### 32 hole rim onto 36 hole hub - "alphabetti spoketti"

Posted:

**25 Nov 2017, 4:43pm**having a 36h hub generator, and some 32h rims that are due to go onto a bike with a 32h IGH in the back, a 32h rim on a 36h hub suddenly had an abnormally great appeal to me.

A quick search of the interweb showed that others had wanted to do this, but mostly hadn't. So I set to and I think I have succeeded, in such a way that I can present clear instructions that will make repeating this only a little bit more awkward than building a conventional wheel, despite the fact that it obviously requires a weird spoke pattern and several lengths of spokes.

The secret is to

a) have a clear plan in mind and

b) to work out the spoke lengths accurately (using fractional crossing values) and

c) to keep careful track of what you are doing as you build the wheel.

It is not very difficult to do this but I would not recommend it as a first wheel build or anything. The hub dynamo (disc compatible) I used had large flanges with the effect of both exaggerating the differences in spoke lengths and necessitating that eight different spoke lengths are notionally required.

In the workings I have used accurate measurements all the way; the time for rounding the values is at the end when you are choosing the spokes and/or cutting them to length. I use letters to identify spoke types/lengths, hence this is 'alphabetti-spoketti'...

This photograph tells most of the story;

It shows a quarter of the spoke pattern (eight spokes), which is (obviously) repeated thrice more around the wheel. There are two unused spoke positions per flange. On the opposite flange, the unused holes are almost opposite, skewed around by 1/36th of a turn. (NB If you have the unused holes set at some other random angle, the spoke lengths won't work out simply.).

There are four different spoke lengths amongst those eight spokes. I have labelled them A,B,C,D. I first worked out the angle error vs how those holes would appear on a 32h flange, and then reworked that into a new 'fractional crossing' value, so that the 32x3 pattern could be suitable adapted with four different spoke lengths per flange.

The hub I used had flanges of 74mm, centreline offsets of 19.5mm and 28.5mm and I used a 32h rim with an ERD of 595mm. A standard 32x3 pattern gave spoke lengths of 284.8mm (left) and 285.6mm (right).

The fractional crossing values and spoke lengths were calculated using a calculator that supports fractional crossing values ( used EDD) and came out as follows

Spoke Crossing Left length Right length

A--------x2.611------279.6mm-----280.3mm

B--------x3.278------288.8mm-----289.5mm

C--------x2.833------282.6mm-----283.3mm

D--------x3.056------285.6mm-----286.4mm

I cut and threaded spokes to the eight exact lengths as best I could (mainly to check the accuracy of my calculations), but in reality most folk would settle for 280mm, 289mm, 283mm, and 286mm. I stashed the different spoke lengths in holes in a piece of labelled card, so that I could keep track of them.

I recommend that you mark the flange holes that are to be unused, and first install all the A and D spokes on both flanges. The valve can go between two A spokes at the rim, i.e. opposite the D locations in the hub flange; in other words you can make one of your A spokes 'the lead spoke'. Then install the inside C and B spokes, and finally the outside C and B spokes. This will mean that you are unlikely to lose track of the build, whilst making for a relatively small amount of time consuming lacing of spokes.

In theory there is a small error that is introduced by the fact that the holes on one flange are not offset by 1/32 of a turn but are instead offset by 1/36 of a turn. In reality this error appears to be lost in the noise; it is probably about the same size error as you would normally get between the effective lengths of inside and outside spokes. Perhaps with flanges about twice the size it would be more significant.

If the spokes face opposite ways from the holes in the flanges (eg leading rather than trailing, and vice versa) then there is a different spoking pattern that requires different fractional crossing values in order to give accurate results, so be sure to copy the pattern carefully.

If building onto a 36h hub with smaller flanges, compute using the same fractional crossing values, and expect to find that the corrections to the normal lengths are very much smaller. You may find that you need even fewer distinct spoke lengths than in the example above.

When I had laced the wheel the way the spokes poked out of the nipples wasn't much less consistent than normal; the wheel trued up in a very normal fashion. With practice I don't think this method would be very much slower than any other wheel build, although there is obviously more time spent preparing the spokes beforehand.

Have fun!

cheers

A quick search of the interweb showed that others had wanted to do this, but mostly hadn't. So I set to and I think I have succeeded, in such a way that I can present clear instructions that will make repeating this only a little bit more awkward than building a conventional wheel, despite the fact that it obviously requires a weird spoke pattern and several lengths of spokes.

The secret is to

a) have a clear plan in mind and

b) to work out the spoke lengths accurately (using fractional crossing values) and

c) to keep careful track of what you are doing as you build the wheel.

It is not very difficult to do this but I would not recommend it as a first wheel build or anything. The hub dynamo (disc compatible) I used had large flanges with the effect of both exaggerating the differences in spoke lengths and necessitating that eight different spoke lengths are notionally required.

In the workings I have used accurate measurements all the way; the time for rounding the values is at the end when you are choosing the spokes and/or cutting them to length. I use letters to identify spoke types/lengths, hence this is 'alphabetti-spoketti'...

This photograph tells most of the story;

It shows a quarter of the spoke pattern (eight spokes), which is (obviously) repeated thrice more around the wheel. There are two unused spoke positions per flange. On the opposite flange, the unused holes are almost opposite, skewed around by 1/36th of a turn. (NB If you have the unused holes set at some other random angle, the spoke lengths won't work out simply.).

There are four different spoke lengths amongst those eight spokes. I have labelled them A,B,C,D. I first worked out the angle error vs how those holes would appear on a 32h flange, and then reworked that into a new 'fractional crossing' value, so that the 32x3 pattern could be suitable adapted with four different spoke lengths per flange.

The hub I used had flanges of 74mm, centreline offsets of 19.5mm and 28.5mm and I used a 32h rim with an ERD of 595mm. A standard 32x3 pattern gave spoke lengths of 284.8mm (left) and 285.6mm (right).

The fractional crossing values and spoke lengths were calculated using a calculator that supports fractional crossing values ( used EDD) and came out as follows

Spoke Crossing Left length Right length

A--------x2.611------279.6mm-----280.3mm

B--------x3.278------288.8mm-----289.5mm

C--------x2.833------282.6mm-----283.3mm

D--------x3.056------285.6mm-----286.4mm

I cut and threaded spokes to the eight exact lengths as best I could (mainly to check the accuracy of my calculations), but in reality most folk would settle for 280mm, 289mm, 283mm, and 286mm. I stashed the different spoke lengths in holes in a piece of labelled card, so that I could keep track of them.

I recommend that you mark the flange holes that are to be unused, and first install all the A and D spokes on both flanges. The valve can go between two A spokes at the rim, i.e. opposite the D locations in the hub flange; in other words you can make one of your A spokes 'the lead spoke'. Then install the inside C and B spokes, and finally the outside C and B spokes. This will mean that you are unlikely to lose track of the build, whilst making for a relatively small amount of time consuming lacing of spokes.

In theory there is a small error that is introduced by the fact that the holes on one flange are not offset by 1/32 of a turn but are instead offset by 1/36 of a turn. In reality this error appears to be lost in the noise; it is probably about the same size error as you would normally get between the effective lengths of inside and outside spokes. Perhaps with flanges about twice the size it would be more significant.

If the spokes face opposite ways from the holes in the flanges (eg leading rather than trailing, and vice versa) then there is a different spoking pattern that requires different fractional crossing values in order to give accurate results, so be sure to copy the pattern carefully.

If building onto a 36h hub with smaller flanges, compute using the same fractional crossing values, and expect to find that the corrections to the normal lengths are very much smaller. You may find that you need even fewer distinct spoke lengths than in the example above.

When I had laced the wheel the way the spokes poked out of the nipples wasn't much less consistent than normal; the wheel trued up in a very normal fashion. With practice I don't think this method would be very much slower than any other wheel build, although there is obviously more time spent preparing the spokes beforehand.

Have fun!

cheers