Spocalc
Damon Rinard's free spoke length calculator

Disclaimer: Harris Cyclery and sheldonbrown.com assume no responsibility for
the accuracy of results derived from this or any other spoke length calculator!

Translations:
French (see below) FranceQuebec flag
Russian Russian flag
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Spocalc (full strength version)

spokecalc gif
Spocalc
(174KB)
To download, click and hold, select "Save this link as..."; Select "Source" from the Format menu.

(Windows users, right click the link and choose "Save Target As...",)

Spocalc is the full strength version and includes hub and rim databases. [No longer being updated, but we link to others which are being updated]

Version Française:
french gifspocalc gif

spocalc-fr.xls

(272KO)
Pour télécharger, cliquez et tenez, sélectionnez <<Save this link as...>>; Sélectionnez <<Source>> du menu <<Format.>>

(Utiliseurs de Windows, cliquez avec le touche a droite et choisissez <<Save Target As...>>)

Merci à Vincent Vallet pour la traduction.

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SpocalcExpress

spocalc gif
SpocalcExpress
(16KB)
To download, click and hold, select "Save this link as..."; Select "Source" from the Format menu.

(Windows users, right click the link and choose "Save Target As...",)

SpocalcExpress has no hub database, no rim database, no instructions, no macros -- just the calculations that operate on the numbers you enter.

Thank Mark Schlueter for this great idea. SpocalcExpress is just like the full version of Spocalc, but less.
Enter one set of hub and rim dimensions and SpocalcExpress gives you the spoke length for radial, 1, 2, 3, 4, and any other cross of your choice. Great for Quicksheet on your Palm.

Version Française:
french gifspocalc gif

SpocalcExpress-fr
(16KB)
Pour télécharger, cliquez et tenez, sélectionnez <<Save this link as...>>; Sélectionnez <<Source>> du menu <<Format.>>

(Utiliseurs de Windows, cliquez avec le touche a droite et choisissez <<Save Target As...>>)

Merci à Vincent Vallet pour la traduction.

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What is Spocalc?

Spocalc is a free Excel spreadsheet I made that calculates spoke lengths for wire-spoked wheels. There are lots of other spoke calculators on the web (see the list I've assembled). Some require you to measure your own rim and hub, but Spocalc includes a database of over 350 hubs and 500 rims. The Spocalc database is also user-modifiable and expandable so you can add more rims and hubs.

Some other spoke calculators require you to re-enter the rim and hub dimensions again and again to get different lengths for different numbers of crosses, but Spocalc automatically gives you spoke lengths for 0, 1, 2, 3, 4 and one other cross of your choosing (even a decimal number! Why would you want to do that?). Having several lengths can come in handy. Print out Spocalc's calculator sheet and take it with you when you buy spokes. If the shop doesn't have the right length for, say, three cross, you can take a glance at the sheet and decide if you could use four cross instead.

I wrote this spreadsheet using Microsoft Excel 5.0 but it has now been updated to Microsoft Excel 97-2003 and you must have Microsoft Excel 97 or higher (Windows, Mac or Android), LibreOffice Calc (free download, Windows or Linux, also see page about format conversion), or Gnumeric (free download, Linux only).

How to run Spocalc macros in Excel

Spocalc has a few macros to help speed data entry. When opening Spocalc, you must choose "Enable" if you wish to use these macros. If your virus checker disables them you can still use Spocalc without the macros - you just have to type in the numbers by hand.

[Updates by John Allen --

In Excel 5.0, macros run from the Tools menu. In newer Excel versions which have ribbons instead of menus, there is no Tools menu, and also no Help menu. Clicking on the tiny question mark at the right-hand side of the ribbon and searching on "Using macros" led me to information:

  1. If the Developer tab is not in the ribbon, then in the File tab, click Options, and then the Customize Ribbon category.
  2. In the Main Tabs list, select the Developer check box, and "OK."
  3. Then, in the Developer tab of the ribbon, click on "Macro Security."
  4. In Macro Security, click on "Disable all macros with notification."

This choice will let you decide whether to run macros or not: a message bar may still come up, warning that macros are disabled. If so, click to enable macros.

Now to use a macro, first select a hub or rim by name, as described below. Then in the Developer tab, click on the Macros icon.: A list of macros will appear. Click on the appropriate macro.

macros run under Microsoft Excel (Windows, Mac) but...

Macros in OpenOffice

Versions of spocalc with macros for OpenOffice have been prepared by Mike Sherman.

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Screen Shots

1. Main calculator sheet

spocalc gif

 

As you can see, by entering the hub and rim dimensions once, you get spoke lengths for all crosses automatically.

Although front wheels are usually symmetrical, which would make the "Left Front" and "Right Front" tables redundant, I've provided separate left and right tables in case you are using a disc-brake hub or other dished front hub.

At the bottom you can see the tabs used to view the instructions and the hub and rim database sheets.

2. Hub database sheet

spocalc hubs

While you may certainly type in the numbers by hand, here you can see how to use the macros to enter all the hub data for you.

Important macro tip: you must first select a cell in the "Select a Hub" column before using the macro to enter the data.

3. Rim database sheet

spocalc rims

 

The rims sheet works just like the hubs sheet: select the cell containing the rim you are using, then click on the appropriate Macro (from the Tools menu, or in the Developer Tab of newer, beribboned Excel versions) to enter the Effective Rim Diameter (ERD) on the calculator page, or type the ERD number into the calculator page by hand.

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How to Measure Hub and Rim Dimensions

There are five hub dimensions: dL, dR, S, WL, WR

John Allen's article on this site describes
additional ways to measure hubs and rims.
Measure twice and select spokes once!

spocalc hubdims

d, flange diameter is measured between centers of opposite holes in the hub flange. It is usually between 38 and 67 millimeters. Note that it is NOT the outside diameter of the hub's flange. Left and right flange diameters are often, but not always, the same. Small errors in this measurement are important only with radial or near-radial spoking.

S, spoke hole diameter, is the through diameter of any spoke hole. It is usually 2.6 mm.

old

W, width from center to flange, may differ between left and right sides of the hub. In this illustration, WL and WR are the dimensions you enter into the spreadsheet for the left and right sides of the hub, respectively. You can use a hub listed in Spocalc's database, or measure your own hub by following these steps:

  1. Measure OLD (Over Locknut Distance).
  2. Measure Dimension A.
  3. Measure Dimension B.
  4. WL = (OLD/2) - A.
  5. WR = (OLD/2) - B.

Not a lot of precision is needed in the width dimensions. A few millimeters' error in width will only lead to a fraction of a millimeter's error in spoke length.

spocalc measurement hub close

I usually measure A and B dimensions by holding the hub locknut against a flat surface (like the edge of my workbench), then measuring from there back to the hub flange with a ruler or caliper.

Note that you must hold the loc nut (not the axle end) against the edge.

Of course, I use two hands for better accuracy. In this photo one hand is working the camera!

There is one rim dimension: ERD

erd

Effective Rim Diameter (ERD) is the diameter on which you want the ends of the spokes to lie. Most people prefer it near the end of the spoke nipple. If you want to measure your own rim (recommended, just to be sure), then follow these instructions:

  1. Insert two old spokes into holes exactly opposite each other on the rim. Count holes to be sure.
  2. Screw some nipples onto the spokes.
  3. Pull them tight and measure dimension A in the figure (the diameter to the edge of the nipples, where the spokes disappears into them). Do this at several spots around the rim and average the measurements.
  4. Measure the length of a nipple (dimension B in the figure) and add it twice (once for each nipple). The result is Effective Rim Diameter (ERD). Thus,

    ERD = A + 2B.

Effective Rim Diameter (ERD) is the dimension you type into the spreadsheet for "ERD, effective rim diameter". Of all the dimensions you actually might measure, ERD is the most critical dimension affecting spoke length, so it makes sense to measure it a few times at different places around the rim. Always count to make sure you use spoke holes that are actually opposite each other!

John Allen's article describes two other ways to measure ERD. It isn't a bad idea to double-check!

ocr

Off-Center or Asymmetric rims make spoke tension more nearly equal when a wheel is dished. These rims require a slight adjustment for spoke lengths. I don't know enough about Excel to make Spocalc smart enough to compensate for rim offset, but I have two work-arounds: the easy way and the exact way.

The Easy Way: Calculate spoke length as if the rim were symmetrical. Then add 1mm to the right side and subtract 1mm from the left side on rear wheels, or add 1mm to the disc side and subtract 1mm from the non-disc side of front wheels.

The Exact Way: The idea is to adjust the hub widths to mimic the rim offset. (The change in spoke length is the same whether the rim moves relative to the hub, or the hub moves relative to the rim.) To do this, just change the left and right flange offsets by the rim offset. Here's how to do it, step by step:

After entering your hub data into Spocalc,

1. Calculate your rim's spoke-hole lateral offset:
- Measure the rim width (W) and divide by two. This is the rim half-width.
- Measure the distance from the near sidewall to the center of the average spoke hole (L).
- Subtract this number from the rim half-width.

The result is the rim's spoke hole lateral offset (or just rim offset), i.e. the amount by which the rim reduces your wheel's dish. It is usually a couple of millimeters. Thus,

rim offset = (W/2) - L.

2. Type over the "W, width from center to flange" hub dimensions in Spocalc:
- Add the rim offset to the right flange width, and
- Subtract rim offset from the left flange width.

Spocalc automatically displays the new spoke lengths.

Fatbike Rims and/or Skinny Hubs

Fatbike rims typically have the two rows of spoke holes far from the centerline. With some hubs, there will be hardly any bracing angle unless you cross spokes over to the far side of the rim. An e-bike hub motor may have narrow spacing between the flanges, so crossing the spokes over may also be useful. Use a rim whose spoke holes are not angled sharply toward the flange on their side. Add the offset between the centerline and the far row of spoke holes to the hub flange spacing when calculating spoke length -- same calculation as the "hard way" for asymmetric rims, described above, except that you have to do it separately for each side of the rim. .

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Troubleshooting Spocalc

The spoke lengths calculated in Spocalc are based on pure 3D trigonometry: they are exact. So unless I've made a mistake in the formulas, any error must lie in the hub or rim measurements.

1. Check and double check "ERD, effective rim diameter". Errors in ERD have a direct effect on spoke length. ERD is also the easiest to get wrong, since rims are rarely round when not built into wheels, and you may measure at a large or small diameter. It is definitely worth measuring ERD at several locations around the rim and averaging. The idea is to reduce the effect of any single measurement falling at a high or low spot. [I describe two additional ways to measure rim diameter in my article on this site -- John Allen]

2. Hub dimensions are less critical: errors here have less effect on spoke length than errors in ERD. With tangential lacing (several crosses, like three or four), flange diameter (d) is less critical than flange width (W). With radial lacing (not advisable with hub brakes or rear wheels) flange diameter becomes relatively more important.

3. Spoke-hole diameter (S) is pretty inconsequential. Errors in spoke-hole diameter contribute directly to errors in spoke length, but since the errors are usually so small (much less than 1 mm) they rarely make a significant difference in spoke length. Many formulas ignore spoke-hole diameter entirely.

4. Also, it may seem obvious, but check to be sure you entered the correct number of spokes (N), and that you read the spoke length from the cell corresponding to the correct number of crosses. I've made both those mistakes before!

5. You can always download a current copy of Spocalc or SpocalcExpress from this page. This will fix problems like accidentally typing over hub or rim dimensions on the database sheets, or typing over formulas on the calculator sheet.

"Hey Damon, I got the macros working. In the Excel [2000] program. Go under Tools, Macros, then Security. Three options are there. I set mine on medium security. Just thought I'd let you know in case others have the same problem. Thanks for the help and the great spoke calculator." -Bob

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Related Sites

Here are a few other pages on Damon Rinard's Bicycle Tech Site you might be interested in:
Hub weights
Rim weights
Spoke weights
Wheel stiffness
24 spokes in 36 hole hubs

Here are a few pages on other sites you might be interested in:

Check spoke tension by ear, by John Allen.
Sheldon Brown's excellent Wheelbuilding page.
Tom Ace's beautiful "3 leading, 3 trailing" pattern.
Hed Wheels. Complete aerodynamic drag numbers tabulated.
Humphries aero wheel summary. More aero drag numbers.
Rowland Cook's unusual lacing patterns.
Wheel Fanatyk, many interesting blog posts and articles about wheelbuilding

Here are manufacturer's sites you might be interested in:
American Classic - site map.
DT Swiss Bicycle Technology Menu
Mavic rims and components
Sun Rims
Tune hubs
Sapim spokes


Other Spoke Length Calculators on the Web

(This lism updated as of December, 2016 and now includes the highest-rated apps for iOS and Android devices. Searching the Google Play site or Apple Apps Store finds others. )

Calculator Free? Allow Decimal Cross? Downloadable? Hub and Rim Database? Lengths for many cross patterns with one data set entry? Notes
Damon Rinard's Spocalc with Excel macros yes yes yes User updatable; no longer updated by Damon Rinard yes Excel is also available for Android devices!
Damon Rinard's Spocalc with Openoffice macros yes yes yes user-updatable; no longer updated by Damon Rinard yes Windows, Linux or Mac
Arno Welzel yes yes no no yes  
Benjamin J. Manthey yes yes yes no no  
Bicycle spoke length calculator (iOS) no no yes no, only preset rims and hubs ? for iPhones and iPads
BikeTechTools yes no no yes, after login no  
DT Swiss yes no no Can save and download calculations after login yes Database of DT Swiss hubs and rims, or input your own data
Earlymotor yes yes no no no Mostly for motorcycles
E-bike calculator yes no no yes no Mostly for e-bike hub motors and calculates with paired spokes but please read this page.
Edd yes no no Non-updatable database, can enter rim and hub dimensions yes  
Freespoke yes yes no yes yes  
Nox yes   yes yes, for their one rim no  
Pete Gray's Spokulator yes         Requires Java-enabled browser, so, not tested.
Prowheelbuilder.com yes no no No, only preset rims and hubs yes  
Recumbents.com yes yes no no no  
Sapim yes yes no Can enter rim and hub dimensions no Unusual rim measurement approach. Also for Android
SON yes no no Database of SON hubs and some rimes no  
spokelength.com yes no no Enter rim and hub dimensions yes Only a single flange spacing number, probably assumes equal spacing both sides.
Spoke Length calculator for Mac yes   yes yes ? No way to test, no Mac here!
United Bicycle Institute yes no no enter rim and hub dimensions no  
Wheeler App for Android yes ? yes yes yes Highest-rated Android app
Roger Musson, Wheelpro yes no no Enter rim and hub dimensions yes Also for straight-pull hubs
Home back to Damon Rinard's Bicycle Tech Page

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If you would like to make a link or bookmark to this page, the URL is:
http://www.sheldonbrown.com/rinard/spocalc.htm

Last Updated: by John Allen