Wheel building - Spoke length question ...

[Kahu]

I need to buy some spokes to build a wheel, I'm using a Sturmey Archer 3 speed hub, and a Rigida 700c rim of 1980's vintage, this rim is very similar to a Mavic G40 / Mavic MA40, I'm using 36 spokes, 3 cross, I think the spokes need to be 285mm long, somebody else has suggested 287mm.
Any advice welcome ....

[Mick F]

I take it you have the hub and the rim already?

If so, take two old spokes and cut their hooks off. Screw on a nipple on each of them and screw them down so the spokes are level with the top of the nipples. Some folk use super glue to hold them in place, but I've never bothered and just been careful.

Thread the prepared spokes through opposite holes and measure the length in millilmetres between the cut ends. Write this down and try a few positions as the rim may not be perfectly round.

By this time, your readings should make some sense. Add this reading to the total overall length of the two spokes added together.
This figure is your Effective Rim Diameter ERD.

Now, you need to measure up your hub. SA hubs are standardised, but personally, I'd measure my own.
Measure the spoke hole circle diameter and the distance between the flanges plus the hole size. Also how far in the flanges are from the outside of the locknuts. SA hubs are symmetrical I believe.

All this info can be applied to a Spoke Length Calculator. There are good ones on line. Pick two or three and see what comes out. In the past, I've found Spoke Calcs to vary a bit.

http://www.bikeschool.com/tools/spoke-length-calculator
http://www.wheelpro.co.uk/spokecalc/
https://leonard.io/edd/

Also, new spokes often come in only even numbers, so round up to the next even number for the length. Don't round down.

Good luck!

[Brucey]

I need to buy some spokes to build a wheel, I'm using a Sturmey Archer 3 speed hub, and a Rigida 700c rim of 1980's vintage, this rim is very similar to a Mavic G40 / Mavic MA40, I'm using 36 spokes, 3 cross, I think the spokes need to be 285mm long, somebody else has suggested 287mm.
Any advice welcome ....

if it is a Rigida AL1320 rim then IIRC (from memory) you need to use ~290 or 291mm spoke lengths x3 on a large flange hub. The ERD of an AL1320 rim is a little smaller than an MA40, there are single eyelets, and the profile is more rounded.

If you can confirm the rim model I can check my rim data.

This is the silver (polished) model AL1320


and this is the black finished model AL1320


cheers

[MikeF]

I take it you have the hub and the rim already?

If so, take two old spokes and cut their hooks off. Screw on a nipple on each of them and screw them down so the spokes are level with the top of the nipples. Some folk use super glue to hold them in place, but I've never bothered and just been careful.

Thread the prepared spokes through opposite holes and measure the length in millilmetres between the cut ends. Write this down and try a few positions as the rim may not be perfectly round.

By this time, your readings should make some sense. Add this reading to the total overall length of the two spokes added together.
This figure is your Effective Rim Diameter ERD.

OR
Measure the complete diameter of the wheel to the outermost part of the rim in more than one place and take the average. Hold a nipple firmly in place and measure the distance from the outside of the rim to the bottom of the nipple slot. The tail end of a vernier gauge is useful, but otherwise use whatever is suitable - even a piece of wire or rod that you can subsequently measure will do. Take several readings in different holes and use the average. Subtract twice the value of these average measurements from the total wheel diameter to give ERD.

[Kahu]

Thanks for your help chaps, much appreciated, Brucey, I don't have the model number for the rim, thanks for offering to find the info though. Mick, I've cut some spokes and used your method to measure the rim, dead handy!
Great stuff chaps, many thanks Kahu.