Stability of home made wheel

Question

I need a new wheel to support more weight (136kg combined for bike, freight and rider) and larger tires (around 42-622). Unfortunately I have not been able to find any wheels to my liking, so I am thinking about making my own. Intended use is commuting and trips on paved surfaces (though curbs from sidewalks can be quite rough around here).

The question is how will I know how much weight my wheels can stand? I notice some pre-built wheels come with load restrictions from the manufacturer, but where would I find this information if I buy rim, spokes, nipples and hub separately? Also, I noticed that some pre-built wheels come with maximum tire pressure limitations. Where would I find this information for an arbitrary rim (from a brand name manufacturer)? Or should I just assume that 32 hole rims are stable enough and support the ETRTO recommended maximum pressures?
And just for reference, which component is the "weak" one determining the maximum load of a wheel? The rim, the spokes or the hub (bearings inside)?

Answer 1

I need a new wheel to support more weight (136kg combined for bike, freight and rider)

Totally doable. I used to weigh 110 kg, and rode on a 20 kg e-bike. I could carry more than 6 kg cargo.

The stock wheels had a total and complete loss of spoke tension in the front (disc brakes there, and inadequate spoke tension and 28 i.e. too few spokes) and loss of tension in some spokes in the rear.

My solution was to build my own wheels.

Here's a guide of how to build durable wheels:

1. Only buy double wall double eyelet (socket) aluminum rims that are powder coated (if black) and not anodized. Today, the best rim choice is probably DT Swiss TK 540. The rim must absolutely have 36 spoke holes. 32 or 28 is not enough.

2. Select DT Swiss Pro Head or similar spherical head nipples, only brass. The reason being that the spherical head as opposed to a conical head allows the nipple to swivel while still having full contact to the rim.

3. Only select 2.34mm/1.8mm/2.0mm triple butted spokes like DT Swiss Alpine III (it has to be Alpine III, normal Alpine is not triple butted). The reason being that the 2.34mm hub head fits well to the hub spoke holes, whereas the 1.8mm middle section is elastic distributing load to many spokes and the 2.0mm screw threads are durable to avoid failure in this fragile area. Never buy any other spokes than high quality stainless steel spokes.

4. Only use 3-cross spoke pattern, never radial or anything stupid. Remember to interlace the spokes when crossing.

5. Buy forged hubs, not CNC machined. Small manufacturers like CNC machining because it is cheaper when producing small numbers of hubs. However, it's very expensive and doesn't result in as strong hub flanges. Large manufacturers like Shimano build forged hubs.

6. Always lubricate with oil-based grease the nipple-to-rim contact and the screw threads of the spokes.

7. Build your wheel to an equal and high spoke tension. At least 1000 N but with TK 540 you can exceed this 1000 N "recommendation" by quite a large margin and still not destroy the nipples or the rim. You need a tensiometer for this. Remember that spoke tension equality is important. You measure equality by plucking the spokes and having an even tone. The left and right side obviously can differ in tension, but all spokes on the left side should have equal tension and all spokes on the right side should have equal tension. If rim trueness requires compromising equal tension a bit, that's fine, it's a marginal rim that's probably still usable. If rim trueness requires compromising equal tension a lot, it's a bad rim and should be discarded.

8. Remember to stress relieve your wheels as described in "The Bicycle Wheel" by Jobst Brandt. You do this by grabbing two pairs of parallel spokes and squeezing hard, so hard that it starts to hurt in your hands. The stress relieving needs to be done at full and final tension.

With those tips, 136 kg is totally doable, even if the rear wheel has asymmetric spoke tension and if the front wheel has a disc brake which can cause loosening of the spokes if applied hard on a heavy bike+rider+cargo combination. The 42-622 tires make the wheel more durable, since they reduce the forces of impacts.

The question is how will I know how much weight my wheels can stand?

By experience, I can say that wheels built according to my instructions can withstand 136kg on a 28-622 tire pumped up to 7 bar, even if the front wheel has a disc brake. Not that 28-622 is recommended. High quality low rolling resistance tires are available as wide as 32-622 and 32-622 doesn't require pumping up to 7 bar.

I notice some pre-built wheels come with load restrictions from the manufacturer, but where would I find this information if I buy rim, spokes, nipples and hub separately?

You won't find this information, but your 136 kg requirement can be met if you select all components well and if you build the wheel well. You may exceed the 1000 N spoke tension recommendation by 20-30% easily, which probably makes a more durable wheel for heavy loads.

Also, I noticed that some pre-built wheels come with maximum tire pressure limitations. Where would I find this information for an arbitrary rim (from a brand name manufacturer)?

This may be caused by non-hooked rims (avoid those!) or just a desire by the wheel manufacturer to avoid loosening of spokes when ridden hard with heavy rider and high tire pressure at the same time. You won't find this information for an arbitrary rim, it's not a hard limit, and usually the tire specs limit the pressure more than what the wheel can withstand.

Or should I just assume that 32 hole rims are stable enough and support the ETRTO recommended maximum pressures?

Why on Earth are you considering 32 hole rims? 32 holes were originally intended for 26" wheels. A 622mm bead seat diameter wheel should have 36 holes. When 559mm bead seat diameter wheels were made for MTBs, then it was noticed that 32 holes result in equal spoke density than 36 holes for 622mm bead seat diameter wheels. Actually, I understand that the first 559mm wheels were made simply by shortening longer rims.

36 holes is the standard. Stick with it. The claim that reducing the number of spoke holes is an "improvement" is called the Great Spoke Scam. Manufacturers cut costs and sell it as an "improvement".

And just for reference, which component is the "weak" one determining the maximum load of a wheel?

In the short term, the spoke. It needs a 1.8mm middle section to be elastic to distribute the load over many spokes and lots of tension to not result in loosening nipples. There needs to be many of them (36, to be precise). However, it could be argued that the rim dictates the number of spokes, so a badly designed rim can mean you don't have enough many spokes.

In the long term, the rim. A rim that isn't double wall is easily damaged by impacts. A rim that is double wall but either is anodized or doesn't have double eyelets (sockets) can easily start to crack around the spoke holes, resulting in a wheel that lasted for maybe 10000 - 50000 km but not more.

If you build your wheels to have radial spoking, then the hub. The flanges will crack, which is very dangerous. However, it could be argued this isn't the fault of the hub but rather the fault of the wheelbuilder, which chose a stupid spoke pattern.

Answer 2

The first question is whether it's a front or back wheel. Assuming the latter there's no reason to limit yourself to 32 spokes. I'd go for 36, and indeed have for similar loads (front and rear, but it's more important at the back with its greater share of the load).

Some rims do have pressure ratings; look for ones sold for touring to get a good combination of width and strength. You'll have to look carefully for tyres of that width that can take high pressures, but you'll find them, because that's fairly common on tandems and some rough-road tourers.

Honestly the weak point is the build. Insufficient tension is the biggest thing to watch out for. With basic branded rims and hubs, and decent double butted spokes, your wheels can be strong enough. Once well-built, and trued an extra time if you didn't stress-relieve it well enough, servicing your hub will likely be the first job, after quite a while.

Dropping off kerbs laden is very harsh, even if you stand up and shift your weight over the wheel that's not dropping . Better to place the bike in the road before mounting. But where I live sidewalk riding is illegal with few (signed) exceptions. Those exceptions all - barring a very few exceptions - have dropped kerbs, so there's no need to drop off the edge.

Don't discount getting a wheel custom built for you. I just bought a hand-built wheel for a sensible price, because I need it before I'll have time to (re-)build one.