Wheel building: 36h Hub with 32h Rim

[caseytronic]

Background
Building a decent wheel with a 36h hub and a 32h rim, while not typical, is quite possible (as explained below).

I chose this odd wheel setup because I had an older geared Schlumpf hub (36h only) that I wanted to use the only rim brake compatible rim that also allowed for a good tubeless wheel (Surly Rabbit hole -32h only). I prefer rim brakes and my hub is too old for disc. The hub is also likely out of any warranty. I posted this build on the Schlumpf hub thread and a few people were interested in how to do it, so I started this thread.

This wheel was a little more difficult to true (had a bit of a hop), but now that its done, it seems just as solid as any other uni wheel I’ve built.

Lacing Pattern
Lacing a 32h rim to a 36h hub involves skipping one hole on opposite sides of each hub flange. I decided to skip holes directly across from each other, and to match the hole skipped on both hub flanges in order to even out tension on the rim as well as possible. I chose the most damaged looking spoke hole to skip and the other on the opposite side. I also had to bevel the spoke holes on both sides ( older hub had only 1 side beveled) since skipping a hole causes 1/2 of the spokes to be oriented backwards coming out of the hub.

Spoke Lengths
Spoke Lengths vary with a 32h rim >> 36 Hub.

The attached diagram should help you understand my explanation below.

After some trial and error and educated guessing, I found the simplest way to understand the spoke lengths is to start at the skipped hole (in red on diagram) in the hub and go outwards.

The spokes angling back over the skipped hole (2 holes away from the skipped hole - in orange) are the longest at about 8-10mm higher than the calculated 36h spoke length. This makes sense because they cross the extra distance over the skipped hole with the most horizontal angle. The next spokes angling over the skipped hole (4 holes away from the skipped hole - in yellow) need to be 4-6mm longer than a 36h spoke length. Proceeding away from the skipped hole more, there are 2 more spoke sets: a set that are 2-4mm longer, and a set that are the same length (or maybe +1mm) as a 36h typical spoke length. NOTE - the length differences are for a 29" rim and a Schlumpf hub.

The diagram shows the length differences for only 1/2 of the spokes on one hub flange, so multiply number of spokes at each length by 4 for the whole wheel:

Whole Wheel:
8 spokes: +0mm (same as 36h to 36h length)
8 spokes: +2mm to +4mm
8 spokes: +4mm to +6mm
8 spokes: +8mm to +10mm

When I built my wheel, I bought only 2 different lengths of spokes, but I found out I needed at least 4 different lengths to make it work well.

I chose 16mm long spoke nipples to maximize the threaded length in case my spoke lengths were a bit too short. This helped.

The picture of the hub and spokes shows How the angle of the spokes gets more perpendicular to the hub/rim as the spokes crossing over the skipped holes get farther from them.

[battleshiplinoleum]

I cannot comment on the method and the accuracy yet,
but compliments on the well-structured post and colourful picture!

[caseytronic]

@battleshiplinoleum

I cannot comment on the method and the accuracy yet,
but compliments on the well-structured post and colourful picture!

Thanks. It took me a while to clarify my explanation and make the picture, so I appreciate the compliment.

I first posted wheel build in the Schlumpf hub thread:

Schlumpf hubs: general discussion

Hi everyone, I thought it is a shame that most of the talk of schlumpf hubs occurs in the ‘brand new broken schlumpf’ thread. So with the teething problems of the first generation hubs being rectified (in a very noble manner by florian i must add), and more and more people enjoying this pretty amazing new piece of equipment i thought it would be time to start a new thread for people to talk and share ideas about their Hubs, the unicycles they are in, shifting techniques etc. I’ll start off, I …

That original post had a much less clear explanation of spoke lengths, so I hope this will clear it up. I also made a few incorrect guesses in determining spoke length. I originally thought the spoke lengths would likely vary between the lengths calculated for a 32h hub/rim and those for a 36h hub/rim. I bought spokes at 2 lengths in-between the 2 calculated values, but it turned out I need 4 different lengths to make it work. I then had to grind down some o f the spokes and dig up some spares I had to get the correct lengths.

It would be interesting to tweak the equations used for spoke length to calculate lengths for 32h rims to 36h hubs and vice versa. I thought about doing this instead of just guessing at spoke lengths, but usually by the time I start my unicycle projects, the nerdly part of my brain is already done for the day.

[leo]

You can combine 4x scare-crows + 2x a pairs of cross-1’s.
makes (4x 3) + (2x 2) = 16 (one side, and 2x 16 = 32).

I would put the spare wholes within the cross-1’s, so it’s all symetric.
And have the spare holes on the other side 90deg twisted.

Edit: hmmm, in case it’s a Schlump then I guess it’s a bit larger rim, and so my solution isn’t the best for that.

[toutestbon]

I think your thread will interest a lot of people if Truebike/Alchemist releases as planned a 36" carbon rim with 32 holes.

I would be curious to test this even though I am so attached to the magura hs33 rim brake.

[caseytronic]

@toutestbon

I think your thread will interest a lot of people if Truebike/Alchemist releases as planned a 36" carbon rim with 32 holes.

I would be curious to test this even though I am so attached to the magura hs33 rim brake.

I also am attached to the HS33. The Surly Rabbit Hole rim I used enables you to use the HS33 with a tubeless compatible lightweight rim. Of course the Rabbit Hole is only available in a 29" and 26" size and is getting harder to find

To All:
I am not sure if my spoke length differences will be the same for a standard unicycle hub with a smaller flange diameter. I expect they will be close though.