may come through the top of the nipples a bit and I can usually still get a very high tension without bottoming out the threads.

Cheap and reliable spoke sourcing - that's the biggest hassle.

waterrockets
01-04-08, 09:44 AM
Nashbar has had nice prices on Wheelsmith double-butted spokes lately. But that's where the "reliable" part comes in -- sometimes they have nothing.

Scooper
01-04-08, 11:37 AM
I always measure ERD using the foolproof method Roger Musson (http://www.wheelpro.co.uk/wheelbuilding/book.php) recommends:

http://i32.photobucket.com/albums/d7/k4drd/Bicycles/Wheels/MeasuringERD.jpg

timin8r
01-05-08, 02:48 PM
Scooper, just another couple seconds of your time. I made two of what you have shown. I presume that, from one end to the other (the top of the nipple to the other end of the spoke) they are meant to be about 201 mm long, 200 for the spoke and another 1 mm or so for the slot. Just checking, to be sure, and because it seems like an odd size and configuration. Like I said I made them but just got back from a funeral and have not taken the time to measure and compare. Looking forward to measuring and to your response. And of course thanks to others for also weighing in.

Scooper
01-05-08, 04:07 PM
Scooper, just another couple seconds of your time. I made two of what you have shown. I presume that, from one end to the other (the top of the nipple to the other end of the spoke) they are meant to be about 201 mm long, 200 for the spoke and another 1 mm or so for the slot. Just checking, to be sure, and because it seems like an odd size and configuration. Like I said I made them but just got back from a funeral and have not taken the time to measure and compare. Looking forward to measuring and to your response. And of course thanks to others for also weighing in.
Basically, you're right; you want the spokes to be exactly 200 mm long, and then screw the spoke into the nipple until the threaded end of the spoke is just even with the bottom of the nipple slot. I use Loctite on the spoke threads to ensure the tip of the threaded end stays even with the bottom of the nipple screwdriver slot.

operator
01-05-08, 04:44 PM
Cheap and reliable spoke sourcing - that's the biggest hassle.

Your LBS should be able to handle this.