rhm

This is a question that comes up every now and then when someone wants to lace modern rims to a pair of hubs from an old English bike, which typically have 32 spokes in the front wheel and 40 in the rear. Modern rims are usually available in both 32h and 36h drillings, and sometimes in both 36h and 40h drillings, but rarely in both 32h and 40h. An exception is the Sun CR18 in the 650A size.

There is no good way to lace a 36h rim to a 40h hub.

But it is easy to lace a 32h rim to a 40h hub. You simply calculate the spoke length for the hub in question as if it had 32 holes, and then buy 16 spokes that are 1.5 mm longer than the calculated length, and the other 16 spokes 4 mm shorter than the calculated length. Of every five holes on the hub, one will not be used.

I have made a drawing (see attached PDF) that explains this. Let me know if it doesn't; as my daughter said, at age two: "makes sense to me!"

iab

What does the completed wheel look like? How do you with the skipped hole on both sides? Aligned? Alternating? If alternating, by how much? Any empirical data on durability?

rhm

The completed wheel looks normal; the spokes meet the rim as expected. You can only tell if count the spokes (or, easier, count the wide spaces; a 40h wheel has ten of them, a 32h wheel has eight) or if you look closely at the hub and see the empty holes, of which there are four on each flange.

The four empty holes on each flange will be opposite one another, forming the corners of a square; the four empty holes on the flanges should be offset from one another by a 1/8 turn (45 degrees), but this doesn't really matter.

The wheel will be as durable as any 32h wheel can be. A wheel built on an internally geared hub does not need to be dished, or not much; so they are inherently strong.

I won't go so far as to say 32h is better than 40h; frankly I much rather find a 40h rim. But they are increasingly rare.

noglider 

Very impressive. How did you calculate the spoke lengths?

mparker326

Thanks for the explanation. I have wanted to try it before but chickened out because the spoke length calculations seemed too intimidating.

JohnDThompson 

Have you tried looking for 40h rims in tandem-oriented shops, eg:

https://www.tandemseast.com/parts/whe...#Tandem%20Rims

pastorbobnlnh 

Rudi,

A great piece of information for a common challenge, especially for vintage IGH fans. I've puzzled this in the past but never took it far enough to come up with a solution. My helmet's off to you for doing so! I've saved it on the computer for future use.

My only suggestion would be to add the directions you used to begin this thread to the PDF and to specify whether this is for a 3X or 4X pattern (or that it doesn't matter).

rhm

I didn't. Spoke length depends on the rim and the number of crosses, which I can't predict. Use one of the many spoke calculator programs to figure out the base spoke size. I drew the picture and measured the distance between the expected hole and the existing hole. My whole point is that this is a cave man approach to a problem that many people would be inclined to overthink. My brain hurts just thinking about it. So I didn't.

?
Yes; as I say, I much prefer to get a matching pair of rims with the correct number of spokes. And I've done pretty well. 40h rims are out there, and you can find them. But that's not what this thread is about.

Ha, you know, I don't think I checked! Between 3x and 4x I don't think it matters. It's really a question of the angle at which the spoke reaches the flange, with smaller numbers of crosses, the discrepancy will be greater.

rhenning

4x spokes need to be longer than 3x spoke with the same rim hub combination. I would love to see the wheels you built or is this only a theoretical wheel build. My Bike Friday uses 24 hole rims with 36 hole hubs so I know some mixing and matching can be done but would love to see a picture of your build. Roger.